Structural studies of some mesoionic 1,3-diphenyl-1,2,3,4-tetrazolium-5-aminides by nitrogen NMR techniques

The N-14 and N-15 NMR data for some 1,3-diphenyl-1,2,3,4-tetrazolium-5-aminides are reported. A typical N-15 NMR spectrum consists of five signals, laying within the ranges: -172 to -192 ppm (N1), -56 to -61 ppm (N2), -103 to -106 ppm (N3), -122 to -129 ppm (N4) and -155 to -260 ppm (N6). The N-14 NMR data suggest the positive charge localization mainly on the N3 ring atom. Protonation of the molecule occurring at the exocyclic N6 atom results in the change of the N-15 chemical shifts of all nitrogen atoms: 9 to 23 ppm for N1, 18 to 25 ppm for N2, 4 to 6 ppm for N3, 5 to 15 ppm for N4 and -70 to -102 ppm for N6 atom, respectively. Synthesis of three new mesoionic compounds, 5-(4-methoxyaniline)-1,3-diphenyl-1,2,3,4-tetrazole 7, 5-(N-cyclohexylamine)-1,3-diphenyl-1,2,3,4-tetrazole 8 and 5-(N-methylamine)-1,3-diphenyl-1,2,3,4-tetrazole 9 are reported.