Preparation of Alcohols via Addition Reactions

Alcohols can be prepared through the reaction of alkenes with water using three synthetic routes: acid-catalyzed hydration, oxymercuration–demercuration, and hydroboration–oxidation.

In the acid-catalyzed hydration of alkenes, a proton is added to the less-substituted carbon in the double bond, forming a more stable carbocation. Subsequently, hydroxyl is added to the more substituted end of the double bond, which follows Markovnikov's rule.

Since a trigonal planar carbocation intermediate is involved in the reaction pathway, the addition of the water molecule on either face is equally probable, and a racemic mixture of alcohols is formed.

Alcohol synthesis via oxymercuration–demercuration of alkenes does not have a conventional carbocation intermediate. Instead, the nucleophilic attack of the double bond on the positively-charged mercury acetate creates a three-membered mercurinium ion intermediate, which can be considered a resonance hybrid with minor carbocation character.

The subsequent hydration of the mercurinium ion is consistent with Markovnikov's rule. Following proton transfer, sodium borohydride replaces the mercury species with a proton to give the final product — alcoho