UNIT-VI

HALOALKANES & HALOARENES

MCQs:
1. Pure CHCl3 and pure CHI3 can be distinguished by
a.Treating with litmus paper b.Treating with aq. KOH.
c.Treating with HCl. d.Treating with aqueous AgNO3
2. The C  Cl bond in chlorobenzene as compared with C  Cl bond in methyl chloride is
a.Longer and weaker b.Shorter and weaker
c.Shorter and stronger d.Longer and stronger
3. Arrange the following compounds in decreasing order of reactivity in S N1 reaction :-

Ph–CH2–Cl

(p) (q) (r) (s)

a. p >q > r > s b. r > p > q > s
c. q > p > r > s d. r > s > p > r
4. Arrange the following compound in decreasing order of reactivity in S N2 reaction.

(p) (q) (r) (s)

Choose the correct option:
a. q > r > s > p b. p > q > r > s
c. b > c > a > d d. c > a > b > d
5. Arrange the following compound in decreasing order of their boiling point
I. Bromopentane
II. 2-Bromo, 2 – methylpropane
III. 2- Bromobutane
a. I > II > III b. II > III > I
c. I > III > II d. III > II > I
6. Correct order of reactivity towards nucleophilic substitution reaction of following is :-

a. II > I > IV > III b. III > IV > I > II

c. III > II > I > II d. IV > II > III > I
7. Which of the following has highest dipole moment:
a.CH3Cl b.CH3F
c.CH3Br d.CH3I
8. Which one of the following has the highest dipole moment?
a.CH2Cl2 b.CHCl3
c.CCl4 d.CH4
9. What is 3- Bromopropene common name?
a.Vinyl bromide b.Allyl bromide

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 c.Tert- butyl bromide d.Prolpylidene bromide
10. What is the catalyst in the chloroalkane reaction of a primary alcohol with HCl?
a.red phosphorous b.concentrated H2SO4
c.anhydrous ZnCl2 d.pyridine
11. Compared to haloalkanes, the reactivity of haloarenes towards nucleophilic substitution
reactions is _________
a) low b) high
c) very high d) equal
12. What is the nature of the circled C atom in the following compound?

a) sp2 hybridized b) allylic

c) benzylic d) vinylic
13. Which of the following is a vinylic halide?
a) CH2=CHCHCl2 b) CH3CHClCH3
c) (CH3)2C=CHCH2Cl d) CH3CH=CClCH2CH3
14. Which of the following cannot be a catalyst in the electrophilic substitution of arenes?
a) FeCl3 b) FeBr3
c) NH3 d) AlCl3
15. the ortho and para isomers formed by electrophilic substitution of arenes can be easily separated
due to the large difference in their ________
a) densities b) solubilities
c) melting points d) boiling points
16. Which of the following has the highest boiling point?
a) Chloromethane b) Dichloromethane
c) Trichloromethane d) Tetrachloromethane
17. The boiling points of isomeric alkyl halides _______ with increase in branching.
a) increase b) decrease
c) remains same d) cannot be determined
18. What is the correct order of boiling of isomeric dichlorobenzenes?
a) ortho>meta>para b) para>meta>ortho
c) para>ortho>meta d) meta>ortho>para
19. Which of the following has the highest density?
a) CH3Cl b) CH2Cl2
c) CHCl3 d) CCl4
20. The C-Cl bond length in chlorobenzene is less than the C-Cl bond length in chloromethane
because of the ________
a) resonance effect in haloarenes
b) difference in hybridisation of carbon in C-Cl bond
c) instability of phenyl cation
d) possible repulsion between nucleophile and chlorobenzene
21. Identiy the following compounds as primary halide:
(a) 1-Bromobut-2-ene (b) 4-Bromopent-2-ene

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 (c) 2-Bromo-2-methylpropane (d) 3-Bromopent-2-ene
22. Which of the following compounds are gem-dihalides ?
(a) Ethylidene chloride (b) Ethylene dichloride
(c) Methyl chloride (d) Benzyl chloride
23. Which is the correct IUPAC name for

