THE EPR-SPECTRUM OF THE DIBENZO[B,H]BIPHENYLENE RADICAL-ANION AND CATION - THE PAIRING PRINCIPLE AND THE MILLS-NIXON EFFECT

The EPR/ENDOR spectra of the radical ions of dibenzo [b,h] biphenylene provide an exception to the rule (the pairing principle) that these s pectra should be similar in the radical cation and anion of planar alt ernant hydrocarbons. It is suggested that this breakdown of the pairin g principle can be understood in terms of the Finnegan-Streitwieser mo del of the Mills-Nixon effect, which, by inducing charge separation an d changes in bond lengths, can exchange the ordering of the energy lev els of adjacent orbitals.