N-Oxoammonium salts are a class of organic compounds with the formula [R<sub>1</sub>R<sub>2</sub>=O]X<sup>âÂÂ</sup>. The cation [R<sub>1</sub>R<sub>2</sub>=O] is of interest for the dehydrogenation of alcohols. Oxoammonium salts are diamagnetic, whereas the nitroxide has a doublet ground state. A prominent N-oxoammonium salt is prepared by oxidation of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, commonly referred to as [TEMPO]<sup>+</sup>. A less expensive analogue is Bobbitt's salt.
Oxoammonium cations are isoelectronic with carbonyls and structurally related to aldoximes (hydroxylamines), and aminoxyl (nitroxide) radicals, with which they can interconvert via a series of redox steps. According to X-ray crystallography, the NâÂÂO distance in [TEMPO]BF<sub>4</sub> is 1.184 à, 0.1 àshorter than the NâÂÂO distance of 1.284 àin the charge-neutral TEMPO. Similarly, the N in [TEMPO]<sup>+</sup> is nearly planar, but the O moves 0.1765 àout of the plane in the neutral TEMPO.
The N-oxoammonium salts are used for oxidation of alcohols to carbonyl groups, as well as other forms of oxoammonium-catalyzed oxidations. The nitroxyl TEMPO reacts via its N-oxoammonium salt.