胺类的直线自由能关系的研究——Ⅰ.芳香胺类中新型σ^-值的求取

A STUDY ON THE LINEAR FREE ENERGY RELATIONSHIPS FOR AMINES Ⅰ. A RELATIVELY COMPLETE SET OF NEW σ^- VALUES FOR ANILINES

本文用苯胺和苯酚的离解常数重新检查了Hammett方程式的有效性.发现了八十个选择的苯胺、七十个苯酚和廿一个N,N-二甲苯胺的pK_a值与取代基常数的直线相互关系能达到满意至优良标准(见表4).提出了以σ_((ArNH_3)^+)^-作为另一有推电子(而非拉电子)共轭效应的官能团的标准反应系的参数,并与少数σ_(I.R.)^-合用以衡量芳香亲核取代反应中的直线自由能关系.计算了一套较为完整的σ^-值,其中七十八个为初级值、五十四个为次级和三级值、八个σ_(I.R.)^-、十一个σ(ArHX^-)^-、七十三个初级σ_R^-和二十三个次级和三级σ_R^-.但带正式电荷的取代基常数必须有保留地接受.这一套σ^-值已证明与其他σ值有优良或至少是满意的相互关系.这套客观的取代基常数用之于芳香亲核取代反应不比Miller从该反应系中求出的数值差.

ABSTRACT The validity of the Hammett equation was reexamined in this paper with dissociation constants of anilines as well as phenols.It has been found that for eighty selected pKa values of anilines,seventy of phenols,and twenty one of N,N-dimethyl anilines could be correlated linearly with the substituent constants with satisfactory or excellent results.The ? scale was proposed as a parameter for another type of standard reaction series in which the functional group is capable of donating electrons conjugatively instead of withdrawing electrons,as is the case with ? in the dissociation of benzoic acids or with ? in aromatic electropbilic substitution.This parameter in combination with a few σ_(I.R.)^- values can likewise be used for measuring the linear free energy relationships in aromatic nucleophilic substitution reactions.A set of relatively complete σ^- values,of which seventy-eight are primary ?,fifty-four secondary and tertiary ?,eight ? eleven ?,seventy-three primary ? and twenty-three secondary and tertiary ?,are presented.However,values of those sub-stituents with formal charges must be accepted with some reservation.This set of σ-values has been shown to have excellent or at least satisfactory correlations with other sets of closely related σ values.This set of objective substituent constants can also be applied to aromatic nucleophilic substitution not any less adequately than that derived by J.Miller right from this very type of reactions.