halohydrinistä

Halohydrins are organic compounds containing both a halogen atom and a hydroxyl group on adjacent carbon atoms. They are typically formed by the addition of a halogen (like chlorine or bromine) to an alkene in the presence of water. The reaction mechanism involves the formation of a cyclic halonium ion intermediate, which is then attacked by water to yield the halohydrin.

The regiochemistry of halohydrin formation is generally observed to follow Markovnikov's rule. This means the hydroxyl group is typically found on the more substituted carbon atom of the original alkene, while the halogen atom is on the less substituted carbon. This regioselectivity arises from the attack of the nucleophile (water) on the more stable carbocation intermediate that forms during the ring-opening of the halonium ion.

Halohydrins are versatile synthetic intermediates. They can be readily converted into epoxides by treatment with a base, which abstracts the proton from the hydroxyl group, leading to an intramolecular nucleophilic attack by the alkoxide on the carbon bearing the halogen, displacing the halide ion. This epoxide formation is a very important reaction in organic synthesis. Furthermore, halohydrins can undergo various other reactions, including dehydrohalogenation to form alkynes or rearrangements under acidic conditions. Their presence in biological systems is also notable, with some halohydrins having antimicrobial or other physiological activities.