EVALUATION OF THE POLAR INDUCTIVE AND MESOMERIC EFFECTS EXERTED ON CONTIGUOUS FUNCTIONALITIES BY N-OXIDOPYRIDINIUM GROUPS

The polar-inductive and mesomeric effects (and mixtures thereof) of N-oxidopyridinium-2-, -3-, and 4-yl functionalities have been evaluated in terms of the ?IB, ?R-, and ?[C with combining macron] scales previously defined. Values were generated from the phenyl para-13C shifts of PhCH2C5H4NO and PhNHC5H4NO, respectively. The parameters obtained successfully account for the phenyl para-13C shifts of the sodium salts of anilinopyridine 1-oxides (VII), prepared in turn by deprotonation of the corresponding precursor nitrogen acids by sodium methylsulphinylmethanide. Results show that the N-oxidopyridinium ring exerts considerably more electron-withdrawing power, by both polar-inductive and mesomeric mechanisms, than in the absence of the N-oxide function.