Markovnikovselective

Markovnikovselective refers to chemical reactions in which the regiochemical outcome follows Markovnikov's rule: in the addition of a protic acid, water, or a halogen to an asymmetrical alkene, the electrophile bonds to the carbon with more hydrogens (the less substituted carbon), and the remainder attaches to the more substituted carbon. The major product is the one derived from the more substituted carbocation intermediate, or its equivalent, and the process often produces the most stable carbocation during the rate‑determining step.

Mechanistic basis and scope

Markovnikovselective additions commonly proceed via ionic or carbocation pathways, where carbocation stability governs regioselectivity. Classic examples include hydrohalogenation (HX) and acid-catalyzed hydration of alkenes, which place the new bond on the more substituted carbon. Oxymercuration-demercuration is a notable method that achieves Markovnikov hydration without carbocation rearrangements, delivering alcohols at the more substituted carbon.

Relation to anti‑Markovnikov selectivity

The term Markovnikovselective is contrasted with anti‑Markovnikov outcomes, where the opposite regiochemistry is observed. Anti‑Markovnikov additions often arise under radical conditions, such as HBr addition in the presence of peroxides or hydroboration-oxidation, where the OH (or halide) ends up on the less substituted carbon.

Limitations and considerations

Rearrangements can complicate outcomes under some ionic additions, as carbocation intermediates may rearrange to more stable species. The observed product distribution reflects a balance between mechanism, substituent effects, and reaction conditions.

Applications

Markovnikovselective processes are central to the synthesis of more substituted alcohols and alkyl halides from alkenes, and they underpin many industrial and laboratory strategies for building complex organic molecules.