M.Sc. DEGREE EXAMINATION, NOVEMBER 2017
First Semester
Chemistry
CONCEPTUAL ORGANIC CHEMISTRY
(CBCS 2015 onwards)
Time 3 Hours Maximum 75 Marks
Part A (10 x 2 20)
Answer all questions.
1. What is hyperconjugation? What types of orbitals are
involved in overlap in this phenomenon?
2. Compare the basicity of the following compounds
3. Strength of the base employed can decide the
elimination/substitution ratio. Illustrate with an
example.
4. In what way, SE 2 and SEi mechanisms can be
distinguished?
Sub. Code
536102
RW-953
2
Ws5
5. Indicate whether CF3 group is activating or deactivating
towards aromatic electrophilic substitution reaction. Is it
ortho/para orienting or meta orienting?
6. What happens when sulphanilic acid is treated with
excess bromine water? Suggest the mechanism of the
reaction.
7. Predict the total number of possible stereoisomers for
Ph CHBr CHBr CHBr Ph. Depict them all.
8. List out the symmetry elements present in the following
compound
9. What is Curtin-Hammett principle?
10. Distinguish between enantiotopic hydrogens and
diastereotopic hydrogens.
Part B x 5 25)
Answer all questions, choosing either or
11. What is Huckel rule? Comment on aromaticity
of annulenes taking [12]-annulenes and
[18]-annulenes as examples.
Or
Explain how benzyne can be trapped. Indicate any
two reactions that go via benzyne intermediate.
RW-953
3
Ws5
12. Write a note on neighbouring group participation.
Or
Explain how solvent polarity and substrate
structure influence the course of aliphatic
nucleophilic substitution reactions.
13.
What is Meisenheimer complex? Describe aromatic
nucleophilic substitution reactions that involve
Meisenheimer complex as intermediate. Discuss the
mechanism in detail.
14. Explain Cahn-Ingold-Prelog rules and indicate how
they can be used to assign the R/S configuration of
Chiral centres.
Or
What are diastereomers? How do they differ from
enantiomers? Illustrate with examples. Indicate
how geometrical isomers can also be considered as
diastereomers.
RW-953
4
Ws5
15. Show that properly substituted biphenyls can
exhibit enantiomerism. Discuss the origin of
chirality in these cases.
Or
Which of the following compounds are optically
active?





Part C x 10 30)
Answer any three questions.
16. Write the IUPAC name for the following compounds

CH3 CHOH CHOH CH2 CH2 CHO

RW-953
5
Ws5
Write a note on kinetic isotope effect.
Illustrate Hammond postulate. 4
17. Account for the following observations
Allylic halides undergo SN1 reactions faster than
ethyl halides
Thiophenoxide anion is more powerful as a
nucleophile compared to phenoxide
More branched olefins are preferentially formed
when alkyl halides undergo HX elimination
E2 reaction is stereospecific
Torylate anion is a good leaving group. x
18. Describe the mechanism of
Vilsmier Haack reaction
Echichibabin reaction and
Gattermann Koch reaction. 3
19. Write notes on
Z-nomenclature
Differences between chiral centre, chiral plane and
chiral axis
Resolution of racemic mixture. 4
RW-953
6
Ws5
20. Compare the stability of chair form of cyclohexane
and boat form of cyclohexane.
Explain why trans decalin is rigid, while cis-decalin
is flexible.
Discuss the stereochemical outcome of E2
elimination of HBr from meso-2, 3-dibromobutane.
What are ansa compounds? 3 2
————————