What defines an alkene in organic chemistry?

An alkene is defined by the presence of at least one double bond between carbon atoms. This double bond, which consists of one sigma bond and one pi bond, is what differentiates alkenes from alkanes, which contain only single bonds. The inclusion of a double bond in alkenes allows them to participate in unique chemical reactions, such as addition reactions, which are significant characteristics of this class of compounds.

The double bond also influences the geometry of the molecule, resulting in planar structures around the carbon atoms involved in the double bond due to sp² hybridization. This geometry affects the physical properties and reactivity of alkenes compared to other hydrocarbons. Understanding this core characteristic is crucial for recognizing alkenes in organic synthesis and reaction mechanisms.