B.Sc.DEGREE(C.B.C.S.S.

) EXAMINATION,MARCH 2019
E6642
Fourth Semester
I
CoreCourse- BASIC ORGANIC CHEMISTRY -
Max.Marks: 60
Time: 3 hrs. (2013 to 2016 Admissions)

Section A

carries 1 mark)
(Answer any 10 questions. Each question

1)How will youprepare benzaldehyde from benzene?

Out of Syllabus. Give one mark to all
reduction
2. Give one exanmple for Clemmenson
in con. HCÊ to form corresponding
Carbonyl compound is heated with Zinc-amalgum
hydrocarbon
CH3COCH3+4H+Zn-Hg+HCl+CH3CH2CH3+H20
benzoic
How would you separate phenol by a chemical method from a mixture of phenol and
3.
acid?
bicarbonate solution is added to a mixture of
Bicarbonate separation-When saturated sodium
bicarbonate to form sodium salt which is
phenol and carboxylicacid, carboxylic acid react with
and it is insoluble in water but soluble in
soluble in water. Less acidic phenol do not react
use of a solvent like ether.
organic solvents .Soit can beseparated by the
acid
OR by the use of NaOH and carbonic

4. Explain NaBH4 reduction with suitable example.

converted to secondary alcohols.
Aldehydes are converted toprimary alcoholsand ketones are
CoH5CH(0H)C,Hs
CH;CHO + NaBH4’CH3CH2OH: CsH_COC6Hs+ NaBH4’

5. What is Wittig reaction?

give alkenes. This reaction is
Aldehydes and ketones react with alkylidine phosphoranes to
called wittigreaction or equation
6. What is Zeisel's method?
 compound is heated with
HI to
It is used for the estimation of alkoxy groups. The treated
given alkoxy nítrate to form :
wirh alcoholic silver
The alkyl iodide formed js then
torm alkyl iodide.
ormed we can estimate the alkOxy group n ne
Silver iodide. From the mass of silver iodide
sample or explanation with equations
ROCH3+HI ’ ROH+CH31; CH3l+AgNO3 ’ CH3NO3+Agl I

7. Phenol is acid.Give reason

the,
fact that the phenoxide ion produced after
The acidic character of phenol is due to the
liberation of a proton from phenol is resonance stabilized.

8. Draw different type of anthraquinones and give their structure.

1,2- athraquinone 1,4 - athraquinone 9,10-athraquinone

(8x1 = 8)

SectionB

(Answer any 6 questions. Each question carries 2 marks)

ethylacetoacetate.
9. What is tautomerism? Explain it in the context of
migration of a proton
Tautomerism is a type of dynamic isomerism which involve the reversible
tautomerism.
and a double bond. Ethyl acetoacetate exhibits keto-enol

Tautomerises
HC -CHz - -0CHs HzC--CH -0CzHs
Acetoacetic ester (AAE) (Enolform)

10. How is benzoin is prepared from Benzaldehyde?

 aluenydes undergo self condensation in presence of cyanide ion to form benzoin. This
reaction isknown as benzoin
condensation
2C6H_CHO KCN ColisCH(OH}COGHs
Benzaldchyde Benzoin

11. Write the mechanism of perkin reaction.

CH-0
(a)
CH;COONa CHOHCH,C HOH
CHOHCH,COOH
180°C H_C-c -AcOH

Benzaldehyde Acetic anhydride

(contains a-H)
H-HCOOH
H,0 +

Mechanism. Perkin reaction is initiated by the formation oa carbanion (nucleophile) generated trom the
inhydridc having replaceable a-H atom followed by nucleophilic addition o aromatic aldehyde bearing n0
-hydrogen atom. It involves following steps.
Siep 1 Hycco8.u
Base
CH;COOH
Curlanign (nueleophile) Acetic acid

