Alkenes react with aqueous acidic solutions to form alcohols. The reaction intermediate is a carbocation. Hence, there is a possibility of rearrangement of the intermediates in such acid-catalyzed reactions. The reaction follows the Markovnikov's rule. Keep in mind that a tertiary carbocation is more stable than a secondary carbocation, which in turn is more stable than a primary carbocation.
Oxidation followed by hydroboration of alkene results in alcohols. The reaction occurs in an anti-Markovnikov fashion. Notice that hydrogen, instead of attaching to the carbon with the highest number of hydrogens, attaches to the carbon with the least number of hydrogens.
Alkenes can be converted to alcohols by oxymercuration-demercuration. The addition of H and OH is in accordance with the Markovnikov's rule. There is no rearrangement in this reaction.
Preparation of an alcohol from an epoxide is shown below. The epoxide (ethylene oxide) ring opens when the nucleophile attacks the carbon-oxygen bond. Note the fact that the nucleophilic carbon is supplied by the Grignard reagent (methyl magnesium bromide).
Alcohols can also be produced from aldehydes and ketones via Grignard reagents. Other methods to synthesize alcohols include the reduction of aldehydes and ketones. These reactions will be discussed in Chapter 22.