Chapter 3, Problem 23P

Interpretation Introduction

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

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

Step1: Initiation via homolytic cleavage of $\text{Br}-\text{Br}$ bond: ${\text{Br}}_{\text{2}}$ initiates the reaction; undergoes homolysis and forms bromine radical atom. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

  

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

  

In subsequent propagation step methyl radical abstracts $\text{Br}·$ radical from another ${\text{Br}}_{\text{2}}$ , and liberates bromoethane and new bromine radical.

  

Step3: Termination: Radicals generated in propagation steps get quenched upon combination with one another. Thus termination steps are essentially the radical− radical combination illustrated as follows: