LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 06

SECOND SEMESTER – APRIL 2008

CH 2500 – ORGANIC CHEMISTRY – I

 

 

 

Date : 23/04/2008                Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

PART – A

Answer all the questions                                (10 ´ 2 = 20 marks)

1. Differentiate bond energy from bond dissociation energy.
2. ‘Methyl iodide cannot be prepared from direct iodination of methane’. Why?
3. What is the major product obtained on the dehydrohalogenation of sec-butyl bromide? Justify your answer.
4. How would you distinguish between 1-butyne and 2-butyne by means of two chemical tests?
5. How is acetylene obtained by industrial process?
6. Explain the mechanism of addition of CCl₄ on R-CH=CH₂.
7. What are enantiomers? Give an example.
8. Mandelic acid has a specific rotation of +158˚. What would be the observed specific rotation of a mixture of 25%(-) and 75%(+) isomer?
9. How would you distinguish maleic acid from fumeric acid?
10. ‘The dipolemoments of NH₃, H₂O and NF₃ are 1.46D, 1.84D and 0.24D respectively’.  Why?

PART – B

Answer any Eight questions                              (8 ´ 5 = 40 marks)

11. Explain the mechanism of chlorination of methane. How does an inhibitor slows down this reaction?
12. How would you control the chlorination of methane? Explain.  Is chlorination of methane or ethane faster? Why?
13. Explain the conformations of n-butane with potential energy diagram on C₂-C₃ rotation.
14. How is 1,3-butadiene prepared? How does it react with a) maleic anhydride b) HBr.
15. Explain the mechanism of dehydration of alcohols. Identify the major product obtained when    4-methyl-2-pentanol is treated with con. H₂SO₄.
16. Explain Corey-House synthesis with a suitable example. What are its limitations?
17. What is peroxide effect? Explain the mechanism.   List any two evidences for the mechanism.
18. ‘Acetylenic hydrogens are acidic in nature’. Substantiate this statement with evidences.
19. What are stereoselective and stereospecific reactions? Explain with an example each.

 

 

 

 

20. a) Discuss the conformational analysis of 1,2-dichloroethane with potential energy diagram.
    b) Give the E or Z notation to the following compounds:

 

21. Explain 1,2- Vs 1,4- addition reaction in 1,3-butadiene with a suitable example.
22. Write all the stereoisomers for 3-bromo-2-butanol, indicate the chiral centers and assign R/S configuration for all of them.

 

PART – C

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

23. a) ‘Bromination of methane is slowed down by addition of fairly large amounts of HBr’.     Why?
24. b) Identify the product obtained in the hydroboration-oxidation of 2,3-dimethyl-1-pentene.     Explain with mechanism.
25. a) Explain the acidity of acetylene in comparison with water, ammonia, alcohol and     hydrocarbons.
26. b) Explain the mechanism of addition polymerization reaction under different catalytic     conditions.
27. a) Write down the structural formulae of the olefins from which the following      products are     obtained on ozonolysis: (i) cyclopentanone and acetone and  (ii) ethylmethyl ketone and     propanaldehyde.
28. b) Explain the mechanism of addition of bromine to propene.
29. a) Identify the product(s) obtained when (i) cyclohexene is treated with NBS and
    (ii) propene is treated with HOCl. Justify your answer.
30. b) Explain the factors affecting the rate of a chemical reaction.
31. a) Write a note on (i) asymmetric synthesis and (ii) Optical purity.
32. b) How would you distinguish enantiomers from diastereomers?
33. a) What are Diels-Alder reactions? Give two examples.   What are the conditions and limitations     for this reaction?
34. b) ‘More substituted alkenes are more stabler’.

 

 

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