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 H-1 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 N-1 atom of the heterocycle. At growing oxidation state of the piperidine nitrogen atom the pyramidal location of substituents at N-1 in the hydroxyl derivative changes to weakly pyramidal in the piperidinoxyl and turned into planar in the oxoammonium cation. Simultaneously the N-1-O-1 bond shortens transforming from an ordinary (1.451 ) through a sesquialteral (1.289 ) into a double (1.189 ) 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.