Which chemical structure is characteristic of alkenes?

Alkenes are defined by the presence of a carbon-carbon double bond within their structure. This specific feature allows alkenes to participate in unique chemical reactions, such as addition reactions, where atoms or groups are added across the double bond. The double bond leads to different bonding angles and reactivity compared to alkanes (which contain only single bonds) and alkynes (which feature carbon-carbon triple bonds).

In alkenes, the double bond (C=C) is a key structural motif that distinguishes them from other hydrocarbons. This structural characteristic not only defines alkenes but also influences their physical and chemical properties, such as boiling points and levels of saturation. This emphasis on the double bond helps clarify why the correct answer identifies this feature as characteristic of alkenes.