Organohalogens are organic compounds that contain one or more halogen atoms (fluorine, chlorine, bromine or iodine). The halogen atom(s) is covalently bonded to a carbon atom. Relatively few organohalogen compounds are found in the terrestrial organisms of nature, but organohalogen compounds are much more common within marine organisms. An organohalogen with an essential role in human biochemistry is thyroxin, the iodine-containing hormone that helps to regulate human metabolism. Simple organohalogens may be produced synthetically from the radical chlorination/bromination of saturated alkanes:

CH₄ + Cl₂ CH₃Cl + HCl

CH₄ + Br₂ CH₃Br + HBr

They may also be produced from the chlorination of alkylbenzenes: C₆H₅CH₃ + Cl₂ C₆H₅CH₂Cl + HCl

The electrophilic substitution of aromatic hydrocarbons using ferric chloride catalyst also produces organohalogens: C₆H₆ + Cl₂ C₆H₅Cl + HCl

And orgaohalogens can be produced from addition reactions involving chlorine/bromine gas (and/or hydrogen chloride...