81. No.

IB-JGT.oJ·DIB I
I
CHEMISTRY
Paper II


ITIme Allowed: Three Hours IIMaximu/ll Marks: 200 I
INSTRUCTIONS
. Candidates should attenJpt Question Nos. 1 and 5 which are compulsory, and THREE of the renulining questiolls selectillg at least ONE
question from Section.
Marks for each question are indicated against each.
Assume suitable t!tJta if considered necessary and indicate the same clearly.
Answers must be written in ENGLISH only.
Unless otherwise indicated, sylnbols and notations have their usuallneanings.
(Contd.)


..
,Section ..
. ,.
Answer any four of the following (in about 150 ,words each) lOx4
Explain the foIlQwing briefly:
Fonnation of corresponding stable ions from the, following molecules.
.. I•
.
o-Br
".
, I
" Which of the following two. compounds will have higher dipole moment and why?



o
11
C .
on

Write the product and outline mechanistic steps for its fonnation

Mg,ether
.0 ..
.. H20, H
.B-JOT-J-DIB 2 (Contd.)

•

Win an amide be fanned' from the reaction of
an acyl chloride with an aqueous solution of
pyridine?' .
Why should show acidic
properties
••
2. Write structure of .B, C and D. Explain the
fonnation of products.


Predict the product and outline mechanistic . steps' for reaction.. 5+5

--........ A

Predict the possible products of following, Diels Alder reaction and explain which product is preferentially fanned and why.?

o
• II CH2=CHCH=CHOCH3+ CH2=CHCH A B
lJ-J<J1r-J-DIIJ 3 (Contd.)
I·

I
Write the structure of the product fonned in
the follo;wing ·Explain briefly its . formation.

.
(3. Give the name of the reaction and· explain the mechanism involved in the formation of the producrs. 10x4
75% 25%


R R. Zn-Hg
..
Hel
OQ
o 2R
•



..DCOOR

B-JGT-J-DIB 4 (Cootd.)

4. Explain briefly
While writing the Diels Alder products for're­action of 2,4,6-cycloheptatrienone with cyclo­pentadiene and with ethene respectively, why do,es it use two pi electrons with cyc1o­
"pentadiene while with e.thene it uses four pi electrons? 15
Why lycopene and beta carotene appear coloured in nature 5
•
Predict the product of following electrocycJic reactions. Indicate and comment upon the
sterle positiqns of hydrogens in the product. 10

..
•
Draw the struct;ure of [18]-Annulene and show how many types of NMR signals 'are given by it. Explain. 10
Section-B
5. Answer any four of the following:
Use aldol condensation to synthesize useful compound from cheap and readily available compounas/reagents, the food' preservative sorbic acid, CH3CH=CH-CH=CHCOOH
10
B-JGT-1-DIB 5 (Contd.)


Considenng' bromination carbonyl com.. pounds as acid catalysed, suggest a reasonable' mechanism in which enol is'an intennediate, use the following compound. 10
R1
tlC-C-R
III 2
R
Reaction of 1 mole of semicarbazide with a
I
mixture of 1 mole each of cyclohexanone' and benzaldehyde precipitates cyclohexanone semi·
•
carbazone, but after a few hours the precipitate is benzaldehyde sernicarbazone.· ExpJain. 10

Why attack of CN-on benzaldehyde does not bring about Cannizzaro reaction while that of OH-brings about it. Write the mechanistic steps and products in the two cases... 10
•
Effect the following conVersion 10
_<..i:six to seven s..po) • .lV ,UBr
6. Why carboxylic acid group of aminQ acids is more acidic (pKa than' carboxylic acid group of acetic acid (pKa 5
B-JGT...J-DIB 6 (Contd.)

'Arrange the following alkenes for their increasing rate of brominati9n in methanol. Justify in a few lines. 5+5

Me,
C=-....
Me/


Me,
.......C=CH2

Me

Me, ,Me


H
n-Bu .
".......C=CH2
H


t..Bu
.......C=CH2
H

Write reaction products in the following;

.. cS
Btl .. tributyl amino •
B-JGT·J-DID 7 (Contd.)


OH
B SbFj-HF

2
. Br2 •
HC.

3

N02.
o
Chlorination

o•
Cl


nitration
2
•

NaHS03



RNH2
eiJ OH

CI
.... .. ?.2 4500C CI
I·.
KNH2
II
2
NH3
cv:.
. NHCOCH2COCH3


B-JOT-J-DIB 8 . (Contd)

.
(Viii)CJ

N
BuLi

2


2
?.2
.
•I
2

.(xii) HO OH ZnCI2 H20
o +CH3CN .• Hel • .
Ether -10· o°c
OH
3
8-JGT-J-DI8 9 (Contd.)


7. A compound with moleCular formula CgH l40
shows the following proton NMR, and IR
bands.

The singlet at 8 3·1 in the proton NMR dis­appears when the sample is shaken with D20. IR 3500 3300 2100 em-I.
I HNMR d s 0 1·5), d
o 1·6), m 8 s 8 and s
•8
the structure of the compound, with justification. 15

When I-butanol is dissolved in superacid at the IH NMR shows signals -at 8 9·5 0 5 m). On raising the tempera­'lure to above O°C all· the above signals decrease largely and then the NMR is dominated by a new singlet at 0 4·0.

Explain the results. 10


A hydrocarbon in its mass spectrum showed molecular. ion at m/z 134 and prominent fragments at mlz 119 and 77 The spectral for this compound are as follows .


IH NMR 8 2·82 (heptet, J 7·0 Hz, 2·28 3H) and 1·22 ppm
7-0 Hz. l3C NMR 8 21·3, 24·2, 38·9, 126·6, 128·6,. 134·8, and 145·7 ppm; IR bands at 3030, 2970, 2880, 1515, 1465 and
815 UVAmax(E) 265 (450).
What is its structure? Justify your answer. 15

B-JGT-J-DI8 10 (Contd.)
. ....

8. Explain the foJlowing with a suitable simple
example for each
C06polymer •
5+5
Examine the structures of the following
synthetic Tell what class of com..
pounds it belongs to and give structure of the
likely monomers..


JVV.,
CH,C-CHCH2CH,C-CHCH,
·1
CI CI

Il-JCJ1r-J-I>II3 11