Alkynes, also known as acetylenes, are acyclic branched or unbranched hydrocarbons having a one or more triple carbon-carbon bonds. In systematic chemical nomenclature alkyne names end in the suffix -yne. The general formula is CnH(2n+2)-4x where x is the number of triple bonds.
Monoalkynes – alkynes that have only one triple bond and the general formula CnH2n-1 – form a homologous series: ethyne (acetylene), CH=CH, propyne, CH3CH=CH, etc. They are prepared by elimination of two hydrogen halide molecules from a dihaloalkane.
Alkynes physically resemble the corresponding alkanes, but chemically their properties are due mainly to the triple bond, and are similar to those of the alkenes. Addition reactions take place in two stages, forming first a substituted alkene and then a saturated alkane. The triple bond being nucleophilic (see nucleophile), alkynes add to unsaturated compounds such as aldehydes or ketones. Alkynes readily polymerize to various products, including aromatic and alicyclic compounds.