LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

LM 40

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2007

CH 3800 – ORGANIC CHEMISTRY – III

 

 

 

Date & Time: 24/04/2007 / 9:00 – 12:00      Dept. No.                                       Max. : 100 Marks

 

 

PART-A

Answer ALL questions.                                                                       (10 ´ 2 = 20 marks)

1. Effect the following conversion.

 

2. State Woodward Hofmann rules for electrocyclization reactions.
3. Predict the sigmatropic reactions in 1,5-systems with examples.
4. Define Norrish type II cleavage reactions. Give an example.
5. What is photosensitization? What is its importance?
6. ‘Convergent synthesis is a better method in organic synthesis than in stepwise synthesis’. Substantiate this statement with a suitable example.
7. What are fragmentation reactions? Give an example.
8. How would you plan the synthesis of 6-methyl-3-octen-2-one by span technique?
9. What is first generation asymmetric synthesis?
10. What are the importance of three component system in Clemmensen reduction?

 

 

 

PART-B

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

11. Draw the correlation diagram for the electrocyclization of 1,3,5-hexatriene. Predict whether the reaction is feasible thermally or photochemically. (5)
12. Find out the products with proper stereochemistry in the following reactions.(2´2½)

 

 

 

 

 

13. Predict the products in the following sigmatropic reactions.

 

 

14. What are the products formed when 4,4-diphenylcyclohexen-2-one undergoes photochemical rearrangement. Write the mechanism of the reaction.
15. Illustrate with any two examples, the structure of a molecule in a photochemically excited state.
16. What is photoisomerisation? Explain with an example.
17. How would you plan the synthesis of 2-methyl-2-butene by disconnection approach? Explain.
18. ‘Symmetric target molecules can be planned by disconnection approach symmetrically’.

Explain this with a suitable example.

19. Explain the role of selectivity and specificity in organic synthesis by taking two examples for each.
20. How are the following conversions effected?
21. a) 2,3-dimethylcyclohex-2-en-one ¾¾®  2,2,3,3-tetramethylcyclohexanone
22. Isopropyl alcohol ¾¾® 1-phenyl-2-methyl-2-propanol
23. Explain the synthesis of 1,2-difunctionalised compounds with two suitable examples.
24. Elucidate the structure of reserpine by synthesis.

 

 

PART-C

Answer any FOUR questions.                                                            (4 ´ 10 = 40 marks)

23     a) How cycloaddition reactions are stereoselective? Illustrate with suitable examples.

1. b) Predict the stereochemistry of electrocyclisation in 4 and 6 electron systems. Give suitable examples.

24     a) Predict the mechanism of following reactions.

 

 

1. b) Derive the equation for Stern-Volmer expression.

 

 

 

 

 

 

25     a) Explain the Paterno Buchii reactions in alkenes and alkynes with examples.

1. b) Explain the following photochemical rearrangement reaction.

 

26. a) Establish the structure of longifolene by synthesis.
27. b) What are the synthetic importance of Reformatsky reaction? Explain with two suitable examples.

 

27. a) What are the synthons and synthetic equivalents in the synthesis of phenyl hydroxyl amine and benzanilide?
28. b) Explain the synthesis of norethisterone.

 

28. Explain the use of the following in the organic synthesis, with an example each. Explain the mechanism.

 

1. a) Diels-Alder reaction
   b)            Knoevenagel reaction
   c)            Perkin reaction
   d)            Electroorganic synthesis.

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