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

Abstract

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 (χ) and isotropic chemical shielding (σ ) 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 ) 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 σ values around them were increased, while their χ and q values were decreased. However, the results indicated that with exception of tautomer B, the order of q and χ 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 χ and q 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 σ values around nitrogen atoms acting as hydrogen donors in hydrogen bond formation (N-H….OH ) were decreased, while its values were increased for nitrogen atoms acting as hydrogen acceptors in hydrogen bond formation(N….H-OH). Copyright © 2016 John Wiley & Sons, Ltd.