Time Allowed: 3 hours Maximum Marks: 300
Candi dates 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 0 fthe fo 11 0 wi ng
(20 x
Predict which 0 fthe fo11owing compoundswouldbe aromatic? Exp1ain the basis 0 f your prediction in minimum possible words.

.... .J
f.

,...:j

"
The value of the barrier 0 f rotation for the marked bond in A is only ab out 14 Kcal/mole. "W"hat could be the reason for this low value 0 f barrier 0 f rotati on in this molecule?
..... .
I
.._
An adduct A is formed by the Diels-Alder reaction of cyclopentadiene with ethyne. "W"hen A is treated with hex achloro cy cl op entadi en e it fo rms the well kno wn pesti cide Aldrin Ep oxidation of C with per acid produces another pesti cide. Dieldrin Draw structures 0 f .A, D and explain how these products are formed.
Comp ound A is photo chromic (it becomes coloured on exp osure to light). The process is reversible giving back the starting material in the dark. Propose a structure for the coloured photoi somer B.
Op
hv of
dark
Ph
A


Illustrate the following terms:


Carbo cati on


Non-classical carb ocation


Carboni urn ion

Carbeniurn ion


Carbenes




Decomp 0 si tion of a diazocomp ound A in methanol gives an alkene B(CsH140), who se IH NMR spectrum shows following si gnal



Oppm. 3.50 5.50 dd, J =17.9 and 7.9 5.80 ddd, J 17.9, 9.2 and 4.3 Hz) 4.20 and 1. 3 -2.7 m).
"W'hat is its structure?

B is unstable and isomerises at room temperature to another compound C.


"W'hen the diazocompound A is decomposed in presence of a diene it is trapped as


an adduct E.
Explain the reactions which give the products C and E.


2. Following two mechanisms are among those which have been postulated for the
decomp ositi on 0 f atyl di azonium salts in aqueous soluti ons containing nuc1 eophilic anion A-Mechanism A



Indicate how the following metho d might be applied to distinguish between the two mechani sms:
Kinetic studies
Study ofrate &product composition as a function of
Solvent isotope studies
Study ofisotope effect resulting from substitution ofD from H at ortho position
Substituent effe ct studi es

Among the norbomane derivatives the acetolysis of the anti-to sylate is lOll times faster than I while the acetolysis of the syn-isomer is only 10 4 times faster than I.
Explain.


il
3-bromo cyc10hexene reacts with NaOH more rapidly than 4-bromocyc1ohexene, which in tum reacts more rapid1 ythan bromocyc10hexane. Explain.

Outline mechanism for the formation of B from

o
.......y0 1. L...J 2. F.tOOC

A
E
kl
I
....... .

ro
A

3. Predict the products of the following reactions and outline the mechanism involved in their transfo rmati 0n:
9
It




J
...
lli)


In cyc10hexane series it is observed that with chromic acid it is the axial hydroxyl
group th at is oxi dised more rapi dlythan equato ri al hydro xy1group by a facto r 0f ab 0ut
but the saponification of the esters of related compounds however shows a reverse
order of reactivities i.e., axial ester group hydrolyses very slowly than the equatorial
ester group. Explain.
The N-benzoyl methyl ester derivatives of the amino acids glycine. alanine and valine
react with N-bronio succinimide to give monobromination products containing
bromine at the a.-carbon atom of amino acids. The order of reactivity is
glycine> alamine valine (23 8
Account for this trend 0f reactivity.



PrOVl de plausible mecham sms for the followmg transformations

.

Explam how the followmg pro ducts could be fonned m these reactions


Explam the followmg


o-deutenofluorobenzene reacts with sodium anude m l1qUld anunorua to amline more slowly than does o-deutenobromobenze, When the reaction of the fluorocompound 1S stopped at 50% converSiOn to amline the sLrting matena!1S found

to be largely devOid of deutenum When the reaction of the bromo-compound 1S stopped at 50% converSIon to anilme, the starting matena! still contams large amount ofdeutenum


Hexylbenzenesulphonate reacts with sodium methoXlde to gIVe hexylmethylether m over 90% yield with only a trace of l-hexene bemg fonned. With potasSlum-t?





butoXlde however, the of t-butylhexylether 1S 69% and 20% of l-hexene 1S fonned
Predict mechamsm for the followmg transfonnations


