LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
THIRD SEMESTER – APRIL 2007
CH 3800 – ORGANIC CHEMISTRY – III
Date & Time: 24/04/2007 / 9:00 – 12:00 Dept. No. Max. : 100 Marks
Answer ALL questions. (10 ´ 2 = 20 marks)
- Effect the following conversion.
- State Woodward Hofmann rules for electrocyclization reactions.
- Predict the sigmatropic reactions in 1,5-systems with examples.
- Define Norrish type II cleavage reactions. Give an example.
- What is photosensitization? What is its importance?
- ‘Convergent synthesis is a better method in organic synthesis than in stepwise synthesis’. Substantiate this statement with a suitable example.
- What are fragmentation reactions? Give an example.
- How would you plan the synthesis of 6-methyl-3-octen-2-one by span technique?
- What is first generation asymmetric synthesis?
- What are the importance of three component system in Clemmensen reduction?
Answer any EIGHT questions. (8 ´ 5 = 40 marks)
- Draw the correlation diagram for the electrocyclization of 1,3,5-hexatriene. Predict whether the reaction is feasible thermally or photochemically. (5)
- Find out the products with proper stereochemistry in the following reactions.(2´2½)
- Predict the products in the following sigmatropic reactions.
- What are the products formed when 4,4-diphenylcyclohexen-2-one undergoes photochemical rearrangement. Write the mechanism of the reaction.
- Illustrate with any two examples, the structure of a molecule in a photochemically excited state.
- What is photoisomerisation? Explain with an example.
- How would you plan the synthesis of 2-methyl-2-butene by disconnection approach? Explain.
- ‘Symmetric target molecules can be planned by disconnection approach symmetrically’.
Explain this with a suitable example.
- Explain the role of selectivity and specificity in organic synthesis by taking two examples for each.
- How are the following conversions effected?
- a) 2,3-dimethylcyclohex-2-en-one ¾¾® 2,2,3,3-tetramethylcyclohexanone
- Isopropyl alcohol ¾¾® 1-phenyl-2-methyl-2-propanol
- Explain the synthesis of 1,2-difunctionalised compounds with two suitable examples.
- Elucidate the structure of reserpine by synthesis.
Answer any FOUR questions. (4 ´ 10 = 40 marks)
23 a) How cycloaddition reactions are stereoselective? Illustrate with suitable examples.
- b) Predict the stereochemistry of electrocyclisation in 4 and 6 electron systems. Give suitable examples.
24 a) Predict the mechanism of following reactions.
- b) Derive the equation for Stern-Volmer expression.
25 a) Explain the Paterno Buchii reactions in alkenes and alkynes with examples.
- b) Explain the following photochemical rearrangement reaction.
- a) Establish the structure of longifolene by synthesis.
- b) What are the synthetic importance of Reformatsky reaction? Explain with two suitable examples.
- a) What are the synthons and synthetic equivalents in the synthesis of phenyl hydroxyl amine and benzanilide?
- b) Explain the synthesis of norethisterone.
- Explain the use of the following in the organic synthesis, with an example each. Explain the mechanism.
- a) Diels-Alder reaction
b) Knoevenagel reaction
c) Perkin reaction
d) Electroorganic synthesis.
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