Chemistry Regents Practice Test 2025 - Free Chemistry Regents Practice Questions and Study Guide

Alkenes are characterized by the presence of a carbon-carbon double bond, which makes them reactive, particularly towards addition reactions. This type of reaction occurs when two reactants add across the double bond, resulting in the formation of a single product with no double bond remaining. Common addition reactions include hydrogenation (adding hydrogen), halogenation (adding halogens like bromine or chlorine), and hydrohalogenation (adding hydrogen halides).

The double bond in alkenes is a region of high electron density, making them susceptible to attack by electrophiles. This is why alkenes readily participate in these addition processes, leading to the saturation of the double bond and the formation of alkanes or other products depending on the specific reagents used in the reaction.

Thus, the tendency of alkenes to readily engage in addition reactions is a defining feature of their chemistry, distinguishing them from other types of hydrocarbons, such as alkanes, which primarily participate in substitution reactions.