What is the first step in the process of radical substitution?

The first step in the process of radical substitution is initiation. This phase involves the generation of free radicals, which are highly reactive species with unpaired electrons. During initiation, a molecule is typically broken down into two or more radicals, often through the application of heat or light. For example, the homolytic cleavage of a bond in an alkane or the breakdown of a diatomic molecule such as chlorine can create radicals that are essential for the following steps in the reaction.

The significance of this step lies in its role as the starting point for the radical substitution mechanism. Once these radicals are produced, they can participate in subsequent reactions, such as propagation, where they react with other molecules to create new radicals and move the reaction forward. The termination step comes at the end of the mechanism when two radicals combine to form a stable molecule, effectively stopping the reaction. Homolysis refers specifically to the bond breaking process that generates radicals and is a fundamental concept but is not the step that initiates the radical substitution process itself as a discrete phase.