LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 31

SECOND SEMESTER – APRIL 2007

CH 2801 – ORGANIC CHEMISTRY – II

 

 

 

Date & Time: 17/04/2007 / 1:00 – 4:00        Dept. No.                                                          Max. : 100 Marks

 

 

PART-A

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

1. Which reagent in the following pair reacts more rapidly with sodium ethoxide in ethanol? Justify your answer.
   Vinyl chloride or allyl chloride
2. Is the nucleophilic substitution at a vinyl carbon easy? Justify your answer with a suitable example.
3. Anti-methyl conformation of 2-bromobutane on dehydro bromination gives trans product

while gauche-methyl form gives cis-2-butene as the major product. Why?

4. What happens when amine oxide such as RCH₂CH₂N(®O)R₂ is heated to 150°C?
5. Give the structure of the most stable free radical and justify your answer.
6. What is memory effect? Explain with an example.
7. Illustrate a free radical rearrangement with an example.
8. Compare endo and exoenzymes?
9. Write a short note on denaturation of nucleic acids.
10. How is the dipeptide, Ala-Gly, synthesized?

 

 

PART-B

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

11. ‘For S_N1 mechanism, a branching increases the rate of the reaction’. Justify this statement with suitable examples.
12. Debromination of meso-2,3-dibromobutane mainly gives trans product while
    (±)-isomer gives mainly cis product. Explain.
13. What happens when 2-methyl-1-propanol is treated successively with CS₂/NaOH, CH₃I and heated to 200°C? Explain.
14. ‘Menthyl chloride on dehydrochlorination gives 100% of one isomer while
    neo-menthyl chloride gives 25% of that isomer and 75% 4-methyl isopropyl cyclohexene’. Explain.
15. The dehydrochlorination in cis and trans 2-chloromaleic acid , the trans isomer reacts about 50 times faster than the cis compound. Explain.
16. 2-butylacetate when heated to 440°C gives 57% 1-butene, 28% trans 2-butene and
    15% cis 2-butene. Explain.
17. Explain in detail the mechanism of Benzil-benzilic acid rearrangement.

 

 

 

18. Predict the product in the following reaction and explain the mechanism.

 

19. How is a polypeptide or protein synthesized by solid phase method?
20. Derive Michaelis Menten equation for enzyme action.
21. Discuss in detail the 2° structure of DNA.
22. Explain in detail any two methods of N-terminal analysis to predict the primary structure of a protein.

 

PART-C

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

23. a) On pyrolysis, erythro and threo isomers of 1-acetoxy-2-deutero-1,2-diphenyl    ethane gave in each case trans-stilbene.  Explain.
24. b) Anti-Markownikov’s rule takes place only for the addition of HBr to an     unsymmetrical alkene and not for any other hydrogen halides. Why? Explain.
25. a) Elimination of HBr from 2-bromobutane and elimination of trimethylamine from
    2-(N,N-dimethylamino)butane give different products in major amounts. Why?
26. b) How does the presence of a neighbouring groups enhance the rate of nucleophilic     substitution reaction? Explain with suitable examples.
27. a) The rates of hydrolysis of alkyl bromides(0.1M) in 0.01M NaOH are in the order

of t-BuBr > MeBr > EtBr > i-PrBr.  Explain.

1. b) How are the rates of nucleophilic substitution reactions are influenced by      electron withdrawing and electron releasing groups? Explain with examples.
2. a) Write the mechanism of the following reactions.

 

 

1. b) Explain the mechanism of following reaarangement reactions.
2. i) Claisen rearrangement
3. ii) Baeyer Villiger rearrangement

27     a) Explain with equations the kinetics of competitive inhibition.

1. b) What are the two methods by which DNA replication takes place?

28     a) Comment on the a-helical structure of proteins.

1. b) What is meant by immobilization of enzymes? Explain in detail.

 

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