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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
FIRST SEMESTER – APRIL 2008
CH 1806 – ORGANIC REACTION MECHANISM & STEREOCHEMISTRY
Date : 28-04-08 Dept. No. Max. : 100 Marks
Time : 1:00 – 4:00
PART – A
Answer ALL questions (10 ´ 2 = 20 marks)
- Identify the products obtained when cis- and trans-1,2-dimethyl-1,2-cyclohexanediol are treated with an acid?
- Explain the formation of the product in the following:
Ph-NH-N=CH-CH2-R - Is Hofmann rearrangement inter or intramolecular? Explain.
- What happens when phenyl magnesium iodide is treated with diphenyl ketene? Identify the intermediate and give the mechanism.
- What happens when ethyl benzene is treated with selenium dioxide? Give its mechanism.
- Explain why the conductivity of boric acid in (–)2,3-butanediol is more than the meso isomer?
- Between erythro and threo form of 1-bromo-1,2-diphenylpropane, which will undergo dehydrohalogenation faster in the presence of a base. And why?
- On what principle cis and trans isomers of 4-t-butyl cyclohexanol is separated by chromatography technique using alumina as the adsorbent?
- Why neomenthyl chloride reacts faster with NaOEt than menthyl chloride?
- What are ORD plane curves?
PART – B
Answer any EIGHT questions ( 8 ´ 5 = 40 marks)
- How would you effect the following conversion? Explain with mechanism.
- Explain with mechanism the formation of product in the following:
- ‘The rate of base-catalysed iodination of aniline in the presence of excess iodide ion is inversely proportional to the square of the iodide concentration’. Derive the rate law and explain with mechanism.
- How is isotopic labeling technique useful in determining the mechanism of a chemical reaction? Explain with two suitable examples.
- Explain the mechanism of ozonolysis of olefins. Identify the products obtained on subjecting the following compounds in ozonolysis followed by reduction.
a) 1,3,5-trimethylbenzene b) 2,3-dimethyl-2-pentene. - How is addition-elimination reaction mechanism useful in identifying the products in oxidation-reduction reactions? Explain with two suitable examples.
- ‘The solvolysis reactions of 2-phenyl-3-pentyl tosylate and 3-phenyl-2-pentyl tosylate with acetic acid give the same products’. Explain with mechanism.
- Explain the pyrolysis reaction of xanthates and acetates with suitable examples.
- Explain Curtin-Hammett principle using the following reaction.
- How is the stable conformation of 1,2-dibromocyclohexane classified by dipole moment measurements?
- Assign R and S notation for the following compounds
- a) b) c) d)
- How the major product in an asymmetric induction reaction can be predicted by Cram’s rule and prelog’s with suitable example.
PART – C
Answer any FOUR questions ( 4 ´ 10 = 40 marks)
- a) How is the determination of order of a reaction helpful in ascertaining the mechanism of organic chemical reactions? Explain with two suitable examples.
- b) What are consecutive reactions? Derive the kinetics for benzoin condensation and explain the mechanism.
- Explain the mechanism of the following rearrangements with suitable examples.
- a) Baeyer-Villiger rearrangement
- b) Beckmann rearrangement
- c) Hofmann rearrangement
- Explain the following with suitable mechanism in oxidation-reduction reactions.
- a) Hydrogen atom transfer reaction
- b) Formation of ester intermediate
- c) Oxidation of alcohols
- Discuss the stereochemistry of the following reactions:
- a) Reaction of cis ans trans 2-aminocyclohexanol with HONO.
- b) Solvolysis reactions of neomenthyltosylate and menthyl tosylate in acetic acid
- c) Reaction of erythro-3-bromo-2-butanol with HBr
- Explain the following
- a) First order asymmetric transformation
- b) Walden inversion
- c) Chemical method of racemisation by cation intermediate formation
- Discuss in detail the stereo selective synthesis of reserpine.
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