Are new bonds made and old ones broken synchronously orasynchronously during pericyclic reactions, in the electronicground state? For almost three decades investigations havefocused on nuclear rearrangements, first by conjectures basedon the energetics of barriers (B) or transition states thatseparate reactants (R) from products (P), and then byclassical molecular dynamics simulations.[1–7]Complementaryaspects of the time-independent electronic structures of R, B,and P have also been considered, in the context of theWoodward–Hoffmann rules for the conservation of orbitalsymmetry[8,9]and analyses of transition structures or inter-mediates.[10–13]