LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

FIRST SEMESTER – NOVEMBER 2012

CH 1812 / 1806 – ORGANIC REACTION MECHANISM & STEREOCHEMISTRY

 

 

Date : 01/11/2012            Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

PART – A

Answer ALL questions:                                                                                (10 x 2 = 20)

 

1. Write the mechanism of Chichibabin reaction.
2. What is primary kinetic isotope effect? Explain with suitable example.
3. “Diazotization of aniline follows second order with respect to nitrous acid” Propose a mechanism for this reaction.
4. What is para-Claisen rearrangement? Explain with mechanism.
5. How does indole prepared from phenyl hydrazine?
6. What is Birch reduction?
7. What happens when cyclohexene on ozonolysis?
8. In α, α’-dimethylsuccinic acid, the meso form predominates at equilibrium over the racemic form. Why?
9. State and explain Cram’s rule with suitable example.
10. What is atropisomerism? Give example.

 

PART-B

Answer ANY EIGHT questions:                                                                   (8 x5 = 40)

 

11. Draw the potential energy diagram of thermodynamic and kinetically controlled product formation of a reaction between 1,3-butadiene and HBr.Explain.
12. Explain the microscopic reversibility with suitable example.
13. Explain the following;
14. a) trapping of intermediate      b) isotope labeling study
15. Explain the mechanism of abnormal Claisen rearrangement.
16. How would you convert 1,7,7’-trimethyl bicycle[2,2,1^1-4]heptan-2-ol into 2,2’-dimethyl-3-methylidene bicycle [2,2,1^1-4]heptane?
17. When treated with p-CH₃C₆H₅SO₂Cl in pyridine, the α-benzilmonoximes undergo Beckmann rearrangement with fragmentation. Explain.
18. Explain any one application for each of the following reagents.
19. a) SeO₂ b) OsO₄
20. How does a carboxylic acid undergoes oxidative decarboxylation? Explain.
21. Explain mutarotation with any one example.
22. Give an example for a first order asymmetric transformation reaction and explain.

 

21. Predict the stereochemical change of acetolysis of 3-methoxy-2-bromobutane in the presence of silver acetate in acetic acid.
22. State Brett’s rule and explain the reactivity of bicyclic rings.

 

PART-C

Answer ANY  FOUR questions:                                                                  (4 x10 = 40)

 

23. a) “Radical bromination of isopentane is more selective than chlorination.” Explain with potential energy diagram.
24. b) How does a Raman spectroscopy is used to determine the mechanism of nitration of benzene? Explain.
25. a) Determine the reaction mechanism of base-catalysed iodination of  aniline in presence of excess of iodide ion from its experimental rate data.
26. b) Predict the products to be expected from acid-catalyzed rearrangement of cis- and trans-1,2-dimethylcyclohexane-1,2-diol and sketch mechanism for the formation.
27. a) “The lactones obtained by the Baeyer-Villiger oxidation of camphor and apocamphor contain 25% and 94% of the abnormal product” Why?
28. b) Explain memory effect with suitable example.

 

26. a) Give mechanism for the following conversions.

(i) Methane into methanol using aq.CrO₃

(ii)Acetaldehyde into acetic acid using O₂ and Ag.

1. b) Complete the following with mechanism.

 

27. a) What are the various products obtained on the acetolysis of 3-phenyl-2-pentyl tosylate?
28. b) Explain the process of separation of racemic alcohols with an example.
29. c) Asssign R,S configurations to the following:

 

28. a) State and explain curtin-Hammett principle with suitable example.
29. b) Explain the following with  applications; (i) cotton effect  (ii) axial haloketone rule.

 

 

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