CHAPTER-1

STRUCTURE & BONDING

1.1.Tetravalency of Carbon

Electronic configuration of carbon shows two unpaired electrons and so it should be

bivalent. However carbon shows tetravalency in its compounds. During compound formation
one electron from its 2s orbital get excite to 2p orbital and it get your unpaired electrons. It
can be understood by following electronic configuration in ground and excited states.

1.2. Hybridization
Mixing of orbitals in valance shell of an atom to produce equivalent no. of orbitals of similar
energy and shape is called as ‘hybridization’ and new orbitals are called as hybrid orbitals.

1.2.1 Types of Hybridization

There are three types of hybridization in organic compounds.

1. sp³ hybridization
2. sp² hybridization
3. sp hybridization
1. sp³ hybridization

Mixing of one s- and three p-orbitals in valance shell of an atom and produce four Sp³ hybrid
orbitals of similar energy and similar shape is called as Sp³ hybridization. Molecule has
tetrahedral shape with bond angle 109º28’ or 109.5º each. Examples are CH4, C2H6 etc.

In CH 4, carbon has sp³ hybridization and it has four sp³ hybrid

orbitals. Each orbital overlap with s-orbital of four H-atoms to form CH4 molecule.
 H
104.5º
C
H H
H
Tetrahedral
2. sp² hybridization:

Mixing of one s and two p-orbitals in valance shell of an atom hybridize

together to give three sp² orbitals of similar energy and shape, called as sp² hybridization.
Molecule has trigonal planar structure with bond angle 120º each.
Examples are C2H4, C3H6 etc.
In C2H4, each carbon has sp² hybridization. One sp² hybrid
orbital of each carbon overlap together while other two sp² hybrid orbitals overlap of two H-
atoms on each carbon. Each carbon also has one unpaired p-orbital which overlap sideways
together to form  bond.

3. sp Hybridization:
Mixing of one s and one p-orbital in valance shell of an atom hybridize together to
give two sp hybrid orbitals of similar energy and shape called as sp-hybridization. Molecule
has linear shape with bond angle 180º.
Examples are C2H4, C3H4 etc.
In C 2H2, each carbon has sp hybridization. One sp hybrid orbital of each
carbon overlap together and other sp hybrid orbital of each carbon overlap with H-atoms.
Each carbon also has two unpaired p-orbitals which undergo sideways overlap together to
form two  -bonds.
1.3 Bond Characteristics:
There are following bond characteristics-
1. Bond length
2. Bond angle
3. Bond energy
1. Bond length:
The distance between nuclei of two bonded atoms is called as bond length. It is very small
distance so it is measured in angstrom (Aº) or picometer (pm). Bond length depends on
hybridization. As %age of S-character increases bond length between carbon atoms
decreases.
Types of %.age C-H bond length
hybridization s character in Aº
sp³ 25 1.11
sp² 33 1.08
sp 50 1.02
2. Bond angle:
The angle between two neighboring covalent bonds is called as bond angle. It depend on
followings:
(a) Hybridization: As S-character increases bond angle also increases
sp³ sp² sp
25% 33% 50%
109.5º 120º 180º

(b) Lone pair of electrons: Bond angle decreases with increase in no. of lone pairs of
electrons.
CH4 NH3 H2O
109.5º 107º 104º
No lone pair One lone pair Two lone pairs
 3. Bond energy:
The energy required to break a bond into its constituent atoms is called as bond energy. It
depends on bond strength i.e. greater the bond strength greater the bond energy. it depend on
hybridization and multiplicity of bonds. e.g. Bond energy of C-H bond in hydrocarbons are
as:
CH4 CH2=CH2 CH= CH
sp³ sp² sp
421 KJ/mole 445 KJ/mole 508KJ/mole
1.4 Localized and Delocalized bonds:
When electrons are restricted to a particular region called as localized bond electrons.
However when electrons are not restricted between two atoms but delocalize to different
centers are called as delocalized electrons and bond called as delocalized bond. it depends on
conjugation, Hyper conjugation and resonance.
Example 1: Delocalization in 1,3 butadiene

Example 2: Delocalization in vinyl chloride

Example 3: Delocalization in Benzene.

1.5 Vanderwaal’s interactions:

Normally non polar molecules do not have permanent dipole moment but due to slight
disturbance in distribution on electrons they get temporary dipole moment. It induces an
opposite dipole in neighboring molecules. It is called as induced- induced dipole attraction.
These forces are also called vanderwaal’s interactions or London forces. They are weak
forces and have a very short range. e.g. Melting point and boiling point in hydrocarbons
increases with increase in molecular weight or size of chain. This is due to vanderwaal’s
forces.
1.6 Hydrogen bonding:
Molecules of hydrogen in which H-atom is bonded with strong electronegative atoms
like N, O & F then H-atom acquires partial positive charge and electronegative atom acquires
partial recharge. At this stage partial positive charged H forms dotted bond with other
electronegative atom. This dotted bond is called as H-bond.
e.g. H-bonding in HF
...H-F....H-F..... H-bond
1.6.1 Types of H-bonding : It is of two types
1. Inter molecular H-bond
2. Intra molecular H-bond
1. Inter molecular H-bond
When H-bond is formed between two similar or different molecules is called as
intermolecular H-bond. e.g. H-bond in H2O molecules.

2. Intra molecular H-bond

When H-bond is formed between atoms of same molecule is called as intra molecular H-bond
e.g. H-bond in Ortho nitro phenol.

1.6.2 Applications of H-bonding

There are following applications.
1. Effect on physical state:
H2O exist in liquid state while H2S exist in gaseous state due to H-bonding in H 2O. O-atom is
more electronegative than S-atom so O-atom form H-bond while S-atom unable to form H-
bond.
 2. Effect on boiling point
Alcohols have higher b. pt. than its corresponding alkanes. alcohols have polar 0-H group
which form H-bond while alkanes being non polar in nature unable to form H-bond.
R- O ....H – O....
| |
H H
3. Effect on solubility:
Ortho nitro phenol is less soluble than p-nitro phenol. o-nitro phenol forms intra
molecular H-bond so it fails to form. H-bond with water while p-nitro phenol form
intermolecular H-bond with water molecules and it is more soluble.
1.7 Electronic effects
There are following electronic effects.
1. Inductive effect
2. Field effect
3. Resonance
4. Hyper conjugation
1. Inductive effect
The shift of electrons of a covalent bond due to its polar nature is called as inductive
effect. When two atoms of different electro negativity are covalently bonded together
electron pair shifts towards more electronegative atom.
As a result of this less electronegative atom acquires +ve charge while more
electronegative atom acquires –ve charge. e.g. Inductive effect in CH3Cl.

Types of inductive effect:

There are two types
i. +I effect ii. -I effect
i. +I effect: electron donating groups or less electronegative atoms show +I
effect. e.g. Alkyl groups like –CH3, -C2H5. Amino group (-NH2) etc.
ii. -I effect: Electron attracting groups or more electronegative atoms show -I
effect. e.g. –Cl, -F, -NO2 etc.
 Applications of Inductive effect:
There are following applications.
A. Stability of carbocation
Carbocations are electron deficient intermediates so groups which show +1 effect
increases stability of carbocation. On this basis relative order of stability of carbocations
is as follows:
+
CH3 < +CH2 – CH3 < +
CH(CH3)2 < +C(CH3)3
Methyl Primary Sec. Tert.
Carbocation Carbocation Carbocation Carbocation
B. Effect on acid strength
Acid strength of carboxylic acids depends on nature of bonding group attached to
carboxylic acids. A group with +1 effect decreases acid strength as-
HCOOH > CH3COOH > CH3CH2COOH
While group with -1 effect increases acid strength as-
CCl3COOH > Cl2CHCOOH > ClCH2COOH > CH3COOH
2. Field Effect:
An effect which operates through field not through bonds called as field effect. It
depends on configuration of molecule. e.g. Dipole moment in cis 2-butane is more than
trans 2-butene.
3. Resonance effect
The displacement of or lone pair of electrons in a conjugated system is called as
resonance of mesomeric effect. Different structures formed are called as resonating or
contributing structures. e.g. resonance in benzene

There are two types of resonance effect

(i) +R or +M effect (ii) -R or –M effect.
(i) +R or + M effect
Electron donating atoms or groups show +R effect. examples are –Cl, -Br,
-OH, -CH3 etc.
 (ii) –R or – M effect
Electron withdrawing atoms or groups show –R effect. Examples are
-NO2, > C= O, -COOR etc.

4. Hyper conjugation:
According to Baker & Nathan displacement of 6-electrons of C-H bond to form C=C bond
is called as hyper conjugation. It is also called as no bond resonance because there is no
bond between C & H-atoms in conjugating structures e.g. Hyper conjugation in Ethyl
carbocation-

Applications of hyper conjugation

There are following applications.
1. Stability of carbocation & free radicals:
Stability of carbocations & free radicals can be explained on basis of hyper conjugation i.e.
more the number of hyper conjugating in this basis relative order of stability of free radicals
& carbocations are as follows:
Tert.free radical > Sec. free radical > Pri. free radical
Tertiary Carbocation >Sec. Carbocation >pri. carbocation
Directive influence:
Ortho & para directive influence of –CH 3 group or any alkyl group can be explained on basis
of hyper conjugation as:
1.8 INCLUSION COMPOUNDS
Addition compounds formed by trapping of organic compounds are called as
Inclusion compounds. These compounds are held together by weak Vander waal’s
forces. A compound which provide space called as host & compound which occupy
space called as guest.
Types of Inclusion compounds
There are two types
1. Channel compounds 2. Cage compounds.
1.Channel compounds
An inclusion compound in which host molecule form a channel like structure like
urea or thiourea for guest molecule is called as channel compounds.

e.g. compounds of urea & hydrocarbons.

2. Cage compounds
An inclusion compound in which host molecule form a cage like structure for guest
molecule is called as cage compounds or clatherates.

e.g. A complex of hydroquinone & SO2.

1.9 AROMATICITY (HUCKLE RULE)
 A compound which shows characteristic similar to benzene or its derivative called as
aromatic compound and phenomena is called as aromaticity. There are following aromatic
characters-
i. Compound must have cyclic planar structure.
ii. Compound must have conjugated system and so there is delocalization of
electron.
iii. It must follow Hackle rule or (4n+2) role where n=0, 1,2.....
Example 1. Benzene

4n+2=6
n=1

Aromatic
Example 2: naphthalene

Example 3: Cyclopentadiene anion

Example 4 Cycloheptatrienyl cation

LONG ANSWER TYPE QUESTIONS –

1. What do you understand by hybridization? Give geometry of the following ;
 i. sp3 ii. sp2 iii. sp ( Kanpur 2011, VBSPU 2004 )
2. Explain sp3, sp2 and sp hybridization with examples. ( Kanpur 2016, VBSPU 2005 )
3. What do you understand by resonance and resonance energy.
4. What is aromaticity ? Explain with examples. (BRAU 2008,2011 )
5. Explain Huckle rule with examples. (Kanpur 2010, Kashi 2011, VBSPU 2001)
6. What is Inductive effect ? What effect it does produce on the strength of an acid and
base. ( Kanpur 2016, VBSPU 2005 )
7. Explain hydrogen bonding and discuss its application. ( Kanpur 2010, VBSPU 2004 )
8. What are carbenes ? What do you understand by singlet & triplet carbene.
(BRAU 2008 )
9. Write short notes on following ;
10. i. Hyperconjugation ( Kanpur 2016, VBSPU 2014 )
ii. Inductive effect
iii. Inclusion compounds
iv. Clathrates (VBSPU 2011 )
11. What are polar and non polar molecules? Give examples of each type. ( Kanpur 2009,
Jhansi 2014 )
12. Which type of bond is more stronger, a σ or п bond why? (Agra 2016, VBSPU 2014 )
13. Explai vander wall’s forces of attraction.
14. Explain the following
i. Methylamine is stronger than ammonia. ( Kanpur 2003, VBSPU 2006 )
ii. Dimethylamine is stronger than trimethylamine. (Agra 2010, Gorakh 2004 )
iii. Propanoic acid is weaker than acetic acid. ( Awadh 2010, VBSPU 2004 )
iv. H2S is gas while H2O is liquid at room temperature.( Kanpur 2009, VBSPU 2007 )
OBJECTIVE QUESTIONS :
1. A п bond is formed by overlapping of –
a. s-s orbital b. s-p orbital
c. p-p orbital head on d. p-p orbital sideways
2. Carbon atom of methane molecule undergoes hybridization :
a. sp b. sp2
c. sp3 d. sp3d

3. Which of the following hybridization has highest bond angle :

a. sp b. sp2
 c. sp3 d. sp3d2
4. The geometry of CH4 molecule is :
a. Linear b. Trigonal planar
c. Octahedral d. Tetrahedral
5. Number of σ bonds in C2H6 molecule is :
a. 4 b. 5
c. 6 d. 7
6. Which type of hybridization is present in carbon atom of ethylene compound :
a. sp b. sp2
c. sp3 d. None of these
7. Inductive effect is shown by ;
a. σ- bond b. п-bond
c. Electrovalent bond d. Hydrogen bond
8. Which of following group has +I effect :
a. –OH b. –COOH
c. –OCH3 d. –CH3
9. Which one has highest boiling point :
a. CH4 b. PH3
c. NH3 d. H2S
10. Maximum no. of hydrogen bonds possible with one H2O molecule is :
a. 1 b. 2
c. 3 d. 4
11. The molecule whose each atom undergoes sp2 hybridization is :
a. HCHO b HCN
c. CH3-O-CH3 d. CH3NH2
ANSWERS :
1. (d) 2. (c) 3. (a) 4. (d) 5. (d) 6. (b) 7. (a) 8. (d) 9. (c) 10. (d) 11. (a)
 CHAPTER-2
MECHANISM OF ORGANIC REACTION
2.1 INTRODUCTION:
Stepwise study of formation of product from a reactant is called as
mechanism of a reaction. It involves bond fission reagents attack and different ionic
and nominal reaction.
2.2 BOND FISSION AND ITS TYPES
Most of organic compounds have covalent character as bond is formed by
sharing of electrons between two atoms. On basis of electronegativity difference and
other factors bond fission is of two types.
2.2.1 Homolytic bond fission
A bond fission in which each bonded atoms gets its shared e- and bond is broken,
called as homolytic bond fission. It is denoted by half curved arrow and product
formed is called as free radical. It occurs in presence of sunlight or perishable.

