Halogenated

Halogenated is an adjective used in chemistry to describe substances in which one or more halogen atoms have been substituted into a molecule. The common halogens are fluorine, chlorine, bromine, iodine, and, less frequently, astatine. Halogenation can occur in many classes of compounds, leading to organohalogen or halogenated compounds.

Halogenated compounds often exhibit properties that differ markedly from their non-halogenated counterparts. The introduction of halogen atoms can increase molecular polarity, alter reactivity, raise boiling and melting points, and affect biological activity and environmental persistence. They range from simple chlorinated or fluorinated hydrocarbons to complex polymers and pharmaceuticals.

Major categories include halogenated hydrocarbons (such as chlorinated solvents like chloroform and carbon tetrachloride, or chlorinated pesticides), halogenated solvents, and fluorinated polymers (for example, polytetrafluoroethylene). Brominated flame retardants and iodinated contrast agents are other prominent examples. Reactions involving halogenation include electrophilic addition to alkenes and radical halogenation of alkanes, as well as substitution reactions where a hydrogen atom is replaced by a halogen.

Environmental and health considerations are a major aspect of halogenated substances. Many are persistent, bioaccumulative, and toxic. Some halogenated compounds have contributed to ozone depletion (notably CFCs and halons) and climate impacts, leading to international regulation such as the Montreal Protocol and broader conventions addressing persistent organic pollutants and chemical safety.

In use, halogenated compounds serve diverse roles, including disinfectants, solvents, pesticides, pharmaceuticals, and advanced materials. Related terms include organohalogen compounds and halogenation reactions.