PG – 714

*PG714* IV Semester M.Sc. Examination, July 2013 (New Scheme) (2010-11 Onwards Watch) CHEMISTRY C 403 OC : Organic Synthesis – II Time : 3 Hours

Max. Marks : 80

Instruction : Answer question number 1 and any five of the remaining questions. 1. Answer any ten of the following :

(10×2=20)

a) What is the major product of the following stereo selective reaction ? Propose a mechanism for its formation.

b) What is asymmetric aldol condensation ? Illustrate with an example. c) Outline one example to show a diastereo selective oxidation. d) Draw the structure of alpine borane. Outline its use in enantioselective synthesis with a suitable example. e) What is asymmetric induction ? Give one example by employing polymer bound chiral catalysts. f) Explain the phenomenon of cavitation. g) What are ionic liquids ? Draw the structure of an ionic liquid and outline its use in organic synthesis. h) Illustrate the application of polymer bound chiral amino alcohols in enantio selective synthesis of homoallyl alcohols. i) Draw the structure of 15-crown-5 and mention the cation with which it forms a stable complex. j) Draw the contributing canonical structures of azulene and give evidences in support of its dipolar structure.

P.T.O.

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k) What are insect repellents ? Give the structures of any two insect repellents. l) Predict the product in the following reactions : –

Br2 OH ⎯→ ? ⎯ ⎯ ⎯→ ? Anthracene ⎯ ⎯

2. a) What is ‘ee’ ? Explain any two methods of determining ‘ee’. b) Explain the addition of allyl boranes to carbonyl group. c) Draw the conformations of the product formed in the following reactions. Indicate the major product in each case and justify your choice i)

ii)

.

(4+4+4=12)

3. a) Explain the mechanism of stereo selective cyclization of polyenes. b) Describe the mechanism of stereoselective reduction of olefins in presence of (S, S) – CHIRAPHOS. c) Predict the product and outline the mechanism :

(4+5+3=12)

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4. a) What is asymmetric amplification ? Explain with an example. b) The following reaction is enantio selective. Draw the structure of the product and propose a mechanism.

c) Give the product and discuss the effect of ultrasound in the following reaction.

(3+5+4=12) 5. a) What is atom efficiency ? Explain how % atom utilisation is determined for the following reaction.

b) Explain microwave assisted Diels Alder reaction and N-alkylation reactions. c) Explain the synthesis of a polystyryl boronic acid and its use in diol protection. (4+4+4=12)

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6. a) Explain the polymer supported synthesis of oligosaccharides. b) Suggest suitable methods for the preparation of the following P.T.C.s and comment on their reactivity. i) nBu 4As +Br − ii) nBu 4As + HSO −4 . c) Describe the synthesis of dicyclohexano – [18]-Crown – 6 and predict the product in the following reaction.

(4+4+4=12) 7. a) How is phenanthrene synthesized ? Explain its reactions. b) Give an account of organophosphorous insecticides. c) Explain the synthesis and applications of the following : i) heptachlor ii) beygon. ———————

(4+4+4=12)