2.2.2 Heterolytic bond fission

A bond fission in which more electronegative atom takes up electron pair, called as
heterolytic bond fission. Reactive intermediate with -ve charge called as carbon ion
and intermediate with +ve charge called as carbocation.

2.3 Types of Reagents

A substance which attacks on substrate and form the product called as reagent. there
are following two types of reagents.
2.3.1 Electrophiles 2.3.2 Nucleophiles
2.3.1 Electrophiles
Those reagents which are electron deficient and have tendency to accept electron pair
i.e. electron loving called as electrophiles. They may have +ve charge or neutral.
A. Positive electrophiles: These electrophiles have +ve charge e.g. H+, CH3+,Cl+ etc.
B. Neutral electrophile: These electrophiles have no charge or neutral in nature e.g.
BF3 , AlCl3 , SO3 , SnCl4 etc.
2.3.2 Nucleophiles
Those reagents which are electron rich and have tendency to share its electron pair i.e.
called as Nucleus loving, called as Nucleophiles. They may have -ve charge or
neutral.
A. Negative Nucleophiles: These nucleophiles have -ve charge. e.g. H -, Cl-, CN-,RO-,
SH- etc.
B. Neutral nucleophiles: These nucleophiles have no charge or neutral in nature e.g.
H2O, ROH, NH3, ROR etc.
Types of organic reactions: There are following types:
2.4.1 Substitution reactions 2.4.2. Addition reactions
2.4.3. Elimination reactions 2.4.4. Rearrangement reactions
2.4.1. Substitution reaction:
Those reactions in which an atom or group is replaced by another atom or group.
Called a substitution reaction. there are following types of substitution reactions.
2.4.1.1. Electrophilic substitution reaction
2.4.1.2. Nucleophilic substitution reaction
2.4.1.3. Free radical substitution reaction
2.4.1.1. Electrophilic- substitution reaction
A substitution reaction in which an atom or group as replaced by an electrophiles
called as electrophilic substitution reaction. It is denoted by SE.
e.g. chlorination of benzene in presence of Lewis acid

2.4.1.2. Nucleophilic substitution reactions

A substitution reaction in which an atom or group is replaced by a nucleophiles,
called as nucleophilic substitution reaction. it is denoted in SN.
e.g. Aqueous hydrolysis of alkyl halide
2.4.1.3. Free radical substitution
A substitution reaction in which an atom or group is replaced by a free radical called
as free radical substitution reaction.
e.g. Chlorination of methane in presence of sunlight.

1.4.2. Addition reaction

A reaction in which a molecule adds are an unsaturated compound (double or triple
bonded) to give a saturated compound called as addition reaction. It is of following
types.
2.4.2.1. Electrophilic addition reaction
2.4.2.2. Nucleophilic addition reaction
2.4.2.3. Free radical addition reaction
2.4.2.1. Electrophilic addition reaction
An addition reaction which initiates by attack of an electrophile called as electrophilic
addition reaction. e.g. Hydrohalogenation of alkenes
R-CH=CH2 + HCl → R-CHCl-CH3
2.4.2.2. Nucleophilic addition reaction
An addition reaction which starts by attack of nucleophile called as nucleophilic
addition reaction. e.g. Addition of HCN on CH3CHO

2.4.2.3. Free radical addition reaction

An addition now which starts by attack of free radical called as free radical addition
reaction. e.g. Hydrohalogenation of alkenes in presence of peroxide.
 2.4.3. Elimination reaction
A reaction in which two atoms or groups eliminate from a molecule to give an
unsaturated product called as elimination reaction. There are following types of
elimination reaction.
2.4.3.1. Unimolecular elimination reaction E1
2.4.3.2 Biomolecular elimination reaction E2
2.4.3.1. Unimolecular elimination reaction (E1 )
An elimination reaction in which rate of reaction depends in which of only one reactant
molecule called as unimolecular elimination reaction . It is denoted by E1
e.g. Reaction of tert. butyl bromide with alc. KOH

2.4.3.2. Bimolecular elimination reaction

An elimination reaction in which rate of reaction depends on cover of two reactant
molecules called as biomolecular elimination reaction E 2
e.g. Reaction of ethyl bromide with alc. KOH

2.4.4. Rearrangement reaction

A reaction in which an atom or group move from one position to other within the
molecule and form a new product called as rearrangement reaction.

2.5. Reactive intermediates

In majority of organic reactions reactants do not change directly into product, form
intermediate which are highly unstable and finally change into product . Some
intermediates are as
2.5.1. Carbocation 2.5.2. Carbanion 2.5.3. Free radical
2.5.4. Carbenes 2.5.5. Nitrenes 2.5.6. Benzynes
2.5.1 Carbocation: A reactive intermediate in which +ve charged carbon has six
electron in valance shell and has tendency to complete its octet called as carbocation. e.g.
CH3+, CH3CH2+ , (CH3)3C+ etc.
Formation of carbocation: It is formed by following ways:

Reactions of carbocation:

Structure: Carbon has Sp² hybridization in carbocation. It has trigonal structure with
bond angle 120º each and a vacant p-orbital.

Stability: The order of stability of different carbocations is as follows:

The above order can be explained by following three effects:

 1. Inductive effects: Alkyl group has +ve inductive effect so it increases electron
density on carbocation and thus increases stability of carbocation. So more the no. of
alkyl groups more will be stability of carbocation.
2. Hyper conjugation effect: It involves delocalization of σ-electrons of C-H bond in
carbocation which forms various hyperconjugating structures. So more the no. of hyper
conjugating structures more will be stability.

3. Resonance effect: It involves delocalization of +ve charge when it is in conjugation

with multiple bond. More the delocalization more will be stability.
 2.5.2. Carbanion: A reactive intermediate in which -ve charged carbon has eight
electrons in valance shell. It also has tendency to share electron pair.

Formation of Carbanion: It is formed by following ways:

C2H5O- + H - CH2CHO → C2H5OH + -CH2CHO .
RCOONa → R- + Na+ + CO2
Structure: Carbon has Sp³ hybridization in carbanion. It has pyramidal structure. It has
neither tetrahedral structure nor has bond angle 109.5º

.
Stability: The order of stability of different carbanion is as follows:

The above order can be explained by following two effects

1. Inductive effect: Alkyl group has +I effect and so it increases electron density on
carbanion and thus destabilizes carbanion . So more the no. of alkyl groups less will be
stability of carbanion.
2.Resonance effect: It involves delocalization of -ve charge when it is in conjugation with
multiple bond. More the delocalization and more will be stability.

The order of stability of different aromatic carbanions is as

The above order can be explained on basis of no. of resonating structures i.e. more the
no. of resonating structures more will be stability.

2.5.3. Free radical: A neutral intermediate in which carbon has seven electrons in
valance shell and has incomplete octet. e.g. ºCH3, CH3CH2º, (CH3)3Cº
Formation: It is formed by following ways:

Structure: Carbon has Sp² hybridization in free radical with one unpaired p orbital. It
has trigonal planer structure with bond angle 120º.

Stability: The order of stability of different free radicals is as follows:

The above order can be explained by following three effects:
1. Inductive effect: Alkyl group has +I effect and so it increases electron density on
carbon free radical and thus stabilizes it. So more the no. of alkyl groups more will be
stability of free radical.
2. Hyper conjugation effect: It involves delocalization of σ-electrons of C-H bond in
free radical that forms various hyper conjugating structures. So more the no. of hyper
conjugating structures more will be stability.

3. Resonance effect: It involves delocalization of unpaired e- when it is in

conjugation with multiple bond . More the delocalization and more will be stability.

The relative order of stability of different aromatic free radicals is as-

The above order of stability can be explained as same as for carbocation.

2.5.4. Carbenes: A divalent neutral intermediate in which C atom has six electrons
in valance shall and has tendency to complete its octet called as carbenes.
e.g. :CH2 , :CCl2 etc.
Formation: It is formed by following ways:

Structure: There are following two states of carbenes:

A. Singlet Carbene: In this state carbon atom has sp² hybridization but it does not
have trigonal shape and has angular shape due to presence of one lone pair of

electrons. It also has a vacant p- orbital . This state is shown by .

B. Triplet state: In this state carbon atom has sp hybridization with linear shape and
bond angle 180º. It also has two unpaired p-orbitals perpendicular to each other. It is

shown by .

Reactions: It gives following reactions:

1. Cyclisation: Carbenes add to multiple bond to form cyclic product. It is also called
as cycloaddition reaction.
 2. Chain insertion reaction: Carbenes inserted on C-H bond to form longer chain
compound.

2.5.5. Nitrenes: A divalent intermediate in which N- atom has six electrons in

valance shell and has tendency to complete its octet called as nitrene.

Formation: It is formed by following ways:

Structure: There are following two states of nitrenes:

A. Singlet nitrene: In this state N-atom has sp² hybridization state but it does not
have trigonal planar shape. It has one bond pair, two lone pairs of electrons and one
vacant p-orbital. It is shown by R- N.
B. Triplet nitrene: In this state N- atom has sp hybridization state but it does not
have linear shape . It has one bond pair, one lone pair of electrons and two p-orbitals
have unpaired electron . It is shown by R- N or R- N.

Reactions: It gives following reactions:

1. Cyclisation: Nitrene adds to multiple bonds to form cyclic product. It is also called
cyclo addition reactions.
 2. Chain insertion reactions: Nitrenes inserted on C-H bond to form amine.

2.5.6. Benzynes: A reactive intermediate in which benzene ring has one triple bond,
called as Benzyne. It has two types of hybridization states. sp² and sp
hybridization.
Formations: It is formed in following ways:

2.6. Methods of determination of reaction mechanism There are following methods:

2.6.1. Product analysis 2.6.2. Isotope effect
2.6.3. Determination of presence of intermediates
2.6.4. Stereochemical evidence 2.6.5. Kinetic evidence
2.6.1. Product analysis
A reaction which gives more than one product, product analysis helps in determination
of reaction mechanism. e.g. Aqueous hydrolysis of tert. butyl chloride gives a racemic
mixture of products which indicate unimolecular reaction mechanism (SN1 ).

Alkaline hydrolysis of ethyl bromide gives ethyl alcohol having inversion

configuration which indicate bimolecular reaction mechanisms (SN2 ).

3.4.2. Isotope effect

Exchange of isotope also affect rate of reaction which helps in elucidation of mechanism of
various reactions.
e.g. In dehydrohalogination of alkyl halide elimination rate of protium hydrogen is faster than
that of deuterium hydrogen.

3.4.3. Determination of Presence of Intermediates

Most of organic reactions proceed in with formation of intermediate, trapping of
intermediates helps in determination of mechanisms.
e.g. Nitrene intermediate in formed in reactions like Curtius, Beckmann etc. Its presence can
be confirmed by its trapping through Cyclisation reactions.

2.6.4. Stereochemical evidence

Stereochemistry of products also help in getting information about a reaction. e.g. Alkaline
hydrolysis of tert. butyl bromide gives racemic mix. (d & l forms) while alkaline hydrolysis
of ethyl bromide give inverted product. It shows that former proceed through S N1 mechanism
while latter proceed through SN2 mechanism.
2.6.5. Kinetic evidence: In this evidence rate of reaction is observed with reference to
various reactants participating in reaction.
e.g. Alkaline hydrolysis of tert. butyl bromide follow S N1 mechanism because rate of reaction
depends upon conc. of only one reactant.

