LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
FIRST SEMESTER – NOVEMBER 2012
CH 1812 / 1806 – ORGANIC REACTION MECHANISM & STEREOCHEMISTRY
Date : 01/11/2012 Dept. No. Max. : 100 Marks
Time : 1:00 – 4:00
PART – A
Answer ALL questions: (10 x 2 = 20)
- Write the mechanism of Chichibabin reaction.
- What is primary kinetic isotope effect? Explain with suitable example.
- “Diazotization of aniline follows second order with respect to nitrous acid” Propose a mechanism for this reaction.
- What is para-Claisen rearrangement? Explain with mechanism.
- How does indole prepared from phenyl hydrazine?
- What is Birch reduction?
- What happens when cyclohexene on ozonolysis?
- In α, α’-dimethylsuccinic acid, the meso form predominates at equilibrium over the racemic form. Why?
- State and explain Cram’s rule with suitable example.
- What is atropisomerism? Give example.
PART-B
Answer ANY EIGHT questions: (8 x5 = 40)
- Draw the potential energy diagram of thermodynamic and kinetically controlled product formation of a reaction between 1,3-butadiene and HBr.Explain.
- Explain the microscopic reversibility with suitable example.
- Explain the following;
- a) trapping of intermediate b) isotope labeling study
- Explain the mechanism of abnormal Claisen rearrangement.
- How would you convert 1,7,7’-trimethyl bicycle[2,2,11-4]heptan-2-ol into 2,2’-dimethyl-3-methylidene bicycle [2,2,11-4]heptane?
- When treated with p-CH3C6H5SO2Cl in pyridine, the α-benzilmonoximes undergo Beckmann rearrangement with fragmentation. Explain.
- Explain any one application for each of the following reagents.
- a) SeO2 b) OsO4
- How does a carboxylic acid undergoes oxidative decarboxylation? Explain.
- Explain mutarotation with any one example.
- Give an example for a first order asymmetric transformation reaction and explain.
- Predict the stereochemical change of acetolysis of 3-methoxy-2-bromobutane in the presence of silver acetate in acetic acid.
- State Brett’s rule and explain the reactivity of bicyclic rings.
PART-C
Answer ANY FOUR questions: (4 x10 = 40)
- a) “Radical bromination of isopentane is more selective than chlorination.” Explain with potential energy diagram.
- b) How does a Raman spectroscopy is used to determine the mechanism of nitration of benzene? Explain.
- a) Determine the reaction mechanism of base-catalysed iodination of aniline in presence of excess of iodide ion from its experimental rate data.
- b) Predict the products to be expected from acid-catalyzed rearrangement of cis- and trans-1,2-dimethylcyclohexane-1,2-diol and sketch mechanism for the formation.
- a) “The lactones obtained by the Baeyer-Villiger oxidation of camphor and apocamphor contain 25% and 94% of the abnormal product” Why?
- b) Explain memory effect with suitable example.
- a) Give mechanism for the following conversions.
(i) Methane into methanol using aq.CrO3
(ii)Acetaldehyde into acetic acid using O2 and Ag.
- b) Complete the following with mechanism.
- a) What are the various products obtained on the acetolysis of 3-phenyl-2-pentyl tosylate?
- b) Explain the process of separation of racemic alcohols with an example.
- c) Asssign R,S configurations to the following:
- a) State and explain curtin-Hammett principle with suitable example.
- b) Explain the following with applications; (i) cotton effect (ii) axial haloketone rule.
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