Theoretical study addressing the effects of tautomerism and explicit/implicit water molecules on NQR and NMR parameters of tetrazole-5-thione

DFT/B3LYP calculations were employed to study the effects of tautomerism and explicit/implicit water molecules on Nuclear Quadrupole Resonance (NQR) and Nuclear Magnetic Resonance (NMR) tensors of nitrogen nuclei in tetrazole-5-thione structure. The obtained results revealed that nuclear quadrupole coupling constant (chi) and isotropic chemical shielding (sigma(iso)) values of nitrogen nuclei in tetrazole ring of five possible tautomeric forms of tetrazole-5-thione, i.e. two thione forms called tautomers A and E and three thiol forms called tautomers B, C, and D, were functions of resonance energy(E-2) values of nitrogen lone pairs. Furthermore, it was observed that by increasing participation of lone pairs of nitrogen atoms in the ring resonance interactions, the sigma(iso) values around them were increased, while their chi and q(zz) values were decreased. However, the results indicated that with exception of tautomer B, the order of q(zz) and chi values of nitrogen nuclei in tetrazole ring was exactly opposite of the order of resonance energy values for the same nitrogen nuclei in all tautomers and their mono-hydrated complexes. In addition, a significant decrease was noticed in chi and q(zz) values when a water molecule was put in different positions near the tetrazole ring in tautomers A-E. The mentioned result can be attributed to hydrogen bond formation between nitrogen nuclei and the oxygen of water. In mono-hydrated complexes, the sigma(iso) values around nitrogen atoms acting as hydrogen donors in hydrogen bond formation (N-H....OH2) were decreased, while its values were increased for nitrogen atoms acting as hydrogen acceptors in hydrogen bond formation(N....H-OH). Copyright (C) 2016 John Wiley & Sons, Ltd.