Alkyne

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

2. * Pyrone Diels-Alder → aromatic species

3. Alkyne-azide reaction → Triazoles

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

   Terminal alkynes

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

   • anion of terminal alkyne + ketone → tetrahedral carbonyl addition compound (alkoxide)
     • alkoxide + aqueous acid → hydroxyalkyne

6. terminal alkyne + dialkylborane + hydrogen peroxide → aldehyde