Chaotun Cao

Comparison of the substituent effects on the 13C NMR with the 1H NMR chemical shifts of CHN in substituted benzylideneanilines

Fifty‐two samples of substituted benzylideneanilines XPhCHNPhYs (XBAYs) were synthesized, and their NMR spectra were determined in this paper. Together with the NMR data of other 77 samples of XBAYs quoted from literatures, the 1H NMR chemical shifts (δH(CHN)) and 13C NMR chemical shifts (δC(CHN)) of the CHN bridging group were investigated for total of 129 samples of XBAYs. The result shows that the δH(CHN) and δC(CHN) have no distinctive linear relationship, which is contrary to the theoretical thought that declared the δH(CHN) values would increase as the δC(CHN) values increase. With the in‐depth analysis, we found that the effects of σF and σR of X/Y group on the δH(CHN) and the δC(CHN) are opposite; the effects of the substituent specific cross‐interaction effect between X and Y (Δσ2) on the δH(CHN) and the δC(CHN) are different; the contributions of parameters in the regression equations of the δH(CHN) and the δC(CHN) [Eqns and 7), respectively] also have an obvious difference. Copyright