Viscosity-controlled,product-selective rearrangement of the cyclopentane-1,3-diyl radical cation derived from an annelated housane by electron transfer: a case of Curtin-Hammett behavior

The fractional-power viscosity dependence of the product ratio 2]/3] approximately eta(alpha(3)-alpha(2)) manifests the different free-volume requirements for the methylene (k(3) approximately eta(alpha)(3)) versus methyl (k(2) approximately eta(alpha)(2)) migrations. The syn/anti-conformational changes (k(1), k(-1)) in the radical cation 1(*+) proceed faster than the structural transformations (k(2), k(3)), which constitutes the first Curtin-Hammett case in radical-cation rearrangements.