antiMarkovnikovlisäys

Markovnikov's rule, a fundamental principle in organic chemistry, describes the regioselectivity of electrophilic addition reactions to unsymmetrical alkenes and alkynes. According to Markovnikov's rule, in the addition of a protic acid HX to an alkene, the hydrogen atom (H) attaches to the carbon atom of the double bond that already has the greater number of hydrogen atoms, and the halide (X) attaches to the carbon atom with fewer hydrogen atoms. This is due to the formation of the more stable carbocation intermediate.

An anti-Markovnikov addition, conversely, describes the addition of a reagent across a double or triple bond in a manner that is contrary to Markovnikov's rule. In an anti-Markovnikov addition, the hydrogen atom attaches to the carbon atom with fewer hydrogen atoms, and the other part of the reagent attaches to the carbon atom with more hydrogen atoms. This outcome is typically achieved through radical addition mechanisms or hydroboration-oxidation. For example, the addition of HBr to an alkene in the presence of peroxides proceeds via a radical mechanism, leading to the anti-Markovnikov product. Hydroboration-oxidation, a two-step process, also results in the anti-Markovnikov addition of water across a double bond. These reactions are important for synthesizing specific isomers of organic compounds.