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The full geometry optimization of the A and B forms of bianthrone and their eight corresponding ions has been performed. From the resulting molecular structure parameters, some structure-bonding relationships are established. The calculated electron affinities, which take into account internal reorganizational energies, suggest that the bianthrasemiquinone radical anion B • - may be the first semiquinone that is stable toward oxidation by dioxygen. This is experimentally proven using electron paramagnetic resonance (EPR) spectroscopy. The B • - radical anion, prepared via the addition of NaOH to B in dimethyl sulfoxide (DMSO) solution, displays a strong well-resolved EPR spectrum. From the simulation of the spectrum and analysis of the line widths, the bimolecular rate constant for the spin−spin exchange between two B • - radicals is determined to be 3.19 × 109 L mol-1 s-1. When the solvent is saturated with O2, evidence for the close proximity and the frequent encounters between the radical and O2 is apparent from the large broadening of the hydrogen hyperfine splittings. The magnitude of the line width broadening reveals that the Heisenberg spin−spin exchange between B • - and O2 is approximately 10% less efficient than that of neutral nitroxide spin labels. This suggests that the DMSO solvation sphere surrounding the B • - radical anion protects it and slightly decreases its collision frequency with O2. When the O2 is expelled from solution, the EPR spectrum reverts to its normal well resolved form with no measurable loss of intensity. The unusual stability of B • - is attributed to the delocalization of its unpaired type electron over a major portion of this large anion.

Local density functional computations, which take into account electron exchange-correlation and employ large one-particle Gaussian basis sets, are used to study the electronic structure and bonding of the of ScO, TiN, and VC low-lying states. While both ScO and TiN have 21+ ground states, arising from the 9af37rX23?r,2 electronic configuration, the VC diatomic is predicted to have a 2A ground state. The VC 2A ground state (8~~3~,~3?r,216,t) is the same as that suggested from EPR matrix-isolation experiments. The spectroscopic parameters ue, WeXe, Be, a,, and p and its derivatives are also computed for the three lowest 2Z+, ZA, and 211 states,

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