LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

AD 18

THIRD SEMESTER – NOV 2006

                              CH 3800 – ORGANIC CHEMISTRY – III

 

 

Date & Time : 25-10-2006/9.00-12.00      Dept. No.                                                    Max. : 100 Marks

 

 

 

Part A

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

1. Write a short note on [4+2]-cycloaddition in dipolar compounds.
2. What is a cheletropic reaction? Give an example.
3. What is Alder’s endo rule. Explain with an example.
4. Define the following. a) Photo quenching b) II law of photochemistry
5. Write a short note on the fate of the excited state molecules in a photochemical reaction.
6. Explain retro synthetic approach with an example.
7. What are annelation reactions? Give an example.
8. How would you plan the synthesis of 3-methyl-6-hepten-2-one by span technique?
9. Give a synthesis based on umpolung concept of seebach.
10. What are the importance of three component system in Clemmensen reduction?

 

 

Part B

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

11. Draw a correlation diagram for the cycloaddition reaction of 1,3-butadiene and ethylene. State whether the reaction is thermally or photochemically feasible.
12. Predict the products in the following pericyclic reactions and explain the mechanism with proper stereochemistry.

 

 

13. Predict the mechanism of the following reaction.

 

14. Derive Stern Volmer expression for photochemical quenching.
15. Explain the photochemical rearrangement of 4,4-diphenylcyclohexenone.
16. What is Barton reaction? Explain its reaction mechanism in a steroidal compound.

 

 

 

17.    Explain the mechanism of Birch reduction. Identify the products obtained when the following are subjected to this reduction: (a) Benzoic acid and (b) Anisole.  Justify your answer.

18.    Explain the importance of electroorganic synthesis over the conventional synthesis in synthesizing bridged compounds with suitable examples.

19.    Explain the synthesis of reserpine.

20.    Explain the mechanism of Reformatsky reaction.  How is this reaction useful in organic synthesis?

21.    Oxymercuration-demercuration reactions follow Markownikov’s addition while Hydroboration-oxidation follows Anti-Markownikov’s addition. Why?  Explain with two suitable examples.

22.    What are stereospecific control elements?  How are they useful in organic  synthesis?

Part C

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

23. Predict the reaction mechanism of the following reactions.

a)

 

b)

 

 

24. a) Predict the products of following reactions.

 

 

1. b) “Cycloaddition reactions are regioselective.” Explain with any two examples.

 

 

 

 

 

 

 

25. a) Photo reduction of benzophenone with diphenylmethanol involves a quantum     yield of 1 compared to that of 2-propanol with 2. Explain.
26. b) Explain the photochemical rearrangement of 4,4-diphenylcyclohexen-2,5-    dienone.
27. a) How would you synthesise Norethisterone?
28. b) What are the advantages of selenium dioxide oxidation? Explain the mechanism      with suitable examples.
29. a) Explain the steps involved in the synthesis of longifoline.
30. b) Identify the product in the following. Explain with mechanism.
    Me₂C=CH-CO-CH₃      A   +   B
31. Explain the following:
32. Perkin reaction is most widely used in the synthesis of coumarin.
33. Benzaldehyde is condensed with ketonic ester in retrograde aldol condensation reaction.
34. Alkylation of active methylene group is an important step in organic synthesis in increasing carbon skeleton.

 

 

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