Illustrated Glossary of Organic Chemistry

Markovnikov's rule (Markovnikov addition): In an addition reaction of a protic acid HX (hydrogen chloride, hydrogen bromide, or hydrogen iodide) to an alkene or alkyne, the hydrogen atom of HX becomes bonded to the carbon atom that had the greatest number of hydrogen atoms in the starting alkene or alkyne.

Addition of hydrogen bromide to propene follows Markovnikov's rule.

Anti-Markovnikov addition of hydrogen bromide to propene, illustrating the peroxide effect.