【摘要】 本文中提出由元素的电负性及原子共价半径两种基本常数以系统计算非共轭体系中基团诱导效应的方法,所得出的诱导效应指数与非共轭化合物在各种反应中的能量变化,平衡常数对数与速度常数对数均形成直筱关系。反应中化学变化的百分率,如产率及转化率等,则与诱导效应指数形成S形曲线。在计算方法中,共价键A—B的极性,以两成键原子的电负性分数,xA/xA+xB,及xB/xA+xB之差δ（键极性指数）表示。一键对于邻近各键上的诱导效应,以这键上的极性强度δ/r,为计算基数,其中r为键的长度。在一非共轭体系中,作用于A—B键的诱导效应,以直接或间接联结于A—B的各键的极性强度,依照远近次序相加的总和i表示: 或简写为其中1,2,3,4……代表各键联结于A—B上的次序,a是代表诱导效应传递时递减率的常数。与A—A键比较,由B原子及其所带基团对于A—B键上所产生的极性效应,以包括B原子在内的全部基团对A—B的诱导效应指数I表示: 如果分子中B,C,…等原子带有形电荷N₁,N₂…等,则除计算i值时应采用由于电荷而校正的原子电负性及共价半径外,还应加由电荷所引起的诱导效应i₊或i_-: 其中r′是带电荷的原子的共价半径;因此总的诱导效应指数是 I=i₀+i+i_±由这样计算出的诱导效应指数,可以正确推出英国学派的全部耢导效应序列及Kharasch等的脂肪基团的相对电负性序列。这指数与Taft的取代基极性常数σ^*基本上完全平行,与由其他方法算出的氢化物中氢的部分电荷也基本上平行。它与脂肪族卤化物及腈类等的电偶极矩形成良好的直线关系。这些事实都说明诱导效应指数能够定量代表有关的诱导效应。非共轭化合物中化学活性与诱导效应之间的关系,可以下式表示: E=AI+B logK=aI+b或log（K/K₀）=aI logk=a′I+b′或log（k/k₀）=a′I 其中E为反应中的能量变化及与键能有直接关系的能量性质,K为反应平衡常数,k为反应速度常数;A,B,a,b,a′,b′均为常数,其值由反应类型及反应条件决定。在很多情况下,用为基准的氢原子也包括在这种关系之内。文中列举各种类型的有机及无机化合物的几百种E,K及k以表明上述几种直线关系的普遍存在。文中讨论诱导效应指数的适用范围,指出在基团立体障碍很大与立体效应不相同的情况下,及共轭效应起主导作用,而又不恒定的情况下,诱导效应指数与化学活性之间并无上述的几种直线关系。最后文中讨论诱导效应指数的用途。一是建立一种统一的定量的诱导效应序列,二是直接表达分子结构与化学活性间的定量关系,三是验证化合物的分子结构式,四是区别分子中不同位置上同种基团的活性,五是推断某些反应的机构,并各以例说明。更多还原

【Abstract】 In this paper, a method for the systematic and quantitative evaluation of the inductive effect exerted over a certain chemical bond in the molecule by a group, from the electronegativities and the atomic radii of its constituent elements, has been presented. The constant for the inductive effect of the group thus obtained is designated as the inductive effect index of the group. It has been found that for a given reaction, the energy changes, the logarithms of the equilibrium constants, and the logarithms of the rate constants can be expressed, respectively, as linear functions of the corresponding inductive effect index involved in the reaction, and that the percentages of chemical changes in the reaction, such as percent yield and conversion, give "sigmoid" curves when plotted versus the latter. These linear functions and sigmoid curves constitute a general quantitative relationship between molecular structure and chemical reactivity.In the calculation of the inductive effect index, the polarity of a covalent bond A-B is expressed as the difference, δ, of the electronegativity fractions x_A/（x_A+x_B） and x_B/（x_A+x_B）. The inductive influence exerted by a certain bond over its neighbouring bonds is expressed in terms of δ/r, where δ is the polarity index of the given bond and γ its bond length. For a non-conjugated system the inductive effect exerted upon bond A-B by all the bonds connected directly and indirectly with A-B is expressed as a summation of （δ/r） as follows: i=1/αΣ(δ_CB/r_CB)+1/α²Σ(δ_ED/r_ED)+… or i=1/αΣ（δ/r）₁+1/α²Σ（δ/r）₂+1/α³Σ（δ/r）₃+…. where 1, 2, 3, 4, ... represent the order of connection of various bonds with A-B, and α is a constant which represents the rate of the reduction of the inductive effect upon propagation along the structural chain. With the bond A-A as a reference standard, the total polar effect brought about by the atom B and all the bonds directly and indirectly connected with it, is expressed by the inductive effect index Ⅰ: I=（δ/r）₀+1/αΣ（δ/r）₁+1/α²Σ（δ/r）₂+…=i₀+i In case the molecule contains formal charges N₁, N₂, N₃, …, on atoms B, C, D respectively, then i₀ and i should be calculated with the corrected electronegativities and atomic radii, and an additional term i₊ or/and i_- should be included in Ⅰ: i_±=1/α（（±N）/r′）₁+1/α²Σ（（±N）/r′）)₂+… where r′ is the atomic radii for the charged atoms. Thus, the total inductive effect index is given by the following equation: I=i₀+i+i_± By means of the inductive effect index, all the series of inductive effects for groups formulated by the English school and the series of relative electronegativities for groups such as those by Kharasch and by Brewster, can be readily deduced from chemical struc ture. The inductive effect index is parallel in magnitude with Taft’s polar substituent constant σ^* for most groups whose σ^* values are known. It is also parallel in magnitude with the partial charges on hydrogen atoms in various inorganic and organic compounds as calculated by different authors. When the inductive effect index is plotted versus the dipole moments of aliphatic halides and nitriles, good linear relationships are obtained. These facts lead to the conclusion that the inductive effect index is a quantitative measure for the inductive effect.For nonconjugated systems, the relationships between chemical reactivities and inductive effect index may be expressed by the following equations:E=AI+B, logK=aI+b, or log（K/K₀）=aI, logk=a’I+b’, or log （k/k₀）=a’I, where E is the energy changes and related properties in a reaction, K is the equilibrium constant and k the rate constant for any member of a series of compounds, and K₀ and k₀ are the same quantities for the compound taken as the reference standard. A, B, a, b, a’ and b’ are all constants whose values are determined by the nature of the reaction and the conditions under which the reaction takes place.In this paper hundreds of series of E, K, and k values for various types of organic and inorganic compounds and radicals have been quoted from the literature to demonstrate the generality of the aforesaid linear functions.The range of the application of inductive effect index has been discussed. It has been pointed out that in case steric effect or conjugative effect predominates or when either of them differs too much in magnitude for a series of compounds, the relationship between chemical reactivity and inductive effect index remains no longer linear.Finally, the usefulness of the inductive effect index has been briefly discussed. Its principal uses are: （1） to establish a general and quantitative series of the inductive effect for groups; （2） to formulate some quantitative expressions for the chemical reactivities based directly on the structure of the molecules; （3） to provide a method for confirmation of the structural formulas for certain compounds; （4） to afford a means for distinguishing the relative reactivities of the same groups but attached to different positions in a molecule; and （5） to give a method for ascertaining the mechanism of certain reactions. Examples have been given for each case.更多还原