2alkene

2-alkenes are alkenes in which the carbon–carbon double bond is between the second and third carbon atoms of the main carbon chain. They include examples such as but-2-ene, pent-2-ene, and hex-2-ene. These are internal alkenes, in contrast to terminal alkenes whose double bond is at the end of the chain. When each double-bond carbon bears two different substituents, 2-alkenes can show geometrical isomerism, described as cis (Z) and trans (E).

Physical properties of 2-alkenes are generally nonpolar, with low solubility in water and higher solubility in organic solvents. Boiling points rise with increasing carbon number and with molecular symmetry; linear isomers typically have higher boiling points than branched ones of the same formula.

Chemical reactivity centers on the C=C bond, which undergoes typical alkene reactions. Hydrogenation adds hydrogen to convert 2-alkenes to saturated alkanes. Halogenation adds vicinal dihalides. Hydrohalogenation adds HX to form alkyl halides, with regioselectivity depending on substitution and conditions. Hydration, under acid catalysis, adds water across the double bond to give secondary or tertiary alcohols depending on the substitution pattern. 2-alkenes can also participate in polymerization under radical initiation to form polyalkenes, serving as important intermediates in organic synthesis and petrochemical processes.

Preparation routes for 2-alkenes include elimination reactions such as dehydrohalogenation of vicinal dihalides, dehydration of secondary alcohols, and various cracking or reforming processes in hydrocarbon streams. They occur as intermediates in the production of many chemicals and materials.