hüdrohalogeerimisel

Hydrohalogenation is a chemical reaction in which a hydrogen halide (HX, where X is a halogen such as fluorine, chlorine, bromine, or iodine) is added to an alkene or alkyne. This reaction results in the formation of a haloalkane or a dihaloalkane, respectively. The addition of HX typically follows Markovnikov's rule, which states that in the addition of a protic acid HX to an alkene, the hydrogen atom attaches to the carbon atom that already has the greatest number of hydrogen atoms. Conversely, the halogen atom attaches to the carbon atom with fewer hydrogen atoms. This regioselectivity arises from the formation of the more stable carbocation intermediate during the reaction mechanism.

The reaction proceeds via an electrophilic addition mechanism. The pi electrons of the alkene or alkyne attack the proton (H+) of the hydrogen halide, forming a carbocation and a halide ion. The halide ion then attacks the carbocation to form the final product. In the case of alkynes, two molecules of HX can add, leading to the formation of a geminal dihaloalkane (where both halogens are on the same carbon) or a vicinal dihaloalkane (where halogens are on adjacent carbons), depending on the reaction conditions. Anti-Markovnikov addition can be achieved under specific conditions, such as in the presence of peroxides during the addition of HBr, which proceeds via a radical mechanism. Hydrohalogenation is a fundamental reaction in organic chemistry, used for the synthesis of various halogenated organic compounds.