What distinguishes an alkene from other hydrocarbons?

An alkene is specifically characterized by the presence of at least one double bond between carbon atoms in its structure. This feature gives alkenes unique chemical properties, such as the ability to undergo addition reactions, which are not typically exhibited by alkanes that only have single bonds, or alkynes that feature triple bonds. The double bond results in a different geometry around the carbon atoms compared to other hydrocarbon classes, leading to potential isomerism and varying reactivity.

The presence of a double bond in alkenes is what fundamentally differentiates them from alkanes, which contain only single bonds, and alkynes, which have triple bonds. Additionally, while hydrocarbons can indeed be branched, this branching does not specifically categorize a compound as an alkene. Thus, the defining characteristic of alkenes is their double bond, setting them apart within the broader category of hydrocarbons.