An H-1 and C-13 NMR study of the benzo[3,4]cyclobuta[1,2]cycloheptenyl cation and anion has been undertaken in order to unravel the electronic structure of these species. The formal addition of two electrons to the cation can be seen as a conversion of a slightly diatropic and aromatic cation into an unstable, highly diatropic but antiaromatic anion. Self-consistent iterative Huckel, MNDO, and AM1 as well as graph-theoretical ring current calculations were carried out in order to clarify this confusion. Comparisons to the isoelectronic biphenylene and biphenylene dianion are especially revealing.
Lombardo,L.; Wege,D., Australian Journal of Chemistry, 1978, vol. 31, p. 1569 - 1584