Electron-transfer induced rearrangements: Radical cations of bridged bicyclobutanes.

The reaction of several bridged bicyclobutanes, 1-7, with photoexcited electron acceptors gives rise to strong spin polarization effects. These results are interpreted in terms of two different types of radical cation intermediates in which spin and charge are localized either in the transannular bicyclobutane bond (A) or in a pi-orbital of the bridging moiety (B). The chemical nature of the bridging unit determines the radical cation structures and influences the rearrangement pathways.