The EPR spectrum of the dibenzo[b,h]biphenylene radical anion and cation: the pairing principle and the Mills–Nixon effect

Abstract

The EPR/ENDOR spectra of the radical ions of dibenzo[b,h]biphenylene provide an exception to the rule (the pairing principle) that these spectra should be similar in the radical cation and anion of planar alternant hydrocarbons. It is suggested that this breakdown of the pairing principle can be understood in terms of the Finnegan–Streitwieser model of the Mills–Nixon effect, which, by inducing charge separation and changes in bond lengths, can exchange the ordering of the energy levels of adjacent orbitals.