CHa
Step 2 CgH-C Nucleoplhilic,
addition
H

Benzaldehyde Carbanion
(no-a-H)
H,O/ -CllCOO1
CaH,H=HCOOH CH,ClH=C-C CoHs-CH
Cinnamic acid

acid.
12. Compare the acidic strength of benzoic acid, acetic acid and phenyl acetic
acid. The Higher
Acidity decreases in the order benzoic acid> phenyl acetic acid> acetic
benzoate ion. The -l effect o
acidity of benzoic acid is due to the resonance stabilization of
Carboxylgroup and benzene
benzene ring stabilize the carboxylate ion. As the distance between
dependence of inductive effect. In Aceti
ring increases acidity decreases because of the distance
decrease the acidity
acid the +leffect of CH3 group destabilize the carboxylate ion and
one use of Resorcinol.
13. Give one method of preparation of Resorcinol. Write
 A, II;O .
OH
NyX Resorcinol
Diazotised m-phenylene diamine
hookworm
Uses:- lt is used as an antiseptic, used for curing urinarv disorder and
14.Which is astrong base urea or guanidine? Substantiate your answer.
Guanidine is a stronger base than wrea because of the greater resonance stabilization or
guanidine and protonated guanidine.
OH

Protonated urca
(Resonance stabilize)

HzN
HNCNH
H>N
Resoeance bybrid
Guanidine
Resonance stabilisation in

HG
HNNH
H2E HNC-GH2
Resonance stabilisation in protonated Guanidine Resonance hybrid

15. Explain and illustrate enolisation. How will you detect it?
Give mnark for keto-enol tautomerism -Using ethyl acetoacetate as an exampL
decolurisation
Ethyl acetoacetate give reactions similar to enols.E.g. Red colur with FeCl3,
Bromine etc.It Also give reactions of Carbonyl groupE.g.firmation of oxime, cyanohydrins et
Keto and Enol forms canbe isolated by Fractional distillation or Knorr's nmethod.

16. How is coumarin prepared?

CHO
(CH,C0)0
CH;COONa -H
OH (Perkin reuction)

Salicylaldehyde Coumarin
Coumarinic acid
(cis-o-Hydroxycinnamic acid) (1,2-Benzopyrone)
 equations involved.
17. How is butanoic acid affected? Write the
conversion of propanoic acid to
CH3CH2COOH+LAH(Reduction)’CH;CH2CHz0H
CH3CH2CH;0H +P+l2-+CH3CH2CH2l
CH3CH2CH2l+KCNCH:CH,CHCN+ CH:CH2CH,CN+H,0/H*’ CH3CH2CHzCOOH

18. How is ethylene oxide prepared? Give its

two important reactions

preparation 1mark
Ethylene oxide
Ethylene chlorohydrin
HOH’ CoHsCH,CH,0H
CGH_CHyCH,OMgBr 2-Phenylethanol
CoH_MgBr H@- ÇH3
Phenyl magnesium bromide
(GR)

H3CCH0
H2G (Hshit) Acetaldehyde Any 2reactions- 1 mark

Section C

question carries 4 marks)

(Answer any 4 questions. Each
groups
acid. Illustrate how the presence of different substituent
19. Define PKa value of an
of acid. Explain.
decreases and increases PKa value
substituent on
given in syllabus. Full marks may be given to effect of
PKa value is not
acidity of carboxylic acids.
after the
carboxylic acid is due to the resonance stabilization of its anion formed
The acidity of
Any factor which stabilizes the carboxylate anion should increase the acidity
removal of proton. acidity.
anion should decrease the
whileany factor that destabilizes the carboxylate

S releases electrons, Swithdras electrons,

Carboxylate anion Carboxylate anion
ldestabilized, acidity decreased) stabillzed, acidity increased]

more acidic
Electron with drawing substituents increases the acidity Eg. Chloroacetic acid is
than acetic acid.
Electron donating substituent decrease acidity. Eg.Acetic acid is less acidic than formic acid
 acidity
suubstituents. The
electron withdrawing
Acidity increases with increase in number of
decreases inthe order
of various Chlorine substituted acids
Cl;C.COOH > ClzCH.COOH> CICH2.COOH and electron
carboxyl group
Acidity decreases with increase in distance between
decreases in the order
withdrawing group. For the following acids acidity
CICH2CH2CH2C00H > CH3CH(CI)CH2C0OH> CH;CH2CH(CI)COOH withdrawing groups. The
of electron
Acidity increases with increase in electronegativity
decreases in the order
acidity of various halogen substituted acids
FCH2.C0OH> CICH2.COOH>BrCH2.COOH>ICH2.C0OH
example-4Marks)
(Any relevant 4points with

20. (1)Describe MPV reduction and the mechanisms involved.

