Polyyne
These compounds are also called polyacetylenes, especially in the natural products and chemical ecology literature,[1] even though this nomenclature more properly refers to acetylene polymers composed of alternating single and double bonds (−CR=CR′−)n with n greater than 1.
[5] Indeed, the substances identified as short chains of "carbyne" in many early organic synthesis attempts[6] would be called polyynes today.
Along with cumulenes, polyynes are distinguished from other organic chains by their rigidity and high conductivity,[7] both of which make them promising as wires in molecular nanotechnology.
[citation needed] The first reported synthesis of a polyyne was performed in 1869 by Carl Andreas Glaser [de], who observed that copper phenylacetylide (CuC≡C−C6H5) undergoes oxidative dimerization in the presence of air to produce diphenylbutadiyne (C6H5−C≡C−C≡C−C6H5).
[12] Around 1971, T. R. Johnson and D. R. M. Walton developed the use of end-caps of the form –SiR3, where R was usually an ethyl group, to protect the polyyne chain during the chain-doubling reaction using Hay's catalyst (a copper(I)–TMEDA complex).
[14] A polyyne compound with 10 acetylenic units (20 atoms), with the ends capped by Fréchet-type aromatic polyether dendrimers, was isolated and characterized in 2002.
[10] Alkynes with the formula H(−C≡C−)nH and n from 2 to 6 can be detected in the decomposition products of partially oxidized copper(I) acetylide ((Cu+)2(−C≡C−) (an acetylene derivative known since 1856 or earlier) by hydrochloric acid.
[23] They can be fairly stable, even against moisture and oxygen, if the end hydrogen atoms are replaced with a suitably inert end-group, such as tert-butyl or trifluoromethyl.
[5] Polyyne chains have also been stabilised to heating by co-deposition with silver nanoparticles,[25] and by complexation with a mercury-containing tridentate Lewis acid to form layered adducts.
[29] Synthetic polyynes of the form R(−C≡C−)nR, with n about 8 or more, often have a smoothly curved or helical backbone in the crystalline solid state, presumably due to crystal packing effects.
[9] Thiarubrine B is the most prevalent among several related light-sensitive pigments that have been isolated from the Giant Ragweed (Ambrosia trifida), a plant used in herbal medicine.
[34] Polyynes such as falcarindiol can be found in Apiaceae vegetables like carrot, celery, fennel, parsley and parsnip where they show cytotoxic activities.
