Hydration of Alkenes: Simple acid-catalyzed hydration of alkenes is a stepwise reaction involving a carbocation intermediate. Rearrangements will often occur and hydroxide anion will bond to the most stable carbocation center in the molecule (Markovnikov's Rule).

Oxymercuration of Alkenes: Oxymercuration of alkenes is a stepwise reaction involving a bridged mercurinium ion intermediate. In asymmetrical alkenes, the alkene carbon which would form the most stable carbocation will bear more of the positive charge and will be attacked by hydroxide anion (or water) to give the addition intermediate; rearrangements do not occur, but the orientation follows Markovnikov's Rule. In a second step, BH₄^- is used to remove the mercury and give the final product.

Hydroboration of an Alkene, with Oxidative Work-up: Reaction of an alkene with BH₃ results in the syn-addition of the boron and a hydrogen across the double bond. Rearrangements do not occur and the hydrogen will bond to the carbon of the alkene which would form the most stable carbocation center (overall anti-Markovnikov's addition). The driving force for the regiochemistry may actually be more steric than electronic, but viewing the reaction as a concerted, but polar transition state, easily rationalizes the observed product distribution.

Formation of 1,2-Diols from Alkenes: Reaction of an alkene with MnO₄^- or OsO₄ results in the formation of a cis-1,2-diol. The reaction involves the formation of an intermediate cyclic ester, which decomposes to give the diol. For OsO₄, reaction with HSO₃- is necessary to decompose the intermediate ester and form the final product.

Preparation of Alcohols by Reduction of Aldehydes and Ketones: Reduction of simple aldehydes and ketones with BH₄^- yields the corresponding alcohol directly. The reaction works well for simple compounds, but reaction of BH₄^- with a-b-unsaturated aldehydes and ketones can result in significant reduction of the double bond.

A much more powerful reductant is LiAlH₄, which will reduce aldehydes, ketones, esters, carboxylic acids and nitriles. Some sample reactions are shown below:

As seen in the first example, the reduction of carboxylate esters results in the addition of two moles of hydride to the carbonyl carbon, with loss of the alcohol portion of the ester, forming the corresponding primary alcohol.