HYDROHALOGENATION

Hydrohalogenation refer to a hydrogen bonding with the element from groups 17 which are called the halogen group.

In the addition of HX to an alkene( H = hydrogen, X = halogen ), the H attaches to the carbon with fewer alkyl substituents and the X attaches to the carbon with more alkyl substituents.

Hydrohalogenation

When both double-bond carbon atoms have the same degree of substitution, a mixture of addition product results.

In the addition of HX to an alkene, the more highly substituted carbocation is formed as the intermediate rather than the less highly substituted one.

Addition of H+ to 2-methylpropene yields the intermediate tertiary carbocation rather than the alternative primary carbocation.

Addition of to 1-methylcyclohexene yields a tertiary cation rather than a secondary one.

A hydrohalogenation reaction is the electrophilic addition of hydrohalic acids like hydrogen chloride or hydrogen bromide to alkenes to yield the corresponding haloalkanes.

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 acid (HX) to form the most stable carbocation(relative stability: 3°>2°>1°>methyl), as well as generating a halogen anion.