LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034
M.Sc. DEGREE EXAMINATION – CHEMISTRY
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FIRST SEMESTER – APRIL 2007
CH 1801 – ORGANIC CHEMISTRY – I
Date & Time: 27/04/2007 / 1:00 – 4:00 Dept. No. Max. : 100 Marks
PART-A
Answer ALL questions. (10 ´ 2 = 20 marks)
- Compare the acid strength of the following. Give suitable explanations.
p-hydroxybenzoic acid, m-hydroxybenzoic acid and benzoic acid. - Suggest a method of trapping the intermediate of a reaction, using a suitable example.
- Define antiaromaticity . Give an example of an antiaromatic compound.
- What is solvent isotope effect? How does it affect the rate of the reaction?
- How would you prove the formation of benzyne in the ammolysis of chlorobenzene?
- Name the electrophile in the nitration of benzene. What are the evidences?
- Free radical chlorination of (S)-sec-butylchloride gives 1,2-dichlorobutane as one of the products. Comment on the stereochemistry of the reaction.
- Depict the symmetry planes on structures of
i) dichloromethane and ii) cis-1, 2-dichlorocyclopropane. - Meso-2, 3-dibromobutane reacts with iodide ion faster than dl-isomer. Why?
- State and explain Cram’s rule.
Part-b
Answer any eight questions. (8 ´ 5 = 40 marks)
- Optically active α – phenylethyl chloride on phenolysis gives an ether with partial retention. Explain the mechanism.
- Outline clearly all the possible consequences of ipso attack in the electrophilic substitution of monosubstituted benzene with suitable examples.
- Explain cotton effect and predict the cotton effect by the sign of the most occupied octant in
- Write the most stable conformation for each of the following:
a) 1,2,2,6,6-pentamethyl-4-hydroxy-4-phenylpiperidine
b) 2-methyl-5-isopropyplcyclohexanone
c) 1,3-di-t-butylcyclohexane - Explain the optical isomerism due to restricted rotation with suitable examples.
- What is mutarotation? Explain with two examples.
- Explain the conformation of cyclohexane with potential energy diagram. What types of strains are associated with rings larger than cyclohexane?
- Explain von Richter rearrangement with mechanism.
- Explain the linear free energy relationship in aromatic electrophilic substitution reactions.
- How would you explain that the rate of base catalysed iodination of aniline in the presence of excess iodide is inversely proportional to the square of the iodide concentration?
- ‘In the Fries rearrangement, aryl esters are converted to acyl phenols in the presence of Lewis acids’. How would you show that the reaction is inter or intra molecular?
- ‘The acetoylsis of threo-3-phenyl-2-butyltosylate gives the racemic product while the erythro isomer proceeds largely with retention of configuration’. Explain.
Part-C
Answer any four questions. (4 ´ 10 = 40 marks)
- a) Explain Bucherer reaction with mechanism.
- b) Explain the Octant rules in the determination of configuration of molecules.
- a) Additon of HBr to 1,3-butadiene is both thermodynamically and kinetically controlled. Explain using a potential energy diagram.
- b) dl-stilbene dichloride undergoes reaction when heated to 200°C with pyridine whereas meso isomer does not.
- a) Explain first order asymmetric transformation with a suitable example.
- b) Explain epimerisation with suitable examples.
- Assign R or S configuration to the following. Justify your answer
- a) Explain Sommelet-Hauser rearrangement with mechanism.
- b) Explain the stereochemistry of the products obtained on heating 3-bromo-2-butanol with HBr.
- Explain the following:
a) Diazotisation of aniline follows third order kinetics.
b) Aryl halides are less reactive than alkyl halides.
c) Benzidine rearrangement follows third order kinetics.
d) Axial haloketone rule.
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