取代基极性效应的相对标量,早期由Hammett方程所定义的σ值来表示。对取代苯胺和苯酚,取代基的σ值包含有两种极性效应,即共振极性和诱导极性,因此又定义了σ~+和σ~-两个不同含意的σ值,它们表示取代基对反应中心是吸电子还是推电子的共振极性效应。为了从混合极性效应中分离出净极性效应,又出现了σ′和σ~*诱导极性取代基常数。 σ~*值是以甲基为标准的极性效应的实验相对值,是Ⅰ效应的相对标量。关于取代 The relative scalar of the polar effect of a substituent, earlier expressed by the value of σ as defined by the Hammett equation. For the substituted anilines and phenols, the σ value of the substituent contains two polar effects, that is, the resonance polarity and the induced polarity. Therefore, the σ values ​​of σ ~ + and σ ~ - which have different meanings are defined, Base-to-reaction centers are electron-withdrawing or electron-induced polar effects of resonance. In order to separate the effect of net polarity from the mixed polarity effect, there appear σ ’and σ ~ * inducing polar substituent constants. The σ ~ * value is the experimental relative value of the polar effect based on methyl and is the relative scalar of the I effect. About to replace