UV, H-1 AND C-13 NMR-SPECTRA, AND AM1 STUDIES OF PROTONATION OF AMINOPYRIDINES

The effect of single and double protonation on the UV, H-1 and C-13 NMR spectra of 2-, 3-, and 4-aminopyridines and their N-methyl and N,N-dimethyl derivatives has been investigated. All the spectra confirm that aminopyridines in diluted acids form monocations by protonation at the ring nitrogen atom and dications in concentrated acids (e.g. 80% D2SO4). The formation of dications decreases in the order: 3 > 4 > 2. Computed values of proton affinity PA(1)ring and PA(2)subst. are in agreement with the above interpretations.