GH 38

LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2008

CH 3808 – PHOTOCHEMISTRY AND ORGANIC SYNTHESIS

 

 

 

Date : 26-04-08                  Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

Part – A

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

1. How hydroxyl groups are added on to carbon-carbon multiple bonds?
2. Draw the Frontier Molecular Orbital picture for the cycloaddition of 1,3-butadiene and ethylene.
3. Predict the product.
4. Give an example for 3,3-sigmatropic rearrangement and explain the mechanism.
5. State Stark Einstein and Grothus Draper laws of photochemistry.
6. What is Norrish type II reaction? Give an example.
7. How protective groups are important in the synthesis of an organic compound?
8. What are synthons? Identify suitable synthetic equivalents for the following synthons.

C₆H₅CH₂⁺, (CH₃)₂CH^¯

9. Write the mechanism of SeO₂ oxidation.
10. Why convergent synthesis is a better technique than stepwise synthesis?

 

Part – B

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

11. Explain the mechanism of NaBH₄ reductions with an example.
12. How regioselectivity is explained in cycloaddition reactions? Give suitable examples.
13. The following compound undergoes sigmatropic rearrangement reaction. Write the mechanism of the reaction and predict the product/s.

 

14. Predict the stereochemistry of the product and write the mechanism of the reaction.

 

15. Explain the Barton reaction in steroidal compounds.
16. How photoisomerisation takes place in alkene compounds? Explain with any two examples.
17. Write the retrosynthesis of the following compounds.
18. How are monofunctionalised compounds prepared from alkylhalides? Write a scheme to explain this.
19. What is electroorganic synthesis? Elaborate on electrooxidation reactions with suitable examples.
20. Discuss on C-C disconnections in 1,3- and 1,4-difunctionalised compounds with examples.
21. Write a short note on aldol and crossed aldol condensation reactions.
22. Bring out the differences between Clemmensen and Wolff Kishner reductions with suitable example.

Part – C

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

23. Write the mechanism of the following reactions and explain.
24. a) Knoevenagel reaction
25. b) Claisen-Schmidt reaction
26. c) Darzen’s reaction
27. How are the following compounds synthesized by retrosynthetic approach?

 

25. a) Write the photochemical rearrangement of 4,4-diphenylcyclohex-2-en-1-one with complete mechanism.
26. b) Explain various photochemical processes taking place in the excited state.
27. a) Explain the mechanism of Paterno Buchii reaction in alkenes.
28. b) Find out the products with proper stereochemistry in the following reactions.
29. Explain the mechanism of the following reactions.

 

 

28. a) Write the complete mechanism of synthesis of cubane.
29. b) Explain the chemoselectivity of the oxidizing agents with suitable examples.

 

 

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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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