alkene (olefin) Unsaturated hydrocarbon compound with the general formula C_nH_2n. Alkenes have a carbon-carbon double bond and form an homologous series whose first members are ethene and propene. They are reactive, particularly in addition reactions. Alkenes are made by the dehydration of alcohols, and are used as fuels and to make polymers.

al·kene / ˈalˌkēn/ • n. Chem. any of the series of unsaturated hydrocarbons containing a double bond and having the general formula C_nH_2n, including ethylene and propylene.