LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 26

FIRST SEMESTER – APRIL 2007

CH 1806 – ORGANIC REACTION MECHANISM & STEREOCHEMISTRY

 

 

 

Date & Time: 27/04/2007 / 1:00 – 4:00         Dept. No.                                                       Max. : 100 Marks

 

 

Part-A

                                                        Answer ALL questions.                     (10 ´ 2 = 20)

1. Suggest a method of trapping the intermediate of a reaction, using suitable example.
2. Define microscopic reversibility with example.
3. What is Arndt-Eistert synthesis?
4. Predict which of the following products would be got in Baeyer Villiger oxidation of cyclohexylmethyl ketone.Why?
5. a) What is the catalyst, reactants and the products in Rosenmund reduction reaction?
   b) What is Corey’s reagent and how is it prepared?
6. Explain axial halo ketone rule with an example.
7. What is epimerisation? Give an example.
8. Explain Prelog’s rule with a suitable example.
9. What are the resolving agents used for the separation of racemic bases? Give the structure of any one.
10. Explain Cram’s rule with an example

 

PART B

Answer any EIGHT questions                               (8 ´ 5 = 40)

11. Give the mechanism of Wolf-Kishner reduction reaction.
12. Predict the product with mechanism.
13. Predict the product of Fischer-Indol synthesis with sutiable evidence.
14. What is memory effect? Explain using a suitable example.
15. What are crossover experiments? How are they helpful in arriving at the mechanism of the reaction?
16. ‘Iodination of aniline is inversely proportional to the square of the iodide concentration’. Explain using suitable mechanism.
17. Explain thermal and cationic racemisation with suitable examples.
18. Explain the conformation of cyclohexane with potential energy diagram.
19. Explain asymmetric synthesis with suitable examples.
20. How are optical rotatory dispersion technique helpful in predicting the configuration of molecules?
21. What atropisomerism?  Explain with a suitable example.
22. Explain the stereoselective synthesis of reserpine.

PART C

Answer any FOUR questions                  (4 ´ 10 = 40)

23. a) Predict the product of the reaction of trialkylborane with carbon monoxide in the presence of ethylene glycol, H₂O and NaOH.
    b)  Give the mechanism of oxidative decarboxylation.
24. Give the mechanism of the following rearrangements
    a) Steven’s b) Beckmann’s                        c) Hofmann’s
25. Explain the following:
    i) Diazotisation of aniline follow third order kinetics.
    ii) The rate law for iodination of acetone depends on the concentration of acetone and the base.  Explain the mechanism using suitable non-kinetic evidence.
26. a) Explain any two methods of resolution of racemic modifications.
27. b) What is optical purity? How will you ascertain it?
28. Assign R or S configuration to the following. Justify your answer
29. a) Explain the stereochemical synthesis of yohimbine.
30. b) Write anote on (i) asymmetric destructions (ii) Second order asymmetric transformations.

 

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