The 2,3-dimethylenetetramethylene biradical

Abstract

The 2,3-dimethylenetetramethylene biradical has a variety of interesting collapse products. We report extended Hückel and Pariser–Parr–Pople calculations of the electronic structure of this molecule as a function of twist around its central bond. Though our calculations point to a twisted triplet ground state they are not definitive. In any conformation the allyl moieties couple only weakly and the lowest singlet state is then a nearly equal mixture of two configurations. An orbital symmetry analysis of the interconversions of the biradical and its collapse products predicts the stereochemical consequences of concertedness in these transformations.