Linear free energy relationships of the H-1 and C-13 NMR chemical shifts in 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)pyridones

Abstract

Linear free energy relationships (LFER) were applied to the H-1 and C-13 NMR chemical shifts in 3-cyano-4(substituted phenyl)-6-phenyl-2(1H)pyridones. The correlation analysis for the substituent-induced chemical shifts (SCS) with inductive (sigma(1)), and various resonance (sigma(R)) parameters were carried out using SSP (single substituent parameter), DSP (dual substituent parameter), and DSP-NLR (dual substituent parameter non-linear resonance) methods, as well as by multiple regression analysis. The presented calculation accounts satisfactorily for the polar and resonance substituent effects operating at pyridone carbon atoms. Negative rho values were found for several correlations (reverse substituent effect). The conformations of investigated compounds have been studied by the use of semi-empirical MO-PM6 method and B3LYP density functional (DFT) hybrid methods. The twist of the plane of 4-substituted phenyl ring (theta(1)) is determined by electronic substituent effects, while the angles theta(2) are almost constant.