Investigation of Substituent Effects on Proton and Carbon-13 Chemical Shifts of 4-Substituted Trans-Stilbenes

Proton and carbon-13 chemical shifts of para-substituted stilbenes have been measured. ¹H-¹H, ¹H-¹³C COSY spectra were obtained to analyze unambiguously the chemical shifts of protons and carbons. A long range coupling between 2-H and α-H was observed in a ¹H-¹H COSY spectrum. The observed chemical shifts have been correlated with Hammett substituent parameters. Among ethenyl protons and carbons, all but the chemical shifts of α-H show good correlation with both dual substituent parameters and single substituent parameters. In addition to this finding, the excellent linear correlations of C-l, and 4′-H of 4-substituted trans-stilbenes are also reported. Besides the correlations of chemical shifts with Hammett parameters, a good correlation between the chemical shifts and the calculated charges of position C-4′ are reported.