Valence isomerization of hexamethyl(dewar benzene) radical cation. Pulse radiolytic investigation

Organic radical ions are important intermediates in a wide variety of electron-transfer reactions. Both the steady-state and time-resolved techniques have been extensively applied to probe various aspects of their chemistry. We have recently established that low-temperature pulse radiolysis can be successfully applied to the kinetic study of radical ion transformations with very low activation barriers. The target of the present investigation is the hexamethyl(Dewar benzene) (HMDB)-hexamethylbenzene (HMDB) system. Studies by the CIDNP technique indicated the presence of two distinguishable radical cations in the system HMDB-HMB. This view has not been supported by a nanosecond spectroscopic observation which failed to reveal any evidence for a radical cation other than HMBsm-bullet+. The aim of this work is to present spectroscopic evidence for two different radical cations HMDBsm-bullet+-HMBsm-bullet+ and the activation barrier for their interconversion