Nitrogen-14 nuclear magnetic resonance. Part IV. Aromatic nitrocompounds

Abstract

The chemical shift of the nitro-group in the ¹⁴N n.m.r. spectra of substituted nitrobenzenes is almost identical for ortho-, para-, and meta-isomers, thus showing that π-electron conjugation has no effect. Substituents in the phenyl ring affect the shift only if they exert a strong inductive effect. Electron-withdrawing substituents, such as formyl and nitro-groups, move the ¹⁴N signal of the nitro-group to higher field, whereas the methyl, hydroxy- and methoxy-groups do not give observable changes. No spectral shifts due to hydrogen bonding are observed for nitrophenols but there is a slight effect due to steric hindrance in ortho-substituted nitrobenzenes.