对位-二取代氮苄叉苯胺还原电位的取代基效应

Effect of Substituents on Reduction Potential of Para-disubstituted N-Benzylidenebenzenamine Derivatives

合成52种4,4'-二取代氮苄叉苯胺衍生物p-XPh CH=NC6H4Y-p作为模型化合物,系统地研究了取代基效应对其还原电位ERed的影响规律.通过研究表明该类化合物的ERed与桥连键C=N的13C NMR化学位移δC(C=N)没有线性关系,ERed和δC(C=N)两者的影响因素有较大差别,仅用Hammett取代基常数不能很好地表达ERed的变化规律.影响ERed的主要因素有:取代基X的场/诱导效应、取代基X和Y的共轭效应,此外取代基X的激发态取代基参数也有重要影响.上述4个参数与52种化合物的ERed有良好的相关性,相关系数为0.9756,标准偏差为0.052 V.在这4个影响因素中,基团X的场/诱导效应、共轭效应和激发态取代基效应对ERed改变的贡献都比较大,而基团Y的共轭效应对还原电位ERed改变的贡献相对较小,但不能忽略它.

52 samples of 4,4＇-disubstituted N-benzylidenebenzenamine（p-XPh CH=NC6H4Y-p） derivatives were synthesized, the effect of substituents on the reduction potential ERed of these compounds was systematically investigated. The result shows that there is not linear relation between their ERed and the chemical shift δC（C=N） of the 13 C NMR of C=N bridge bond in the molecules. The factors affecting ERed are obvious different from that affecting on δC（C=N）, and the change regularity of ERed can not be expressed well by only employing Hammett substituent constant. The main factors affecting the ERed are the field/inductive effect of substituent X, the conjugative effects of substituents X and Y, and the excited-state substituent constant of substituent X plays an important role of influence on ERed. Above four parameters have good correlations with the ERed of the 52 samples of compounds, the correlation coefficient of the correlation equation is 0.9756, and the standard derivation is 0.052 V. Among the four factors, the contributions of the field/inductive effect, the conjugative effect and the excited-state substituent constant of group X to the changes of ERed are relative large, while the contribution of the conjugative effect of group Y is relative small, and can not be ignored.