Alkaline hydrolysis of ethyl bromide follows SN2 mechanism because rate of reaction depends
on concentration of two reactants.
2.7.Assigning formal charges
Formal charges in different intermediates and ions can be assigned by following formula ---
Formula charge = No. of valance electrons - (No. of non bonding e - or unshared electrons -
1/2 of bonding electrons)
Examples: 1. Formal charge on carbon in carbocation CH3+ = 4 - (0 + 6/2) = 4 -3 = +1
-
2. Formal charge on carbon in CH3 = 4 - (2 + 6/2) = 4 - 5 = -1

3. Formal charge on nitrogen in methyl nitrene (CH3N̤ ։ ) = 5 - ( 4 + 2/2) = 5 - 5 = 0

LONG ANSWER TYPE QUESTIONS :
1. Write short note on following : (Jhansi 2010,11,15, VBSPU 2011 )
a. Half head arrows b. double headed arrows
2. Write short note on following : (KU 2009,11,15, VBSPU 2007 )
a. Electrophiles b. Nucleophiles
c. Carbonium ions d. Carbanions e. Free radicals
3. Why is a tertiary carbocation stable whereas tertiary carbanion is unstable.
(Gorakh. 2010,11,15, VBSPU 2011 )
4.Write formation and stability of aliphatic free radicals.
(Lucknow 2010,12,15, VBSPU 2012 )
5. What are different type of organic reactions ? Explain then with examples.
(Agra 2011,15, VBSPU 2011 )
6. What are different methods of determination of reaction mechanism ?
(Jhansi 2010, Gorakh 2011 )
7. What are free radicals ? Explain stability of different types of free radicals.
(KU 2005,11,15, VBSPU 2007 )
8. Explain the following : (Jhansi 2010,11,15, VBSPU 2011 )
a. Benzyl carbanion is more stable than ethyl carbanion.
b. Tertiary carbonium ion is more stable than pri. and secondary carbonium ion.
9. What is carbocation ? Discuss the relative stability of 1֠ , 2֠ & 3֠ carbanions.
(Gorakh. 2010,11,15, KU 2011 )
10. Define the following with suitable examples: (Awadh 2005,11,15, VBSPU 2007 )
(a) Substitution reactions (b) Addition reactions
(c) Elimination reactions (d) Markownikoff's rule
(e) Anti-Markownikoff's rule
OBJECTIVE TYPE QUESTIONS :
1. +I effect is shown by ;
(a) -NO2 (b) -CI (c) –Br (d) -CH3
2. The most stable carbocation is:
(a) methyl carbocation (b) primary carbocation (c) secondary carbocation
(d) tertiary carbocation
3. A free radical is:
(a) shortly lived species (b) neutral in nature
(c) paramagnetic (d) all of these
4. Which one is the characteristic feature of a free radical?
(a) Presence of negative or positive charge (b) Presence of unpaired electron
(c) Presence of even number of electrons (d) Associated with high stability
5. Which of the following statements is wrong?
(a) A tertiary free radical is more stable than a secondary free radical
(b) A secondary free radical is more stable than a primary free radical
(c) A tertiary carbocation is more stable than a secondary carbocation
(d) A primary carbocation is more stable than a secondary carbocation
6. Which is most stable carbocation?
(a) n-Propyl cation (b) iso-Propyl cation
( c) Ethyl cation (d) Triphenylmethyl cation
7. Which of the following carbocations is most stable?

8. Which of the following is the most stable compound?

(a) Ph3C+ (b)Ph2CH +
(c) Ph2CH2 (d) PhCH2+
9. Which one of the following carbanions is the least stable?
(a) CH3CH2- (b) HC≡C-
(c) (C6H5)3C - (d) (CH3 )3C-
10. Carbenes are the reactive intermediates in:
(a) Carbylamine reaction (b ) Reimer-Tiemann reaction
(c) Hofmann's bromamide reaction (d) Wittig reaction

11. Anti-Markownikoff's addition of HBr can be observed in:

(a) propene (b) but-1-ene
(c) but-2-ene (d) pent-2-ene

ANSWERS :

1. d 2. d 3. d 4.b 5.d 6.d 7.d 8.a 9.d 10.b 11.b

CHAPTER-3

Alkanes and Cycloalkanes

3.1. Alkanes
3.1.1. Introduction: Alkanes are saturated hydrogen atoms and have general formula
CnH2n+2 where n= 1,2,3.... They are named by adding suffix -ane e.g. CH4 - methane,
C2H6-Ethane.
3.1.2. Classification: On basis of degree of substitution alkanes are classified as:
1. Primary carbon (1֠ ): A carbon atom attached with only one alkyl group.

2. Secondary carbon (2֠ ): A carbon atom attached with two alkyl groups

3. Tertiary carbon (3֠ ): A carbon atom attached with three alkyl groups

4. Quaternary carbon (4֠ ): A carbon atom attached with four alkyl groups.

3.1.3. Method of preparation: Following methods :

1. From Unsaturated Hydrocarbon (Sabatier& Sandeyer reaction):
Hydrogenation of unsaturated hydrogenation in presence of Ni gives alkanes.
e.g. Hydrogenation of ethane.

2. Reduction of alkyl halide: Reduction of alkyl halide gives alkenes.

3. By Wurtz reaction: Long chain alkanes are prepared by this method. Alkyl halides are
treated with Na in presence of ether gives alkanes.
4. By Frankland’s method: It is similar to Wurtz reaction. Zn is used in place of Na &
ether.

5. Corey-House Synthesis: Alkyl halide is treated with R2CuLi gives alkanes.

6. Kolbe electrolysis method: Na or K salt of carboxylic acid electrolyte to give alkanes.

e.g. Electrolysis of sodium acetate.

7. Decarboxylation of Salt: Decarboxylation of salt in presence of soda lime gives alkanes.

3.1.4. Physical properties:

1. Members from C1-C4 exists in gaseous state. C5 to C15 exist in liquid state and next higher
members exist in solid state.
2. They are insoluble in water but soluble in organic solvent.
3.1.5. Chemical properties: Alkanes give following reactions:
1. Halogenation: Alkanes undergo halogenation by free radical mechanism in presence of
sunlight. e.g. Chlorination of methane.
2. Nitration : With conc. HNO3 alkenes give nitro alkanes.

3. Sulphonation : With fuming H2SO4 alkanes give alkane sulphonic acid.

4. Oxidation : Under different conditions give different products as :

a. complete oxidation : Alkanes give CO2 & H2O with emission of energy.

b. Incomplete oxidation : Alkanes give partial oxidised products.

5. Pyrolysis or Cracking : Strong heating of alkanes break into lower hydrocarbons, called as
cracking or pyrolysis.

6. Isomerisation : In presence of Lewis acid an alkane change into its other isomeric alkane.

7. Aromatization : On heating in presence of catalyst change into aromatic compound.

3.2 CYCLOALKANES
3.2.1.Introduction : Cycloalkanes are saturated cyclic hydrocarbons having general formula
CnH2n where n = 3,4,5…. They are named by adding prefix cyclo-

3.2.2. Methods of preparation :

1. From unsaturated compounds : Catalytic hydrogenation of unsaturated compounds give
cycloalkane.
2. From haloalkanes : Reduction of haloalkanes give cycloalkanes.

3. Wurtz reaction : Terminal dihalides with Na in presence of ether gives cycloalkanes.

4. Frankland reaction : Terminal dihalides with Zn gives cycloalkanes.

5. Wislicenus reaction : Ca or Ba saltof dicarboxylicacids on distillation gives cyclic ketone

followed by reduction gives cycloalkane.

6. Diekmann ֙s reaction : Diesters give cycloketones followed by reduction gives

cycloalkane.

7. Perkin ֙s method : Dihalides with sodiomalonic esters give cyclic carboxylic acids
followed by decarboxylation gives cycloalkane.
8. Diel ֙s-Alder reaction : Cycloaddition of 1,3 butadiene with ethene gives cyclohexene
followed by reduction gives cyclohexane.

9. Thorpe- Ziegler ֙s method : In this method α, ω dinitriles undergo intramolecular

cyclisation and give cycloalkane.

10. Simmon ֙s- Smith reaction : Simmon ֙s- Smith reaagent adds on double bond to give
cycloalkane.

11. By Carbene : Carbenes add on double bond to give cis & trans products.

3.2.3. Physical properties : 1. Cycloalkanes from C3 – C8 exist in liquid state and next higher
members exist in solid state.
2. Melting pt. & boiling pt. increses with increase in size of molecules.
3. They are soluble in nonpolar solvent like ether and insoluble in polar solvent.
3.2.4. Chemical properties : Cycloalkanes give following reactions ;
1. Hydrogenation : Cycloalkanes on hydrogenation gives open chain alkanes.
2. Hydrohalogenation : Cycloalkanes on hydrohalogenation gives n-alkyl halide.

3. Halogenation : In presence of sunlight gives halogen substituted cycloalkane except

cyclopropane.

3.2.5. Bayer ֙s strain theory : This theory explains stability of cycloalkanes on basis of
following points ;
i. Each carbon atom in cycloalkane has sp3 hybridization but still it neither has
tetrahedral shape nor bond angle 109.5֠ . They show deviation from normal
tetrahedral bond angle which results instability of ring. So more the deviation
more will be instability of cycloalkanes.
ii. As we know that cycloalkanes show deviation from tetrahedral bond angle 109.5֠
and angle deviation or angle strain for some cycloalkanes are as :
Strain = ½(109°28’– bond angle) where all the carbon atoms in the ring are in the
same plane.

As we see from above, angle deviation decreases from cyclopropane to cyclopentane so

former is more stable and latter is less stable. Further angle deviation starts to increase which
again destabilise higher rings.
3.2.6. Limitations of Bayer ֙s strain theory : There are following limitations of Bayer ֙s
strain theory ;
 i. According to this theory Higher cycloalkanes should be unstable due to high angle
deviation but it is found that higher cycloalkanes are stable that was not explained
by Bayer ֙s theory.
ii. According to this theory cyclopropane must be very unstable but it is found that
cyclopropane has stability.
3.2.7. Theory of stainless rings : This theory was given by Sache & Mohr. According to this
theory cyclohexane and next higher rings do not exist in planar form but exist in puckered
form. Due to this deviation from normal tetrahedral bond angle is relieved. There are two
ways of puckeed structures, boat form and chair form. In these forms each C- atom has two
types of bonds, axial and equitorial bonds. A bond perpendicular plain of ring called as axial
bond and a bond parallal to plain called as equitorial bond.
Between boat & chair forms, chair form is more stable than boat form because
steric interaction occur between axial atoms in boat form while it is absent in chair form.

3.2.8. Banana bond in cyclopropane : Each C- atom in cyclopropane has sp3 hybridization

but it does not have bond angle 109.5֠ , it has bond angle 60֠ . Bond strength depends
onextent of overlapping i.e. more the overlapping more will be bond strength.
In cyclopropane C-C bond angle is not symmetrical but it is bent and give
banana shape. It gives stability to molecule.
LONG ANSWER TYPE QUESTIONS :
1. Discuss general methods of preparation of alkanes and discuss their properties.
( Agra 2007,09 VBSPU 2006,08 )
2. Write short notes on following : ( Jhansi 2011,15 KU 2006,08 )
a. Wurtz reaction b. Kolbe’s reaction
c. Corey-house reaction d. Banana bond in cyclopropane
3. Write a note on photohalogenation of reaction. ( Luck. 2001,04 VBSPU 2006,08 )
4. Write short notes on following reaction : ( Agra 2008,09 VBSPU 2006,08 )
a. Halogenation b. Nitration
c. Sulphonation d. Aromatization
5. Discuss stability of cycloalkanes on basis of Bayer’s strain theory.
( Agra 2002,09 VBSPU 2004,05 Gorakh. 2008 )
6. Explain the following : (VBSPU 2002,09 KU 2004,05 Gorakh. 2008 )
a. Why chair form is preferred over boat form ?
b. Cyclobutane is more stable than cyclopropane.
c. Cyclohexane is more stable than cyclopentane.
7. What is bayer’s strain theory ? What are its limitations ? ( Agra 2008 VBSPU 2004,11 )
8. Write short notes on following : ( Agra 2011,15 KU 2006,08 )
a. Cracking b. Freund method
c. Diel’s Alder reaction d. Wolf-kishner reduction
OBJECTIVE TYPE QUESTIONS :
1. Alkanes contain :
a. C-C bond b. C=C bond
c. C≡C bond d. Hydrogen bond
2. Alkanes have general formula ;
a. CnH2n b. CnH2n+2
c. CnH2n-2 d. CnH2n-6
3. Sodium or potassium salt of a fatty acid on electrolysis gives :
a. Alkyne b. Alkene
c. Alkane d. Diene
4. Halogenation of alkane is :
a. Electrophilic substitution b. Nucleophilic substitution
c. Free radical substitution d. None of these
5. The ring of cycloalkane consists of :
a. C atoms b. C and N atoms
c. C and S atoms d. C and O atoms
6. Cycloalkanes have general formula ;
a. CnH2n-2 b. CnH2n
c. CnH2n+2 d. CnH6n
7. The most reactive cycloalkane is ;
a. Cyclopropane b. Cyclobutane
c. Cyclohexane d. Cycloheptane
8. Formation of alkane by action of zinc and alkyl halide is called as:
(a) Wurtz reaction b. Frankland reaction
(c) Kolbe's reaction (d) Clemmensen reaction
9. When Grignard reagent (CH3MgBr) is treated with water, we get:
(a) ethane (b) ethyl alcohol
(c) methyl alcohol (d) methane
10. Action of heat on a mixture of sodium propionate and sodalime produces:
(a}methane (b) ethane
(c) propane (d)ethylene
11. Ethane can be prepared by: .
a. heating sodalime with sodium acetate b. electrolysis of sodium succinate
c. electrolysis of sodium acetate d. all of these
12. Wurtz reaction is used to prepare:
a. methane only b. symmetrical alkanes
c. Unsymmetrical alkanes d. all of these
13. For the conversion of CH3OH into methane, the reagent used is:
a. sodium b. P and HI
c. hydrogen d. sodium hydroxide
14. By Wurtz reaction, a mixture of methyl iodide and ethyl iodide gives:
a. propane b. ethane
c. butane d. a mixture of the above three
15. Select the correct statement about alkanes:
a. they are polar in nature b. they are soluble in water
c. they are non-combustible d. their dipole moment is zero
16. Photochemical chlorination of alkane is initiated by a process of:
a. pyrolysis b. substitution
c. homolysis d. peroxidation
17. Zinc-copper couple that can be used as a reducing agent is obtained by:
a. mixing zinc dust and copper gauze b. zinc coated with copper
c. copper coated with zinc d. zinc and copper wires welded together

ANSWERS ;
1.a 2.b 3.c 4.c 5.a 6.b 7.a 8.b
9.d 10.b 11.d 12.b 13.b 14.d 15.d 16.c
17.a
 CHAPTER-4
STEREOCHEMISTRY OF ORGANIC COMPOUNDS
4.1 ISOMERISM:
A phenomena in which two or more compounds having same molecular formula but
have different physical and chemical properties, called as Isomerism and forms are
called as isomers.
Types of Isomerism: Following types of Isomerism

4.2. Structural isomerism: Following types;

4.2.1. Chain isomerism: An structural isomerism which has different no. of carbon atoms in
chain, called as chain isomerism e.g. C4H10 has following chain isomers-

4.2.2. Position isomerism: A structural isomers which has difference in position of

functional group called as position isomerism. e.g. C3H7OH has following two isomers:

4.2.3. Functional isomers: A structural isomerism which has difference in position of

functional groups having same molecular formula called as functional isomerism.
e.g. C3H7OH has following isomers-

4.2.4 Metamerism: A structural isomerism which has different alkyl groups attached with
same functional group called as metamerism e.g. C4H10O has following isomers-
C2H5OC2H5 CH3OC3H7
4.2.5. Tautomerism: A structural isomerism in which H-atom transfer from one centre to
other centre and a dynamic equilibrium exists between these forms called as tautomerism. It
is also called as keto-enol tautomerism.

