LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

GH 53

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2008

    CH 3800 – ORGANIC CHEMISTRY – III

 

 

 

Date : 25/04/2008            Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART-A

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

1. What is group transfer reaction? Give an example.
2. State Woodward Hofmann rules for electrocyclization and cycloaddition reaction.
3. Give an example for 3, 3-sigmatropic rearrangement and explain the mechanism.
4. What are hot ground state reactions? Give an example.
5. Write a short note on photoisomerisation with an example.
6. What is retrosynthetic approach in organic synthesis? Give an example.
7. What are regiospecific reactions? Give an example.
8. What happens when phthalic anhydride is heated with acetic anhydride in the presence of sodium acetate?
9. What is the function of three layer solvent system in Clemmensen reduction?
10. How would you prepare bicyclic compounds using electroorganic synthesis?

 

PART-B

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

 

11. Draw the 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 sigmatropic reactions.

 

13. Explain regioselectivity in cycloaddition reactions with examples.
14. Explain the Barton reaction in steroidal compounds.
15. Discuss di-p-methane rearrangement with an example.
16. How photoreduction of benzophenone takes place by 2-propanol? Explain the mechanism of reaction.
17. Write a note on Birch reduction. What are the products obtained when benzoic acid and anisole are subjected to this birch reduction?  Explain the mechanism.
18. How is selenium dioxide used as an oxidizing agent? Explain with two examples and mechanism.
19. Explain the steps involved in the synthesis of cubane.
20. How would you plan the synthesis of the following compounds using span technique?
    a) 1-phenyl-1-pentanone
    b) 3-methyl-6-hepten-2-one
21. Identify the stereochemistry of product obtained in the hydroboration-oxidation reaction on unsymmetrical alkenes. How does this reaction differ from oxy-mercuration-demercuration reaction?
22. Explain the steps involved in the synthesis of norethisterone.

 

 

 

 

PART-C

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

 

23     a) Predict the mechanism of following reactions.

 

1. b) There are two rearrangements involved in the following reaction. Identify them and write the mechanism.
2. a) The following reaction involves two steps. Explain the mechanism of the reaction.
3. b) The following compound undergoes 5, 5-sigmatropic rearrangement reaction. Predict the product and write the mechanism of the reaction.

25     a) Write a short note on the photochemistry of a,b-unsaturated ketones with an example.

1. b) Explain the Paterno Buchii reactions in alkenes and alkynes with examples.
2. a) Explain the mechanism of Wittig reaction. How is this reaction useful in organic synthesis?
3. b) Establish the structure of reserpine by synthesis.
4. a) Explain the importance of Reformatsky reaction in organic synthesis.
5. b) What are stereospecific control elements? How are they useful in organic synthesis?
6. a) Explain the steps involved in the synthesis of longifoline.
7. b) ‘Alkylation of active methylene group is an important technique in increasing carbon chain in organic synthesis’ – Justify this statement with suitable examples.

 

 

 

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