Polyyne

, the simplest polyyne A polyyne is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, with n greater than 1. These compounds are also called polyacetylenes, especially in the natural products and chemical ecology literature, even though this nomenclature more properly refers to acetylene polymers composed of alternating single and double bonds (which are polyenes) with n greater than 1. They are also sometimes referred to as oligoynes, or carbinoids after "carbyne" , 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. The simplest polyyne is diacetylene or butadiyne, . Along with cumulenes, polyynes are distinguished from other organic chains by their rigidity and high conductivity, both of which make them promising as wires in molecular nanotechnology. Polyynes have been detected in interstellar molecular clouds where hydrogen is scarce.

, the simplest polyyne]] A polyyne is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, with n greater than 1. These compounds are also called polyacetylenes, especially in the natural products and chemical ecology literature, even though this nomenclature more properly refers to acetylene polymers composed of alternating single and double bonds (which are polyenes) with n greater than 1. They are also sometimes referred to as oligoynes, or carbinoids after "carbyne" , 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. The simplest polyyne is diacetylene or butadiyne, . Along with cumulenes, polyynes are distinguished from other organic chains by their rigidity and high conductivity, both of which make them promising as wires in molecular nanotechnology. Polyynes have been detected in interstellar molecular clouds where hydrogen is scarce. Organometallic polyynes capped with metal complexes are well characterized. As of the mid-2010s, the most intense research has concerned rhenium ( , n = 3–10), ruthenium ( , n = 4–10), iron ( ), platinum ( , n = 8–14), palladium ( , n = 3–5, Ar = aryl), and cobalt ( , n = 7–13) complexes. polyynes. ]] ==Structure== Synthetic polyynes of the form , 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. For example, when the cap R is triisopropylsilyl and n is 8, X-ray crystallography of the substance (a crystalline orange/yellow solid) shows the backbone bent by about 25–30 degrees in a broad arch, so that each C−C≡C angle deviates by 3.1 degrees from a straight line. This geometry affords a denser packing, with the bulky cap of an adjacent molecule nested into the concave side of the backbone. As a result, the distance between backbones of neighboring molecules is reduced to about 0.35 to 0.5 nm, near the range at which one expects spontaneous cross-linking. The compound is stable indefinitely at low temperature, but decomposes before melting. In contrast, the homologous molecules with n = 4 or n = 5 have nearly straight backbones that stay at least 0.5 to 0.7 nm apart, and melt without decomposing. ==Occurrence== ===Biological origins=== A wide range of organisms synthesize polyynes. These chemicals have various biological activities, including as flavorings and pigments, chemical repellents and toxins, and potential application to biomedical research and pharmaceuticals. In plants, polyynes are found mainly in the euasterids, especially in the sunflower, carrot, ginseng and bellflower families. However, they can also be found in some members of the tomato, olax, and sandalwood families. The earliest polyyne to be isolated was dehydromatricaria ester (DME) in 1826; however, it was not fully characterized until later. The simple fatty acid 8,10-octadecadiynoic acid is isolated from the root bark of the legume Paramacrolobium coeruleum of the family Caesalpiniaceae and has been investigated as a photopolymerizable unit in synthetic phospholipids. ]] 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. The thiarubrines have antibiotic, antiviral, and nematocidal activity, and activity against HIV-1 that is mediated by exposure to light. ]] ]] ]] Polyynes such as falcarindiol can be found in Apiaceae vegetables like carrot, celery, fennel, parsley and parsnip where they show cytotoxic activities. Aliphatic -polyynes of the falcarinol type were described to act as metabolic modulators and are studied as potential health-promoting nutraceuticals. Falcarindiol is the main compound responsible for bitterness in carrots, and is the most active among several polyynes with potential anticancer activity found in Devil's club (Oplopanax horridus). Other polyynes from plants include oenanthotoxin and cicutoxin, which are poisons found in water dropwort (Oenanthe spp.) and water hemlock (Cicuta spp.). ]] Ichthyothere is a genus of plants whose active constituent is a polyyne called ichthyothereol. This compound is highly toxic to fish and mammals. Ichthyothere terminalis leaves have traditionally been used to make poisoned bait by indigenous peoples of the lower Amazon basin. Dihydromatricaria acid is a polyyne produced and secreted by soldier beetles as a chemical defense. ===In space=== The octatetraynyl radicals and hexatriynyl radicals together with their ions are detected in space where hydrogen is rare. Moreover, there have been claims that polyynes have been found in astronomical impact sites on Earth as part of the mineral chaoite, but this interpretation has been contested. See Astrochemistry. ==See also== Cyanopolyyne Enediyne Enyne Isanolic acid Polyene ==Notes== ==References==

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