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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Yukawa–Tsuno equation ： ウィキペディア英語版 Yukawa–Tsuno equation The Yukawa-Tsuno Equation, first developed in 1959,〔Yukawa Y, Tsuno Y. "Resonance Effect in Hammett Relationship. II. Sigma Constants in Electrophilic Reactions and their Intercorrelation." ''Bull. Chem. Soc. Jap.'' 32 965-71 (1959)〕 is a linear free-energy relationship in physical organic chemistry. It is a modified version of the Hammett equation that accounts for enhanced resonance effects in electrophilic reactions of para- and meta-substituted organic compounds. This equation does so by introducing a new term to the original Hammett relation that provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive or negative) in its transition state. The Yukawa-Tsuno Equation can take the following forms: ::::::::$\backslash log\; \backslash frac\; =\; \backslash rho(\backslash sigma\; +\; r(\backslash sigma^+\; -\; \backslash sigma))$ ::::::::$\backslash log\; \backslash frac\; =\; \backslash rho(\backslash sigma\; +\; r(\backslash sigma^-\; -\; \backslash sigma))$ where and represent the rate constants for an X-substituted and unsubstituted compound, respectively; represents the Hammett reaction constant; represents the Hammett substituent constant; and represent the Hammett substituent constants for reactions in which positive or negative charges are built up at the reactive center, respectively; and represents the Yukawa-Tsuno parameter. ==Background== The Hammett substituent constant, , is composed of two independent terms: an inductive effect and a resonance polar effect . These components represent the consequences of the presence of a particular substituent on reactivity through sigma and pi bonds, respectively. For a particular substituent, the value of is generally assumed to be a constant, irrespective of the nature of the reaction; however, it has been shown that for reactions of para-substituted compounds in which the transition state bears a nearly full charge, does not remain constant, and thus, the sum $\backslash sigma\; =\; \backslash sigma\_R+\backslash sigma\_I$ is also variable. In other words, for such reactions, application of the standard Hammett Equation ''does not'' produce a linear plot. To correlate these deviations from linearity, Yasuhide Yukawa and Yuho Tsuno proposed a modification to the original Hammett Equation which accounts exclusively for enhanced resonance effects due to the high electron demand during such reactions. 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「Yukawa–Tsuno equation」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.