Proton Hyperfine Splittings in the Electron Spin Resonance Spectra of Hydrocarbon Ions: A Comparison of the Colpa-Bolton and Giacometti–Nordio–Pavan Relations

Abstract

The Giacometti–Nordio–Pavan modification of McConnell's relation between proton hyperfine splittings and spin densities has been shown to reduce to a simpler form than that originally proposed. It has been demonstrated further that the Giacometti–Nordio–Pavan modification should not be regarded as arising from a nearest-neighbor effect. A statistical analysis of the available experimental proton hyperfine splittings from even-alternant hydrocarbon ions indicates, however, that the Colpa–Bolton relation is superior to the Giacometti–Nordio–Pavan relation in explaining the differences between proton splittings in corresponding cation and anionx radicals. These results are valid within the framework of Hückel molecular-orbital theory.