a)1-Bromo-2-ethylpropane b)1-Bromo-2-ethyl-2-methylethane
c)1-Bromo-2-methylbutane d) 2-Methyl-1-bromobutane
24. What should be the correct IUPAC name for diethylbromomethane?
a)1-Bromo-1,1-diethylmethane b)3-Bromopentane
c)1-Bromo-1-ethylpropane d)1-Bromopentane
25. Which of the following are secondary bromides?
(a) CH3CH2Br (b) (CH3)3C CH2Br
(c) CH3CH(Br)CH2CH3 (d) (CH3)2CBrCH2CH3
26. Pure chloroform is obtained by treating
(a) Ethanol with bleaching powder (b) Acetone with bleaching powder
(c) Chloral with Sodium hydroxide (d) CCl4 with moist Iron
27. 1,1 Dichloropropane on hydrolysis gives
a) Propanone b) Propanal
c) Ethanal d) 1,1-propandiol
28. Among the following ,the molecule with the highest dipole moment is :
a) CH3Cl b) CH2Cl2
c) CHCl3 d) CCl4
29. Which of the following represents Freon?
a) Ethylene dichloride b) Ethylidene dichloride
c) Tetrafluoro ethylene d) Dichlorodifluoromethane
30. Which of the following molecules is chiral?
(a) Butan-2-ol (b) Propan-2-ol
(c) 1-chlorobutane (d) Butanamine

ANSWERS:
1. d 2. c 3. c 4. b 5. c 6. a 7. a 8. a 9. b 10. c
11. a 12. c 13. d 14. c 15. c 16. d 17. b 18. c 19. d 20. b
21. a 22. a 23. c 24. b 25. c 26. c 27. d 28. a 29. d 30. a

ASSERTION REASON TYPE QUESTIONS:

These questions consist of two statements, each printed as Assertion and Reason. While
answering these questions, you are required to choose any one of the following four responses.
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the
Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the
Assertion.

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 (c) If the Assertion is correct but Reason is incorrect.
(d) If the Assertion is incorrect but Reason is correct.

1. Assertion : CHCl3 is stored in dark bottles.

Reason : CHCl3 is oxidised in dark.
2. Assertion : Phosphorus chlorides (tri and penta) are preferred over thionyl chloride for the
preparation of alkyl chlorides from alcohols.
Reason : The order of reactivity of alcohols with a given haloacid is 3°>2°>1°.
3. Assertion : Presence of a nitro group at ortho or para position increases the reactivity of
haloarenes towards nucleophilic substitution.
Reason : Nitro group, being an electron withdrawing group decreases the electron density over
the benzene ring.
4. Assertion: The boiling points of alkyl halides decrease in the order RI> RBr> RCl>RF
Reason: The boiling points of alkyl chlorides, bromides and iodides are considerably higher than
that of the hydrocarbon of comparable molecular mass.
5. Assertion: SN2 reaction proceeds with inversion of configuration.
Reason: SN2 reaction occurs in one step

Answers:
1. (c) 2. (d) 3. (a) 4. (b) 5. (b)

TWO MARKS QUESTIONS:

1. Write IUPAC names of

(a) (b)
Ans: (a) 1-Chloro-2-methylbenze
(b) Chlorophenylmethane
2. Write the products of the following reactions:

Ans:

3. Predict the order of reactivity of the following compounds in SN 1and SN2 reactions:

Ans:

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4. Why does NO2 group show its effect only at ortho- and para- positions and not at meta-
position during nucleophilic substitution reaction?
Ans: The presence of nitro group at ortho- and para-positions withdraws the electron density
from the benzene ring and thus facilitates the attack of the nucleophile on haloarene. The
carbanion thus formed is stabilised through resonance. The negative charge appears at ortho-
and para- positions with respect to the halogen substituent is stabilised by –NO2 group while
in case of meta-nitrobenzene, none of the resonating structures bear the negative charge on
carbon atom bearing the –NO2 group. Therefore, the presence of nitro group at meta- position
does not stabilise the negative charge and no effect on reactivity is observed by the presence of
–NO2 group at meta-position.
5. Which of the following compounds will have the highest melting point and why?

Ans: II, due to symmetry of para-positions; it fits into crystal lattice better than other isomers.
6. Write the structures and names of the compounds formed when compound ‘A’ with molecular
formula, C7H8 is treated with Cl2 in the presence of FeCl3.

Ans: o- and p-chloro toluene.

7. Chlorobenzene is less reactive towards nucleophilic substitution reaction. Give two reasons.
Ans. Chlorobenzene is less reactive towards nucleophilic substitution due to –
1. Resonance , C- Cl bond acquires a partial double bond character and becomes stronger than
a single bond.
2. sp2 hybridisation in C of C-X bond, the carbon becomes more electronegative and holds the
electron pair of C-X bond more tightly decreasing the bond length.
8. (i) Phenol cannot be converted to chlorobenzene by reacting with HCl. Why?
(ii) How will convert Benzene to biphenyl ?
Ans. (i) In phenol, due to resonance, the carbon –oxygen bond has a partial double bond
character and is difficult to break being stronger than a single bond. Therefore it can not be
converted to chlorobenzene by reacting with HCl.
(ii)

