Acid‐Promoted Electron Transfer with Inverse Kinetic Isotope Effect for Disproportionation of Nitroxyl Radicals in CH3CN

Though electron transfer (ET) and proton transfer (PT) are extensively involved in organic reactions, they remain unclear in acid-enabled disproportionation of nitroxyl radicals, especially in organic solvents. Here we unveil the acid-promoted electron transfer (APET) mechanism with inverse kinetic isotope effect (KIE) for the disproportionation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in CH3CN. Kinetic experiments relying on on-line detection of electron paramagnetic resonance (EPR) was conducted together with theoretical calculations, giving consistent insights on the mechanisms. Moreover, the significant effect of water as cosolvent was revealed. The findings here will encourage further mechanistic understandings and method developments for nitroxyl-participated organic reactions.