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

The 13C NMR chemical shifts of seven N-1-p-substituted phenyl-5-methyl-4-carboxy uracils have been measured in deuterated dimethyl sulfoxide (DMSO-d6). The correlation analysis for the substituent-induced chemical shifts (SCS) with inductive (σI), and various resonance (σR) 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 ρ values were found for several correlations (reverse substituent effect).