The ethylenedione radical anion (C2O2-), a possible intermediate in the reduction of carbon monoxide by alkali metals, was investigated using molecular orbital methods. At the Hartree-Fock level the anion is predicted to be linear, in agreement with Linnett's double-quartet theory, but inclusion of electron correlation at the MP2 level leads to the prediction that the anion is bent in a planar trans configuration, which is in agreement with the reported MINDO/3 structure.
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