Cis-2-butene is an organic compound with the chemical formula C₄H₈. It is an alkene, meaning it contains a carbon-carbon double bond. The "cis" designation indicates that the two methyl groups (–CH₃) attached to the double bond are on the same side, which affects its physical properties and reactivity compared to its trans isomer. Cis-2-butene is a colorless gas at room temperature and is used in various chemical reactions, including polymerization. It can be found in small amounts in natural gas and is also produced during the refining of petroleum. Its structure contributes to its unique characteristics in chemical processes.