Loyola College M.Sc. Chemistry April 2007 Organics Substit.,Addition & Elimination Rxns Question Paper PDF Download

 

LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

LM 32

SECOND SEMESTER – APRIL 2007

CH 2808 – ORGANIC SUBSTIT., ADDITION & ELIMINATION RXNS

 

 

 

Date & Time: 17/04/2007 / 1:00 – 4:00 Dept. No.                                      Max. : 100 Marks

 

 

PART – A

Answer ALL questions                                                                       (10 ´ 2 = 20 marks)

 

  1. What are p-complexes in an aromatic electrophilic substitution reaction?
  2. Define partial rate factor and explain.
  3. The rate of acid-catalyzed hydrolysis of benzamide is -0.298 and the relative electron withdrawing effect of -NO2 substituent is + 0.710. Calculate the relative reactivity of  the

nitrobenzamide.

  1. How does nitrous acid react with aromatic 1° and 2° amines?
  2. Explain why iodination of benzene requires HNO3?
  3. Explain Hofmann’s elimination rule with a suitable example.
  4. Among acetic anhydride and n-propyl alcohol, which one is more powerful nucleophile? Justify your answer.
  5. What happens when threo and erythro DL pair of 3-bromo-2-butanol is treated with HBr? Explain.
  6. ‘SN1 rates are greatly increased when there is a double bond in the b-position’. Why?
  7. What happens when isobutyl acetate is strongly heated?

 

 

PART – B

Answer any eight questions                                                          (8 ´ 5 = 40 marks)

 

  1. Explain the effect of electrophile in the reactivity of aromatic substitution reactions.
  2. Describe the various products formed from the reaction of electrophile attacking at the ipso position in nitrobenzene.
  3. Predict the mechanism for the following reaction.

 

 

 

 

  1. Explain neighboring group assistance in free radical reactions.
  2. Explain why in the abstraction step of photochemical chlorination of ethane, ethyl radical formed but not the hydride radical.
  3. Predict the products with mechanism for the following:
    a) Wohl-Ziegler reaction         b) Eglinton reaction
  4. Identify the products obtained when erythro and threo isomers of 1-acetoxy-2-deutero-1,2-diphenylethane is subjected to pyrolysis. Explain.
  5. ‘Acetolysis of both 4-methoxy-1-pentylbrosylate and 5-methoxy-2-pentylbrosylate gave the same mixture of products’. Explain.
  6. ‘Solvolysis of syn-7-p-anisyl-anti-7-norborn-2-enyl p-nitrobenzoate was only 2.5 times faster than that of the saturated compound’. Explain.
  7. ‘Menthyl chloride undergoes dehydrochlorination at a slower rate comparing neomenthyl chloride’. Why?   Identify the products obtained and explain the reaction.
  8. ‘Dehydrohalogenation of 2-fluorohexane mainly gives Hofmann product while
    2-iodohexane gives Zaitsev’s product as major’. Explain.
  9. Explain von-Ritcher rearrangement with mechanism. Give the main evidence for the mechanism.

PART – C

Answer any four questions                                                            (4 ´ 10 = 40 marks)

 

  1. a) Explain the mechanism of bimolecular aliphatic electrophilic substitution with  examples.
  2. b) Describe the effect of solvent on the reactivity of chlorination reaction of  2,3-dimethylbutane.
  3. a) Give the mechanism of sulphonation of benzene. What are the various sulphonating  agents? Give evidences for the mechanism.
  4. b) Give the evidences for the syn, anti, and non stereoselective electrophilic addition of olefins.
  5. Predict the product for the following

 

 

 

 

 

 

 

 

 

 

 

  1. a) How does the presence of a cyclopropyl neighbouring group enhance the rate of     nucleophilic substitution reaction? Explain with two examples.
  2. b) 2-butylacetate on pyrolysis gives a mixture of products with different yields. Why?
  3. a) ‘p-methoxybenzhydryl hydrogen phthalate on solvolysis in methanol results a     racemic ether’. Justify your answer.
  4. b) Explain Bucherer reaction taking b-naphthol as an example.
  5. a) Identify the stereochemistry of the products obtained on the dehydrobromination of        different conformers of 1,2-dibromo-1,2-diphenylpropane.
  6. b) How does selenide elimination help in the synthesis of a,b-unsaturated ketones?

 

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