(MesCHO)3AJ + (CH)hC=0
(CH}hCHOH ScHon
R
Sec. alcohol Acetone
Ketone Isopropyl alcohol
Mechanism. Aluminium isopropoxide foms a loose evclie coordination complex with carbony l1c group. This
omplex by hydride transfer (H)to carbonyl carbon gies mixed alkoxide. that hy drolyses to corresponding
Joohol.
-Me=0 R

R
(MeCHO)3AI
AlOHCMte)
OAOHCMeyh
Akdetydea ketone Al. isopropoxide
Mned aum1num kuxndc
(Cyclic coordination complex)

MeCHOH
(Me,CHO);A| CCHOH
R
(R-CH. CaH; or H) Pr1or Sc alcohol

(2Marks)
(2). Anthracene isaromatic substantiate based on structure Any relavant 4 points 2 marks

(6) Orbital picture (M.0. Concept). Each of the fourteen carbon atoms in anthracene (lying at th.
corners of the fused hexagons) is an sp² hybrid carbon and is attached to three other atoms hw
g-bonds. These g-bonds formed by the overlapping of the trigonal (sp') orbitals of one carbon with
similar orbitals of other carbon atoms and s-orbitals of hydrogen (cf. naphthalene). Consequently, all
fourteen carbons and ten hydrogens are situated in one plane.
An unhybridized p-orb1tal on each carbon atom is n a ptane
perpenoicuiar to ine ring sysiem
overlaps though less efficiently, with the unhybridised p-orbitals of adjacent carbons. This forms a
T-cloud above and below the plane of the rings. This r-cloud consists three partially overlapping
Sextels with two pairs of electrons in common. (There are fourteen such -electrons in anthracene Le,
it follows (4n+2) T-Hückel rule and hence aromatic in character.
 H

T-clouds |
H

H -H or

H
M.0. Picture of Anthracene

are they prepared?

different functional derivatives of carboxylic acids? How
Z1. What are the
Examples for each class.

(1) acid chlorides (RCOCI)

RCOOH+SOCl2+RCOCI
CsHsCOCI(Benzoyl chloride)
Examples CH3COCI (acetyl chloride),
(2)acid anhydride RCO.0.COR
RCO.0.COR
RCOOH+ RCOCI+ Pyridine’
anhydride),CsHsCO.0.COC6Hs(Benzoic anhydride)
Examples CH3C00COCH3(acetic
(3)acid amide RCO.NH2

RCOCI+NH3-’RCONH2
Examples CHCONHz (acetamide),CsHsCO.NHz(Benzamide)

(4)esters RCO.OR'
R'OH+ RCOC|’ RCOOR'

CH3CO0CH3(methyl acetate),CcHsC00CzHs( ethyl Benzoate)

Examples marks)
with one example of each derivative 1*44
(Method of preparation
synthetic use of diethyl malonate.
22. Illustrate any four
 carboxylic acids
involving
L Synthesis of carboxylic acids. Some representative syntheses of givcn below:
malonic ester are often called malonic ester syntheses of carboxylic acids areexamples show how malonic
1. Synthesis of alkylacetic acids. The following three representative
cster is used for the synthesis of alkylacetic acids :
(1) n-Valeric acid (n-propylacetic acid or pentanoicacid).
2KOH n-CgHCH(COOK>
N +rCH,L nCyH,CH(CO0C,Hsh
[HCOOC?Hs)el
Monosodiomalonic ester
(-NaBr)
Ethyl n-propytmalonate

+ 2HCI 200C CH;(CH2),CH,COOH + COT

n-Cqi,CH(COOH):
(-2KCI) n-Valeric scid (Pentanoic acid)
n-Propylmalonic acid

2. Synthesis of dicarboxylic actds. Substituted malonic acids are

thermall:
(1,3-Dicarboxvlic acids).
(1) Substituted malonic acids heating. However, if the substituted malonic esterS are careiuli
unstable and readily lose CO, on acidificatlion at low temperatures, substitutcd malonic acids (1, 3
hydrolysed in alkali, followed by
dicarboxylic acids) can be obtained. For example,
ÇHs
CHsCH)-cOOC;Hsh
L.:OH CH;CH-COOH2
2. HLow temp. Ethyimethylmalonic acid
EthylmelhyImalonic ester
(2-Ethyl-2-methyl propane-1, 3-dioic acid)
acetoacetic acid can be prepared as foilows:
Synthesis ofB-Keto acids. For exanple,

