Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond. The number of hydrogen atoms in an alkene is double the number of carbon atoms, so they have the general formula:
For example, the molecular formula of ethene is C2H4, while for propene it is C3H6.
Here are the names and structures of four alkenes:
Butene has two straight-chained isomers, as the double bond can be placed in two different places or locations: