The radical cation of 1,4-dihydropentalene and its photochemical formation from bicyclo [3.3.0] octa-2,6-diene-4,8-diyl cation

Abstract In contrast to recent claims by Rhodes and Glidewell, comparison of both ESR and electronic absorption spectra shows that the photoproduct of the recently characterized radical cation of bicyclo [3.3.0] octa-2,6-diene-4,8-diyl is identical to the 1,4-dihydropentalene radical cation, i.e. a linear conjugated tautomer of the former produced by two hydrogen shifts. Ab initio calculation indicate that the tetracyclic diyl radical cation postulated by Rhodes and Glidewell is inaccessible under their experimental conditions ( h ν ⩽ 2.2 eV).