Thermodynamic Destabilization of N-Centered Radical Cations by a γ-Keto Group

Article abstract of DOI:10.1021/ja00537a010

Vertical ionization potentials measured by PE spectroscopy and formal oxidation potentials measured by cyclic voltammetry are compared for several 9-substituted 9-azabicyclo<3.3.1>nonan-3-one derivatives and their nonketo analogues.The compounds studied include hydrazines, 2-tetrazenes, p-phenylenediamines, p-tert-butylanilines, and tert-butylamines.The formal potential for one-electron oxidation is raised 3.2-7.4 kcal/mol by the presence of the keto group, depending on the amount of positive charge at N₉ in the radical cation.In contrast, the formal potential for 3-oxobutyltrimethylhydrazine is only 0.5 kcal/mol higher than that of butyltrimethylhydrazine, although the change in vertical ionization potential is as large in the acyclic as in the bicyclic hydrazine.