Investigation of substituent effects on the 1H and 13C NMR spectra of (Z)‐N‐(arylmethylene)‐arylamine N‐oxides (α,N‐diaryl nitrones)

Substituent effects on the 1H and 13C chemical shifts of 18 differently substituted (Z)‐α,N‐diaryl nitrones [N‐(p‐X‐benzylidene)phenylamine N‐oxides (Series I) and N‐(benzylidene)‐p‐Y‐phenylamine N‐oxides (Series II)] have been obtained. A correlation has been found between the chemical shifts of the azomethine proton (H‐α) and the Hammett σ parameters and the Swain and Lupton F and R parameters. Correlations of the chemical shifts of C‐1 and C‐4′ in Series I, and of C‐α and C‐1′ in Series II, with the same parameters have been investigated. In addition, the chemical shifts of the aromatic protons and carbons of the p‐disubstituted (m‐disubstituted in one case) benzene rings correlated with the appropriate substituent increments (Zi). These correlations confirm the dual behaviour of the nitrone group and the presence of through‐resonance in these nitrones.