homolytically

In chemistry, homolytically describes a bond-cleavage process in which the two electrons of a covalent bond are distributed evenly between the two fragments. Each fragment retains one electron, producing two radicals (A• and B•). The term contrasts with heterolytic cleavage, in which both electrons go to a single fragment and charged species are formed.

Homolytic cleavage can be induced thermally or photochemically. In photolysis, light supplies the energy to break the bond and generate radicals; many reactions in organic chemistry proceed via homolytic steps, especially under radical initiators or UV irradiation. The energy required is described by the bond dissociation energy for AB → A• + B•; bonds with lower dissociation energies are more prone to homolytic cleavage.

Common examples include the homolytic cleavage of chlorine gas (Cl2 → 2 Cl•) under ultraviolet light, and the cleavage of the O–O bond in hydrogen peroxide to yield two hydroxyl radicals (HO•). In hydrocarbon chemistry, C–H and C–C bonds can also undergo homolytic cleavage under appropriate energetic conditions to form carbon-centered or alkyl radicals that drive subsequent reactions.

Understanding homolytic processes is central to radical chemistry, polymerization, combustion, and atmospheric chemistry, where radical intermediates control reaction pathways. It stands in contrast to heterolytic cleavage, which generates ionic intermediates.