 The two 14N chemical shifts are similar (about 200 ppm, relative to nitric acid on the sigma scale, on which increased shielding corresponds to increased chemical shift).NMR spectral measurements shows that the chemical shift of N1-H drops slightly, whereas the chemical shift of N3-H drops considerably (about 190 vs. 145 ppm).This change indicates that the N1-H tautomer is preferred, possibly due to hydrogen bonding to the neighboring ammonium.