9. Give reasons:
(i) C-Cl bond length in chlorobenzene is shorter than C–Cl bond length in CH3–Cl.
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 (ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride
Ans: (i) In chlorobenzene each carbon atom is sp2 hybridised. Due to resonance there is a
partial double bond character , so bond length is short.
(ii) In chlorobenzene carbon to which chlorine is attached is sp2 hybridised and is more
electronegative than the corresponding carbon in cyclohexyl chloride which is sp3 hybridised.
10. Draw the structure of major monohalo product in each of the following reactions :

Ans: (i)

THREE MARKS QUESTIONS:

1. Write the equation for the following name reaction-
(a) Williamson’s ether synthesis
(b) Wurtz-fittig reaction
(c) Swart reaction
Ans. (a) Williamson’s reaction
RONa + R’X  ROR’ + NaX
(b) Wurtz-fittig reaction-
C6H5Cl + 2Na + Cl CH3 (dry ether)  C6H5 CH3 + 2NaCl
(c)Swart reaction-
CH3Cl + AgF  CH3 F + AgCl
2. How do you convert the following
(i) Toluene to benzylalcohol
(ii) Benzene to 4-bromonitrobenzene
(iii) Benzylalcohol to 2-phenylethanoicacid
Ans: (i)

(ii)

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 (iii)

3. How are the following conversions carried out?

(i) Aniline to chloro benzene
(ii) Chloro benzene to p-nitrophenol
Ans: (i)

(ii)

4. What happens when

(i) bromobenzene is treated with Mg in the presence of dry ether,
(ii) chlorobenzene is subjected to hydrolysis ?
Ans: (i) When bromobenzene is treated with Mg in the presence of dry ether,
phenylmagnesium bromide is formed.

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 (ii) Chlorobenzene does not undergo hydrolysis under normal conditions. However, it
undergoes hydrolysis when heated in an aqueous sodium hydroxide solution at a temperature
of 623 K and a pressure of 300 atm to form phenol.

5. Draw the structures of major monohalo products in each of the following reactions

Ans:

6. Explain why the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
Ans: In chlorobenzene, the Cl-atom is linked to a sp2 hybridized carbon atom. In cyclohexyl
chloride, the Cl-atom is linked to a sp3 hybridized carbon atom. Now, sp2 hybridized carbon
has more s-character than sp3 hybridized carbon atom. Therefore, the former is more
electronegative than the latter. Therefore, the density of electrons of C−Cl bond near the Cl-
atom is less in chlorobenzene than in cydohexyl chloride.
Moreover, the −R effect of the benzene ring of chlorobenzene decreases the electron density of
the C−Cl bond near the Cl-atom. As a result, the polarity of the C−Cl bond in chlorobenzene
decreases. Hence, the dipole moment of chlorobenzene is lower than that of cyclohexyl
chloride

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7. Although chlorine is an electron withdrawing group, yet it is ortho-, para- directing in
electrophilic aromatic substitution reactions. Why?
Ans: Chlorine withdraws electrons through inductive effect and releases electrons through
resonance. Through inductive effect, chlorine destabilises the intermediate carbocation formed
during the electrophilic substitution
Through resonance, halogen tends to stabilise the carbocation and the effect is more pronounced
at ortho- and para- positions. The inductive effect is stronger than resonance and causes net
electron withdrawal and thus causes net deactivation. The resonance effect tends to oppose the
inductive effect for the attack at ortho- and parapositions and hence makes the deactivation less
for ortho- and paraattack.Reactivity is thus controlled by the stronger inductive effect and
orientation is controlled by resonance effect.

8. Write: (i) Fittig Reaction

(ii) SandmeyerReaction
(iii) Balz-Schiemann reaction
Ans: (i)

(ii)

(iii)

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9. Give reason why-
(i) Aryl halides are less reactive towards nucleophilic substitution reaction than Alkyl halides
(ii) Chloromethane react with KCN to form ethanenitrile as the main product but with AgCN
it form methyl carbylamines.
(iii) Alkyl chloride react with aqueous KOH leads to the formation of alcohols but in presence
of alcoholic KOH leads to formation of alkenes.
Ans. (i) Aryl halide are less reactive because its C-X bond has partial double bond character
due to resonance.
(ii) Because KCN is ionic while AgCN is covalent in nature.
(iii)Because aq. KOH contains OH - ions which are strong nucleophiles but Alc. KOH
contains alkoxide ions which are more stronger base and will remove H + .
10. How will you distinguish between the following pairs-
(i) Chloroform and Carbontertrachloride
(ii) Chloromethane and Iodomethane
(iii) Chloromethane and Chlorobenzene
Ans. .(i) On adding aniline and KOH, Chloroform gives foul smell of isocyanide while Carbon
tetrachloride does not react.
(ii) On adding aq. NaOH followed by adding dil. HNO3 and AgNO3 , Chloromethane gives
gives white ppt. while Iodomethane gives yellow ppt.
(iii) On adding aq. NaOH followed by adding dil. HNO3 and AgNO3 Benzyl Chloride gives
white ppt. while Chlorobenzene does not react.

