Structural Effects on the pH-Dependent Redox Properties of Organic Nitroxyls: Pourbaix Diagrams for TEMPO, ABNO, and Three TEMPO Analogs

Electrochemical studies of the reduction and oxidation reactions of five different organic nitroxyls have been performed across a wide pH range (0–13). The resulting Pourbaix diagrams illustrate structural effects on their various redox potentials and on the p<i>K</i>_a values of the corresponding hydroxylamine and hydroxylammonium ions. Evidence is also given for the reversible formation of a hydroxylamine <i>N</i>-oxide when nitroxyls are oxidized in alkaline media. Structural effects on the thermodynamics of this reaction are assessed