A Comparative 1H‐ and 13C‐NMR Study of the Dianion and Dication of Biphenylene

Biphenylene dianion has been prepared by Li reduction of the parent hydrocarbon. It is stable below −30° and was characterized by its 1H‐ and 13C‐NMR spectra. A comparison of these data with those of the dication indicates the existence of ion pairs in the dianion case which are responsible for a different charge distribution. The diamagnetic ring currents of both ions, however, are of comparable magnitude, and both are more diatropic than the parent hydrocarbon. Predictions of the π‐charge‐density effect on 1H chemical shifts are improved by calculations that use the linear and quadratic electric‐field effect equation instead of the simple Spiesecke‐Schneider relation.