A retrospective appraisal of the Pople point-dipole model of ‘‘ring-current’’ effects on 1H-NMR chemical shifts in planar, condensed, benzenoid hydrocarbons

A set of well-established, 1H-NMR chemical shift data for 66 nonhindered protons in 16 different condensed, benzenoid hydrocarbons is systematically compared with predictions of (a) the Pople point-dipole ’’ring-current’’ model and (b) nine other distinct ring-current approaches, of varying degrees of sophistication. Provided that it is based on relative ring-current intensities calculated via McWeeny’s (or Pople’s) quantum-mechanical formalism, the point-dipole model gives rise to an empirical correlation with experimental 1H-NMR chemical shifts in a wide range of condensed, benzenoid hydrocarbons which is as good as that obtained when predictions of other, ostensibly more refined, ring-current theories — as well as calculations effected by application of Blustin’s very recent ’’π-bond’’ model — are regressed against the same experimental data.