An acetylide ion is an alkyne that has had a proton (hydrogen) removed from the terminal end. So, for example, the alkyne HCH3C≡CH could be deprotonated to form the acetylide ion HCH3C≡C-. Once it has been deprotonated it becomes a strong nucleophile.

Acetylide ions are very useful in organic chemistry reactions in combining carbon chains, particularly addition and substitution reactions.