Aminoxyl denotes a radical functional group with general structure R2N–O•.
It is commonly known as a nitroxyl radical or a nitroxide, however IUPAC discourages the use of these terms, as they erroneously suggest the presence of a nitro group.
[1] Aminoxyls are structurally related to hydroxylamines and N-oxoammonium salts, with which they can interconvert via a series of redox steps.
Sterically unhindered aminoxyls bearing α-hydrogens are unstable and undergo rapid disproportionation to nitrones and hydroxylamines.
[2] Sterically hindered aminoxyls without α-hydrogens, such TEMPO and TEMPOL, and are persistent (stable) radicals and find use in a range of applications, both on the laboratory scale and in industry.