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

Abstract 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.