Effect of substituents on the C-13 NMR chemical shifts of para-substituted alpha-phenyl-beta-pyridylacrylic acids

The C-13 NMR spectra of para-substituted alpha-phenylcinnamic and 3- and 4-pyridylacrylic acids, with a wide range of substituents effects, were determined in deuterated dimethylsulfoxide (DMSO-d(6)). The effect of substituents in both the alpha-phenyl and beta-pyridine groups in these acids is investigated using linear free energy relationships and multiple regression analysis as applied to C-13 NMR chemical shifts of the C-alpha and C-beta of the ethylenic bond and the carboxylic group carbon. Dissection of the alpha-phenyl substituent effects into the inductive and resonance components, using the dual substituent parameter (DSP) method, points to a blend of inductive and resonance effects in the pi-electronic system. (C) 1997 Elsevier Science B.V.