LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

DB 25

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – November 2008

    CH 3808 – PHOTOCHEMISTRY AND ORGANIC SYNTHESIS

 

 

 

Date : 03-11-08                   Dept. No.                                          Max. : 100 Marks

Time : 9:00 – 12:00

Part-A

Answer ALL questions.                                                                                                                                   (10 ´ 2 = 20)

1. What is Stobbe reaction?
2. Calculate the percentage yield of aspirin formed?

 

25 g                                                        22 g                                         20 g

3. Define umpolung concept. What are its advantages?
4. What is the thermal reaction between allylic anion and acrolein?
5. Draw the FMO picture for photochemical electrocyclization of 1,3,5-hexatriene.
6. What are cheletropic reactions? Give examples.
7. What is the stereochemistry of (1,5) sigmatropic rearranged product? Represent it with an FMO diagram.
8. Write the equation involving oxidation of organic compound using neutral KMnO₄ solution.
9. Define photoquenching. How does it take place?
10. What are hot ground state reactions?

 

Part-B

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

11. Identify the product and explain the mechanism of reaction.
12. Using alcohol, how are various monofunctionalised compounds synthesized?
13. Explain any five guidelines with example for the C-C disconnections.
14. How FGI plays an important role in the retro synthesis of an organic compound?
15. Explain the mechanism of LiAlH₄ reduction? What are the functional groups reduced by this reagent? Give an example.

 

16. Predict the product and explain the mechanism of following reactions.
17. Using electroorganic synthesis, how are the following compounds prepared?

 

 

 

18. Explain the mechanism of following reaction.
19. Write a short note on the effect of substituents on the cycloaddition reactions.
20. With atleast 5 degenerate structures being drawn, explain the degenerate sigmatropic rearrangement in the following compound.
21. Explain the photoreduction of benzophenone using
22. a) diphenylcarbinol b) 2-propanol
23. Predict the products in the following photochemical reactions with mechanism.

 

Part-C

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

23. Explain the mechanism of following reactions. (3 + 4 + 3)
24. a) Mannich reaction
25. b) Perkin reaction
26. c) Benzoin condensation.
27. Predict a suitable mechanism for the following reactions. (5 + 5)
28. a) Draw the correlation diagram for the cycloaddition reaction of 1,3-butadiene and ethylene. State whether the reaction is thermally or photochemically feasible. (6)
29. b) How chemoselective are the oxidizing agents? Explain this with suitable examples. (4)
30. a) Explain the synthesis of longifolene. (7)
31. b) How catalytic hydrogenation can control stereochemistry in alkynes? (3)
32. a) How regioselective reactions are converted into regiospecific with the help of controlling elements. Discuss with suitable examples.                                                                                                              (5)
33. b) Bring out a suitable retrosynthesis for the following target molecules. (5)
34. a) How does 4,4-diphenylcyclohexan-2,5-dienone undergo photochemical rearrangement. Give a detailed account of it.                                                                                                                         (7)
35. b) Explain the mechanism of Paterno Buchii reaction in alkynes. (3)

 

 

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