FIVE MARKS QUESTIONS:

1. Give one example each of
a) Markwonikov’s addition.
b) Kharasch effect.
c) Finkelstein reaction
d) Dehydro halogenation (b elimination reaction)
e) Wurtz reaction
Ans. a)

b)

c) C2H5Cl + NaI (with acetone)  C2H5I + NaCl

d)

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 e)

2. Account for the following:

1) Halo alkanes have higher boiling point than the corresponding parent alkane.
2) Boiling point of halo alkanes RI>RBr>RCl> RF
3) Halo alkanes are polar in nature but sparingly soluble in water.
4) Kharasch effect is possible only with HBr and not with HCl and HI.
5) Alcohol reacts with thionyl chloride to give pure halo alkane.
Ans. 1) Due to high mol. Mass
2) Due to high mol. Mass
3) Cannot form H-bonds with water molecules & cannot break H-bonds between water
molecules
4) Both steps of mechanism are exothermic in case of HBr while in case of HCl or HI either step
is exothermic
5) Other by product are gases leaving behind the pure RX
3. Write the structure of the major organic product in each of the following reactions:
a) CH3CH2CH2OH+SOCl2 
b) CH3 CH=CH2 +HBr 
𝐷𝑟𝑦 𝑒𝑡ℎ𝑒𝑟
c) RBr +Mg →
𝐸𝑡ℎ𝑎𝑛𝑜𝑙
d) CH3CH2Br + KCN →
e) C6H5ONa +CH3Br 
Ans.a) CH3CH2CH2OH+SOCl2  CH3CH2CH2Cl + SO2 + HCl
b) CH3 CH=CH2 +HBr  CH3CH(Br)CH3
𝐷𝑟𝑦 𝑒𝑡ℎ𝑒𝑟
c) RBr +Mg → RMgBr
𝐸𝑡ℎ𝑎𝑛𝑜𝑙
d) CH3CH2Br + KCN → CH3CH2CN + KBr
e) C6H5ONa +CH3Br  C6H5OCH3 + NaBr

CASE BASED QUESTIONS:

1. Scientists discover CFC is not alone in destroying Ozone. There is another culprit While climate
change continues to affect the mainlands, the cold frigid regions of Antarctica and the Arctic are
no different to it. While the role of chlorofluorocarbons (CFC) has been widely established, an
international team of researchers has found a new element that is damaging the Ozone over the
Arctic.
The new culprit is Iodine. Over a hundred researchers from 20 countries, including the Indian
Institute of Tropical Meteorology (IITM), Pune, in collaboration with Extreme Environments
Research Laboratory, Switzerland, The Cyprus Institute, and NOAA Physical Sciences
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 Laboratory, joined hands to analyse the changes in the Arctic. The researchers found that the
chemical reactions between Iodine and Ozone were the second highest contributor to the loss of
surface Ozone.
HOW IS IODINE DAMAGING OZONE?
The team of researchers conducted observations from March to October 2020 on a ship in the
high Arctic region and found that Iodine enhances springtime tropospheric Ozone depletion.
They developed a chemical model to show that chemical reactions between Iodine and Ozone
are the second highest contributor to the loss of surface Ozone.
The study further suggests that the atmospheric increase in Iodine loading due to enhanced
anthropogenic Ozone-induced ocean Iodine emissions, as well as the thinning and shrinking of
Arctic sea ice expected in the near future, will probably lead to increases in Iodine emissions.
"These results indicate that iodine chemistry could play an increasingly important role in the
future and must be considered for accurate quantification of the ozone budget in the Arctic,"
IITM said in a release.

1. What are Freons?

2. Give any one use of chloroflourocarbons.
3. Do you think the use of CFCs should be banned? And What will happen if ozone layer is
destroyed?
OR
How does freon-12 deplete ozone layer?

