alkynyl

Alkynyl is a term used in organic chemistry to denote a substituent or functional group that contains a carbon–carbon triple bond (C≡C). It is derived from an alkyne by removal of one hydrogen atom, generating a moiety that can be attached to another molecule. The alkynyl unit can be terminal, where the triple bond is connected to a hydrogen-bearing carbon (as in ethynyl, -C≡CH, and in phenylacetylene, Ph–C≡CH), or internal, where the triple bond lies between two carbon substituents (R–C≡C–R′).

Common alkynyl substituents include ethynyl (-C≡CH) and propargyl (-CH2–C≡CH), the latter attaching to a molecule through the methylene group. The carbon–carbon triple bond of an alkynyl group is sp-hybridized, giving a linear geometry at the bond and contributing to the distinct electronic properties of the unit.

In synthetic chemistry, alkynyl groups are versatile building blocks. They participate in reactions such as the Sonogashira coupling, which forms carbon–carbon bonds between terminal alkynes and aryl or vinyl halides; copper-catalyzed azide–alkyne cycloaddition (CuAAC), a widely used click reaction to make 1,2,3-triazoles; and formation of acetylide anions by deprotonation, enabling nucleophilic substitutions. Alkynyl fragments are found in pharmaceuticals, natural products, and advanced materials, and they are important handles for further functionalization in organic synthesis.