Formation of a transient radial ion pair in the reactions of 1,5-dihydroflavin with hydride acceptors

The formation of a transient radical ion pair has been detected directly in the reactions of 1,5-dihydroriboflavin-2′,3′,4′,5′- tetraacetate (FlH₂) with hydride acceptors (tetracyano-p- quinodimethane, tetracyanoethylene and p-benzoquinone derivatives) in deaerated acetonitrile, providing unequivocal evidence for an electron transfer pathway in the overall two-electron redox reactions of FlH₂ with hydride acceptors.