The Radical Ions of Benzo[b]biphenylene, a Test for HMO Models of Biphenylene and its Derivatives

Abstract ESR.‐spectra are reported for the radical anion and the radical cation of benzo[b]‐biphenylene (III). Comparison of the proton coupling constants (aHμ) for III · ⊖ and III · ⊕ with π‐spin populations (ϱμ), calculated by the McLachlan procedure, permits a lower limit of 0.77 to be set for the parameter κ = β′/β where β′ represents a reduced value of the HMO integral for the two essentially single bonds linking the benzene with the naphthalene π‐system. The differences in the aHμ values for III · ⊖ and III · ⊕ are substantially larger than those generally found for the two corresponding radical ions of alternant, purely benzenoid hydrocarbons, but they closely parallel the analogous differences observed for the radical anion and the radical cation of biphenylene.