LM 29

             LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

SECOND SEMESTER – APRIL 2006

                     CH 2808 – ORGANIC SUBSTITUTION, ADDITION & ELIMINATION RXN

 

 

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

Part-A

                                                    Answer ALL questions.      (10 ´ 2 = 20)

1. Predict the product with mechanism
2. What is ipso attack? Give the possible mechanism for ipso attack.
3. What are stable, persistent and inert free radicals? Give example.
4. Predict the product of the reaction of dihydropyran with primary alcohols in the presence of acids with mechanism.
5. Predict the product.
6. How would you explain that trans-2-acetoxycyclohexyl brosylate with acetate in glacial acetic acid gives only trans diacetate?
7. Explain Grunwald-Winstein equation.
8. Which of the following is more nucleophilic? Why?                                                       Benzene or mesitylene;  Phenoxide or p-nitrophenoxide
9. Explain Hofmann’s rule in elimination reactions with a suitable example.
10. What are ambident nucleophiles? Give an example.

PART B

Answer any EIGHT questions                        (8 ´ 5 = 40)

1. Give the mechanism of the following:

1. a) Wohl-Ziegler bromination          b)Wittig rearrangement.
2. a) Predict the product with mechanism
3. b) Explain Bartons reaction.
4. Give the mechanism of oxymercuration reaction. Also give the evidences for the free radical mechanism for the cleavage of Hg.
5. Predict the product with mechanism and evidence.
6. Define isoinversion. Explain using a suitable example.
7. Using suitable resonance-stabilizing structures explain why halogens are deactivators but o, p-directors.
8. How would you show that the transition state in S_N2 reaction must be linear?
9. Threo DL pair of 3-bromo-2-butanol with HBr gave DL-2,3-dibromobutane while the erythro pair gave meso isomer. Explain.
10. Explain ion-pair mechaism. What are its evidences?
11. ‘Basic hydrolysis of a-bromopropionate ion with concentrated base gives a product with inverted configuration but with dilute base, retention product is formed’. Explain.
12. What happens when the following are subjected to pyrolysis?
    (i) 2-acetoxybutane     (ii) Xanthate from isobutyl alcohol
13. Solvolysis in acetone-water at 85°C of syn-7-p-anisyl-anti-7-norborn-2-enyl p-nitrobenzoate was only 2.5 times faster than that of the saturated compound’.

PART C

Answer any FOUR questions                   (4 ´ 10 = 40)

23. How are the following synthesized from benezene?
    a) m-nitroacetophenone b) p-chlorobenzoic acid
    c)p-propylbenzen sulphonic acid                       d) m-bromopropylebenzene.
24. a) How are the following conversions effected?
25. b) Propose a synthesis for the following compounds using Robinson annulations.
26. a) Give the mechanism of free radical substitution at an aromatic substrate. Substantiate it with suitable evidences.
    b) 2,3-dimethylbutane gives different ratio of products in aliphatic and aromatic solvents. Why?
27. a) Endo-anti-tricyclo[3.2.1.02-4]octan-8-yl-p-nitrobenzoate is solvolysed about 10¹⁴times faster than p-niotro isomer containing C=C’. Explain.
28. b) How would you show by reactions the mechanistic border line region between S_N1 and S_N2 reactions?
29. a) Solvolysis of L-threo-3-phenyl-2-butyltosylate in acetic acid gives threo product in major amount’. Explain.
30. b) What is ‘Product spread’ in elimination reactions? Explain with suitable examples.
31. a) Explain Bucherer reaction with mechanism.
32. b) Expalin the following:
    (i)     Acetolysis of both 4-methoxy-1-pentylbrosylate and 5-methoxy-2-pentylbrosylate give                    the same mixture of products.

• Both erythro- and threo-1-acetoxy-2-deutero-1,2diphenylethane on pyrolysis give the same product.

 

 

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