LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 28

SECOND SEMESTER – APRIL 2006

                                                     CH 2801 – ORGANIC CHEMISTRY – II

 

 

Date & Time : 19-04-2006/FORENOON     Dept. No.                                                       Max. : 100 Marks

 

 

Part-A

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

1. Which of the following is a better nucleophile? Why?
   a) Phenol or ethanol             b) nitride or fluoride
2. ‘Dehydrochlorination of neomenthylchloride gives two different alkenes.’ Explain
3. ‘endo-anti-tricyclo[3.2.1.0^2-4]octan-8yl-p-nitrobenzoate is solvolysed 10¹⁴ times faster than p-nitro isomer containing C=c’. Explain
4. Arrange the following in the decreasing order of nucleophilicity. Justify your answer.    OAc^–, ClO₄^–, H₂O, p-brosyl, OH^–
5. Pyrolysis of iso-butylacetate gives a mixture of two alkenes in a ration 3:2. Explain with mechanism.
6. Give any four differences between DNA and RNA.
7. How are enzymes classified on the basis of their mode of action?
8. ‘When the leaving group cannot act as a nucleophile, substitution can take place at the bridgehead’. Explain.
9. Write a note on NADP.
10. Threo DL pair of 3-bromo-2-butanol with HBr gives DL-2,3-dibromobutane while erythro isomer gives meso. Explain

Part-B

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

11. Solvolysis of syn-7-p-anisyl-anti-7-norborn-2-enyl-p-nitrobenzoate in acetone    water is 2.5 times faster than its saturated analog.  Explain.
12. Acetolysis of both 4-methoxy-1-pentylbrosylate and 5-methoxy-2-pentyl brosylates give the same mixture of products.
13. Explain the ion-pair involvement in S_N1 mechanism. What are the evidences of ion-pair mechanism?
14. ‘2-octylbrosylate with 75% aqueous acetone gives 2-octanol with 77% inversion but with sodium azide gives 100% inversion’. Explain with mechanism.
15. Explain the mechanism of Steven’s rearrangement.
16. Explain the mechanism of Hofmann rearrangement. Is it inter or intramolecular? Explain.
17. Explain the primary structure of protein.
18. What are conjugated proteins? How does the protein structure in heamoglobin assist in oxygen transfer?
19. Explain normal and abnormal Claisen rearrangement with mechanism.
20. What are the types of RNA? How are they helpful in protein synthesis? Explain.
21. Explain the immobilization of enzymes.
22. ‘2-butylacetate on pyrolysis gives a mixture containing 57% 1-butene and
    43% 2-butene.  Explain.

Part-C

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

23. a) 2-bromo-2-methylbutane with EtO^– gives 70% 2-methyl-2-butene but with
    Et₃C-O^– gives 12% only. Explain with mechanism.
24. b) Explain how free radical monobromination of 1-bromo-2-methylbutane yields a product with a high degree of retention in configuration.
25. a) b-(Syn-7-norbornenyl)ethylbrosylate undergoes acetolysis about 140,000 times faster than its saturated analog. Explain.
26. b) Explain Swain-Scott relationship with a suitable example.
27. a) Explain the orientation of double bond in elimination reactions with suitable examples.
28. b) Pyrolysis of erythro and threo isomers of 1-acetoxy-2-deutero-1, 2-diphenyl ethane gives the same alkene.  Explain with mechanism.
29. a) What are coenzymes? Explain the various sources of coenzymes and their functions.
30. b) What are long and short lived free radicals?  How are they prepared?  How are they useful in organic synthesis?
31. Explain the following
32. a) Erythro-3-bromo-2-butanol with HBr gives meso product
33. b) Rate of solvoysis of Ph-CH₂-CH₂-OTs with 75% CF₃COOH is 3040 times faster than CH₃-CH₂-OTs
34. c) Solvolysis of exo-2-norbornyl brosylate is 350 times faster than its endoisomer
35. d) Pyrolysis of xanthates give COS as one of the products.
36. Explain the following:
37. a) Ambident nucleophile
38. b) Fischer-Indole synthesis
39. c) Allosteric enzymes

 

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