homolizie

Homolysis, or homolytic cleavage, is the breaking of a chemical bond in which each fragment retains one of the bond’s two electrons, producing two radical species. This contrasts with heterolysis, where both electrons are transferred to a single fragment, yielding ions.

In practice, homolytic cleavage occurs under photochemical or thermal conditions. Photochemical homolysis happens when a bond absorbs light, promoting electrons to an excited state and weakening the bond until it splits, forming radicals. Thermal homolysis occurs when sufficient thermal energy overcomes the bond dissociation energy, leading to bond rupture with the formation of radicals. The process is fundamental to radical chemistry and often governs reaction pathways in organic synthesis, polymerization, and combustion.

Common examples include the cleavage of hydrogen molecules (H2 → 2 H•) and chlorine molecules (Cl2 → 2 Cl•) under appropriate irradiation or energy input. Peroxides (R–O–O–R) undergo homolysis of the O–O bond to give alkoxy radicals, enabling radical polymerization and various transformations. Homolytic cleavage is a key step in radical chain reactions, atmospheric chemistry, and photochemical processes.

Radical species produced by homolysis are typically highly reactive due to their unpaired electrons. Their detection often relies on electron spin resonance (ESR or EPR) spectroscopy, which identifies unpaired electrons, or on time-resolved spectroscopic methods that track transient intermediates.

See also: heterolysis; bond dissociation energy; radical chemistry; photochemistry.