Time Allowed: 3 hours Maximum Marks: 300
Candidates should attempt Question Nos. 1 and 5 which are compulsory, and any three 0 f the remaining questions selecting at least one question from each Section. Assume suitable data if considered necessary and indicate the same clearly.
1. Answer any three 0f the fo110wing: (20 x 3
Which of the following compounds are aromatic Give reasons to justify your answer.
8H ........

II m
lV v
p Ka of cycloheptatrine is ab out 39 but that of cyclopentadiene is 16. Explain.
The triene can be readily deprotonated twice with a base to give a stable dianion In contrast to this, the neutral anal0 gue is quite unstab1e. Expl ain it.
Give stereochemistry of the pro duct that you would. exp ect from each of the following electro cyclic reactions:




(H.

l
I","r

l
Pro vi de mechanism for the fo 110wing re acti0ns (Dse "electron pushin arrows 0nly, do not
use words)




.....
.•1
...
0It
..
'L...... ........_

Formulate a mechanism for the depletion of atmo spheric ozone layer by CFC.
2. Givemech anism 0fthe followingre acti0ns:

(Dse"electron pushing' arrows only. do not use words)
/-......

PH t.J. ... l. .1-(OOi f
CJ
,_.......

o 2. tl G

I

II
/-·'··0




H
o
Explain the following:

"When ci s-2 -cWorocyc1 ohexanol is treated with a base, the product is cyc1ohexanone.


"Why does tins -1-bromo-4 -t-butyl cyc10hexane undergo E2 reaction in presence of GEt ion much more slowly than corresponding cis-isomer?



3. Predict the pro duct(s) 0fthe following reactions and give the mechanism of their formation


DMF'"
"
"

.RONO

IiI I-tA ..

...'
-iJ
"......., C

G "






:to
•
IldoI c... ••"
"

Which compound 1n the followmg pus will hydrolyse fasler


"

Outlme the mechamsm of fonnation of B from A m the folloWIng reactions

Q

•

"



Give the mechamsm 0f the followmg reaeli on










on II
H r



il Explain the following points about this condensation reaction: jiil (i)"W"hy is this condensation catalysed only by eN not by OH and GEt ions? jiil "W"hy do e1 ectronattracting substituents inhibit thi s condensati on? ji "W"hy do e1 ectronattracting substituentsinhibit thi scondensation?

H r

In principle one of the following Diels-JUder reactions could give two products, while the other must product only one. Explain ji H

0
II II
H H
il ji
il m ·le 7 ji

H r
v


SECnON B

5. Jl..nswer any three of the following:
(20 x
Givemechanism 0 fthe followingtrans formations:

(XNHoo:t

H IF oro r
H
il 00 Mg}EIhrir Q-OOH ji
OJ.l
H

H O MilO..




00
H .. .....)I



il ji


O}0
H 0"

f . t"


H0 r
OH



Explain the following:




Optically active cis-2, 3-elimethylcyc1obutane on reaction with eliazomethane yields an 0 ptically inactive mes 0 pro du ct.


Solvolysis 0 f optically active 3-phenyl-4-bromobutane in hot acetic aci d yi e1ds an optically inactive ester.


Give mechanism to account for the formation ofthe following product(s)
M. I
lWH..
A



I
1..JI!!lI!I !!1hIble MoN JIabk!l 25..
R.BH A
"" btiJrto group) " lllO'W.
"W'hen acetone is treated with a base, a higher boiling li quid .p. 130° can be isolated from there actionmixture. The spectral data 0 fthiscompoundare asfollows 1620,1695 UV; /...max 238 nm 11,700) 1H NMR; Owm 1.9 2.1 6.15
MS; rillI. (R.A.) De du ce the structure 0 f the co mpo und.
6. "W'hat i s sigmatropi c reacti on Illustrate and si gmatropic reacti ons.
"W'hy is thermal cyc1oaddition of 3-butadiene and ethylene easy but addition difficult?
E.xplain the foll owing ob servations:

Dravv structures be form ed in the foll owing reactions:




7. Drawstructures 0ftherepeating Wlits 0fthe fo110wingpolymericmateri als


Teflon


Tetylene


Nylon
Natural rubb er

The light catalysed reaction 0 f nitro syl chloride with cyclohexane gives an intermediate whi ch has an imp ortant role in the formation 0 f nylon 6. mat is the structure of this interme diate? Outline the furth erstepswhi chwould benecessary forthe ny10nsynth esis.




mat are nucl eotides and nucl eo sides? Draw the structure of a nucleotide.

men a nucleotide -cyclic adenylic acid) is treated with aqueous sodium hydroxide the or pro duct that is 0 btaind is, -adenylic acid (rather than 5'­adenylic acid). Gi ve an explanation to accoWlt for the preference to the cleavage 0 f Cs-oxygen bond in the hydrolysis.



Silk consists of whose polypeptide chains are made up of the repeating amino acid sequence: Gly-Ser-Gly-i.Ja-Gly-.fJa. mat characteristics of these amino acid side chains appearto favourthest ability 0 f -sheet structure?




Predict the mechanism of the following reactions



I·'
". ·1




....

8. The following dienes in ethanol have Amax.'s at 231 nm 21,000),236 nm 12,000). 245 nm
265 nm 6,400) and 282 nm Indicate which diene corresponds to whi ch sp ectrum.



"W"hich compound A or B is expected to show lower stretching frequency for C 0 group in the IR sp ectrum

How do trimeric phosphonitrillic halides comp are with b emene m structure and re activity?



A characteristic peak at rWz 58 is shown by 2-pentanone 86] in the mass spectrum. An isomer of this gives peaks at rWz 71 and 43, but not at mlz 58. "W"hat is the structure 0 f this compound? Another isomer of this gives peaks at rWz 86 and 57. Identify this isomer.




Sp eetral data of a comp ound (molecular formula C1H.S02) are given below. Suggest a structure to this comp ound which is consistent to the sp eetral data




UV; Amax. (etOH; 256 nm 324 nm


IR; 3175-3275 (broad). 1667 (strong), 1616, 1580, 1484, 1456, 1383, 1230, 1205, 11 51, 111 5 and 1029


IH NMR; (6ppmJ 10.83 which disapp ears on additi on 0 f 0 9.59
7.31 -6.79
Ms; m/z (Relative abundance): 122 121 93 29 (31