1alkenes

1-alkenes, also called terminal alkenes or α-olefins, are alkenes in which the carbon–carbon double bond is at the end of the carbon chain, i.e., between carbon 1 and carbon 2. Their general formula for acyclic relatives is CnH2n (n ≥ 2). The simplest examples are 1-propene (propene), 1-butene, and 1-pentene, with longer homologues continuing the same pattern. Because the double bond is terminal, 1-alkenes do not exhibit geometric (cis-trans) isomerism.

Nomenclature and properties: IUPAC names specify the double bond location as 1-alkene, but common usage often leaves the locant implicit (propene, butenes, etc.). Physically they range from gases or low-boiling liquids at room temperature, with boiling points increasing with chain length. They are nonpolar, relatively flammable, and generally immiscible with water. The C=C bond is the principal reactive site, enabling typical alkene chemistry such as electrophilic addition.

Production and occurrence: In industry, the most important 1-alkenes are linear α-olefins, produced mainly by selective oligomerization of ethylene to give mixtures of C4 to C20 α-olefins, tailored for downstream applications. Shorter 1-alkenes can be obtained by cracking or dehydrogenation of larger hydrocarbons; they also appear in petroleum fractions in minor amounts.

Reactions and applications: 1-alkenes undergo standard alkene reactions, including hydrogenation, hydrohalogenation, hydroboration-oxidation, and hydration to alcohols. They also participate in oxidation, hydroformylation to aldehydes, and various catalytic rearrangements. They are key feedstocks for polymer synthesis, most notably polyethylene from ethene and polypropylene from propene, and serve as precursors for detergents, lubricants, plasticizers, and other organic intermediates.

Notes: Unlike many internal alkenes, 1-alkenes generally lack E/Z isomerism; stereochemistry becomes relevant mainly in longer internal alkenes. As with other volatile hydrocarbons, safety and environmental considerations apply.