CH-rg +Nø•HCoOC;Hsa] CH3 -CH(COOC;Hs)z NaC]

CH;OCH2COOH CH;COCH(COOH)2
Co,t
AcetoRcetc acid Acetyi malonic acid

5. Synthesis of cycloalkane carboxylic acids. Sodiomalonic ester condenscs with suitable

polymethylene halides to form cycloalkanc carboxylic acids as the end products. For cxample,
Cyclopentane carboxylic acid, can bc synthesised as follows :
Br SE rcction Br
tocHsN
CBr
EncoocH),|N
(-NaBr)
cooc-Hs)2 -CH_OH
coocHS)sN&SN rcaction(-Naß)
CO; + 2CH,OH -coOH
()Ho COOC;Hs
(2) A

Cyclopentane carboxylic acid

(Any four applications 1*4=4 marks)

23. How is anthranilic acid prepared? Write the chemical reactions of Anthranilicacid.
 NH NaOH COONa NaOCI
COONa CoOH
coNH, NH2
Sod.salt of Anthranilic acid
Phthalimide phthalimic acid (Sod. salt)
Anthranilic
acid

Getylation. Its -NH2 group can bc acctylated to yive

N-acetyl anthranílic acid.
CH3COCI NHCXH)
N-Acetyl anthranilic ac id
On heating it decarboxylates to form aniline.
NH2
COOH
Cot
Aniine

Esterification. Can be esterified by alcohols in presence of acid catalyst.

ÑH, CH,OHH ÄH,
+ H0
COOH
COOCH3
Anthranilic acid Methyl anthranilate
Sait formation with acids and bases.

+ NaOH
GH,
+ H30
COONa
Anthranilic acid
Sod. anthranilate
NH GH JCI
HCI
~COOH
COOH

(Preparation 1 Mark
Any 3Reactions 3Marks)
24. Describe any four synthetic applications of acetoacetic ester.
 L. Synthesis of carboxylic acids. For example,
(1) n-Butyric acid (Ethylacetic acid) or Butanoic acid.
CH_ONa
CH,CO¥CH CO÷OC,H,
CH,COCH,CO0C,Hs (CH,COHCOOC;H,] Nø -Nal
HOH HO H
-CaH_01I
Carbanion (nuclcoplhile) .

Acid hydrolysis
CHsOH + CHCH,CH,COOH + CH;CO0H
n-Butyric acid (B°anoic acid)

IL Synthesis of methyl ketones : For example

(1) Pentanone-2 (Ethylacetone) or Methyl n-propyl ketone :
HË0H
CH,COCHCH_)|cojoC,Hs HOH
Ketonic
CH;COCH,CH,CH, + CO, + CzH,0H
hydrolysis
Monoethylacetoacetic ester Methyl n-propyl ketone
(Pentanone-2)

L Synthesis of diketones and dicarboxylic acids :

(1) Acetylacetone (Pentane-2,4-dione) :
ÇOCH;
CzHsONa CHCoCH9.
CHJCOCH,COOC,Hs -CyHsOH (CHCOHcooC,H_] Nà -NaCi
Acetoacetic ester (AAE) Sodioaceioactic ester Acetylacetoacetic ester
(Ethyl-3-oxobutanoatc)
Ke!onic
CsH;OH, + CO, + CH; hydrolysis
Acctylacotone
(Pentane-2, 4-dione)

VI. Synthesis of 1, 3-diols. On reduction with LiAIH4, it gives 1, 3-diols. For example, 13
ButanedioB can be synthesised in following manner.
QH
LiAlH4
CH;COCH2cOOC;Hs HCH-ÔH,H,OH
Acetoaceticester 1,3-Butanediol

(Any four applications 1*4=4 marks)

