Alkynes are hydrocarbons that have at least one triple bond between carbon atoms. The alkynes are traditionally known as acetylenes, though the name acetylene is also used to refer specifically to the simplest member of the series, known officially as ethyne.

Physical properties

Unlike an alkane an alkyne is unstable and very reactive. This gives rise to the intense heat of the acetylene flame used in welding.

Examples

The simplest alkyne is ethyne (acetylene):

Reactions

1. Diels-Alder reaction

1. * Pyrone Diels-Alder → aromatic species

1. Alkyne-azide reaction → Triazoles

1. enediynes (alkyne - alkene - alkyne) → aromatics (Bergman cyclization)

Terminal alkynes

1. terminal alkyne + strong base → anion of terminal alkyne

1. • anion of terminal alkyne + methyl or primary alkyl halide → new carbon-carbon bond

1. • anion of terminal alkyne + ketone → tetrahedral carbonyl addition compound (alkoxide)

1. • • alkoxide + aqueous acid → hydroxyalkyne

1. terminal alkyne + dialkylborane + hydrogen peroxide → aldehyde