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General structure of a halohydrin, where X = I, Br, F, or Cl
Structure of the halohydrin 2-chloroethanol

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.[1] 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).[2] 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.[2] This is the reverse of the formation reaction from an epoxide. Epoxidation in biological systems can be catalyzed by halohydrin dehalogenase.


  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "halohydrins".
  2. ^ a b William Reusch. "Addition Reactions of Alkenes". Virtual Textbook of Organic Chemistry.