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Linear acetylenic carbon, also called carbyne, is an allotrope of carbon that has the chemical structure (−C≡C−)''n'' as a repeating chain, with alternating single and triple bonds.〔 R.B. Heimann, S.E. Evsyukov, L. Kavan, eds. (1999), ''Carbyne and carbynoid structures'' (book), page 452. Volume 21 in the series ''Physics and Chemistry of Materials with Low-Dimensional Structures'' ISBN 0-7923-5323-4〕〔 〕 It would thus be the ultimate member of the polyyne family. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is – forty times that of diamond, the hardest known material.〔 〕 It has also been identified in interstellar space, however, its existence in condensed phases has been contested recently, as such chains would crosslink exothermically (and perhaps explosively) if they approached each other.〔 ==History and controversy== The first claims of detection of this allotrope were made by V. I. Kasatochkin and others in 1967〔〔 As cited by Kroto(2010).〕 and repeated in 1978.〔 As cited by Kroto(2010). 〕 However, in 1982 P. P. K. Smith and P. R. Buseck re-examined samples from several previous reports and showed that the signals attributed to carbyne were in fact due to silicate impurities in the samples.〔 As cited by Kroto(2010). 〕 In 1984, a group at Exxon reported the detection of clusters with even numbers of carbons, between 30 and 180, in carbon evaporation experiments, and attributed them to polyyne carbon.〔 As cited by Kroto(2010). 〕 However, these clusters later were identified as fullerenes.〔 In 1991, carbyne was allegedly detected among various other allotropes of carbon in samples of amorphous carbon black vaporized and quenched by shock waves produced by shaped explosive charges. In 1995, the preparation of carbyne chains with over 300 carbons was reported. They were claimed to be reasonably stable, even against moisture and oxygen, as long as the terminal alkynes on the chain are capped with inert groups (such as tert-butyl or trifluoromethyl) rather than hydrogen atoms. The study claimed that the data specifically indicated a carbyne-like structures rather than fullerene-like ones.〔 〕 However, according to H. Kroto, the properties and synthetic methods used in those studies are consistent with generation of fullerenes.〔 H. Kroto (2010), (''Carbyne and other myths about carbon'' ). RSC Chemistry World, November 2010. 〕 Another 1995 report claimed detection of carbyne chains of indeterminate length in a layer of carbonized material, about 180 nm thick, resulting from the reaction of solid polytetrafluoroethylene (PTFE, Teflon) immersed in alkali metal amalgam at ambient temperature (with no hydrogen-bearing species present). The assumed reaction was : (−−−)''n'' + 4 M → (−C≡C−)''n'' + 4 MF, where M is either lithium, sodium, or potassium. The authors conjectured that nanocrystals of the metal fluoride between the chains prevented their polymerization. In 1999, F. Cataldo observed that copper(I) acetylide (()2) after partial oxidation by exposure to air or copper(II) ions releases polyynes H(−C≡C−)''n''H, with ''n'' from 2 to 6, when decomposed by hydrochloric acid, and leaves a "carbonaceous" residue with the spectral signature of (−C≡C−)''n'' chains. He conjectured that the oxidation causes polymerization of the acetylide anions into carbyne-type anions C(≡C−C≡)''n''C2− or cumulene-type anions C(=C=C=)''m''C4−. Also, thermal decomposition of copper acetylide in vacuum yielded a fluffy deposit of fine carbon powder on the walls of the flask, which, on the basis of spectral data, was claimed to be carbyne rather than graphite.〔 Finally, the oxidation of copper acetylide in ammoniacal solution (Glaser's reaction) produces a carbonaceous residue that was claimed to consist of "polyacetylide" anions capped with residual copper(I) ions, : −C(≡C−C≡)''n''C− . On the basis of the residual amount of copper, the mean number of units ''n'' was estimated to be around 230. In 2004, an analysis of a synthesized linear carbon allotrope found it to have a cumulene electronic structure—sequential double bonds along an ''sp''-hybridized carbon chain—rather than the alternating triple–single pattern of linear carbyne.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「linear acetylenic carbon」の詳細全文を読む スポンサード リンク
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