4.3.Stereoisomerism: It arises due to different arr5angement of atoms in 3-dimensional

space called as stereoisomerism. It is of following two types;
4.3.1. Optical 4.3.2. Geometrical
4.3.1. Optical isomers: An stereoisomerism in which optically active compound rotate plane
polarized light either right side or left side called as optical isomerism and isomers called as
optically active isomers. The isomers that rotate plane polarized light to right side called as
dextro rotatory (d-form) and isomer that rotate light towards left side called as laevo rotatory
(l-form)
Plane polarized light: Normal light has oscillations in all directions but when it is passed
through a polarizer (Nicol prism) then oscillation occurs only in single direction such a light
is called as plane polarized light.

4.3.1.1. Elements of symmetry: Following types of elements of symmetry

A. Plane of symmetry
B. Axis of symmetry
C. Centre of symmetry
A. Plane of symmetry: A hypothetical plane which divides a molecule into two equal halves
called as plane of symmetry. It is denoted by σ:
e.g. Plane of symmetry in meso tartaric acid
B. Alternating axis of symmetry: An element of symmetry in which a compound is rotated
through a hypothetical axis called as alternating axis of symmetry. it is denoted by Cn.
e.g. Cyclohexane has six fold axis of symmetry i.e. gives same appearance 6 times in 360
rotation.
C. Centre of symmetry: An imaginary point in a molecule from which if lines are drawn,
molecule can be divided into two equal parts. It is denoted by ‘i’
e.g. 3, 4 dimethyl cyclohexane 1,4 dioic acid has centre of symmetry

4.3.1.2. Chirality or Asymmetric Centre: A compound is said to be chiral or asymmetric

when it cannot be divided into two equal parts i.e. it does not have any element of symmetry.
A chiral compound is optical active compound as it can rotate plane polarized light either
right side (clockwise) or left side (anti clockwise). e.g. d & l forms of lactic acid.
4.3.1.3. Optical isomerism in Lactic acid: It is an optically active compound because it has
one chiral centre. Its formula is CH3CHOHCOOH. It has following isomers.
a. d(+) lactic acid: It rotates plane polarized light towards right side. This isomer is called as
dextrorotatory or d(+)form.
b. (+) Lactic acid: It rotates plane polarized light towards left side. This isomer is called as
laevorotatory or l (-) form.

c. Racemic mixture form: An equimolar mixture of d & l form is called as racemic mixture.
It is an optically inactive form.
Enantiomers: Those optically active forms which form non super imposable mirror image of
each other are called as enantiomers. e.g. d & l forms of lactic acid are enantiomers
4.3.1.4.Optical Isomerism in Tartaric acid: Tartaric acid has formula HOOC
CHOHCHOHCOOH. It has two chiral centers and has following isomers.
a. d(+) Tartaric acid: This isomer rotates plane polarized light towards right side. It is called
as dextrorotatory or d(+) form.
b.l (+) Tartaric acid: It rotates plane polarized light towards left side. It is called as laevo
rotatory or l(+) form.

c. Meso Tartartic acid: It is an optically inactive form because it has a plane of symmetry
and can be divided into two equal parts so it does not rotate plane polarized light.

d. Racemic mixture form: An equimolar mixture of d & l form of tartaric acid is called as
racemic mixture. It is an optically inactive form.
4.3.1.5. Erythro & Threo isomers: Erythro & Threo words are used to differentiate
diasteromers containing two chiral centers which are bonded with two pairs of common
atoms or groups. Erythro & threo are carbohydrates so they are also called as erythrose &
threose. A form in which similar groups are present on same side called as Erythro form
while a form in which similar groups are present on opposite sides are called as Threo form.
Both Erythro & Threo forms also have two optically active forms named as d or l form.
Diasteromers: Those optically active or inactive forms which are non super impossible
mirror image of each other are called as diasteromers. e.g. d-Erythrose & d- threose, d-
Erythrose & l-threose l-Erythrose & l-threose, l- Erythrose & d- threose
Racemisation: A process in which there is possibility of formation of two products in equal
amount and they are enantiomers, called as racemisation. e.g. Aqueous hydrolysis of 2-
bromobutane by NaOH.

Inversion of Configurations (walden Inversion) : When a reaction takes place at a chiral

centre so that product has invert configuration to that of reactant called as Inversion of
configuration (walden inversion) e.g. Aqueous hydrolysis of 2- bromobutane in presence of
aqueous NaOH gives 2-butanol. This new occurs through S N² mechanism. It this reaction
both leaving and attacking groups partially attach of rate determining step which finally give
invert product.

Retention of Configuration: A reaction in which product retain configuration to that of

reactant is called as retention of configuration. e.g. Reaction for 2- butanol with SOCl 2 gives
2-cholorobutane form with retention of configuration. This reactions occurs through internal
nucleophilic substitution reaction (SNi).

4.3.1.6. Resolution of Racemic mixture: Following methods are used for resolution of
racemic mixture:
A. Mechanical separation
B. Biochemical separation
C. Chemical separation
A. Mechanical Separation: It is an old method of separation. In this method crystals of
racemic mixture are separated by hand picking.
B. Biochemical Separation: It was discovered by Pasteur, certain microorganism like
penicillium are allowed to grow on racemic mix. so that one of isomer is consumed by
organism and other isomer is left. It is an economically lossful method.
C. Chemical methods: In this method racemic mix. is treated with some chemicals which
form diasteromeric salts which have different properties like solubility, melting pt. etc. It
helps in separation of mixture..)
4.3.1.7. D-L Configuration (Relative configuration): Before 1951, There was no absolute
method for determination of configuration of a molecule. To resolve this problem
glyceraldehyde was taken as standard. It exists in two forms D-glyceraldehyde & L
glyceraldehyde. D-glyceraldehyde has secondary -OH group on right side while L-
glyceraldehyde has sec.-OH group on left side.

In this system configuration of an unknown compound is determined relative with D & L

glyceraldehyde so it is also called as Relative configuration. A compound which can be
converted or prepared from D called as D form while from L called as L. form.

4.3.1.8. R-S Nomenclature or Absolute configuration: In 1951 three scientist Cahn, Ingold
& Prelog proposed a configuration called as R-S Configuration or absolute configuration
Here R & S are symbols for latin words Rectus & Sinister which mean right & left sides
respectively. This rule is based on following sequence rules –
Sequence Rule 1: According to this rule all four atoms or groups attached with central
carbon have their priority on basis of atomic numbers i.e. an atom with highest atomic no. has
highest priority while an atom with least atomic no. has least priority.
Sequence rule 2: According to this rule if two or more atoms attached with central carbon
are same then priority is decided by next atom. e.g. If –CH 3 & -C2H5 groups are attached with
central carbon, -C2H5 gets priority over –CH3 .
Sequence rule 3: According to this rule if a group has multiple bonds then it is counted
double and triple times. e.g. -C = C- counted two times.
Sequence rule 4: If a group or atom with least priority does not present at bottom then all
groups are rotated so that atom with least priority comes at bottom.
Assignment of R.S configuration for some molecules:
4.3.2. Geometrical Isomerism: An stereoisomerism which arise due to restricted rotation
along double bond or cyclic system called as geometrical isomerism. A form which has
similar groups on same side called as cir form and a form which has similar groups on
opposite side called as transform so this isomerism is also called as cis-trans isomerism.

4.3.2.1. Geometrical isomerism in Oximes: Oximes are formed by reaction of carbonyl

compounds (Aldehydes or ketones) with hydroxylamine as
Due to C= N oximes also show geometrical isomerism as free rotation is not possible . It has
two forms syn & anti forms. A form which has both H & -OH group on same side called as
syn form which H & - OH on opposite side called as anti form.

4.3.2.2. E-Z Nomenclature: If three or four different groups are attached along C=C double
bond then cis-trans nomenclature cannot be applied . So a new system of nomenclature E-Z
nomenclature was applied. Here E & Z symbols are used for German words Entgegen &
zussamen which mean opposite and together respectively. It is based on following sequence
rules.
Sequence rule 1: According to this rule priority of groups depend upon atomic no. i.e. atom
with highest atomic no. gets highest priority and atom with least atomic no gets least priority.
Sequence rule 2: According to this rule of groups or atoms of some priority remain on same
side isomer denoted by symbol ֜Z֜ and of groups or atoms of some priority on opposite side
isomer denoted by symbol ֜E֜.

Representation of 3-dimensional structure of organic Compounds: Following formulae

have been used to represent 3-dimensional structure of molecules .
1. Fischer Projection formula
2. Newmann projection formula
3. Sawhorse projection formula
4. Flying wedge formula
1. Fischer Projection formula: In this formula vertical lines show bonds that below plane of
paper and horizontal lines show bonds that above plane of paper. The inter section of vertical
& horizontal times show carbon atom or chiral centre. e.g. Tartaric acid

1. Newmann Projection Formula: The molecule as viewed from front side so that
nearer carbon atom is shown by point and further carbon as shown by circle each
carbon has three atoms or groups at an angle of 120֠ each.

2. Sawhorse projection formula: Two adjacent carbon atoms diagonally slanted so that
rearer C-atom left side and farther C-atom right side. Each C-atom has three atoms or
groups at 120º angle to each other.
3. Flying Wedge formula: Two carbon atoms are attached by plane bond, remaining
groups are attached with dotted line and thick line . Dotted line show below the
plane or away from observer while thick line show above the plane or towards the
observer.

4.4. Conformational isomerism: An isomerism which gives different isomers due to

free notation along C-C single bond called as conformational isomerism. Different
isomers are called as compounds or conformational isomers.
4.4.1.Conformational isomerism in ethane : Following conformers are formed ;
1. Staggard confirmer: This from has all H-atoms apart from each other and have
minimum repulsion.
2. Eclipsed confirmer: This form has all H-atoms as close as to one another and have
maximum repulsion.
3. Gauche or skew conformer: A rotation of 60º from staggard to eclipsed form
gives a no. of conformers called as gauche or skew forms which have intermediate
stability.
The relative stability of above conformers as follows: Staggard > Gauche > Eclipsed
4.4.2. Conformational isomerism in n-butane : following conformers are formed.
1. Antiform: Both terminal methyl groups are present on opposites side called as anti
form or fully staggard form . It is most stable from with lowest energy.
2. Syn form: Both terminal methyl groups overlap each other called as syn form or
fully eclipsed form. It is least stable form with highest energy.
3. Partially staggard form: Both terminal methyl groups are present opposite to H-
atoms called as partially staggard form.
4. Partially eclipsed form: Both terminal methyl groups overlap H-atoms called as
partially eclipsed form.
5. Gauche forms: Conformers other than above called as Gauche or show forms.
Energy of n-butane changes with rotation due to formation of different conformers as
shown below :
 4.4.3. Conformational isomerism in cyclohexane: According to Sache & Mohr
theory cyclohexane exists in following two puckered forms:
1. Chair form: Cyclohexane has boat form, each carbon has two H atoms, one in
axial and other is equitorial. It is less stable than chair form due to axial interaction.
2. Chair form: Cyclohexane has chair form. In this form no axial interaction so it is
more stable than boat form.

