Hydrohalogenation

A hydrohalogenation reaction is the electrophilic addition of hydrogen halides like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes. 400px|Hydrogen bromide addition to an alkene

If the two carbon atoms at the double bond are linked to a different number of hydrogen atoms, the halogen is found preferentially at the carbon with fewer hydrogen substituents, an observation known as Markovnikov's rule. This is due to the abstraction of a hydrogen atom by the alkene from the hydrogen halide (HX) to form the most stable carbocation (relative stability: 3°>2°>1°>methyl), as well as generating a halogen anion.