SEcnON B

5. .Pillswer any three 0 f the fo 11 0 wi ng
(20 x

Claisen rearrangement of allyl ether A often gives a product B (instead of the expectedproduct). Howisthisunwantedproductformed?Additi on ofasmall amount of a weak base such as Ph N Me2 helps to prevent the unwanted reaction. "Wbat could be the role 0 f the base? Expl ain.
p-AJ....



t
"Wby does the acetolysis of threo-3-phenyl-2-butyl tosylate give the threo racemic products, while that 0 f erythro isomer gives the product with the retention 0 f configuration? Explain.
Outline mechanism for the following transformati on (Show the mechanism by e1 ectron pushing arrows only. words not required):
. n.
Q..CM,Cl

g
NlllI:t Cl-...
160-10"
O . Y .
.
cq of....o:;r

B.
Treatment of phthalimide 1 with bromine in aqueous sodium hydroxide followed by aci dification with aceti c acid affords compound 2. Sp ectral data of 2 are summarised below. Deduce the structure of 2 and provi de a mechanism for its formation. Comp ound 2 reacts with HNO, to gIVe an unstable product 3 When 3 is treated WIth trans-trans-2, 4-hexadiene it fonns an adduct 5. Identify 3 and explamhow 5 lS fonned from 3



Compound 2
MIS, rrJz 137 119 93
3940 3380 3300-2400 1665 1245 765

NMR 652 J 8.0 Hz)
6.77(1H,d,J=80Hz)
7.23 J 8.0 Hz)
7.72(1H,d,J=80Hz)
860 br.S, disappears on addition ofD,O)
Identify the products of the folloWIng sequence of reactions and explam how these are
fonned



When compound A lS heated at ItlS transfonned to compound C and D Via a cyclic tetraene Propose a structure for B and describe the process mvolved m the converSiOn 0f A B C and C D
H II'

f"h

.
A
Provide mecharusm for the folloWIng transformations


m



iL

I



Identify the pro ducts A and B 1n the reaction given below

R

H"n./"I""w""'"

II
12'.C


"



Explam the followmg


(il Polyethylene cannot b e prepared by catiome polymenzation whereas polystyrene can

Anion polymenzation is a good method for the preparation of n-polyac1onitrile but

not for p01 butylene Why radicals prefer to add at carbon I of iSoprene rather than carbon 3 and 4


Both the polymers, poly cWande) and poly (vmylidene cWande) are prepared by free radical processes, but the fanner is amorphous and the Latter is higWy crystalline


In SBR (styrene-butadiene rubber) why do most double bonds have a trans configuration?




Give mechamsm 0f the fall owmg transfonnati ons


15)

Fonnaldehyde reacts with ammonia to give A [C6H12 N4]. A reacts with HN03 to give
a vvell knovvn explosive Predict the structure of B and show how B is
fonned from A.
"W'hen bromoketone is treated with potassium-t-butoxide in t-butyl alcohol at
room temperature it gives B. But when A is treated with LDA in THF at
follovved by heating it gives C. Explain why different reacti on conditions give
different pro ducts.




/1k
A
L,. C
1.,

8. Predict the po sition 0 f ab sorption bands for the carb onyl group in the IR sp ectra of the following comp ounds:

p-nitroaniline exhibits a pronounced red shift in the K-band, which is not observed in
o or m-isomer. Explain.
Calculate the An:ax, for the triene whi ch contains both a hetero annular and
homoannular diene. Your calculation should be based on the homoannular diene.

Predict the structure of a fragment ion which is responsible for the appearance of a
stro ng ch aracteri sti c peak at rrJz 149 in th e mas s sp ectra 0 f th e esters 0 f the phthali c
aci d. Give the mechanism 0 fits fonnati on from diethyl phthalate.
Treatment of A with KOH gives a compound B(C]HlOO]. Spectral data of B are given
below. What is its structure and howis it fonned? Explain.

;"..?V.........
....

IR; 1710 cm?l


fwm=115(6H,
21

6.8


7.3



Deducethestructureafacompoundonthebas!softhespeclraldatagivenbelow

Molecular fonnula C"H15N03


UV,Aw.x <210nm(s> 280nm(s=900)


1R, Cm" 3300,1710,1670 em"
1HNMR,fwm 2.21
3.37

3.76
(3H


4.34




6.80 -718 dd)
(One proton does not show, it exchanges with