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 (Z_i). These correlations confirm the dual behaviour of the nitrone group and the presence of through-resonance in these nitrones.