Also called butene, any of four isomeric compounds belonging to the series of olefinic hydrocarbons. They are formed during the cracking of petroleum to produce petrol; they can also be prepared by the catalytic dehydrogenation of butanes. The major part of the butenes is utilised for the production of octanes, which are important constituents of petrol. On dehydrogenation, normal butenes form butadiene, the principal starting material for synthetic rubber.