Experimental and Theoretical Studies of the Redox Potentials of Cyclic Nitroxides

• Published in: Journal of organic chemistry Vol. 73; no. 17; pp. 6763 - 6771
• Main Authors: Blinco, James P, Hodgson, Jennifer L, Morrow, Benjamin J, Walker, James R, Will, Geoffrey D, Coote, Michelle L, Bottle, Steven E
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05-09-2008
• Subjects: Acetonitriles - chemistry; Algorithms; Aza Compounds - chemistry; Chemistry; Cyclic N-Oxides - chemistry; Electrochemistry; Exact sciences and technology; Free radicals chemistry; Heterocyclic compounds; Heterocyclic compounds with only one n hetero atom and condensed derivatives; Isoindoles - chemistry; Models, Theoretical; Organic chemistry; Oxidation-Reduction; Piperidines - chemistry; Preparations and properties; Pyrrolidines - chemistry; Reactivity and mechanisms; MO method; Nitroxyl; Nitrogen heterocycle; Ab initio method; Theoretical study; Experimental study; Isoindole derivatives; Pyrrolidine derivatives; Cyclic voltammetry; Cyclic compound; Oxidation potential; Organic free radical; Acetonitrile; Piperidine derivatives; Aromatic compound; Oxidation; Redox potential; Chemical synthesis
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo801099w

The redox potentials of 25 cyclic nitroxides from four different structural classes (pyrrolidine, piperidine, isoindoline, and azaphenalene) were determined experimentally by cyclic voltammetry in acetonitrile, and also via high-level ab initio molecular orbital calculations. It is shown that the potentials are influenced by the type of ring system, ring substituents and/or groups surrounding the radical moiety. For the pyrrolidine, piperidine, and isoindolines there is excellent agreement (mean absolute deviation of 0.05 V) between the calculated and experimental oxidation potentials; for the azaphenalenes, however, there is an extraordinary discrepancy (mean absolute deviation of 0.60 V), implying that their one-electron oxidation might involve additional processes not considered in the theoretical calculations. This recently developed azaphenalene class of nitroxide represents a new variant of a nitroxide ring fused to an aromatic system and details of the synthesis of five derivatives involving differing aryl substitution are also presented.