Chapter 7, Problem 40P

Interpretation Introduction

Interpretation:A reasonable rate expression corresponding to chlorination of methane reaction should be proposed.

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

Step 1- Initiation via homolytic cleavage of $\text{Cl}-\text{Cl}$ bond: ${\text{Cl}}_{\text{2}}$ initiates the reaction; undergoes homolysis to yield chlorine radicals. Energy for homolytic cleavage is provided by the heat or ultraviolet light.

  

Step 2: Propagation: In the first of the propagation steps $\text{Cl}·$

radical generated from step 1 abstracts hydrogen radical from methane as follows:

  

In subsequent propagation step chloromethyl radical abstracts $\text{Cl}·$ radical from another ${\text{Cl}}_{\text{2}}$ , and liberates dichloromethane and new $\text{Cl}·$ radical.

  

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