Diyne

In chemistry, a polyyne /ˈpɒlɪʌɪn/ is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, (−C≡C−)
n with n greater than 1. The simplest example is diacetylene or buta-1,3-diyne, H−C≡C−C≡C−H.

These compounds have also been called oligoynes, or carbinoids after "carbyne" (−C≡C−)
∞, the hypothetical allotrope of carbon that would be the ultimate member of the series. The synthesis of this substance has been claimed several times since the 1960s, but those reports have been disputed. Indeed, the substances identified as short chains of "carbyne" in many early organic synthesis attempts would be called polyynes today.

Polyynes are distinct from polyacetylenes, polymers formally obtained by polymerization of acetylenes. The backbones of polyacetylenes have alternating single and double bonds (−CR=CR'−)
n. In biochemistry and plant biology, "polyacetylene" is routinely used to describe naturally occurring polyynes and related species.

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

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