Carbon-13 substituent chemical shifts in N-1-p-substituted phenyl-5-methyl-4-carboxy uracils

The C-13 NMR chemical shifts of seven N-1-p-substituted phenyl-5-methyl-4-carboxy uracils have been measured in deuterated dimethyl sulfoxide (DMSO-d sigma). The correlation analysis for the substituent-induced chemical shifts (SCS) with inductive (sigma(I)), and various resonance (sigma(R)) parameters were carried out through SSP (single substituent parameter), DSP (dual substituent parameter), and DSP-NLR (dual substituent parameter non-linear resonance) methods, as well as through multiple regression analysis. The presented calculation relative to the polar and resonance effects accounts satisfactorily for substituent effects at uracil carbon atoms. Negative rho values were found for several correlations (reverse substituent effect). (C) 2006 Elsevier B.V. All rights reserved.