text: Halogenation of saturated hydrocarbons is a substitution reaction. The reaction typically requires free radical pathways. The regiochemistry of the halogenation of alkanes is largely determined by the relative weakness of the C–H bonds. This trend is reflected by the faster reaction at tertiary and secondary positions. 
  Fluorinations with elemental fluorine () are particularly exothermic, so much so that highly specialised conditions and apparatus are required. The method electrochemical fluorination generates small amounts of elemental fluorine in situ from hydrogen fluoride. The method avoids the hazards of handling fluorine gas. Many commercially important organic compounds are fluorinated using this technology. Aside from  and its electrochemically generated equivalent, cobalt(III) fluoride is used as sources of fluorine radicals.
  Free radical chlorination is used for the industrial production of some solvents:
  Naturally-occurring organobromine compounds are usually produced by free radical pathway catalyzed by the enzyme bromoperoxidase. The reaction requires bromide in combination with oxygen as an oxidant. The oceans are estimated to release 1–2 million tons of bromoform and 56,000 tons of bromomethane annually.
  The iodoform reaction, which involves degradation of methyl ketones, proceeds by the free radical iodination.