Olefin

Olefin, commonly called an alkene, is a hydrocarbon containing at least one carbon–carbon double bond. The general formula for acyclic alkenes is CnH2n, reflecting the loss of two hydrogens relative to alkanes. The defining feature is the C=C bond between two sp2-hybridized carbons. The simplest examples are ethene (ethylene, C2H4) and propene (propylene, C3H6).

Structure and reactivity: The double bond is planar and restricts rotation, giving potential cis–trans (geometric) isomerism in disubstituted alkenes. Alkenes are more reactive than alkanes, undergoing electrophilic addition across the C=C bond. They can be hydrogenated, halogenated, hydrohalogenated, or hydrated, and are efficient monomers for polymerization to polyolefins such as polyethylene and polypropylene.

Production and use: Major alkenes are produced by steam cracking of naphtha or gas-oil fractions and by dehydrogenation of alkanes. Ethene and propene are the most important industrial monomers, underpinning the plastics industry and the manufacture of a wide range of derivatives, including alcohols, glycols, and detergents. Alkenes with larger chains or branching find use as fuels, solvents, and intermediates.

Reactions and safety: Alkenes undergo a range of addition reactions, and can be polymerized under Ziegler–Natta or metallocene catalysts to yield polyolefins. They also participate in oxidation, ozonolysis, and rearrangements under suitable conditions. Safety: Alkenes are typically flammable and may form explosive peroxides in some contexts; storage and handling require controls and inhibitors to prevent unwanted polymerization.