Radical Ions in the Pentalene Series. Part. I. 1,3,5‐tri‐t‐butylpentalene

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Abstract
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.

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