LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2012

CH 3808 – PHOTOCHEMISTRY AND ORGANIC SYNTHESIS

 

 

Date : 21-04-2012             Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

Part-A

Answer ALL questions.                                                                                                          (10 ´ 2 = 20)

1. Write the mechanism of Mannich reaction.
2. Calculate the percentage yield of aspirin formed?

 

25 g                   20 g                 20 g                   20 g

3. Write a short note on the following terms.

Synthons, FGI and FGA

05     What are the advantages of electro organic synthesis?

4. How is Birch reduction done in toluene?
5. Draw the FMO orbital diagram of 1,3,5-hexatriene for thermal electrocyclization.
6. Why group transfer reactions are neither cycloaddition nor sigmatropic rearrangement reactions?

08     How will you effect the following conversion?

9. State the laws of photochemistry.
10. Write short notes on intermolecular energy transfer processes.

 

Part-B

Answer any EIGHT questions.                                                                                                  8 ´ 5 = 40)

11. Explain the benzoin condensation reaction and its mechanism. What is the order of the reaction with respect to the substrate? Why?
12. Explain any five types of C-C disconnections with examples.
13. What are protecting groups? How are carbonyl and carboxylic acid groups protected and deprotected?
14. Explain chemoselectivity and stereoselectivity. How can these be converted into “specificity” reactions?
15. Compare the nature of reduction reactions of LiAlH₄ with that of NaBH₄? (2 x 2½)
16. How catalytic hydrogenation can control stereochemistry in alkynes? Explain with any two examples.
17. Compare the KMnO₄ oxidations in acidic, basic and neutral conditions.
18. Draw the correlation diagram for the electrocyclization of 1,3-butadiene for disrotation.

19     a) State Woodward Hofmann rules for electrocyclization and cycloaddition reaction.

1. b) Identify the possible products in the following reaction.
2. Predict the products in the following reactions and explain the mechanism.
3. Write a short note on various photochemical processes taking place in the excited state.
4. Write the mechanism of photochemical rearrangement of 4,4-diphenyl-2-cyclohexenone.

 

Part-C

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

23. Write a short note on the following. (4 + 3 + 3)
24. a) Stobbe reaction
25. b) Wittig reaction
26. c) Darzen’s reaction
27. Perform retrosynthesis and subsequently synthesize the given compounds. (5 + 5)

 

25. a) Define Natural reactivity and Umpolung concept with examples. What is the importance of these concepts?    (4)
26. b) Explain the mechanism of Knoevenagal and Reformatsky reactions. (6)

 

26. a) Write the mechanism of following reaction (4).
27. b) Write the correlation diagram for the cycloaddition reaction of two ethylene molecules. State whether the reaction is thermally or photochemically feasible. (6)
28. a) How is norethisterone synthesized? (6)
29. b) Explain regioselectivity in cycloaddition reactions with examples. (4)
30. a) Explain the photoreduction of benzophenone using (6)
31. i) diphenylmethanol and ii) 2-propanol.
32. b) Write a short note on the photochemistry of a,b-unsaturated ketones. Give an example. (4)

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – NOVEMBER 2012

CH 3808 – PHOTOCHEMISTRY AND ORGANIC SYNTHESIS

 

 

Date : 01/11/2012            Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

Part-A

Answer ALL questions:                                                                                                         (10 ´ 2 = 20)

1. How is diborane specific in its reactivity towards substituted alkenes?
2. Draw the FMO picture of the excited state HOMO of 1,3,5-hexatriene.
3. What are regioselective reactions? Give an example.
4. What are the products formed when ethyl bromide is reduced electrochemically on platinum electrode?
5. Predict the stereochemistry of the product.
6. What is Fries photochemical rearrangement? Write the mechanism of the reaction.
7. What are the synthons prepared from the following synthetic equivalents?
8. a) 2-bromobutane b) acetyl chloride
9. What is the geometry of excited state ethylene molecule? Give reasons.
10. What are group transfer reactions? Give examples.
11. What is oxy-Cope rearrangement reaction? Give an example.

 

Part-B

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

11. Why Wittig Horner reaction is preferred to Wittig reaction? Mention the advantages of the Wittig Horner reaction with an example.
12. Explain the synthesis of following difunctionalised compounds.
13. a) 1,3-propanediamine b) ethyl acetoacetate
14. How are protection, activation and attachment of bridging group done repeatedly in the synthesis of a polypeptide?
15. Explain the mechanism of following reactions.
16. a) oxidation of an 2-butene by KMnO₄ in basic medium.
17. b) Wolff Kishner reduction of acetophenone
18. Write the complete mechanism of electroreduction of nitrobenzene.
19. Perform retrosynthetic analysis and suggest a suitable synthetic method of the following. (3 + 2)

 

17. Draw correlation diagram for the electrocyclization of 1,3-butadiene by con rotation. Predict whether the reaction is thermally or photochemically allowed.
18. If hydrazobenzene in acid medium undergoes (3,3)- and (3,5)-sigmatropic rearrangements, what are the products formed? Explain the mechanism of the reaction.

 

19. Explain the mechanism of the following reaction and predict the stereochemistry of the mentioned H atoms in the product.
20. What is Barton reaction? How does it take place in steroids? Explain with an example.
21. How does 4,4-diphenylcyclohex-2-en-1-one undergo Zimmerman rearrangement to form various photochemical products?
22. Explain the Norrish type-I and type-II reactions with an example each.

 

Part-C

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

23. a) Write the stereochemical importance of Stobbe reaction. (2)
24. b) Explain 1,2- and 1,4-Michael addition reactions. (5)
25. c) How unnatural synthons are used to prepare 1,2-difunctionalised compounds? Explain with an example. (3)
26. a) How are C-C disconnections done? Explain any four guidelines. (6)
27. b) Perform retrosynthetic analysis and suggest a suitable synthetic route to the following compound (4)
28. a) Explain protection and deprotection of an amine. (4)
29. b) Explain the mechanism of the following reactions with examples. (3+3)
30. i) NaBH₄ reduction of an imine ii) Peracid oxidation
31. a) Explain the synthesis of cubane. .           (5)
32. b) How mercuric acetate acts as a dehydrogenating agent? Explain with any two examples.                                                                                                    (5)
33. a) Predict a suitable mechanism for the following thermal reaction.            (4)
34. b) Discuss the FMO interactions in the 1,3-, and 1,5-sigmatropic rearrangement reactions. How is the stereochemistry altered in the product? (6)
35. a) Explain photoisomerisation reaction of stilbene. How is the process controlled by photosensitizers?                                                                            (6)
36. b) Explain the di-p-methane rearrangement reaction with an example. (4)

 

 

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