Nucleophilic substitution of the nitro group in 4-nitro-3-pyridinecarboxanilide 1-oxide (IIa) afforded 4-hydroxy- (IIb), 4-chloro- (IIc), 4-methoxy- (IId), 4-ethoxy- (IIe), and 4-dimethylamino-3-pyridinecarboxanilide (IIf). The 1H and 13C NMR chemical shifts of the pyridine moiety were correlated with the Hammett constants of the substituent in position 4, with the exception of compound IIb. The reason of this phenomenon is discussed.