4.4.4. Conformation of monosubstituted cyclohexane:

Monosubstituted cyclohexane exists in two forms. Axially substituted and Equatorially
substituted. e.g. Methyl cyclohexane exists in axial and equitorial forms. Equitorial form is
more stable than axial form because in former case no interaction takes place between -CH 3
group and other atoms while in latter case steric interaction occurs.
4.4.5. Conformation of disubstituted cyclohexane: To explain conformation of
disubstituted cyclohexane we take example of 1,3 dimethyl cyclohexane. It exists in forms
like cis diaxial, cis diequitorial and trans axial-equitorial. Among these forms cis diequitorial
is most stable while cis diaxial is least stable form. This is because cis diaxial has most steric
interaction while cis diequitorial has least steric interaction, trans axial equitorial has
intermediate stability.
LONG ANSWER TYPE QUESTIONS :
1.What do you mean by isomerism? Discuss the different types of structural isomerism with
example. (Kanpur 2011, VBSPU 2009)
2. Write short notes on following : ( Jhansi 2010,11,12, VBSPU 2007,15 )
i. specific rotation ii. Elements of symmetry
iii. Molecular Chirality iv. Stereogenic centre
3. Define term optical activity. ( Agra 2004 , VBSPU 2005 )
4. 2. Write short notes on following : ( Jhansi 2008,09,10, VBSPU 2007,15 )
i. Enantiomers ii. Diasteromer
iii. Meso Form iv. Racemisation
5. Write short notes on following : ( Jhansi 2005,10, Agra 2000,02,03 )
i. specific rotation ii. Elements of symmetry
iii. Molecular Chirality iv. Stereogenic centre
6. What are sequence rules? How are these used for assigning R and S configurations ?
Discuss with suitable examples. ( Jhansi 2009,14, K.U. 2000,02,03 )
7. Write short notes on following : ( Jhansi 2010,11,12, VBSPU 2007,15 )
i. Geometrical isomerism ii. E-Z system of nomenclature
iii. Conformation
8. Assign R or S configuration to each of following :

9. Write a note on retention of configuration.

10. Which of following pairs show geometrical isomerism ?

OBJECTIVE TYPE QUESTIONS :

1. The isomers of a compound posses the same :
a. Molecular weight b. Same physical & chemical properties
c. Structura formula d. Same functional group
2. Which of the following compound shows geometrical isomerism :
a. 1-Pentene b. 2-Pentene
c. 2-methyl, 2-pentene d. 2-methyl, 2-butene
3. Geometrical isomerism due to C=N bond is shown by :
a. Aldoxime b. Ketoxime
c. Phenyl hydrazone d. All of above
4. Which conformation has highest potential energy :
a. Eclipsed b. Skew
c. Staggard d. All of above
5. d- Tartaric acid & meso tartaric acids are :
a. Diasteromers b. Enantiomers
c. Staggard d. All of above
6. D (-) lactic acid has :
a. R- configuration b. S- configuration
c. May be R or S configuration d. None of the above
7. Which of following compound is optically active :
a. CHCl3 b. CH3CH2OH
c. CH3CH2COOH d. CH3CH(OH)COOH
8. Which of following compound exhibit geometrical isomerism :
a. X2C=CY2 b. X2C=CXY
c. XYC=CXY d. XYY2C=CXY
9. Molecule is chiral if :
a. contains plane of symmetry b. contains centre of symmetry
c. nonsuperimposable on its mirror image d. superimposable on its mirror image
10. R & S nomenclature is used by :
a. conformation isomers b. configurational isomers
c. geometrical isomers d. optical isomers
11. Isomers that can be converted through rotation about single bond are :
a. conformers b. diastermers
c. enantiomers d. positional isomers
12. Reason for geometrical isomerism is :
a. Presence of asymmetric carbon atom b. presence of different groups on C=C
c. restricted rotation around C=C d. different groups on same carbon

ANSWERS ;
1.a 2.b 3.d 4.a 5.a 6.a 7.d 8.c 9.c
10.d 11.a 12.b
 CHAPTER-5
Alkenes, Cycloalkenes, Dienes and Alkynes

Alkenes
5.1.1. Introduction: Alkenes are unsaturated hydrocarbons acyclic hydrocarbon containing
at least one carbon to carbon double bond and have general formula C nH2n where n= 2,3,4....
Each carbon atom has sp2 hybridization. They are named by adding suffix –ene.
e.g. CH2=CH2, CH3-CH=CH2, CH3-CH=CH- CH3
Ethene, Propene Butene-2

5.1.2. Methods of preparation: There are following method for preparation of alkenes.
1. By dehydration of alcohol: In this method alcohol is treated with dehydrating agent like
conc. H2SO4 or P2O5 to give alkenes.
e.g. Dehydration of ethanol in presence of conc. H2SO4 to give Ethene.

Mechanism: It occurs in following steps-

Note: When an alcohol on dehydration give more than one alkene then that alkene will be
major product which is more substituted.
e.g. Dehydration of 2-butanol gives two types of alkenes (1- butene & 2- butene). In these
alkenes 2 -butene is major product.
 3. From alkyl halide: In this method alkyl halide is treated with alcoholic KOH to give
alkene.. e.g. - ethyl chloride treated with alco. KOH to give Ethene.

Mechanism: It occurs in following steps-

E1 Mechanism: An elimination reaction in which one molecule participate in rate

determining step is called as unimolecular elimination reaction.
e.g. Dehydrochlorination of tertiary butyl chloride.
Mechanism: It occurs in following steps-

E2 Mechanism: An Elimination reaction in which two molecules participate in rate

determining step is called as bimolecular elimination reaction.
e.g. Dehydro chlorination of 1- chloro propane.

3. By dihalides: In this method dehalogenation of vicinal dihalides in presence of zinc gives

alkene. e.g. Dechlorination of 1-2 dichloroethane in presence of Zn.
4. Kolbe’s method: In this method Na are K salt of dicarboxylic acid is electrolyzed to give
alkene. for e.g. - Electrolysis of potassium succinate gives Ethene.

Saytzeff rule: According to this rule when there is possibility of formation of more than one
alkene that alkene is major product which is more substituted.
e.g. Dehydration of 2-butanol gives two types of alkenes (1-butene, 2-butene ) so butene-2 is
major product.

Hoffmann rule: According to this rule when there is possibility of formation of more than
one alkene that alkene is major product which has less substituted. This is because tertiary
amine react with carbocation to form quaternary intermediate and intermediate losses proton
to give less substituted alkene. e.g. Dehydration of 2-butanol in presence of trimethyl amine.
Physical properties: a. Alkenes from C2-C4 exist in gaseous state, from C5-C14 exist in liquid
state and next higher members exist in solid state.
b. Melting point and boiling point increases with increases in chain length.
c. They are soluble in non polar solvent like benzene and in soluble in water.
Chemical Properties:
I. Electrophilic addition reaction : Alkenes undergo electrophilic addition reactions which
are as follows:
A. Hydration of alkenes: Hydration of alkenes gives alcohol .
e.g. Hydration of Ethene to give ethanol.

Mechanism: It involve following steps.

MarkoniKov’s rule: According to this rule when a polar reagent adds on asymmetric alkene
the negative part of reagent goes to that double bonded carbon which has less number of
hydrogen atoms.
e.g.: Hydration of propene gives a mixture of 2-propanol & 1-propanol in which & 2-
propanol is major product.

2. Hydroboration-oxidation reactions: This method is used for preparation of Pri. alcohol.

In this method asymmetric alkene (Propene) is treated with diborane to give tri alkylborane
followed by oxidation give pri. alcohol.
e.g. Hydroboration oxidation of propene give 1-propanol as follows:
3. Hydrohalogenation: Hydrohalogenation of alkene gives alkyl halide.
e.g. Reaction of propene with HBr gives a mixture of alkylhalide in which 2-Bromopropane
is major product according to Markonikov’s rule.

5. Halogenation: Halogenation of alkene gives dihalide. e.g. Reaction of Ethene with

bromine to form 1,2 dibromo ethane.
6. Addition of hypohalous acid (HOCl) : Addition of hypohalous acid on alkene gives
haloalcohol. e.g. Reaction of hypoclorus acid on ethene gives 2 chloroethanol.

7. Addition of sulphuric acid H2SO4 ; Addition of H2SO4 acid on alkene gives bisulphate
followed by hydrolysis gives alcohol.
e.g. Reaction of ethene with Sulphuric acid gives ethane bisulphate followed by hydrolysis
gives ethanol.

8. Ozonolysis: Reaction of alkene with ozone first gives an intermediate called as ozonide
followed by hydrolysis gives carbonyl compound (aldehyde or ketone) .
e.g. Reaction of ethene with O3 first gives ozonide followed by hydrolysis give two
molecules of formaldehyde.

Note: This reaction has significance in determination of types of alkene and carbonyl
compound for e.g. Propene of on ozonolysis gives one molecule of Formaldehyde and one
molecule of acetaldehyde.
Hydrogenation of alkene: Hydrogenation of alkene in presence of catalyst (Ni or Pt) gives
alkane. e.g. Hydrogenation of ethene gives ethane.

II. Polymerization: A process in which a large no. of molecule combined together to form a
large molecule is called as polymerization & the molecule is called as polymer.
e.g. Polymerization of ethene gives polythene.

III. Substitution reaction: Alkanes undergo substitution reaction to give substituted product.
Ÿ e.g. Chlorination of propane & high temperature gives 3-chloropropane.

Cycloalkenes
5.2.1. Introduction: Ÿ Those cyclic hydrocarbon which have one or more double bond (=)
are called as cycloalkene. They have general formula CnH2n-2.

5.2.2. Methods of preparation: There are following methods;

1. Dehydration of cyclic aclohol: Dehydration of cyclic aclohol in presence of concentrate
H2SO4 gives cycloalkenes.
e.g. Dehydration of cyclohexanol gives cyclohexene.

2. Dehydrohalogenation of cyclic alkylhalide: Dehydrohalogenation of cyclic alkylhalide in

presence of alc. KOH gives cycloalkenes.
e.g. Dehydrochlorination of chloro cyclohexane gives cyclohexene.

3. Dehalogenation of vic. dihalides: Dehalogenation of cyclic dihalide in presence of Zn

gives cycloalkene.
e.g.: Dechlorination of 1, 2- dichlorocyclohexane gives cyclopropene.

5.2.3. Chemical properties: Cycloalkenes give following reactions:

1. Hydration of cycloalkene: Hydration of cycloalkene gives cyclic alcohol.
e.g. Cyclobutene with H2O gives cyclobutanol

2. Hydrohalogenation of cycloalkene: hydrohalogenation of cycloalkene gives

halocycloalkane.
e.g. Cyclopropene with HCl gives chlorocyclopropane.

3. Halogenation of cycloalkene: Halogenation of cycloalkene gives cyclic dihalides.

e.g. Cyclopropene with Cl2 gives 1,2 dichloro cyclopropane.
4. Hydrogenation of cycloalkene: Hydrogenation of cycloalkene gives cycloalkane.
e.g. Hydrogenation of cyclopropene gives cyclopropane.

5. Ozonolysis of cycloalkene: Ozonolysis of cycloalkene gives dicorbonyl compound.

e.g. Cyclopropene on ozonolysis gives 1,3 propanedial

Dienes
5.3.1. Introduction: Those compound which contain two double bonds are called as dienes.
They have general formula CnH2n-2.
5.3.2. Types of dienes: There are following types:
1. Cumulated dienes: Those dienes in which double bonds are present on adjacent C-atoms
are called as cumulated dienes. e.g. Allene.

2. Conjugated dienes: Those dienes in which double bond and single bond are present at
alternate position are called as conjugated dienes. e.g.

3. Isolated dienes: Those dienes in which double bonds are separated by more than one
single bond, are called as isolated dienes. for e.g. 1,4 penta- diene.
Allene
5.4.1. Structure of cumulated dienes: Allene is an example of cumulated diene. The
terminal carbon atoms have sp² hybridization and central carbon has sp hybridization. The
bond angle formed by the three carbons is 180°, indicating linear geometry for the carbons of
allene. It can also be viewed as an "extended tetrahedral" with a similar shape to methane. It
is shown in the following structure.

5.4.2. Method of preparation of allene: There are following methods

1. From gem-dihalide: Dehydrohalogenation of 2,2-dichloropropane gives allene

2. Dehalogenation: Dechlorination of 2,3 dichloro propene gives allene

3. Dehydration: Dehydration of propene 2-ol gives allene.

5.4.3.Chemical properties: Allene gives following reactions:

1. Hydrogenation: Hydrogenation of allene gives propane.

2. Halogenation: Chlorination of allene gives tetra halide.

3. Hydrohalogenation: Hydrohalogenation of allene gives gem dihalide .

4. Ozonolysis: Ozonolysis of allene gives 2 molecules of formaldehyde and one molecule of

CO2.

1,3-butadiene
5.5.1. Structure of 1,3-butadiene: Each carbon in buta-1,3-diene is sp 2 hybridization and the
sp2 hybridized orbital of C1 is overlap with 1s orbital of 2 H atom to form sp 2 -s σ-bond and
also sp2 orbital of C2 to form sp2 - sp2 σ-bond. Similarly C4 and C2 overlap with 1s of 1H
atom to form sp2-s σ-bond and it is also overlapped with C1 and C3. Hence the σ bond
structure of 1,3-butadiene is represented as

5.5.2. Methods of preparation: There are following methods

1. Dehydration of 1,4 butane diol: Dehydration of 1,4 butane diol gives 1,3 butadiene.

2. By dehydrohalogenation of 1,4- dichlorobutane: Dehydrochlorination of 1,4

dichlorobutane gives 1,3 butadiene.
3. From cyclohexene: By ding cyclohexene its breaks into 1,3 butadiene and ethene.