Section D

(Answer any 2 questions. Each question carries 12marks)

25. Explainthe following giving mechanisms
a) Benzoincondensation 3marks

Aromatic aldehydes undero self condensation in presence of cyanide ion to form benzoin. This
reaction is known as benzoin condensation
 2C7H_CHO :CN
KCN
CoHsCH(0H)COC,H_ CGH_C
Benzaldel1yde Benzoin
TmeenaNIsm. 1t is belteved hat nucleonhilic addition ol cyan1dc ion lo aromalic aldehydC generaics a
Benzil

aryl aldehyde followcd by proton shift and

Fenso (a new nucleophile) that uddls to another molccule of
removal of cyanide ion to form benzoin.

KCN
Ar--n (Nuceophil)
CN
Carbanion (A)
(Nucleophile)
OH
Proton shift
KCN
(ii) Ar-C: -Ar
H H
(EN: H CN

(A) OH
Carbanion (resOnance stubiliie)
Ar --Ar
H
Benzoin

(b). Mannich reaction 3 markS

The condensation of formaldehyde with an active hydrogen compound in presence of an amine to form §
amino carbonylcompound is called Mannich reaction.
CHCOCH-CH; CH-O (CH;hÅH CH^CU}HHGCH)h
2-Butarne Formakdehyde Dimethylamine Mannich base

Mechanism. It 1s believed to nvolve following steps :

() (CH,)NH +
CH (CHs)h-CH, (Nàcleophilie addition]
transfer
CH-CHØ (CH)})G-CH,ÖH
H
H Protonation) H0
(G) (CH)hN-CH,ÖH (CH),N=CH:
An imine salt

base
(ii) R R-=CH
Ketone Enolisable Carbanion (resonance stabilized)

(iv) R- -CH +
HCTYCHÙ)h R -CH CHNCH)
Mannigh base
From step (iil) From step (i) (B-aminocarbonyl compound)
 3 Marks
(c) Wolf Kishner reduction
in a high
with a base
Carbonyl compounds can be reducedto alkanes by refluxingtheir hydrazones
boiling solvent.

KOH
’ CHsCH,CH3. + N2 + H,0
Acetone Propane

Mechanism. The first step of the reaction involves Ducleopbilic addition to C=0 group, 10liowe
penerate carbanion which undergoes
climination of water to formn hydrazone, The step (i) util ises the base to hydrogen to carbanion in last StGp o
addition of
Sequence ot rcactions to eliminate water and nitrogen with
give alkanc.
R. -H»0 R -H¬0
+ HsN-KH,
Carbanion
Hydrazine IIydrazonc H

+ H»0 R .H + Hz0
R (-:ÖH)
(From step )
R. + H0
Ri -N
R' H
(Ftom step in Carbanion Alkane/Arylalkane

(d) Claisen Rearrangement 3marks

When o-allylether of phenol is heated to 200°C it rearrange to o-allyl phenol.

OH
OCH,CH=i;
200°C
CH-CH=CH,

Alykhe of henol o-Alyl Pbenol

(Phoeyl alyi eheri

OH
CH,H=H,
CH:

26. Explain the following with examples

 (a) Aldol condensation
(3 Marks)
Two
dilute mol
alkaliecultoe forman aldehyde orcompound.
of ketone containing a-hydrogen atom combine itself in the presence of
B-hydroxy
CH:COCH:
Ba(OH)>
Propanone (2 mol) 4-Hydroxy-4-methyl-2-pentanone
(Diacetonylalcohol)
(b) Lederer Manasse reaction (3 Marks)
VVnen phenol is treated with formaldehvde in the presence of dilute acid or alkali at iower
temperatures
to form phenol
formaldehyde resin.
H-oH
Hor :OH -(ll20)
Phenol
o-Hydroxymcthyl HCHO

-Csil;OH

phenol (excess)

CH,
OH
moCll2 -OH

CH,
CH, HO CH,
CI;

