Chapter 25, Problem 25.16P

Interpretation Introduction

Interpretation:

The major product of the reaction is to be predicted and a complete mechanism for the reaction is to be drawn.

Concept introduction:

Halogen molecules undergo homolysis when irradiated with UV light to produce two radical atoms. Homolysis is the type of bond dissociation where each atom gets one of the bond electrons. The radical is an atom or molecule with an unpaired electron. It is highly unstable, and therefore a highly reactive species. This homolytic dissociation is called initiation.

Being reactive, a radical will react with other species present. This produces another radical, which can continue the reaction is a step called propagation. The reaction is generally branched as each initiation step produces two radicals. The propagation steps continue as long as radicals are present, and may be terminated by a reaction between two radicals.

The reaction generally results in substitution, often of a hydrogen atom from the hydrocarbon skeleton. When there are distinct types of hydrogen atoms in the reactant, the hydrogen removed is one that will lead to the formation of the most stable radical. The relative stability of radicals changes in the same was as the stability of carbocation. This determines the major product of the reaction.