L. Blancafort et al., Theoretical study of the 1,2 rearrangement of housane radical cations: Keyrole of a transient cyclopentane-1,3-diyl intermediate, J AM CHEM S, 121(45), 1999, pp. 10583-10590
CASSCF computations suggest that the ground-state potential energy surface
of housane radical cations is centered around a conical intersection (and i
ts surrounding Jahn-Teller-type surface) at a planar, symmetric cyclopentan
e-1,3-diyl geometry, In our reactivity model, this region is connected to t
he reactants via a bridge-bending coordinate and to the products via a shif
t coordinate. The preference for the spin-localized planar intermediate is
caused by the preferential energy stabilization along a charge localization
coordinate (the derivative-coupling coordinate at the conical intersection
). Mechanistically, our computations show that the reaction proceeds in two
steps: the breakage of the one-electron bond of the reactants, which produ
ces the asymmetric, quasi-planar intermediate and is the rate-determining s
tep, and the subsequent 1,2 rearrangement, which is essentially barrierless
. The reaction results in the selective 1,2 migration of the original endo
substituent of the reactant.