Proton magnetic resonance of planar condensed benzenoid hydrocarbons

Abstract

Second-order, iterative analyses of the P.M.R. spectra of 15 different unsubstituted, condensed, benzenoid hydrocarbons are reported; all the spectra dealt with have been obtained in a common, isotropic solvent (CCl₄), and the chemical shifts they afforded have, where solubility permitted, been individually extrapolated to infinite dilution. More coupling constant data have been derived to test an earlier empirical equation, and discrepancies for overcrowded protons, observed previously, are confirmed. Dilution effects are discussed and it is concluded that a systematic comparison of experimental and theoretically calculated chemical shifts can be made reliably only when the experimental shifts have all been obtained by iterative, second-order analysis at (or near) infinite dilution, in a common, isotropic solvent.