Alkali metal over-reduction of an electron acceptor in the presence of a hydrogen atom donor, in hexamethylphosphoramide (HMPA), results in a radical that is not simply the anion radical of the acceptor. This new species exhibits an enigmatic EPR pattern. Using 15N and 2H labeling studies, the “HMPA degradation product” was found to be the anion radical of N, N′-dimethyl-1, 4-diazabutadiene. DFT calculations support this assignment and a ...