σ-Bishomoconjugation (σ-Bishomoaromaticity) in 4C/3(2)e Cations-Scope and Limitations.

For the seco-dodecahedradiene 1, in which the distance dππ between the carbon atoms of the two double bonds ranges from 2.90 to 3.20 Å and pyramidalization angles Φ range from 14.9 to 35.5°, the geometrical prerequisites for in-plane (σ)-homoconjugative (σ-bishomoaromatic) electron delocalization in 4C/3(2)e cations could be better defined. Whilst the 4C/3e radical cation is persistent in a matrix, the 4C/2e dication in superacid medium is, at best, an intermediate en route to the stable bisallylic dication.