Z2butene

Z2butene, also written as Z-2-butene or cis-2-butene, is an alkene with the formula C4H8 and is the cis isomer of but-2-ene. The Z designation indicates that the two higher-priority substituents (the methyl groups) lie on the same side of the carbon–carbon double bond.

Structure and nomenclature: The molecule has a CH3-CH=CH-CH3 backbone with the two methyl groups on the same side of the double bond. It is the stereochemical counterpart to E-2-butene (trans-2-butene).

Physical properties: Z-2-butene is typically a colorless, flammable gas or low-boiling liquid at room temperature, with a boiling point near 0 °C or just below. Like other alkenes, it is relatively nonpolar and can be separated from isomers by distillation due to small differences in physical properties.

Production and occurrence: It is produced in petrochemical processes and occurs in various fractions of crude oil and natural gas liquids. It exists in equilibrium with its trans isomer, with the relative amounts depending on temperature and processing conditions.

Reactions: As a simple alkene, cis-2-butene participates in standard addition reactions. Bromine addition gives 2,3-dibromobutane, with the cis isomer producing the meso form, whereas the trans isomer yields a pair of enantiomers. Hydrogenation yields butane; hydration yields 2-butanol; hydrohalogenation with HX also furnishes 2-bromobutane due to the molecule’s symmetry.

Applications and significance: Z-2-butene serves as a chemical building block and reference compound in stereochemistry studies. It is often encountered in refinery streams and is separated from the trans isomer for specific industrial uses.

Safety: It is flammable and can be irritating if inhaled or contacted with skin or eyes. Proper ventilation and storage away from heat or ignition sources are required.