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In organic chemistry, the tropylium ion is an aromatic species with a formula of ()+. Its name derives from the molecule tropine (itself named for the molecule atropine). Salts of the tropylium cation can be stable, e.g., tropylium tetrafluoroborate. It can be made from cycloheptatriene (tropylidene) and bromine or phosphorus pentachloride.〔''Tropylium tetrafluorate'' Organic Syntheses, Coll. Vol. 5, p.1138 (1973); Vol. 43, p.101 (1963). (link )〕 It is a heptagonal, planar, cyclic ion; as well, it has 6 π-electrons (4n+2, where n=1), which fulfills Hückel's rule of aromaticity. It can coordinate as a ligand to metal atoms. The structure shown is a composite of seven resonance contributors in which each carbon carries part of the positive charge. In 1891 G. Merling obtained a water-soluble salt from a reaction of cycloheptatriene and bromine.〔Merling, G. (1891), ''Ueber Tropin''. Berichte der deutschen chemischen Gesellschaft, 24: 3108–3126. 〕 The structure was elucidated by Eggers Doering and Knox in 1954.〔''The Cycloheptatrienylium (Tropylium) Ion'' W. von Eggers Doering, L. H. Knox, ''J. Am. Chem. Soc.'', 1954, 76 (12), pp 3203–3206 〕 〔''Aromaticity as a Cornerstone of Heterocyclic Chemistry'' Alexandru T. Balaban, Daniela C. Oniciu, Alan R. Katritzky Chem. Rev., 2004, 104 (5), pp 2777–2812 〕 ==Mass spectrometry== The tropylium ion is frequently encountered in mass spectrometry in the form of a signal at m/z = 91 and is used in mass spectrum analysis. This fragment is often found for aromatic compounds containing a benzyl unit. Upon ionization, the benzyl fragment is cleaved off as a cation (PhCH2+), which rearranges to the highly stable tropylium cation (C7H7+). 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「Tropylium cation」の詳細全文を読む スポンサード リンク
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