3. Alkyl halide (haloalkanes) and aryl halide (haloarenes) are formed when hydrogen atoms in an
aliphatic or aromatic hydrocarbon are replaced by halogen atoms. Haloalkanes have halogen
atom(s) attached to an alkyl group’s sp3 hybridized carbon atom(s), whereas haloarenes have
halogen atom(s) attached to an aryl group’s sp2 hybridized carbon atom(s). Many halogen-
containing organic compounds exist in nature, and some of them have clinical applications.
Alkyl halides are prepared by the free radical halogenations of alkanes, addition of halogen acids
to alkenes, replacement of -OH group of alcohols with halogens using phosphorus halides,
thionyl chloride, or halogen acids. Aryl halides are prepared by electrophilic substitution to arene.
Fluorine and iodides are best prepared by the halogen exchange method. These compounds find
wide applications in industry as well as in day-to-day life. These compounds are generally used
as solvents and as starting materials for the synthesis of a large number of organic compounds.

1. Which is the best method for the conversion of an alcohol into an alkyl chloride?
Answer: By using SOCl2 in presence of pyridine
2. A solution of KOH hydrolyses CH3CHClCH2CH3 and CH3CH2CH2CH2Cl. Which one of
these is more easily hydrolysed?
Answer: In aq. KOH SN1 mechanism takes place and the formed carbocation is stabilized. Thus
2° carbocation is more stable carbocation than 1° therefore hydrolyses faster than
CH3CH2CH2CH2Cl
2.Give a chemical test to distinguish between C2H5Br and C6H5Br.
Answer: Both are heated with aqueous NaOH. C2H5Br gives ethanol and NaBr, which on reacting
with AgNO3, gives yellow precipitate of AgBr. C6H5Br does not respond to this test.
3. Why the C – Cl bond length in chlorobenzene is shorter than that in CH 3 – Cl.
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 Answer: In haloalkanes, the halogen atom is attached

to sp3-hybridized carbon while in haloarenes it is attached to sp2 -hybridized carbon whose size
is smaller than sp3 orbital carbon. Therefore C – Cl bond in chloro-benzene is shorter than alkyl
chloride.
4. Chlorobenzene is extremely less reactive towards a nucleophilic substitution reaction. Give
two reasons for the same.
Answer: The reasons are:(i) Due to resonance/diagrammatic repre-sentation, C – Cl bond
acquires a partial double bond character. As a result, the C – Cl bond in chlorobenzene is shorter
and hence stronger. Thus, cleavage of C – Cl bond in benzene becomes difficult which makes it
less reactive towards nucleophilic substitution.

3. In case of optically active alkyl halides, the product formed as a result of SN 2 mechanism has the inverted
configuration as compared to the reactant. This is because the nucleophile attaches itself on the side
opposite to the one where the halogen atom is present. When (–)-2-bromooctane is allowed to react with
sodium hydroxide, (+)-octan-2-ol is formed with the –OH group occupying the position opposite to what
bromide had occupied. Thus, SN2 reactions of optically active halides are accompanied by inversion of
configuration. In case of optically active alkyl halides, SN1 reactions are accompanied by racemisation.
Can you think of the reason why it happens? Actually the carbocation formed in the slow step being sp2
hybridised is planar (achiral). The attack of the nucleophile may be accomplished from either side
resulting in a mixture of products, one having the same configuration (the –OH attaching on the same
position as halide ion) and the other having opposite configuration (the –OH attaching on the side opposite
to halide ion). This may be illustrated by hydrolysis of optically active 2-bromobutane, which results in
the formation of (±)-butan-2-ol.

1. Why SN1 reactions are accompanied by racemization in optically active alkyl halides.
Answer: SN1 reactions are accompanied by racemization in optically active alkyl halides
because the nucleophile will have an equal opportunity to attack on sp2 hybridised carbocation
from either sides to give a racemic mixture.
2. Write the structure of an isomer of compound C4H9Br which is most reactive towards SN1
reaction.
Answer: (2-Bromo-2-methyl propane) or tert-butyl bromide is most reactive towards SN1
reaction as it Br can form 3° carbocation.
3. What is the difference between SN1 and SN2?(any one difference)
Answer: The SN1 reaction is a unimolecular reaction, while the SN2 reaction is a bimolecular
reaction. In the SN1 reaction, the nucleophile attacks the carbon atom of the alkyl halide. In the
SN2 reaction, the nucleophile attacks the carbon atom of the alkyl halide in the presence of a
base.
4. Is (±)-Butan-2-ol optically inactive?if yes then give reason.
Answer: (±)-Butan-2-ol is optically inactive because in racemic mix one type of rotation is
cancelled by other.

OR
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 Why does SN2 result in inversion of configuration? Give one example.
Answer: In SN2 reaction, the nucleophile attacks from the backside of the leaving group. So,
the configuration of molecule is inverted.

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