Synthesis and structure of redox derivatives of 4-(2-Amino-2-oxoethyl)-2,2,6,6-tetramethylpiperidine-1-yloxyl

According to X-ray diffraction (XRD) analysis and 1H NMR spectra 2-(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)acetamide, 4-(2-amino-2-oxoethyl)-2,2,6,6-tetramethylpiperidin-1-yloxyl, and 4-(2-amino-2-oxoethyl)-2,2,6,6-tetramethyl-1-oxopiperidinium perchlorate in the crystalline state and in solution possess the chair conformation, equatorial orientation of CH2C(O)NH2 group, and differ by the geometry of the N1 atom of the heterocycle. At growing oxidation state of the piperidine nitrogen atom the pyramidal location of substituents at N1 in the hydroxyl derivative changes to weakly pyramidal in the piperidinoxyl and turned into planar in the oxoammonium cation. Simultaneously the N1-O1 bond shortens transforming from an ordinary (1.451 Å) through a sesquialteral (1.289 Å) into a double (1.189 Å) bond. The insignificant changes in the structure of compounds in the transition piperidinoxyl-oxopiperidinium cation correspond to the low energy of the transition process and result in the ease of the redox-reactions involving this pair.