在共轭体系中,取代基的电性效应通常指诱导效应和共轭效应的总和,取代基常数包括诱导效应指数(I)和共轭效应指数(C)两部分。本世纪三十年代,出现了著名的Hammett方程和Hammett常数(σ)。蒋明谦等利用元素电负性和原子的共价半径两种基本常数,又提出了一种计算取代基的诱导效应指数(I)和共轭效应指数(C)的经验公式,并根据计算出来的诱导效应指数和共轭效应指数,定义了一种取代基常数——代基当量(S)。代基当量可用来解释某些有机分子的物理性质、化学 In a conjugated system, the electrical effect of a substituent usually refers to the sum of an inductive effect and a conjugate effect. The substituent constants include the induction effect index (I) and the conjugate effect index (C). In the thirties of this century, the famous Hammett equation and Hammett’s constant (σ) appeared. Jiang Mingqian and other elements of the use of the elemental electronegativity and the atomic covalent radius of two basic constants, but also put forward a calculation of substituent induced effect index (I) and the conjugate effect index (C) empirical formula, and calculated Induction effect index and conjugate effect index, defines a substituent constant - generation equivalent (S). Substituent equivalents can be used to explain the physical properties of certain organic molecules, chemistry