Which functional group contains the structure –C≡C–?

The functional group characterized by the structure –C≡C– is known as an alkyne. Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. In the structure –C≡C–, the three lines signify that there is a triple bond between two carbon atoms, which is the definitive feature that identifies a compound as an alkyne.

Alkenes, on the other hand, only contain a carbon-carbon double bond, noted by the structure –C=C–, while alkanes consist solely of single bonds between carbon atoms, represented as –C–C–. An aromatic ring refers to a specific cyclic structure that possesses alternating double and single bonds, following Huckel's rule of aromaticity, which does not relate to the presence of a triple bond.

Thus, recognizing the unique triple bond present in the structure indicates that it indeed corresponds to an alkyne.