https://doi.org/10.1351/goldbook.M03707
'In the addition of hydrogen halides to unsymmetrically constituted [unsaturated] @[email protected], the halogen atom becomes attached to the carbon bearing the lesser number of hydrogen atoms.' Originally formulated by Markownikoff (Markovnikov) to generalize the orientation in additions of hydrogen halides to simple @[email protected], this rule has been extended to polar @[email protected] as follows. 'In the @[email protected] addition of a polar molecule to an alkene or alkyne, the more electronegative (nucleophilic) atom (or part) of the polar molecule becomes attached to the carbon atom bearing the smaller number of hydrogen atoms.' This is an indirect statement of the common mechanistic observation, that the more electropositive (electrophilic) atom (or part) of the polar molecule becomes attached to the end of the multiple bond that would result in the more @[email protected] @[email protected] (whether or not a @[email protected] is actually formed as a @[email protected] in the @[email protected]). Addition in the opposite sense is commonly called '@[email protected] addition'.
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1137 [Terms] [Paper]