Substituent effect study on δc values of the bridge group carbons in disubstituted cinnamyl aniline series

The 13C nuclear magnetic resonance (NMR) chemical shifts δc of bridge group carbons (C‐β, C‐α, and C═N) were measured in this work for a wide set of substituted cinnamyl anilines p‐XC6H4CH═CHCH═NC6H4Y‐p (X = NO2, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, CO2Et, Cl, F, H, Me, MeO, or NMe2) and were used to study the substituent effect. In the study on 13C NMR chemical shifts of the titled compounds with single substituent changed, for every bridge carbon δc, the effect of cinnamyl substituent X is opposite to that of aniline substituent Y. That is, the action of the same substituent on different aromatic rings is different from the 13C NMR chemical shifts, and for C‐β, C‐α, and C═N, the choice of correlation equation depends on the ratio ρF(Y)/ρR(Y). When the ratio ρF(Y)/ρR(Y) is close to 1, the chemical shifts of bridge carbons can be well correlated with the single‐parameter equation; otherwise, it is better to adopt the dual‐parameter equation for correlation, and the further the values of ρF(Y)/ρR(Y) stray from 1, the more suitable the corresponding δc values are to be correlated with the dual‐parameter equation. In the study on δc of model compounds with simultaneous variations of substituents X and Y, for δc(C═N), a multi‐parameter correlation equation is obtained, and the substituent cross‐interaction item Δσ2 is suitable to scale the interaction between substituents; however, for δc(C‐α and C‐β), the substituent cross‐interaction item Δσ2 is perhaps too small to be observed. The multi‐parameter correlation equations can be recommended to predict well the corresponding δc values of disubstituted cinnamyl anilines. Copyright © 2012 John Wiley & Sons, Ltd. In the study on δc values of the bridge group carbons in disubstituted cinnamyl aniline series(XPhCH=CHCH=NPhY), with a single substituent changed, the ratio ρF(Y)/ρR(Y) decided the choice of correlation equations, and the effect of cinnamyl substituent X is opposite to that of aniline substituent Y; With simultaneous variations of substituents X and Y, the δc values of all bridge carbons were correlated by multi‐parameter correlation equations with parameters σF and σR.