Question

For the unrelated radical reactions shown below, identify the reaction type: initiation, propagation, or termination initiation propagation termination initiation propagation termination initiation propagation termination

??

Answer 1

Concepts and reason

Radical monochlorination:

The substitution of chlorine that takes place by replacing the hydrogen atom in an alkane in free radical pathway is represented as radical monochlorination. According to the type of reactant, the number of products can be determined.

Halogenation substitution reaction:

Halogens in the presence of heat or light react with alkanes to give alkyl halides. The general scheme for halogenation under light or hv is given below:

Fundamentals

Three steps for radical monohalogenation are:

I.Initiation

II.Propagation

III.Termination

Example for radical monochlorination is as follows:

Initiation:

Under the presence of light, hemolytic cleavage of a halogen bond occurs forming two chlorine radicals.

Propagation:

The chlorine radical abstracts hydrogen from the alkane chain forming hydrogen chloride and an alkyl radical.

The alkyl radical abstracts a chlorine atom from another molecule of ${\rm{C}}{{\rm{l}}_{\rm{2}}}$ and forms alkyl bromide and another chlorine radical which can be used in the reaction mechanism again.

This process continues in a cyclic way.

Termination:

Three possible pairs of radicals combine to end the reaction. This reaction removes the radicals and do not continue the cycle.

Formation of ${\rm{C}}{{\rm{l}}_{\rm{2}}}$ :

Formation of new alkane chain:

Formation of alkyl chloride:

(a)

The given reaction is:

The reaction type is initiation.

(b)

The given reaction is:

The reaction type is termination.

(c)

The given reaction is:

The reaction type is propagation.

Ans: Part a

Part b

Part c