M.Sc Chemistry Organic Chemistry-I Question Paper 2007

 

LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 24

FIRST SEMESTER – APRIL 2007

CH 1801 – ORGANIC CHEMISTRY – I

Date & Time: 27/04/2007 / 1:00 – 4:00      Dept. No.                                       Max. : 100 Marks

 

 

PART-A

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

1. Compare the acid strength of the following. Give suitable explanations.
   p-hydroxybenzoic acid, m-hydroxybenzoic acid and benzoic acid.
2. Suggest a method of trapping the intermediate of a reaction, using a suitable example.
3. Define antiaromaticity . Give an example of an antiaromatic compound.
4. What is solvent isotope effect? How does it affect the rate of the reaction?
5. How would you prove the formation of benzyne in the ammolysis of chlorobenzene?
6. Name the electrophile in the nitration of benzene. What are the evidences?
7. Free radical chlorination of (S)-sec-butylchloride gives 1,2-dichlorobutane as one of the products. Comment on the stereochemistry of the reaction.
8. Depict the symmetry planes on structures of
   i) dichloromethane and      ii) cis-1, 2-dichlorocyclopropane.
9. Meso-2, 3-dibromobutane reacts with iodide ion faster than dl-isomer. Why?
10. State and explain Cram’s rule.

Part-b

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

11. Optically active α – phenylethyl chloride on phenolysis gives an ether with partial retention. Explain the mechanism.
12. Outline clearly all the possible consequences of ipso attack in the electrophilic substitution of monosubstituted benzene with suitable examples.
13. Explain cotton effect and predict the cotton effect by the sign of the most occupied octant in

 

14. Write the most stable conformation for each of the following:
    a) 1,2,2,6,6-pentamethyl-4-hydroxy-4-phenylpiperidine
    b) 2-methyl-5-isopropyplcyclohexanone
    c) 1,3-di-t-butylcyclohexane
15. Explain the optical isomerism due to restricted rotation with suitable examples.
16. What is mutarotation? Explain with two examples.
17. Explain the conformation of cyclohexane with potential energy diagram. What types of strains are associated with rings larger than cyclohexane?
18. Explain von Richter rearrangement with mechanism.
19. Explain the linear free energy relationship in aromatic electrophilic substitution reactions.
20. How would you explain that the rate of base catalysed iodination of aniline in the presence of excess iodide is inversely proportional to the square of the iodide concentration?
21. ‘In the Fries rearrangement, aryl esters are converted to acyl phenols in the presence of Lewis acids’. How would you show that the reaction is inter or intra molecular?
22. ‘The acetoylsis of threo-3-phenyl-2-butyltosylate gives the racemic product while the erythro isomer proceeds largely with retention of configuration’. Explain.

Part-C

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

23. a) Explain Bucherer reaction with mechanism.
24. b) Explain the Octant rules in the determination of configuration of molecules.
25. a) Additon of HBr to 1,3-butadiene is both thermodynamically and kinetically           controlled. Explain using a potential energy diagram.
26. b) dl-stilbene dichloride undergoes reaction when heated to 200°C with pyridine whereas meso isomer does not.
27. a) Explain first order asymmetric transformation with a suitable example.
28. b) Explain epimerisation with suitable examples.
29. Assign R or S configuration to the following. Justify your answer

 

27. a) Explain Sommelet-Hauser rearrangement with mechanism.
28. b) Explain the stereochemistry of the products obtained on heating 3-bromo-2-butanol with HBr.
29. Explain the following:
    a) Diazotisation of aniline follows third order kinetics.
    b) Aryl halides are less reactive than alkyl halides.
    c) Benzidine rearrangement follows third order kinetics.
    d) Axial haloketone rule.

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