Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired molecule. These three possible reactions result in six different arrow-pushing patterns in radical mechanisms, such as homolysis, addition to a π bond, hydrogen abstraction, halogen abstraction, elimination, and coupling. These six patterns can be categorized into three typical steps, initiation, propagation, and termination, of a radical mechanism. Typically, these radical reactions are governed by two key factors: steric hindrance and electronic stabilization.
