Using an aqueous acid, such as H3O+ or H2SO4, as a reagent in a reaction with an alkene will result in the formation of an alcohol:

The reaction takes place on the most substituted carbon, following Markovnikoff selectivity. Additionally, hydride and/or methyl rearrangement can occur, causing the alcohol group to be added to a more highly substituted carbon adjacent to the alkene bond:

Hydride Shift

Methyl Shift

The reaction mechanism is depicted below:

In the first step, the alkene is protonated by the acid, removing the double bond and causing 1 carbon to carry a positive charge. In the second step, water arrives at the reaction site, attaching to the molecule in a nucleophilic attack. The third reaction step involves another water molecule using its free electrons to deprotonate the oxygen, resulting in a regeneration of the H3O+ acid as well as an alcohol functional group being added to the original molecule.

While H3O+ is displayed in these examples, the same reaction occurs using dilute H2SO4.