¹³C NMR study of the substituent effects in <i>ortho</i>‐substituted nitrobenzenes

Abstract

Abstract 13 C NMR chemical shifts of 22 ortho ‐substituted nitrobenzenes are reported. Except for those on C‐3 and C‐5, the effects of the interacting nitro group and the substituent are non‐additive. The chemical shifts of the ipso , ortho and para carbons in the spectra and those of monosubstituted benzenes are linearly dependent. Multiparameter correlation analysis shows a predominant field/inductive effect on the ipso compared with both the ortho and para carbon chemical shifts. It shows that the Reynolds non‐electronic factors evaluate the substituent chemical shifts of the ipso and ortho positions much better than the Charton steric parameters. Moreover, both in ortho ‐ and para ‐substituted nitrobenzenes the substituent exerts almost the same shift on the ipso carbon atom. This suggests that the studied compounds, except those carrying very bulky groups, show a high tendency to be planar.