CH3CHCHCH2

CH3CHCHCH2, also known as but-2-ene or crotonylene, is an organic compound with the chemical formula C4H8. It is a straight-chain alkene, meaning it contains four carbon atoms and a carbon-carbon double bond. The double bond is located between the second and third carbon atoms, giving it the "-2-ene" designation. But-2-ene exists as two geometric isomers due to the presence of the double bond: cis-but-2-ene and trans-but-2-ene.

In cis-but-2-ene, the two methyl groups (CH3) are on the same side of the double bond. In trans-but-2-ene, the two methyl groups are on opposite sides of the double bond. These isomers have different physical properties, such as melting and boiling points. But-2-ene is a colorless gas at room temperature and pressure. It is flammable and has a distinct odor.

But-2-ene is typically produced as a byproduct of petroleum refining processes, such as catalytic cracking. It can also be synthesized through the dehydration of butanol or the dehydrohalogenation of halobutanes. It is used as a feedstock in the petrochemical industry for the production of various chemicals, including polymers and other organic compounds. Its isomers can be separated by fractional distillation or other physical methods.