Polyyne

The polyynes are a group of organic compounds with alternating single and triple bonds, for example buta-1,3-diyne (diacetylene), C4H2.

Along with cumulenes, polyynes are distinguished from other organic chains by their rigidity, which makes them promising for molecular nanotechnology. Polyynes are found in interstellar molecular clouds where hydrogen is scarce.

Cyanopolyynes such as cyanoacetylene, C3HN, (expanding the definition to any triple bond functional group) are particularly common in these interstellar clouds. They were first detected around 1970. Cyanoacetylene is one of the molecules that is known to exist because of the Miller-Urey experiment. This molecule appears in the large glass container, where water is being boiled.

Naturally occurring polyynes
Naturally occurring polyynes exist, and many are associated with medicinal properties. The acetylenic fatty acid 1 (scheme 1) is isolated from the root bark of the legume Paramacrolobium caeruleum of the Showy Mistletoe Family. The stems and leaves of members of this family have been used for the treatment of cancer in Java and Indonesia.

The naturally occurring pigment thiarubrine B (2) has been isolated from the giant ragweed (Ambrosia trifida). Plants containing this type of compound have been used to treat skin infections and intestinal parasites by native people in Africa and Canada.

The inner bark and roots of Devil's club is used by native Americans to treat a variety of ailments. One of the polyynes isolated is oplopandiolacetate (3). Dihydromatricaria acid (4) is a polyyne obtained from the soldier beetle.

Because of the potential medicinal properties of these polyynes, their synthetic pathways are being studied with the hope that these can be replicated industrially by organic synthesis. Many such procedures involve a Cadiot–Chodkiewicz coupling.

Polyynes in space
The octatetraynyl radicals and hexatriynyl radicals together with their ions are detected in space.