A halohydrin or a haloalcohol is a type of organic compound or functional group in which one carbon atom has a halogen substituent, and another carbon atom has a hydroxyl substituent. The halogen and hydroxyl substituents are usually on adjacent carbons. These compounds are derived from alcohols are therefore characterized by the presence of both the hydroxyl functional group (-OH) and a halogen functional group.
Halohydrin are usually prepared by treatment of an alkene with a halogen (often bromine), in the presence of water (see halohydrin formation reaction). Halohydrins may also be prepared from the reaction of an epoxide with a hydrohalic acid.
In presence of a base, such as potassium hydroxide, a halohydrin may undergo internal SN2 reaction to form an epoxide. This is the reverse of the formation reaction from an epoxide. Epoxidation in biological systems can be catalyzed by halohydrin dehalogenase.