m. phil entrance question 2014-chemistry

8/10/2019 M. Phil Entrance Question 2014-Chemistry

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SIKKIM UNIVERSITY

Department of Chemical SciencesM. Phil. Entrance Test Examination 2014

Organic Specialization

Full Marks: 60 Time: 2 hour

Answer any Four questions. (15 x 4 = 60)

1. a) Radical monochlorination of a compound having molecular formula C4H8 gave a

mixture of monochlorinated products, A, B, C, and D, that were then separated and

characterised. It was found that both A and Bexisted as a pairs of enantiomers (ie. A/A',

B/B') and that AandBwere diastereomers. The relative yields of the products was A= B

> C > D (you could check this by calculating the % yields expected). In a series of

reactivity studies with AgNO3/ H2O / EtOH, the relative rates of reaction were C> A=

B> D. With NaI / acetone, the relative rates of reaction were D> A> B> C

a. Identify the monochlorinated isomers A, B, C and Dand the original hydrocarbon

H. 5

b. How many types of hydrogen are there in the original hydrocarbon H ? 1

c. What would the major isomer have been if the company had used a radical

bromination instead of chlorination? 1

b) Compare the acidity of Haand Hb.Give proper reasoning to support your answer. 3

Ha Hb

c) Write products with mechanism giving consideration to stereochemistry. 2

MeEt

HCl

KCN AgCN

Acetone H2O

d) Write down the mechanism of following reaction. Account for the fact that the

compound in which R = H reacts 35 times as fast as the one in which R = CH3. 3

R

Br

RNO2

R

R

O2N N

HN


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2. a) Explain differing outcome in both the following pairs of reactions with mechanis. (3+3 = 6)

OH

NH2t-Bu

OH

NH2t-Bu

O

t-Bu

CHO

t-Bu

HNO2H2SO4

HNO2H2SO4

but

MeMe

OH

O

PhO

O

Ph

but MeMe

OH

O

Ph

O

O

Ph

x

i)

ii)

b) For preparation of product which reaction you will choose and why? 4

c) Explain the change in regioselectivity in following pairs of reactions. 5

O

CN KNH2(1equiv)KNH2(2equiv)

MeI MeI

O

CNO

CN

O

NH2NHSO2Ar

2 equiv LDA

NH2NHSO2Ar

NaOEt

i)

ii)

3. Write appropriate reagents for following transformations. (10 x 1.5 = 15)

HN

O

OOO

O

O

O

O

O O

O

A

B

C

D

E

F

G H

I J

Ph

PhMe

OPh H

Me

O

H H

Ph Ph

Me

OH

LiAlH4

PhMgBr


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4. a) Give mechanism for following transformations. (2.5 x 2 = 5)

O

O

CO2CH3O

+

O

CO2CH3

N

i) Na, Liq. NH3

ii) H3O+

O

i)

ii)

b) How following transformation can be achieved? (1.5 x 4 = 6)

Me CHO

O

I

O O

O

Me

Oi)

ii)

c) What products do you expect from following reactions? In which case the reaction will be

faster and why? 2

IIAgClO4

H2O

AgClO4

H2O

d) Write as many diene compounds possible from which following compound can be prepared

by ozonolysis. 2

O

O

O

5. a) Write the structure of A and B with due consideration to the stereochemistry. Give reason

for your choice of stereochemistry. 5

Me

Me

HO2C

Me

CO2H

Me

I2/K2CO3I2/K2CO3A B

b) Write the structure of A and B. Give reason for your answer. 2

Me MeMCPBA

A + BMajor Minor

c) How will you explain following difference in products? 2

D D

F

KNH2

NH3(l)

D D

FD D

BrD NH2

KNH2

NH3(l)


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d) Write the products of following reaction. Give reasons for your answer. 6

MeO CO2Me OMe

CO2MeOMe

MeCO2Me

A B C

6.a) Write reagents and conditions for following multistep synthesis. 10

b) Give appropriate reagents for following transformations. (1 x 5 =5)

i.

HO CH3

HH3C OH

H

dl-Pair

ii.

OH

OH


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7. a) An organic compound has the molecular formula C12H17NO. Identify the compound using thespectroscopic data given below. Give step by step explanation for you logical structural

elucidation. 7

max (KBr disc): 3296, l642 cm-11H NMR (CDCl3 solution):07.23-7.42 (m, 5H); 5.74 (brs, exch. D2O , lH); 5.14 (q, J = 6.7Hz, lH);

2.15 (t, J = 7.1 Hz, 2H); 1.66 (m, 2H); 1.48(d,J = 6.7 Hz, 3H); 0.93 (t,J= 7.3 Hz, 3H) ppm.13C{IH} NMR (CDC13solution): 172.0 (C), 143.3 (C), 128.6, 127.3, 126.1,48.5 (CH),38.8 (CH2), 21.7 (CH3), 19.1 (CH2), 13.7 (CH3) ppm.

Mass spectrum: m/e 191(M+, 40), 120(33), 105(58), 104(100), 77(18), 43(46).

b) A compound having molecular formula C7H8O, gives following1H and

13C NMR spectra.

Deduce the structure of the compound from these NMR value. Give explanation for you logical

structural elucidation and assignments. 4


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c) Deduce the structure of following compound (C11H14O2) fro following 13C NMR spectrum? 4

Thank you

m. phil entrance question 2014-chemistry

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