The effect of spacers on the antiaromaticity of bisfluorenyl dications was examined. For systems such as 4a-c in which extensive delocalization of the positive charge through the pi-system is not possible, a relationship based primarily on localized hyperconjugation as well as the distance between the fluorenyl systems and their antiaromaticity was demonstrated. Dications 2a-c and 3a-c also show the relationship, but it is further modulated by delocalization through the pi-system. Calculated assessment of antiaromaticity was supported by experimental shifts for 2a,b and 3a-c.
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