The ¹³C and ¹⁵N NMR spectra of 1-aminoimidazole 2, 1-aminopyrazole 3, 4-amino-1,2,4-triazole 4, 1-amino-1,2,4-triazole 5, 1-aminobenzimidazole 12, 2-aminoindazole 13, 1-aminoindazole 14, 2-aminobenzotriazole 15 and 1-aminobenzotriazole 16 have been recorded in neutral (CDCl₃ or [²H₆]DMSO) and acid (CF₃CO₂H and SO₄H₂) conditions. The X-ray crystal structures of two polymorphic forms of N-aminobenzimidazolium picrate 12d have been determined. The main differences between the forms are due to the twist of an ortho-nitro group of the picrate anion up to 53° leading to a different hydrogen bond network. In the two crystals, the relative disposition of both ions is similar being held together by N⁺–H ⋯ O^–/O₂N three centre hydrogen bonds. The basic pK_as of 1-aminoindole 11, compounds 12 and 13 and 9-aminocarbazole 17 have been measured. Finally, all monoprotonated cations on N-aminoazoles (from pyrrole 1 to carbazole 17) have been calculated. When there is a pyridine-like nitrogen atom on the ring, this is the preferred site of protonation although in sulfuric acid the amino group is also protonated, only 1-aminoindole and 9-aminocarbazole protonate on the amino group.