HO∴OH−: a model for stable three-electron bonded peroxide radical anions

The potential surface of the hydrogen peroxide anion is explored, with special attention to the three-electron bonded form. The stability of this conformer is found to be sensitive to the level of computation. The artefacts that are encountered at low computational levels are qualitatively analyzed in valence bond terms. The breathing-orbital valence bond method, which is by nature free from these artefacts, yields a bonding energy and a barrier to rearrangement for the three-electron bonded conformer in good agreement with sophisticated calculations at the CCSD(T) level. This conformer is predicted to be bonded by 26.6 kcal/mol relative to the separate fragments, but should not be experimentally observable due to its extremely facile rearrangement to hydrogen-bonded conformers. On the other hand, substituting the hydrogens for alkyl or other groups should lead to stable RO∴OR′− species that cannot rearrange to hydrogen-bonded forms, and should make possible the experimental observation of O∴O three-electron bonds in radical anion peroxides.