The application of the Hammett equation to ¹³C N.M.R. spectrometry. II. C_β resonances: a test of dual substituent parameter relationships

Abstract

Previous studies (Part I) have shown that the ¹³C resonance positions of the β-carbon of both meta- and para-substituted β-nitrostyrenes are well correlated by means of the Hammett equation if σ+ constants are used for para + R substituents. These data have now been supplemented with measurements made on five additional series: cinnamic acids, cinnamate ions, styrenes, β,β-dimethyl- and β,β-dicyano-styrenes.     The combined information has been analysed by means of three ?dual substituent parameter? versions of the Hammett equation. The results confirm that all three are only approximations, but that the Yukawa- Tsuno and Ehrenson-Brownlee-Taft relationships are significantly better than Swain's F/R treatment.