Comparison of the 13 C (C = N) chemical shifts of substituted N ‐(phenyl‐ethylene)‐anilines and substituted N ‐(benzylidene)‐anilines

Comparison of 13 C NMR of C = N bond chemical shifts δ C (C = N) in substituted N ‐(phenyl‐ethylene)‐anilines XArC(Me) = NArY (XPEAYs) with that in substituted N ‐(benzylidene)‐anilines XArCH = NArY (XBAYs) was carried out. The δ C (C = N) of 61 samples of XPEAYs were measured, and the substituent effect on their δ C (C = N) were investigated. The results show the factors affecting the δ C (C = N) of XPEAYs are quite different from that of XBAYs. A penta‐parameter correlation equation was obtained for the 61 compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the inductive effects of substituents X and Y are major factors affecting the δ C (C = N), while the conjugative effect of them have very little effect on the δ C (C = N) and can be ignored. The substituent‐specific cross‐interaction effects between X and Y and between Me of C = N bond and substituent Y are important factors affecting the δ C (C = N). Also, the excited‐state substituent parameter of substitute Y has certain contribution to the δ C (C = N). Copyright © 2015 John Wiley & Sons, Ltd.