CHE-06 Organic Reaction Mechanism Solved Assignment 2018

Description

CHE-06 Solved Assignment For IGNOU BSC 2018
Course Title: Organic Reaction Mechanism
This Solution Is Valid Till: 31st December 2018

Questions:

1. a) Write the product and indicate the type of reaction that is taking place in the following:
   
   b) Write the full reaction and mark the nucleophile and electrophile in each case.
   i)Reaction between potassium cyanide and 1-chloropropane
   ii)Reaction between hydrogen bromide and cis 2-butene
   iii)Reaction between sodium methoxide and benzyl bromide
   iv)Acid catalysed reaction of water with cyclopentene
   v)Reaction between ethanal and hydrogen cyanide

2. a) Draw and explain potential energy diagram for the reaction of addition of HCl to 1, 3-butadiene at a low and high temperatures.
   b) Write the main product of the following reactions giving reasons for your answer.

3. a) Arrange the following in the increasing order of electrophilic substitution. Justify your answer.

   b) Explain the following:

   i) Electron withdrawing substituents at carbonyl carbon increase its reactivity towards nucleophilic addition reactions.
   ii) Reaction of primary amine, in presence of an acid, with carbonyl compound gives an imine. The rate of reaction increases by an increase in acidity but beyond a certain limit, the rate decreases with further increase of acidity.

4. a) In the following pairs which of the carbocation is more stable and why?
   i) NC – CH – CH₂ ⁺ CH₂  CH₃  or  NC – CH₂ – CH₂ CH₂ ⁺C H₂
            sec. carbocation                              p–carbocation
   ii) CH₃ CH₂ ⁺C H – CH₂ CH₂ CH₃ or CH₃ (CH₂)₄ ⁺C H₂
            sec. carbocation                               p–carbocation
   b) Explain the following:

   i) Aromatic aldehydes are less reactive than aliphatic aldehyde.

   iii) In Wittig reaction, the methyl, primary and secondary alkyl halide can be used to prepare Wittig reagent (ylide) but not tertiary alkyl halide.

5. a) Explain the following:
   i) E2 elimination does not give rearranged product.
   ii) E1 elimination does not involve isotope effect.
   iii) Hofmann elimination gives less substituted alkene
   iv) An anti elimination is faster than syn-elimination.
   v) The elimination of HCl from chlorofumaric acid is 50 times faster than chloromalic acid.
   b) How would you prepare cis and trans alkene from alkyne? Give its mechanism.
6. a) How are following compounds prepared using ethereal solution of diazomethane? Write the mechanism of the reactions.
   i) CH₃CH₂COOCH₃
   ii) CH₃CH₂OCH₃
   b) Taking suitable examples explain 1,3-dipolar cyclo-addition reactions.

7. a) How free radicals are generated using redox reaction? Give at least two examples. What are the major advantages of such reactions?
   b) Complete following reactions:

8. a) Write the mechanism of following rearrangement reactions
   i) Wagner-Meerwein rearrangement
   ii) Curtius rearrangement
   b) Taking suitable examples, discuss the migrating aptitude of the migrating group in Pinacol-pinacolone rearrangement reactions.
9. a) Using FMO method explain why [1,3] sigmatropic rearrangement of protons in alkenyl chain does not occur.
   b) Write the mechanism of Paterno-Buechi reaction.

10. a) How are following conversions carried out?
    i) 6-hydroxy-6-Methyl- 2-heptanone from 5-bromo-2-propanone using Grignard reagent
    ii) Cyclopentyl methyl ketone from acetoacetic ester
    iii) Barbituric acid from molonic ester
    iv) Propanol from ethylene oxide
    v) Butane from chloromethane
    b) Classify organic dyes according to their chemical composition.