• Publisher-DOI

The ESR. spectra of the radical anion and cation of 1, 3, 5-tri-t-butylpentalene (II) have been reexamined under higher resolution. With the assistance of the ENDOR. technique, the coupling constants of all protons in II⁻. and II⁺. could be determined. The experimental data agree satisfactorily with the values predicted by the simple MO model which suggests that the π-spin distributions in II⁻. and II⁺. should not strongly differ from those in the corresponding radical ions of parent pentalene (I). As in the case of other non-alternant hydrocarbons, the proton coupling constants for II⁻. are very sensitive to experimental conditions, due to the association of the radical anion with its counterion. Spectra of II⁻. taken at low temperatures (down to 133 and 163 K for ESR. and ENDOR., respectively) have not revealed specific line-broadening which could arise from the bond shift between the two Kekulé-structures of pentalene.