2Butene

2-Butene is an unsaturated hydrocarbon in the alkene family with the formula C4H8. Its structure features a carbon–carbon double bond between the second and third carbons of a four‑carbon chain, giving CH3‑CH=CH‑CH3. The compound exists as two geometric isomers: cis-2-butene (Z-2-butene) and trans-2-butene (E-2-butene). These stereoisomers arise from restricted rotation about the double bond and exhibit different physical properties and reactivity. In cis-2-butene, the two methyl groups are on the same side of the double bond; in trans-2-butene, they are on opposite sides.

Industrially, 2-butene is produced as part of refinery streams and can be formed by dehydrogenation of butane or through cracking processes. It is typically separated and purified as needed for use as a chemical feedstock. The two isomers can be further distinguished by their physical properties, including melting and boiling behavior, which reflect their differing shapes and dipole moments.

Reactions of 2-butene include typical alkene additions. Hydrogenation converts it to butane; halogenation adds across the double bond to give vicinal dihalides; and acid-catalyzed hydration adds water to form 2-butanol. Hydration of 2-butene is a common laboratory route to sec-butanol. As a reactive building block, 2-butene serves as a starting material for further transformations to other butane derivatives and, through polymerization chemistry, can participate in the production of copolymers and specialized lubricants.

Safety note: 2-butene is flammable, and its vapors can form explosive mixtures with air. It should be handled with appropriate precautions in well‑ventilated areas.