Organic Chemistry: Structure and Function
Organic Chemistry: Structure and Function
8th Edition
ISBN: 9781319079451
Author: K. Peter C. Vollhardt, Neil E. Schore
Publisher: W. H. Freeman
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Chapter 3, Problem 32P

(a)

Interpretation Introduction

Interpretation: Potential-energy versus reaction-coordinate diagrams for the two propagation steps in mechanism for monobromination of pentane should be sketched.

Concept introduction: The mechanism for monobromination comprises of three stages illustrated as follows:

Step1: Initiation via homolytic cleavage of BrBr bond: Br2 initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

  Organic Chemistry: Structure and Function, Chapter 3, Problem 32P , additional homework tip  1

Step2: Propagation: In first of the propagation steps bromine radical from step 1 abstracts hydrogen radical from methane as follows:

  Organic Chemistry: Structure and Function, Chapter 3, Problem 32P , additional homework tip  2

In subsequent propagation step methyl radical abstracts Br· radical from another Br2 , and liberates bromoethane and new bromine radical.

  Organic Chemistry: Structure and Function, Chapter 3, Problem 32P , additional homework tip  3

Step3: Termination: Radicals generated in propagation steps get quenched upon combination with one another illustrated as follows:

  Organic Chemistry: Structure and Function, Chapter 3, Problem 32P , additional homework tip  4

(b)

Interpretation Introduction

Interpretation:The locations of the transition states and whether each transition state is early or late should be indicated.

Concept introduction:In general, the exothermic reactions are characterized by an early transition state while the endothermic reaction is characterized by a late transition state.

In the former case, the transfer of H is not very advanced while in latter transition H is appreciably advanced when the transition state is reached.

(b)

Interpretation Introduction

Interpretation: The similar plot for reaction of pentane with I2 and difference from bromination plot should be indicated.

Concept introduction: In general the exothermic reactions are characterized by an early transition state while the endothermic reaction is characterized by a late transition state.

In the former case, the transfer of H is not very advanced while in latter transition of H is appreciably advanced when the transition state is reached.

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