What characteristic reaction do alkenes typically undergo?

Alkenes are characterized by the presence of a carbon-carbon double bond, which makes them highly reactive compared to alkanes. The double bond is a site of high electron density, making alkenes susceptible to reactions that can break this bond and form new bonds with other atoms or groups.

Addition reactions involve the addition of atoms or groups across the double bond of the alkene, leading to the formation of saturated compounds (alkanes) or other products. Common examples include the addition of hydrogen (hydrogenation), halogens (halogenation), and water (hydration) to alkenes.

This reactivity in addition reactions is the primary characteristic of alkenes and distinguishes them from other types of organic compounds, such as benzene, which undergo substitution reactions instead. The other types of reactions listed—elimination, substitution, and combustion—do not fundamentally capture the typical response of alkenes to reactants. Thus, addition reactions are the most characteristic for alkenes, highlighting their reactivity and versatility in synthesis and chemical transformation.