LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
THIRD SEMESTER – NOVEMBER 2012
CH 3808 – PHOTOCHEMISTRY AND ORGANIC SYNTHESIS
Date : 01/11/2012 Dept. No. Max. : 100 Marks
Time : 9:00 – 12:00
Part-A
Answer ALL questions: (10 ´ 2 = 20)
- How is diborane specific in its reactivity towards substituted alkenes?
- Draw the FMO picture of the excited state HOMO of 1,3,5-hexatriene.
- What are regioselective reactions? Give an example.
- What are the products formed when ethyl bromide is reduced electrochemically on platinum electrode?
- Predict the stereochemistry of the product.
- What is Fries photochemical rearrangement? Write the mechanism of the reaction.
- What are the synthons prepared from the following synthetic equivalents?
- a) 2-bromobutane b) acetyl chloride
- What is the geometry of excited state ethylene molecule? Give reasons.
- What are group transfer reactions? Give examples.
- What is oxy-Cope rearrangement reaction? Give an example.
Part-B
Answer any EIGHT questions: (8 ´ 5 = 40)
- Why Wittig Horner reaction is preferred to Wittig reaction? Mention the advantages of the Wittig Horner reaction with an example.
- Explain the synthesis of following difunctionalised compounds.
- a) 1,3-propanediamine b) ethyl acetoacetate
- How are protection, activation and attachment of bridging group done repeatedly in the synthesis of a polypeptide?
- Explain the mechanism of following reactions.
- a) oxidation of an 2-butene by KMnO4 in basic medium.
- b) Wolff Kishner reduction of acetophenone
- Write the complete mechanism of electroreduction of nitrobenzene.
- Perform retrosynthetic analysis and suggest a suitable synthetic method of the following. (3 + 2)
- Draw correlation diagram for the electrocyclization of 1,3-butadiene by con rotation. Predict whether the reaction is thermally or photochemically allowed.
- If hydrazobenzene in acid medium undergoes (3,3)- and (3,5)-sigmatropic rearrangements, what are the products formed? Explain the mechanism of the reaction.
- Explain the mechanism of the following reaction and predict the stereochemistry of the mentioned H atoms in the product.
- What is Barton reaction? How does it take place in steroids? Explain with an example.
- How does 4,4-diphenylcyclohex-2-en-1-one undergo Zimmerman rearrangement to form various photochemical products?
- Explain the Norrish type-I and type-II reactions with an example each.
Part-C
Answer any FOUR questions: (4 ´ 10 = 40)
- a) Write the stereochemical importance of Stobbe reaction. (2)
- b) Explain 1,2- and 1,4-Michael addition reactions. (5)
- c) How unnatural synthons are used to prepare 1,2-difunctionalised compounds? Explain with an example. (3)
- a) How are C-C disconnections done? Explain any four guidelines. (6)
- b) Perform retrosynthetic analysis and suggest a suitable synthetic route to the following compound (4)
- a) Explain protection and deprotection of an amine. (4)
- b) Explain the mechanism of the following reactions with examples. (3+3)
- i) NaBH4 reduction of an imine ii) Peracid oxidation
- a) Explain the synthesis of cubane. . (5)
- b) How mercuric acetate acts as a dehydrogenating agent? Explain with any two examples. (5)
- a) Predict a suitable mechanism for the following thermal reaction. (4)
- b) Discuss the FMO interactions in the 1,3-, and 1,5-sigmatropic rearrangement reactions. How is the stereochemistry altered in the product? (6)
- a) Explain photoisomerisation reaction of stilbene. How is the process controlled by photosensitizers? (6)
- b) Explain the di-p-methane rearrangement reaction with an example. (4)
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