Summary

Alkyl and aryl halides may be classified as mono-, di-, or polyhalogen compounds depending on the number of halogen atoms they carry, and, based on where the halogen sits, as alkyl (sp3 C-X), allylic, benzylic, vinylic, or aryl (sp2 C-X) halides. Both common and IUPAC nomenclature name them as halosubstituted hydrocarbons, and dihalogen compounds are further described as gem- or vic-dihalides depending on whether the two halogens sit on the same carbon or on adjacent carbons.

Alkyl halides are prepared from alcohols (by reaction with a hydrogen halide, a phosphorus halide, or thionyl chloride), from hydrocarbons (by free-radical halogenation of alkanes, or by addition of a hydrogen halide or a halogen to an alkene), and by halogen-exchange reactions such as the Finkelstein and Swarts reactions. Aryl halides are prepared by direct halogenation of an arene or by diazotisation of an aromatic amine followed by the Sandmeyer reaction.

The boiling points of organohalogen compounds are higher than those of the hydrocarbons they are derived from, because of the greater polarity and polarisability of the carbon-halogen bond; they generally increase with the size and number of the halogen atoms present. …