(c) Reformatsky reaction (3 Marks)

a-bromoesters react with aldehyyde or ketone in the presence of Zincto form an intermediate organozinc
followed by
compound. Intermediate compounds undergo nucleophilic addition to carbonyl compound
unsaturated ester and
acid treatment togive B-hydroxy ester. B-hydroxy ester dehydrate readily to a,ß
Reformatsky reaction.
finally gives u,ß -unsaturated acid on hydrolysis. This reaction is called
Zn R 0ZnBr H;0/H® ROH
Br-Hcooc,Hs R Benzene CH,CO0CHs
B-Hydroyesier
Ethyl bromoacetate Ketone or aldehyde
(a-Bromoester) (R=CH3, CzHs or H)
(3 Marks)
(d) Fries Rearrangement
The acy!
phenyl esters are heated with anhydrous AlCl, undergoes intramolecular rearangement.
When
to 0- or p- positions of the aronatic nucleus to torm phenolicketones.
groupmigrates
 OH
OCOCH, OH
AICly
cOCH;

CoCH)
p-Hydroxyphenyl methyl ketone
Phenyl acetate o-Hydroxyphenyl ine1yl ketone (oHydroxyacetophenone)
(o-Hydroxyacctophenone)
2Marks
27. (a)Starting from acetic acid how can you prepare malonic ester.

1.Clh. P -.EN
H;C-COOH
Acetic acid
2. K;CO; cicoox
Pot.chloroacetate (KCN)
:NEC-CH,CO0K
Pot. cyanoacetate

H,C(CN)COOK + 2C,H,OH + 2HCI H,C(COOC,Hs), + NH,C) + KCI

Pot. cyanoacctatc Ethyl malonate
2 Marks
(b) Explain the action of heat on urea. What is Biuret test?
an aqueous solution of biuret 1s treaued
When heated gently, urea losses ammonia to form biuret. When a
colour is formed. This test is called biuret test. lt is
with dilute NaOH and a drop of CuSO4. A violet
characteristic test for compounds having the grouping - C0- NH CHR-CO-NH
A
H, NCOÑH2 H, NCoNH) H,ÑCOÑHCOoÑH, :NHË
Biuret

2 Marks
(c) Why is urea stronger base than ordinary amide?
terms resonance stabilization of protonated
The weak basisity of ordinary amide can be explained in
amides.

:ØH

Protonated amide : Resonnce stabilized

resonance stabilized to a greater extent and

Compared with ordinary amides the protonated urea is
hence urea is more basic than ordinary amides.
OH
H
H2Ny-N3
Resonznce bybrid
Protonatcd urca
(Resonunce stabilized)
any 1 method of preparation 2 marks
(d) Giveone method of preparation of Guanidine
NH
H2NC*N: NHCI Pressure
|12Ñ-NH)HCI
Cyanamide Guanidine hydrochloride
 (e) How will
you prepare Acryilic acid from acetylene 2 marks

HCECH + CO + Ni(CO)4 ’ H,C=CHCOOH

() Give one
Acetylenc IICI
Acrylic acid
method of preparation of Fumaric acid
Any one correct method of preparation2 marks

HÌOciIcoOH
Bromosuceinic acid
ale. KOH
11O0CCH=CHCOOH
Fumaric acid
+ KBr + LO

Z6. (a) Describe any three syntheticapplications of

Methyl lithium.
1. Preparation of methane

CH_Li+H20’ CH4+LiOH
2. Preparation of Ethanol

CH3Li+ HCHO (H;o/H:)’ CH3CH20H

3. Preparation of Ethyl benzene (Any 3 correct applications 4 marks)

CH3Li+ CGHsCH,Br’ CsH;CH,CH3+LiBr

(b) Give one method of preparation of Methyl Lithium
CH3Cl + 2Li (Dry Ether/-100C/N2) ’ CH3Li + LiCl (Any one method of preparation 2marks)

(c) Give one method of preparation of Grignard reagent.

RX + Mg (Dry Ether) ’ RMgX (Any one method of preparation 2marks)

(d Describe any three synthetic applications of Grignard reagent.

1. Preparation of alkanes
RMgX +H20’ RH+Mg(OH)X

monochloroethers
2. Preparation of higher ethers from
RMgX +CI-CH;0CzHRCH,0C;Hs+Mg(CI)X
(Any 3correct applications 4 marks)
3.Preparation of tert-alkyl amines
CIMgC(CH:); + H;N-0CH; ’ HN-C(CH:)3