4. By dehydrogenation: Dehydrogenation of 1-butene gives 1,3 butadiene.

5.5.3. Chemical properties : It gives following reactions:

1. Hydrogenation: Hydrogenation of butadiene gives mixture of two products called as
butene-1 & butene -2 in which butene -2 is major product.

2. Halogenation: Chlorination of butadiene gives a mixture of two product in which 1,4

product is (major).

3. Hydrohalogenation: Hydrochlorination of butadiene gives a mixture of two products in

which 1,4 product is major product.
4. Hydration: Hydration of butadiene gives a mixture of two products in which 1,4 product
is major product.

5. Ozonolysis: Ozonolysis of butadiene gives two molecules of formaldehyde are molecule

of glyoxal.

6. Diel’s Alder reaction: Butadiene reacts with ethene to give cyclohexene.

Alkynes
5.6.1. Introduction: Those unsaturated hydrocarbons which have C≡C are called as alkynes.
They have general formula CnH2n-2 . Where n= 2,3,4............ Each carbon in alkyne has sp
hybridization and they are named by adding suffix -yne.
The first few members of this series are represented by the following structures:

5.6.2. Classification of Alkynes: Generally alkynes can be categories in to following two

categories.
a. Terminal Alkyne: A Terminal Alkyne is an alkyne in whose molecule there is at least one
hydrogen atom bonded to a triply bonded carbon atom. Or simply, the alkynes in which the
triple bonded carbon atoms are at the extreme positions.

Where, both R will be H or same alkyl group

b. Non-terminal alkynes: Non-Terminal Alkynes, on the other hand have triple bond at any
place other than the end positions.

5.6.3. STRUCTURE AND BONDING IN ALKYNES : Each carbon atom of ethyne has
two sp hybridized orbitals. Carbon-carbon sigma (σ) bond is obtained by the head to head
overlapping of the two sp hybridized orbitals of the two carbon atoms. The remaining sp
hybridized orbital of each carbon atom undergoes overlapping with the 1s orbital of each of
the two hydrogen atoms in the same plane to form two C-H sigma bonds. The H-C-C bond
angle is of 180°. Each carbon has two unhybridized p orbitals which are perpendicular to
each other as well as to the plane of the C-C sigma bond. The 2p orbitals of one carbon atom
are parallel to the 2p orbitals of the other carbon atom, which undergo sidewise overlapping
to form two π bonds between two carbon atoms. Thus ethyne molecule has two C–C π bonds,
two C–H σ bonds and one C–C σ bond, ethyne is a linear molecule.

5.6.4. Method of preparations: There are following methods.

1. Dehydrogenation: Dehydrogenation of hydrocarbons give alkyne.
e.g. Dehydrogenation of ethane first give ethene and then ethyne.

2. Dehydrohalogenation of vic. dihalides: Dehydrohalogenation of vic. dihalides gives

alkyne. e.g. Dehydrochlorination of 1,2 dichloro ethane gives ethyne.

3. Dehalogenation of tetrahalides: Dehalogenation of tetrahalides in presence of Zn gives

alkyne. e.g. Dechlorination of tetrachloro ethane gives ethyne.

4. Kolbe’s method: In this method electrolysis of Na or K salt of unsaturated dicarboxylic

acids gives alkyne. e.g. Potassium maleate on electrolysis gives ethyne.

5. From chloroform: Reaction of chloroform with silver (Ag) gives ethyne.

6. From Alkyne: Higher alkynes can be prepared by the reaction of Na or K acetylide with
alkyl halide. e.g. Reaction of sodium acetylide with methylchloride gives propyne.
5.6.5. Physical Properties: 1. First three members from C2 - C4 exist in gaseous state
members from C5 –C8 exist in liquid state and next higher members exist in solid state.
2. Melting point and boiling point increases with increase in molecular weight.
3. Acetylene is partially soluble in polar solvent but other numbers are not soluble in polar
solvent. They are soluble in non polar solvent like benzene.
5.6.6. Chemical Properties: They show following properties:
I. Acidic nature: Acetylene has acidic character due to very high percentage of s-character.
With highly reactive metals or base it form salt.
e.g. Acetylene with sodamide & sodium form sodium acetylide as-

II. Electrophillic addition: Alkynes give following addition reactions :

1. Hydrohalogenation: Alkynes undergo hydrohalogenation to give dihalide.
e.g. Acetylene with HBr gives 1,1 dibromo ethane.

2. Halogenation: Alkynes on halogenation gives tetra halide.

e.g. Propyne on chlorination gives 1,1,2,2 tetra chloro propane.

3. Hydrogenation: Alkyne on hydrogenation first gives alkenes and then alkane.

e.g. Ethyne on hydrogenation first gives ethene and then ethane.

4. Hydration: Alkynes on hydration gives enol compounds which tautomerise to give

aldehyde or ketone. e.g. Propyne on hydration gives acetone.
5. Hydroboration-oxidation: Hydroboration of alkyne first gives trialkenyl borane followed
by hydrolysis gives aldehyde or ketone.
e.g. Propyne on hydroboration - oxidation gives propanal.

6. Addition of hypochlorus acid: Addition of two molecules of hypochlorus acid gives

dichloro aldehyde or ketone.
e.g. Propyne adds two molecules of hypochlorus acid gives dichloro propanone.

7. Ozonolysis: Alkyne on ozonolysis first gives an intermediate called as ozonoide which

hydrolyzed to give dialdehyde or diketone.
e.g. Acetylene and propyne on ozonolysis first give ozonide which hydrolyze to give
dicarbonyl compounds.

8. Addition of sulphuric acid: Alkyne adds sulphuric acid to give bisulphate followed by
hydrolysis gives enol form with tautomerise to give corbonyl compound.
e.g. Acetylene with sulphuric acid give acetaldehyde.
III. Nucleophilic addition reaction: There are following reaction:
1. Addition of HCN: Alkyne adds HCN _ to give nitrile.
e.g. Acetylene adds HCN to give propene nitrile or cynoethene.

IV. Polymerization: Three molecules of acetylene polymerize together to give benzene.

LONG ANSWER TYPE QUESTIONS :

1. Discuss the general methods of preparation of alkenes and discuss their properties.
( Kashi 2007,12 VBSPU 2010,15 )
2. Write short notes on following : ( KU 2009,12 Gorakh 2007,15 )
a. Hydroboration oxidation b. Hydroxylation
c. Epoxidation d. Saytzeff rule
3. What is ozonolysis ? How it is used to known the structure of alkene ? Illustrate your
answer with ozonolysis of 2-methyl 2-butene and 2-methyl propene -1.
( KU 2004,12 VBSPU 2011,15 )
4. Write short notes on following : ( KU 2006,12 VBSPU 2010,11,15 )
a. oxidation of alkenes b. Peroxide effect
c.Ozonolysis d. Reduction of alkynes under different condition
5. Give the mechanism of addition of HBr to propene in presence of peroxide.
( KU 2003,12 VBSPU 2000,11 Luck. 2002,03 )
6. 4. Write short notes on following : ( KU 2006,12 VBSPU 2010,11,15 )
a. Dehydration of alcohols b. Dehydrohalogenation of alkyl halide
c.Oxymercuration- demercuration d. Reduction-oxidation of alkenes
7. What are dienes? Classify them. Give M. O. picture of 1,3 butadiene.
( KU 2002,09 VBSPU 2007,11 Luck. 2008)
8. Give a brief account of electrophilic addition of 1,3 butadiene. (Gorakh 2001 )
9. What are allenes ? describe their methods of preparation and properties.
( KU 2002,07 VBSPU 2009,11 Luck. 2008)
10. What are alkynes ? describe their methods of preparation and properties.
11. Discuss relative acidity of ethane, acetylene and ethylene.
OBJECTIVE TYPE QUESTIONS :
1. Ethylene is produced by:
(a) dehydration of acetic acid (b) electrolysis of methyl alcohol
(c) mixing acetic acid and calcium formate (d) passing C2H5OH vapors over hot Al2O3
2. Baeyer's reagent is:
(a) alkaline KMn04 solution (b) acidic KMnO4 solution,
(c) neutral KMnO4 solution (d) aqueous bromine solution
3.The negative part of the addendum adds on to the unsaturated carbon atom joined to the
least number, of hydrogen atoms. This statement is called:
(a) Saytzeff rule (b) Kharasch effect
(c) Markownikoff's rule (d) Anti-Saytzeff rule
4. 1,2-dibromopropane on reaction with ale. KOH yields:
(a) acetylene (b) propylene
(c) propyne (d) none
5. ...... is obtained when iodoform is heated with Ag powder.
(a) CH4 (b) C2H4
(c) C2H6 (d) C2H2
6. Benzene is a polymer of:
(a) methane (b) acetylene
(c) ethane (d) ethylene
7. Acetylene on ozonolysis gives:
(a) glycol (b) glyoxal and formic acid
( c) formaldehyde (d) none of the above
8. Addition of HOCl to ethyne gives:
(a) ethyl chloride (b) vinyl chloride
(c) dichloroacetaldehyde (d) ethylidene chloride
9. Which of the following is the most stable alkene?
(a) R2C=CR2 (b) RCH=CHR
(c) RCH=CH2 (d) H2C=CH2
10. Which of the following on reductive ozonolysis give only glyoxal?
(a) Ethylene (b) Benzene
(c) Toluene (d) Acetylene
11. Anti-Markownikov's addition of HBr is/are observed in :
(a) propene (b) but-I-ene
(c) but-2-ene (d) pent-3-ene
12. Which of the following reagents can be used to distinguish between propene and
propyne?
(a) Schiff's reagent (b) Lucas reagent
(c) Grignard reagent (d) Ammonical AgN03
13. Hydration of which one of the following yields a ketone?
(a) Propyne (b) Ethene
(c).Propene (d) Ethyne
14. Which of the following gives propyne on hydrolysis?
(a) AI4C3 (b) Mg2C3
(c) B4C (d) La4C3

ANSWERS ;
1.d 2.a 3.c 4.d 5.d 6.b 7.c
8.c 9.a 10.a 11.c 12.d 13.a 14.b
CHAPTER- 6
Arenes and Aromaticity
6.1. Introduction : Arene is generally used for aromatic hydrocarbons. Benzene and its alkyl
derivatives are important parts of arenes. The general formula of arenes is CnH2n-6y (where
y =Number of rings) so the percentage of carbon in arenes is more than that of aliphatic
hydrocarbons. Compounds like benzene, which have relatively few hydrogens in relation to
the number of carbons, are typically found in oils produced by trees and other Natural Plants.
Early chemists called such compounds aromatic compounds because of their pleasing smell.
In this way, they were differentiating from aliphatic compounds, with higher hydrogen-to-
carbon ratios, that were obtained from the chemical degradation of fats. The chemical
meaning of the word “aromatic” now signifies certain kinds of chemical structures. Aromatic
compounds are now regarded as a class of compound which contains at least one benzene
ring. They are also known as benzenoids. In other cases compound which do not contain
benzene ring but they still behave as aromatic compounds. Such compounds are known as
non-benzenoids.
1. Alkyl benzenes

2. Alkenyl benzenes

3. Non benzenoid aromatic compound

6.2. NOMENCLATURE OF BENZENE DERIVATIVE

Nomenclature of benzene derivatives depends on IUPAC system and some derivatives have
common names.
1. Monosubstituted benzene: These are named by prefixing the name of the substituent to
‘benzene’ Example:
2. Disubstituted benzene: When there are two substitutents on the ring, three positional
isomers are possible and their positions are indicated by ortho, meta and para or by numbers.
Example:

3. Polysubstituted benzene: When three or more substituent are placed on benzene then
numbers are used to indicate the position. Example:

4. Fused polycyclic arenes: There are many polycyclic arenes having one or more benzene
rings fused in ortho positions. Example:

6.3. MOLECULAR ORBITAL STRUCTURE OF BENZENE

All six carbon atoms in benzene are sp 2 hybridized. All hybrid orbitals overlap each other and
with s-orbitals C-C and C-H bonds to form σ bond. It is the modern view of structure, in
benzene each carbon is sp2 hydrides with bond angle 1200 . So it is cyclic and planner. Each
carbon contains one unhybrid p orbital (pz) which is perpendicular to the σ plane and π-e -
undergoes delocalization, each carbon is overlap with two carbon atoms to form sp 2 -sp2 σ
bond and with H-atom to form sp2 - s σ bond.
6.4. Method of preparation of benzene: There are following methods:
1. From acetylene: Polymerization of acetylene give benzene.

2. From phenol: Heating of phenol with zinc dust gives benzene.

3. From sodium benzoate: From sodium benzoate C6H5COONa on react with sodalime
(NaOH and CaO) to give benzene.

6.5. Physical properties:

1. Benzene is a colorless liquid with boiling point 80ºC.
2. It is in soluble in water beet soluble in organic solvent like alcohol ether.
6.6. Chemical properties: Why benzene undergo electrophilic substitution reaction all
though double bonds. Benzene has cyclic planer structure with conjugating of single &
double bond due to which it shows resonance & therefore it is highly stable. Due to high
stability it does not undergo addition reaction but undergo electrophilic substitution it show
following resonating structure & resonance hybrid.
I. Electrophi8lic substitution reaction of benzene: There are following reaction:
1. Halogenation
2.. Nitration.
3. Sulphonation
4. Friedal-craft reaction
1. Halogenation (Chlorination ): In the absence of sun light and in the presence of FeCl 3 or
AlCl3, benzene gives chlorobenzene.
2. Nitration: In the presence of H2SO4 benzene on react with HNO3 gives nitrobenzene.
This reaction is known as nitration.

