α-halosulfones in the Ramberg–Bäcklund reaction, via a three-membered ring sulfone intermediate. cis alkenes can be manufactured from trans alkenes through oxidation In organic chemistry, an alkene, or olefin, is a hydrocarbon containing one or more carbon–carbon double bonds. The double bond may be internal or at the terminal position. Terminal alkenes are also known as α-olefins. The International Union of Pure and Applied Chemistry (IUPAC) recommends using the name "alkene" only for acyclic hydrocarbons with just one double bond; alkadiene, alkatriene, etc. The Hofmann elimination is unusual in that the less substituted (non-Zaitsev) alkene is usually the major product. Alkenes are generated from α-halosulfones in the Ramberg–Bäcklund reaction, via a three-membered ring sulfone intermediate. cis alkenes can be manufactured from trans alkenes through oxidation to the (anti) bromohydrin and then treatment with selenocyanate anion. After the anion displaces bromide with inversion of configuration, the resulting compound rearranges and eliminates cyanate and selenium through cyclic intermediates.