SOMO , definition

We are, of course, aware of the strict Hiickel definition linking aromaticity to the presence of 4n + 2 rc-electrons, On the other hand, we note that the radical cations discussed below have SOMOs, which have one electron less than the Hiickel requirement and which show cyclic homoconjugation, even though the parent molecules assume alternative structures. In view of the precedence established for the radical anion (156) of bicyclo[6.1.0]nonatriene [416,417], in order to emphasize the dramatic difference between the structures of these radical cations and their precursors, and for reasons of convenience, we will refer to these species as homo- or bis-homoaromatic. The paradigm of these remarkable species is found in the barbaralane system. 

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