What defines an alkene?

Alkenes are specifically defined as hydrocarbons that contain one or more carbon-carbon double bonds. This structural feature is critical in distinguishing alkenes from other types of hydrocarbons. In an alkene, the presence of the double bond introduces unsaturation, meaning that not all valences of the carbon atoms are satisfied with hydrogen atoms, allowing for the potential addition of other atoms or groups in reactions—this property is significant in organic chemistry and the reactivity of alkenes.

In contrast, the other options define different types of hydrocarbons. Hydrocarbons with triple bonds refer to alkynes, which are distinct from alkenes due to their triple bond configuration. Saturated hydrocarbons, which contain only single bonds, are known as alkanes and are fully saturated with hydrogen atoms. Lastly, hydrocarbons that contain only single bonds fall into the alkane category as well. Thus, the defining characteristic of an alkene is its double bond, making the correct choice distinctly focused on that structural aspect.