Markovnikovtype

Markovnikovtype refers to a class of reactions whose regioselectivity follows Markovnikov's rule in the addition of electrophiles to unsaturated substrates such as alkenes and alkynes. In these processes the electrophilic part of the reagent adds to the carbon that bears more hydrogen atoms (the less substituted carbon), generating a carbocation (or carbocation-like character) at the more substituted carbon. A nucleophile then attacks that center, yielding the more substituted product overall.

Common examples include acid-catalyzed hydration of alkenes, hydrohalogenation (addition of HX), and certain oxymercuration- and electrophilic addition reactions. For instance, the addition of water to propene under acidic conditions predominantly gives 2-propanol, and the addition of HBr to propene yields 2-bromopropane. In many Markovnikov-type reactions, the outcome is the formation of products where the new bond resides on the more substituted carbon, reflecting greater stability of the intermediate carbocation.

Mechanistically, Markovnikov-type additions often proceed via a two-step process with a carbocation intermediate, though some variants can occur through concerted or alternative pathways that still deliver the same regioselective outcome. The concept helps organize literature and synthetic planning around regioselectivity in electrophilic additions.

Limitations and alternatives include anti-Markovnikov additions, which can predominate under different conditions (for example, hydroboration-oxidation giving alcohols at the less substituted carbon, or peroxide-initiated hydrohalogenation yielding anti-Markovnikov products). Markovnikov-type terminology is commonly used to categorize products and mechanisms that follow this regiochemical preference.