Structure of lithium-p-semiquinonates in non-aqueous solution

The reaction of phenyllithium with p-quinones (1,4-benzoquinone, 2,6-di-tert-butyl-1,4-benzoquinone, 1,4-naphthoquinone) in tetrahydrofuran gave the phenyl radical, which goes to biphenyl, and the corresponding lithium semiquinonate. The latter can also be obtained by direct reaction between lithium and the p-quinone. Electron spin resonance spectroscopy showed that a solution of the lithium derivative contains both monomeric and dimeric species. Adducts with 4-methylpyridine have also been prepared. Quantum-mechanical calculations were consistent with the ESR results. Related experiments with potassium derivatives were also performed.