LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 54

FOURTH SEMESTER – APRIL 2008

CH 4500 – ORGANIC CHEMISTRY – II

 

 

 

Date : 26/04/2008                Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

 

Part-A

                                                     Answer ALL questions.                              (10 ´ 2 = 20)

 

1. ‘cyclopropane is more reactive than cyclohexane’. Why?
2. What are the conformers possible for cyclohexane? Which one is more stable? Why?
3. How would you distinguish methanol from ethanol by means of chemical tests?
4. ‘Williamson’s synthesis is useful for the preparation of both simple and mixed ethers’. Justify this statement with suitable examples.
5. Arrange the following in the increasing order of their acidity. Justify your answer.

Monochloroacetic acid, Dichloroacetic acid, Acetic acid, Formic acid and Trichloro acetic acid.

6. What happens when maleic acid is treated with bromine? Identify the stereochemistry of the product obtained?
7. Name the electrophile in nitration of benzene. What are the evidences for its existence?
8. ‘Aniline does not undergo Friedel-Craft’s reaction’. Why?
9. How would you prepare the following from benzene diazonium chloride?
   (i) Benzene   and  (ii) Benzoic acid
10. Give the mechanism of Reimer-Tiemann reaction.

 

Part-B

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

 

11. Explain Baeyer’s strain theory in the stability of cycloalkanes.
12. How are alcohols prepared from hydroboration-oxidation method? Explain with mechanism.
13. An amide(A) having molecular formula C₃H₇ON on hydrolysis gives an acid C₃H₆O₂(B). (B) on chlorination in the presence of red phosphorus produces a chloroacid(C).The latter on boiling with aqueous NaOH and subsequent acidification forms lactic acid(D).Write the reactions and identify the structure of A, B, C and D.
14. What happens when benzaldehyde is heated with alcoholic KCN solution? Explain the mechanism.
15. How would you prepare 4-methylpentanoic and 3-methylbutanoic acid using diethyl malonate?
16. Explain the mechanism of Hofmann-bromamide reaction. Name the intermediate in this reaction.
17. ‘Nitration of benzene is irreversible while sulphonation of benzene is a reversible reaction.’ Explain.
18. What are sulpha drugs? Explain the mechanism of action of  sulpha durgs.
19. What happens when 3-bromo-2, 3-dimethyl pentane is treated with alcoholic KOH? Identify the different products obtained and explain with mechanism.
20. Explain the mechanism of Baeyer-Villiger rearrangement.
21. Explain the synthetic utility of acetoacetic ester with examples.
22. Explain aromaticity, antiaromaticity and nonaromaticity with suitable examples.

 

 

 

Part-C

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

 

23. a) Explain the mechanism of reduction of CH₃COOC₂H₅ by LiAlH₄.
24. b) Compare the stereochemistry of products obtained in S_n1 and S_n2 reactions.
25. a) How are grignard reagents used in the preparation of primary, secondary and     tertiary alcohols? Explain with suitable examples.
26. b) Explain the mechanism of preparation of ethers by oxymercuration-    demercuration method.
27. a) How are the following compounds prepared?
    (i) acrylic acid             (ii) cinnamic acid      (iii) maleic acid
28. b) Explain the action of heat on a-, b- and g-hydroxy acids and identify the     products obtained.
29. a) Explain the mechanism of sulphonation of benzene
30. b) ‘Halogens are deactivating groups but o-, p- directing’.
31. a) How will you synthesise the following compounds from benzaldehyde?

(i) Mandelic acid         (ii) m-Benzaldehydesulphonic acid

1. b) Write a note on: (a) Cannizaro reaction (b) Perkin reaction
2. a) Explain Claisen and abnormal Claisen rearrangements with mechanism.
3. b) How would you convert m-nitrophenol from nitrobenzene? Explain all the steps involved in this process.

 

 

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