An alkyne is a molecule that has a triple bond between two carbon atoms. They have general formula CnH2n-2. They are also called acetylenes. The smallest alkyne is acetylene, also called ethyne. Alkynes are hydrophobic: this means they dissolve well in organic solvents but not in water.
Alkynes are more reactive than usual hydrocarbons simply because they have triple bonds. For example, they are more reactive than alkenes in many reactions. If the alkyne is at the end of a molecule, it is easy to remove the proton with a strong base. Then, the alkyne can be used in addition reactions. For example, it can be added to a ketone. Alkynes are also easy to reduce to double bonds. They can be made into both trans and cis double bonds. Alkynes are also used a lot in pericyclic reactions.