Studies on the Proton Magnetic Resonance Spectra in Aromatic Systems. III. Discussions on the Substituent Shielding Parameter and π-Electron Charge Density

Abstract

The revised substituent shielding parameter has been proposed in ortho and meta ¹H shift for estimating the π-electron charge densities in substituted benzene series, and, also the resonance contribution has been proved to be a dominant factor in determining the meta ¹H shift. The π-electron charge density calculated from simple sum rule of the revised shielding parameter showed passable agreement with those from HMO treatment.