3.Sulphonation: In the presence of H2SO4, benzene on react with H2SO4 gives benzene
sulphonic acid. This reaction is known as sulphonation reaction.
4. Friedal Craft reaction: It is of two types :
A. Friedal craft alkylation: In the presence of anhydrous AlCl3, benzene reacts with R-X to
give alkyl benzene. This reaction is known as Friedal Craft alkylation.
B. Friedal craft acylation: In the presence of anhydrous AlCl 3, benzene reacts with R-CO-X
to give acetophenone. This reaction is known as Friedal Craft acylation.
II. Birch reduction: When benzene is treated with alcohol, Na and Liq. NH 3, gives 1.4
dihydro benzene. This is called Birch reduction.
III. Complete reduction: Hydrogenation of benzene in presence of Ni gives cyclohexane.

IV. Halogenation (Addition of halogen): Halogenation of benzene in presence of sunlight

gives hexahalo benzene. e.g. Chlorination of benzene gives benzene Hexachloride.

6.7. Orientation and ortho/para ratio :

In benzene all six c-atoms are same so substituent can be attached to any carbon atom but it is
not so in monosubstituted benzene. In monosubstituted benzene this position of incoming
substituent is decided by substituent present on benzene ring. This is called as directive
influence of group. It is of two types.
1. Ortho-Para directing groups
2. Meta directing or deactivating groups
1.Ortho-Para directing groups: Those groups which increase electron density at ortho &
Para positions are called as ortho- Para directing groups.
e.g. are alkyl groups- CH3 , -C2H5 , -C6H5 Halogens (-Cl, -Br,) -OH, -NH2 , etc
2. Meta directing or deactivating groups : Those groups which decrease electron density
of Ortho-Para position or increase electron density at Meta position are called as Meta
directive influence groups. e.g. -CHO , -COOH, -NO2 , -COR etc.
Directive influence of –OH in Phenol: In Phenol, -OH group shows Ortho-Para directive
influence because its loan pair of e- is in conjugation with double bonds in benzene ring and
it increases e- density and Ortho-Para position. it is shown below-
Directive influence of Nitro group: Nitro group shows meta directive influence in nitro
benzene. There is resonance of single and double bond. O atom draw e- from N and e-
density decreases at ortho and P position. Therefore meta position has more e- density than
Ortho-Para position. It is shown in the following structures-

.
Ortho-para ratio: The relative amount of O/P isomers in a disubstituted benzene is called as
ortho-para ratio. It depends on following factors-
1. Polar effect of substituent
2. Size of substituent
3. Interaction between substituent and electrophile
The size of alkyl group has greater effect on the amount of ortho & para products. larger the
size of alkyl group smaller is the amount of ortho product due to steric effect . Ortho-para
ratio of some alkyl substitutents is shown below:

6.8. Hydrocarbon derivatives of benzene: There are following derivatives:

1. Alkyl benzene
2. Alkenyl benzene
3. Alkynyl benzene
4. Biphenyls benzene
5. Condensed rings benzene.
1. Alkyl benzene: A derivative of benzene in which H is replaced by alkyl group is called as
alkyl benzene.

Methods of preparation of Toluene : There are following methods -

1. Wurtz- Fitting reaction: In this reaction methyl bromide is treated with bromo benzene
in presence of Na & ether gives toluene.

2. Oxidation: Oxidation of methyl cyclo hexane gives toluene.

Physical properties:
1. Toluene is a colorless liquid with boiling 110ºC.
2. It is insoluble in water but soluble in organic solvent like C6H6 .
Chemical properties: There are following methods.
1. Electrophilic Substitution reaction:
2. Alkyl group substitution reaction: When halogenation is carried out in presence of
sunlight then alkyl group undergo substitution.

3. Alkenyl benzene: A derivatives of benzene in which H is replaced by Alkenyl group is

celled as Alkenyl benzene.

Preparation of ethyl benzene: There are following method. By dehydration: Dehydration of 2-

phenyl ethanol gives ethenyl benzene.
By dehydrohalogenation: Dehydro halogenation of two bromo ethyl benzene gives ethenyl
benzene

Physical properties: 1. It is a color less liquid with boiling point 145ºC.

2. It is insoluble in water and soluble in organic solvent.
Chemical Properties: There are following reaction. Electrophilic Substitution reaction:
Addition reaction: There are following reaction.
A. Hydrogenation: Hydrogenation at low temperature gives ethyl benzene.

B. Halogenation: Halogenation of alkenyl benzene gives dihaloalkyl benzene.

C. Hydrohalogenation: Hydrohalogenation of Alkenyl benzene gives haloalkyl benzene

D. Hydration: Hydration of alkenyl benzene gives Alcohol.

3. Alkynyl benzene: A derivatives of benzene in which hydrogen is substituted by Alkynyl

group is called as Alkynyl benzene.
Preparation of ethenyl benzene
1. Dehydrogenation: Dehydrogenation of ethenyl benzene gives ethenyl benzene

Dehydrohalogenation: Dehydrohalogenation of bromo ethenyl benzene gives ethynyl

benzene

Physical properties : 1. It is colorless liquid with boiling point 170ºC.

2. It is soluble in water.
Chemical Properties: 1. Electrophilic substitution reaction-
2. Acidic character: It reacts with reactive metal or base to form salt.

3. Reduction: Hydrogenation at low temperature. First gives Ethenyl benzene and then gives
ethyl benzene.

4. Hydrohalogenation: It adds two molecules of Hydrogen halide as follows:

4. Biphenyl benzene: Biphenyl is the simplest and most important example of an aromatic
hydrocarbon in which the two rings are directly linked to each other. It occurs in coal-tar. The
structure of biphenyl, including the numbering of this system, is given as-

Methods of preparation:
i. Fittig reaction: In this reaction two molecules of Aryl halide is treated with Na in
presence of ether gives biphenyl.

ii. Ullmann reaction: In this reaction aryl halide is treated with copper to give biphenyl.

Physical properties : 1. It is colorless crystalline solid m.p. 71°C.

2. It has a characteristic odour.
3. It is insoluble in water but soluble in organic solvents like alcohol and ether.
Chemical properties: Biphenyl have two benzene ring so it give characteristic property of
benzene i.e. Electrophilic substitution reaction. Substituents mostly attack at para position of
benzene due to steric hindrance effect. It undergo following Electrophilic substitution
reaction –
1. Chlorination : Chlorination of biphenyl first gives 4- Chlorobiphenyl and further
chlorination gives 4,4' dichloro biphenyl.
2. Nitration : Nitration of biphenyl first gives a mixture of 4- Nitro biphenyl and 2-
Nitrobiphenyl. Further nitration gives a mix. of 4,4’-dinitro biphenyl and 2,4’-dinitro
biphenyl.

3. Sulphonation : Sulphonation of biphenyl gives Biphenyl 4-sulphonic acid.

Fused Polynuclear hydrocarbons : Those hydrocarbons in which aromatic rings are fused
together at Ortho position are called as Fused polynuclear hydrocarbons.

Naphtahlene (C10H6) : It has two benzene rings fused together at ortho-position.

Methods of preparation : Following methods :
1. Synthesis : On heating 4- Phenyl butene-1, naphthalene is formed.

2. From Tetralin : On reduction tetralin gives naphthalene.

Physical properties : 1. It is a colorless crystalline solid with melting point 80֠ C.

2. It is insoluble in water but soluble in organic solvent.
Chemical properties: It gives following reactions-
I. Addition reactions : Following reactions-
1. Addition of Hydrogen : Under different condition give different products as-

2. Addition of Chlorine : Gives naphthalene tetrachloride.

II. Electrophilic Substitution reaction : It gives following electrophilic substitution

reactions-
III. Oxidation reactions : Under different condition gives different products as-
Molecula orbital picture of Naphthalene :
On basis of molecular orbital theory naphthalene has planar structure. So each C-aton in
naphthalene has sp2 hybridization with one unpaired p-orbital on each C-atom. These
unpaired p-orbitals undergo sideways overlapping and form delocalized electron cloud above
and below the plane of naphthalene ring.

Anthracene ( C14H10) : It has two benzene rings fused together at ortho-position.

Methods of preparation : Following methods :
Physical properties : 1. It is a colorless crystalline solid with melting point 217֠ C.
2. It is insoluble in water but soluble in organic solvent.
Chemical properties: It gives following reactions-
1. Reduction : Anthracene on reduction gives following products under different conditions
as –

2. Oxidation ; Anthracene on oxidation gives following product as :

3. Addition of Maleic anhydride : Anthracene on addition of Maleic anhydride gives
addition product as-

4. Electrophilic substitution reactions : Anthracene undergo electrophilic substitution

reactions and gives following products :

Molecula orbital picture of Anthracene :

On basis of molecular orbital theory Anthracene has planar structure. So each C-aton in
Anthracene has sp2 hybridization with one unpaired p-orbital on each C-atom. These unpaired
p-orbitals undergo sideways overlapping and form delocalized electron cloud above and
below the plane of Anthracene ring.
LONG ANSWER TYPE QUESTIONS :
1. Explain the structure of benzene on basis of molecular orbital theory.
( KU 2007, Agra 2003,09,10, VBSPU 2007,10,13 )
2. Discuss mechanism of electrophilic substitution in benzene.
( Kashi 2012,14 , Luck. 2012, VBSPU 2007,10,13 )
3. Give the mechanism of sulphonation of benzene.
( Kashi 2012,14,16, VBSPU 2002,09,13 )
4. Write short notes on following : ( KU 2007, Agra 2003,08,10, VBSPU 2007,10,13 )
i. Resonance ii. Friedal-Craft reaction
iii. Nucleophilic aromatic substitution iv. Huckle rule
5. What is aromaticity ? What are the conditions for aromaticity ?
( KU 2007, Agra 2004,09,10, Jhansi 2007,10,13 )
6. Explain activation and deactivation of benzene ring by taking example of –OH and –NO 2
group. ( Kashi 2010,12,14 VBSPU 2002,09 )
7. Discuss nuclear and side chain halogenations of benzene.
8. What are alkynyl benzenes ? Describe their methods of preparation and properties.
9.(a) What are polynuclear hydrocarbons ? Give their classification.
(b) How naphthalene is obtained from coal tar ?
( Kashi 2011,15, Agra 2009,13 )
10. Describe synthesis and important properties of naphthalene .
( KU 2006, VBSPU 2012,13 )
11. What is anthracene ? How anthracene is obtained from coal tar ?
( KU 2006, Jhansi 2002,09,13 )

OBJECTIVE TYPE QUESTIONS ;

1. Aromatic compounds are:
(a) open-chain compounds (b) closed-chain compounds
(c) both open and closed-chain compounds
(d) closed-chain compounds which are structurally similar to benzene
2. The general formula of arenes is:
(a) CnH2n (b) CnH2n – 4
(c) CnH2n + 2 (d) CnH2n-6
3. The carbon atoms in benzene are:
(a) sp2 -hybridized (b) sp-hybridized
(c) sp3 -hybridized (d) non-hybridized
4. The benzene molecule is:
(a) trigonal (b) tetrahedral
(c) planar (d) pyramidal
5. The number of п-electrons in benzene molecule is:
(a) 6 (b) 3
(c) 5 (d) 4.
6. Benzene gives mainly:
(a) substitution reaction (b) addition reaction
(c) elimination reaction (d) all of these
7. Six carbon atoms of benzene are of:
(a) one type (b) two types
(c) three types (d) six types
8. The nitro group in nitrobenzene is:
(a) ortho-directing (b) meta-directing
(c) para-directing (d) ortho- and para-directing
9. Which of the following is meta-directing group?
(a) –COOH (b) -OH
(c) –NH2 (d) –CI
10. In the nitration of benzene with a mixture of conc. HNO 3 and conc. H2S04, the active
species involved is:
(a) NO3- (b) NO2
(c) NO2- (d) NO2+
11. In the sulphonation of benzene, the electrophile involved is:
(a) HS04- (b) S03
(c) SO2 (d) S042-
12. Among the following groups the group that deactivates the benzene ring for further
electrophilic substitution, is:
(a) methyl (b) amino
(c) hydroxyl (d) chloro
13. The reaction of chlorine with toluene in presence of ferric chloride gives predominantly:
(a) benzoyl chloride (b) m-chlorotoluene
(c) benzyl chloride (d) 0- and p-chlorotoluene
14. Nitration of benzene in presence of conc. H2SO4 at 100°C gives:
(a) nitrobenzene (b) m-dinitrobenzene
 ( c) o-dinitrobenzene (d) p-dinitrobenzene
15. Chlorobenzene when condensed with chloral in the presence of conc. H2S04 yields:
(a) Gammexane (b) DDT
(c)TNB (d) C6Cl6
16. The chemical name of DDT is:
(a) dichloro dinitrotoluene (b) dichloro dimethyl toluene
(c) p,p'-dichloro diphenyl trichloroethane (d) none of the above
17. Gammexane is:
(a) hexachlorobenzene (b) benzene hexachloride
(c) p-dichlorobenzene (d) chlorobenzene
18. Benzene diazonium chloride is treated with Cu 2Cl2 in HCl gives chlorobenzene,
reaction is called :
(a) Perkin’s reaction (b) Etard reaction
( c ) Gatterman reaction (d) Sandmeyer’s reaction
19. Picric acid is a yellow coloured compound, Its chemical name is:
(a) trinitrobenzene (b)2,4,6-trinitrophenol
(c) trinitrotoluene (d) trinitroaniline
20. Phenol is heated with CCl4 and alk.KOH.to form salicylic acid. The reaction is known
as:
(a) Friedal crafts reaction (b) Rosenmund reaction
(c) Reimer-Tiemann reaction (d) Perkin's reaction

ANSWERS :
1.d 2.d 3.a 4.c 5.a 6.d 7.a
8.b 9.a 10.d 11.b 12.d 13.d 14.a
15.b 16.c 17.b 18.d 19.b 20.c
 CHAPTER-7
Alkyl & Aryl Halides

7.1 Introduction
A derivative of hydrocarbon in which H – atom is replaced by
halogen atom , called as alkyl or aryl halide. Its general formula is RX or ArX where
X= F, Cl, Br or I. They are named as adding prefix –halo.
e. g. CH3Cl Chloromethane
7.2 Classification of Alkyl halides
On basis of no. of halogen atoms they are classified as-
1. Monohalides
2. Dihalides
3. Polyhalides

1. Monohalides : They contain only one halogen atom. It is of following types –

a. Primary alkyl halide : In this type halogen bonded atom has only one alkyl group.
b. Secondary alkyl halide : In this type halogen bonded atom has two alkyl groups.
c. Tertiary alkyl halide : In this type halogen bonded atom has three alkyl groups.

