NOVEL PHOTOCHEMICAL-REACTIONS OF C8H10 RADICAL CATIONS

The radical cation of bicyclo[2.2.2]octa-2,5-diene produced in a gamma-irradiated Freon matrix at 77 K shows a broad charge-resonance absorption band with lambda(max) = 680 nm. In contrast to earlier experiments in argon matrices, it was found that the primary photoreaction of this species is a cleavage to yield the recently described complex cation between benzene and ethylene whose lambda(max) happens to coincide with that of the above precursor cation. This complex cation can in turn be converted eventually to 1,3,5,7-octatetraene radical cation. In the presence of an excess of ethylene, the above complex cation undergoes a photoaddition yielding a C10H14.+ whose spectrum indicates the presence of a linear conjugated triene chromophore. The electronic structure of the different radical cations involved in this study is discussed and a reaction scheme is proposed.