but2ene

But-2-ene, also written as but-2-ene, is an unhindered hydrocarbon in the alkene family with the formula C4H8. It consists of a four-carbon chain with a carbon–carbon double bond between the second and third carbons, giving the structural unit CH3–CH=CH–CH3.

The compound exists as two geometric isomers due to restricted rotation about the C=C bond: cis-2-butene (where the two methyl groups are on the same side) and trans-2-butene (where the methyl groups are on opposite sides). The two forms have identical connectivity but different spatial arrangements, and trans-2-butene is generally more thermodynamically stable.

Physically, but-2-ene is a colorless, volatile hydrocarbon that is typically produced as a gas or a low-boiling liquid at room temperature, depending on the isomer. It is nonpolar and only sparingly soluble in water, with physical properties (such as boiling point) differing slightly between the cis and trans isomers due to their distinct molecular geometries.

Production and occurrence overlap with broader hydrocarbon processing. But-2-ene can be obtained from petroleum cracking and catalytic processes in refineries, and it can also be produced by elimination reactions, such as the dehydration of 2-butanol under acidic conditions.

Reactivity follows typical alkene patterns: the double bond undergoes hydrogenation to butane, halogen addition to give dihalides, hydrohalogenation to form bromo- or iodo-butanes, and various polymerization or copolymerization routes when used as a comonomer. It serves as a chemical feedstock and precursor in organic synthesis and industrial chemistry. See also cis-2-butene and trans-2-butene.