Loyola College M.Sc. Chemistry April 2008 Organic Reaction Mechanism & Stereochemistry Question Paper PDF Download

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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)

 

  1. Identify the products obtained when cis- and trans-1,2-dimethyl-1,2-cyclohexanediol are treated with an acid?
  2. Explain the formation of the product in the following:
    Ph-NH-N=CH-CH2-R
  3. Is Hofmann rearrangement inter or intramolecular? Explain.
  4. What happens when phenyl magnesium iodide is treated with diphenyl ketene? Identify the intermediate and give the mechanism.
  5. What happens when ethyl benzene is treated with selenium dioxide? Give its mechanism.
  6. Explain why the conductivity of boric acid in (–)2,3-butanediol is more than the meso isomer?
  7. Between erythro and threo form of 1-bromo-1,2-diphenylpropane, which will undergo dehydrohalogenation faster in the presence of a base. And why?
  8. On what principle cis and trans isomers of 4-t-butyl cyclohexanol is separated by chromatography technique using alumina as the adsorbent?
  9. Why neomenthyl chloride reacts faster with NaOEt than menthyl chloride?
  10. What are ORD plane curves?

PART – B

 

Answer any EIGHT questions                   ( 8 ´ 5 = 40 marks)

 

  1. How would you effect the following conversion? Explain with mechanism.

 

  1. Explain with mechanism the formation of product in the following:

 

 

  1. ‘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.
  2. How is isotopic labeling technique useful in determining the mechanism of a chemical reaction? Explain with two suitable examples.
  3. 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.
  4. How is addition-elimination reaction mechanism useful in identifying the products in oxidation-reduction reactions? Explain with two suitable examples.
  5. ‘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.
  6. Explain the pyrolysis reaction of xanthates and acetates with suitable examples.
  7. Explain Curtin-Hammett principle using the following reaction.

 

 

 

 

 

  1. How is the stable conformation of 1,2-dibromocyclohexane classified by dipole moment measurements?
  2. Assign R and S notation for the following compounds
  3. a)  b)                                c)                                 d)

 

 

 

 

 

 

  1. 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)

 

  1. a) How is the determination of order of a reaction helpful in ascertaining the mechanism of organic chemical reactions? Explain with two suitable examples.
  2. b) What are consecutive reactions? Derive the kinetics for benzoin condensation and explain the mechanism.
  3. Explain the mechanism of the following rearrangements with suitable examples.
  4. a) Baeyer-Villiger rearrangement
  5. b) Beckmann rearrangement
  6. c) Hofmann rearrangement
  7. Explain the following with suitable mechanism in oxidation-reduction reactions.
  8. a) Hydrogen atom transfer reaction
  9. b) Formation of ester intermediate
  10. c) Oxidation of alcohols
  11. Discuss the stereochemistry of the following reactions:
  12. a) Reaction of cis ans trans 2-aminocyclohexanol with HONO.
  13. b) Solvolysis reactions of neomenthyltosylate and menthyl tosylate in acetic acid
  14. c) Reaction of erythro-3-bromo-2-butanol with HBr
  15. Explain the following
  16. a) First order asymmetric transformation
  17. b) Walden inversion
  18. c) Chemical method of racemisation by cation intermediate formation
  19. Discuss in detail the stereo selective synthesis of reserpine.

 

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