This document contains a 25 question exam on organic chemistry concepts. It is divided into 3 parts: Part A contains 10 short answer questions worth 1 mark each, Part B contains 5 short essay questions worth 5 marks each, and Part C contains 4 longer essay questions worth 10 marks each. The questions cover a range of topics including stereochemistry, conformations, substitution and elimination reactions, reaction mechanisms, and more. Students have 3 hours to complete the exam which is out of a total of 75 marks.

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APRIL 2013 55701/MCR1A
Time : Three hours Maximum : 75 marks
PART A — (10 × 1 = 10 marks)
Answer any TEN questions.
All questions carry equal marks.
Each answer should not exceed 50 words.
1. Establish the relationship between the hydrogens
of the following molecule as homotopic/
enantiotopic/diastereotopic.
2. Draw the stereochemical structure of
(R)-2-bromooctane in the Fischer form.
3. Explain why cis-4-t-butylcyclohexanol gets
oxidised at a faster rate compared to the trans
isomer.
4. Draw the conformational forms of cis-9-methyl
decalin and trans-9-methyldecalin.
(6 pages)

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5. The diaxial form of cis-1,3-cyclohexanediol is
relatively stable. Why?
6. Why does ‘A’ react at a faster rate than ‘B’ with
isopropyl iodide under SN2 condition?
7. Compare the reactivity of the following two
compounds (C and D) towards nucleophilic
substitution :
8. Illustrate how phenoxide ion exhibits ambident
nucleophilic character.
9. Aqueous sodium bicarbonate treatment of picryl
chloride gives picric acid even at 35°C. But 2-nitro
chlorobenzene gives 2-chlorophenol only at 130°C.
Explain why.
10. Illustrate Zeigler alkylation with an example.

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11. What is the reactive species involved in Reimer-
Tiemann reaction? How can this reactive
intermediate be prepared?
12. Explain how 1,3,5-tribromobenzene can be
prepared from aniline.
PART B — (5 × 5 = 25 marks)
Answer any FIVE questions.
All questions carry equal marks.
Each answer should not exceed 200 words.
13. What is meant by asymmetric synthesis? Explain
the significance of Cram’s rule.
14. (a) Draw the possible stereoisomers of 1,2 and
1,3-dimethyl cyclobutanes. Identify the
active forms in each case.
(b) Draw the most stable conformers of
(i) 1,2-ethane diol and (ii) 1,2-dibromoethane.
(3 + 2)
15. Discuss the conformational features of different
geometrical forms of 1,2- and 1,4-dimethyl-
cyclohexanes.
16. Describe the different mechanisms of base
catalysed ester hydrolysis.

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17. (a) Compare the similarities in the mechanism
of Claisen condensation and Dieckmann
condensation.
(b) Explain what is meant by primary kinetic
isotope effect. (3 + 2)
18. The rho value for alkaline hydrolysis of methyl
esters of substituted benzoic acid is 2.38. The rate
constant for the alkaline hydrolysis of methyl
benzoate is 1
1
4
s
m
10
2 −
−
−
× . Calculate the rate
constant for the alkaline hydrolysis of methyl
m-nitrobenzoate, if the sigma value of meta
methyl group is 0.71.
19. Discuss the course of electrophilic substitution
reactions on pyrrole, thiophene and pyridine.
PART C — (4 × 10 = 40 marks)
Answer any FOUR questions.
All questions carry equal marks.
Each answer should not exceed 500 words.
20. Explain the chiral characteristics associated
allenes, biphenyls and spiranes. Indicate how the
R/S configuration can be assigned to the
enantiomers of allenes and biphenyls
systematically.
[P.T.O.]

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21. (a) Indicate how the conformational factors
influence the esterification of cyclohexanols
and oxidation of cyclohexanols.
(b) Compare the stereochemical features of
cis and trans-decalins. (5 + 5)
22. Explain why (a) 3
2OCH
ClCH reacts with iodide in
acetone several times faster than methyl chloride
(b) Cl
CH
SCH
CH
ClCH 2
2
2
2 is hydrolysed by water
much faster than any primary halide (c) Allyl
halides react at a faster rate than vinyl halides
(d) thionyl chloride involved chlorination of an
optically active alcohol retains the configuration at
the substitution centre (e) when the solvent is
changed from methanol to N, N-dimethyl
formamide, the rate of the reaction of methyl
iodide with sodium azide is increased by 4
10
5
.
4 ×
fold. (5 × 2)
23. (a) Compare the mechanism of Meisenheimer
complex involved substitution and the
benzyne intermediate involved substitution.
(b) The course of aromatic nucleophilic
substitution reaction of the following
compounds by sodamide is governed by
benzyne mechanism. Predict the product(s)
in each case. (5 + 5)

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24. Account for the following : (5 × 2)
(a) Friedel Crafts alkylation may lead to poly
alkylation.
(b) Chlorine is ortho/para orienting, but
deactivates the ring during aromatic
electrophilic substitution.
(c) Diazonium coupling on 2-naphthol takes
place at C–1.
(d) When aniline is acetylated, the ring is
deactivated towards electrophilic attack.
(e) Bromination of aromatic hydrocarbons take
place in the presence of ‘halogen carriers’.
25. (a) What is ‘absolute configuration’ of a chiral
molecule? How does it differ from relative
configuration?
(b) What happens when 4-t-butyl cyclohexanone
is reduced with sodium borohydride?
Explain.
(c) Comment on the nature of the intermediate/
transition state involved in the nucleophilic
substitution at carbonyl carbon.
(d) Explain how isotope labeling is helpful in
determining the mechanism of organic
reactions.
(e) Discuss the fate of nitration on aniline using
nitrating mixture. (5 × 2)
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