1. Dihalides : They contain two halogen atoms. It is of following types –

a. Vicinal Dihalides b.Geminal Dihalides
a. Vicinal Dihalides : Dihalides having two halogen atoms on adjacent carbon atoms.
 e. g.

b. Geminal Dihalides : Dihalides having two halogen atoms on same carbon atom.
e. g.

3. Polyhalides : These halides contain many halogen atoms.

7.3 Methods of preparation of Monohalides : There are following methods :

1. From Alkanes : Halogenation of alkanes in presence of sunlight gives different alkanes.

2. From Alkenes : Hydrohalogenation of alkenes gives alkyl halides.

3. From Alcohols : Reaction of alcohols on halogen acids give alkyl halides.

Reaction of alcohol with PX3, PX5 and SOCl2 also give alkyl halide.

4. From Silver salt ( Borodine – Hansdeker reaction ) : Silver salt with halogen gives alkyl
halide.

5. From Halogen exchange ( Finkiestein reaction ) : Alkyl chloride or bromide with NaI
gives alkyl iodide.

Physical properties : ℹ. Lower members exist in gaseous state while higher members exist
in liquid & solid state.
ℹℹ. They are insoluble in water but soluble in organic solvent.
ℹℹℹ. Both boiling point & melting point increases with increase in size and molecular
weight of compounds.
Chemical properties : Alkyl halides give following chemical reactions.
I. Nucleophilic Substitution reactions
II. Other reactions

I. Nucleophilic Substitution reactions : These reactions are as ;

1. Formation of alcohols : Alkyl halide with aqueous NaOH or KOH gives alcohols.
RX + NaOH (aq) → ROH + NaX
C2H5Br + NaOH (aq) → C2H5OH + NaBr
2. Formation of thialcohols : Alkyl halide with NaSH or KSH gives thioalcohols.
RX + NaSH → RSH + NaX
C2H5Br + NaSH → C2H5SH + NaBr
3. Formation of ethers ( Williamsons synthesis ) : Alkyl halide with sodium alkoxide gives
ether.

4. Formation of ethers : Alkyl halide with sodium thioxide or sod. mercaptide gives
thioether.

5. Formation of amines : Alkyl halide with ammonia gives a series of pri., sec., tert. And
quarternary amines.
6. Formation of alkyl cyanide : Alkyl halide with KCN gives alkyl cyanide.

7. Formation of alkyl isocyanide : Alkyl halide with AgCN gives alkyl isocyanide.

8. Formation of nitro alkanes : Alkyl halide with AgNO2 gives nitroalkanes

.
II. Other reactions : These reactions are as :

1. Reduction : In presence of reducing agents like Na/ C2H5OH or Sn/ HCl gives alkane.

2, Formation of alkenes : In presence of alc. KOH alkyl halide undergo

dehydrohalogenation reaction ( Elimination reaction ) gives alkene.

3. Wurtz reaction : In presence of Na & ether alkyl halide gives alkane.

4. Friedal- Craft reaction : Alkyl halide in presence of Lewis acid with benzene gives alkyl
benzene. This reaction is called Friedal- Craft alkylation reaction.

Methods of Preparation of dihalides : There are following methods :

1. From Aldehydes & Ketones : Reaction of Aldehydes & Ketones with PCl 5 gives gem-
dihalides.

2. From alkenes : Halogenation of alkenes gives vicinal dihalides.

3. From Glycols : Glycols with PCl5 gives vicinal dihalides.

Physical properties : ℹ. Lower members exist in liquid state while higher members exist in
solid state.
ℹℹ. They are insoluble in water but soluble in organic solvent.
ℹℹℹ. Both boiling point & melting point increases with increase in size and molecular
weight of compounds.
Chemical properties : Di halides give following chemical reactions.
1. Formation of glycols : Vicinal dihalides with aqueous KOH or NaOH gives glycols.
2. Formation of alkene : Vicinal dihalides with Zn dust or alc. KOH gives alkene.

3. Formation of dicarboxylic acids : Vicinal dihalides with KCN gives followed by

hydrolysis gives dicarboxylic acids .

Methods of Preparation of Trihalides (Chloroform) : There are following methods :

1. From Ethanol & Acetone : Ethanol & Acetone with bleaching powder gives
choloroform.
2. Haloform reaction : Methyl ketone and acetaldehyde react with Cl 2 in presence of alkali,
form Chloroform.
CH3-CO-R + 3Cl2 + 4NaOH → CHCl3 + RCOONa + 3NaCl + 3H2O
3. From Carbontetrachloride : Reduction of Carbontetrachloride gives Chloroform.
CCl4 + 2H → CHCl3 + HCl
Physical Properties :
1. Chloroform is a colorless heavy liquid with boiling point 61֠C.
2. It is insoluble in water but soluble in organic solvent.
Chemical Properties :
1. Oxidation : Oxidation of Chloroform in presence of sunlight gives Phosgene gas.

2. Reduction : Reduction of Chloroform gives methylene chloride.

3. Hydrolysis : Hydrolysis of Chloroform with aq. KOH gives Potassium formate.

4. Nitration : Nitration of Chloroform with HNO3 gives Chloropicrin or nitrochloroform.

5. Reaction with Ag : Chloroform with Ag gives acetylene.

6. Reimer-Tiemann reaction : Chloroform with phenol in presence of alkali gives

salicyaladehyde.
7. Carbylamine reaction : Chloroform with Primary amine (aniline) in presence of alkali
gives Isocyanide.

Methods of Preparation of Tetrahalides (Carbontetrachloride) : There are following

methods :
1. From methane : Chlorination of methane in excess gives CCl4.

2. From Carbon disulphide : Chlorination of CS2 gives CCl4.

Physical Properties :
1. CCl4 is a colorless heavy liquid with boiling point 71֠C.
2. It is insoluble in water but soluble in organic solvent.
Chemical Properties :
1. Reduction : Reduction of Carbontetrachloride gives CHCl3.
CCl4 + 2H → CHCl3 + HCl
2. Hydrolysis : Hydrolysis of Carbontetrachloride gives Phosgene.
CCl4 + H2O → COCl2 + 2HCl
Methods of Preparation of Arylhalides : There are following methods :
1. From Benzene: Halogenation of Benzene in presence of Lewis acid (AlCl 3) gives
halobenzene.

2. Sandmeyer’s reaction : In this reaction diazonium salt is treated with aryl diazonium salt
with corresponding halogen acid gives arylhalide.
3. Hunsdiecker reaction : This reaction is used for preparation of arylbromide. In this
reaction silver salt of aromatic acid is treated with Br2, gives bromobenzene.

4. From Phenol : Phenol with PCl5 gives chlorobenzene.

Physical Properties :
1. Aryl halides are generally colorless liquids or solids.
2. They are insoluble in water but soluble in organic solvent.
Chemical Properties : Since arylhalides contain both halogen and aaromatic nucleus so its
reactions can be devided into two catagories as-
I. Reactions due to halogen atom ( Nucleophilic substitution reactions ) : There are
following reactions –
1. Hydrolysis : Hydrolysis of arylhalide in presence of aq. KOH or NaOH at high
temperature & pressure gives Phenol.

2. Formation of ether : Chlorobenzene with Sodiumalkoxide gives ether.

3. Formation of Aniline : Chlorobenzene with ammonia gives aniline.

4. Formation of Cyanide : Chlorobenzene with CuCN gives cyanobenzene.

5. Wurtz-Fittig reaction : Chlorobenzene with methyl chloride in presence of Na gives

Toluene.
6. Fittig reaction : Two molecules of Chlorobenzene in presence of Na gives biphenyl.

7. Ullmann reaction : Two molecules of Iodobenzene in presence of Cu gives biphenyl.

II. Reactions due to Benzene nucleus ( Electrophilic substitution reactions ) : There are
following reactions –
Synthesis of DDT (Dichlorodiphenyl-trichloroethane) : It is prepared by heating Chloral
with Chlorobenzene in ratio 1:2 in presence of conc. H2SO4.

Synthesis of BHC (Benzene hexachloride) : It is prepared by heating benzene with excess

of Cl2.
C6H6 + 3Cl2 → C6H6Cl6

Relative reactivity of Aryl halide, alkyl halide and allyl halide :

Alkyl and allyl halide are more reactive than aryl halide. Because halogen atom in aryl halide
form double bond with benzene ring due to conjugation of double bond with lone pair of
electrons on halogen atom but it is not possible in case of Alkyl and allyl halide. So Alkyl
and allyl halide undergo nucleophilic substitution reaction easily but aryl halide does not
undergo nucleophilic substitution reaction easily, it gives under high temperature & pressure.
It is shown in following resonating structures-
LONG ANSWER TYPE QUESTIONS :
1. What are alkyl halides ? Describe the methods of preparation and important chemical
properties of alkyl halides.
2. Discuss the mechanism of SN1 and SN2 reaction of alkyl halides along with energy profile.
(Agra 2002,04, VBSPU 2001,07, 10, Luck. 2010,12 )
3. What are dihalogen derivatives of alkanes ? Describe their classification.
4. What are polyhalogen compounds ? Describe methods of preparation, properties and uses
of chloroform.
5.How will you prepare vinyl chloride ? discuss its important properties and uses.
6. Explain the following statement :
a. Allyl chloride is more reactive than vinyl chloride.
b. Vinyl chloride is less reactive than ethyl chloride.
c. Allyl chloride is more reactive than alkyl chloride.
7. Write a note on haloform reaction.
8. Give the method of formation of chloroform from ethyl alcohol.
9. Complete the following reactions :

OBJECTIVE TYPE QUESTIONS ;

1. The compound having insecticidal properties is :
a. Gamaxene b. Lindane
c. 666 d. All of above
2. The compound BHC is:
a. Aromatic b. Alicyclic
c. Heterocyclic d. Polycyclic
3. Which of following compound does not give precipitate with alc. AgNO3
a. Sodium chloride b. Benzyl chloride
c. Benzal chloride d. Benzo trichloride
4. Chlorobenzene on reduction with Ni-Al couple in presence of base forms:
a. Benzene b. Toluene
c. Xylene d.Styrene
5. The formula of benzyl chloride is :
a. C6H5CHCl2 b. C6H5COCl
c. C6H5CH2Cl d. C6H5CCl3
6. Benzyl chloride with aq. KOH to form :
a. Chlorobenzene b. Benzoic acid
c. Benzyl alcohol d. Benzaldehyde
7. Benzyl chloride on oxidation with dil. HNO3 or alkaline KMnO4 gives :
a. Benzoic acid b. Cinnamic acid
c. Phthalic acid d. Succinic acid
8. Chlorobenzene reaccts with chloral and conc. H2SO4 to form :
a. Gammaxene b. DDT
c. Benzotrichloride d. Benzyl chloride
9. DDT is :
a. Dichlorodiphenyltrichloroethane b. Dichlorodiphenyltrichloromethane
c. Diphenyldiethyltrichloroethane d. Dibromodiphenyltrichloroethane
10. C6H5CH2Cl + 2Na+ ClCH3 → C6H5CH2CH3 + 2NaCl reaction is called as :
a. Reimer Tiemann reaction b. Friedal-Craft reaction
c. Fittig reaction d. Wurtz-Fittig reaction
11. C6H5Cl + 2Na+ Cl C6H5→ C6H5. C6H5 + 2NaCl reaction is called as :
a. Reimer Tiemann reaction b. Friedal-Craft reaction
c. Fittig reaction d. Wurtz-Fittig reaction
12. C6H5Cl + 2Cu+ Cl C6H5→ C6H5. C6H5 + 2CuCl reaction is called as :
a. Reimer Tiemann reaction b. Ullmann reaction
c. Fittig reaction d. Wurtz-Fittig reaction

ANSWERS :
1.d 2.b 3.d 4.a 5.c 6.c 7.a
8.b 9.a 10.d 11.c 12.b