The influence of halogen bonds on tautomerism: the case of 3-mercapto-1,2-azoles (pyrazoles, isoxazoles, isothiazoles)
DFT calculations at the B3LYP/6-311++G(d,p) computational level have been carried out on three tautomeric pairs of 3-mercapto-1,2-azoles (pyrazoles, isoxazoles, and isothiazoles) to study the effect of halogen bonds (XBs) on the position of the equilibrium. As halogen bond donors, we have selected Br2, Cl2, BrCl, ClF and BrF and compare them with HF as a hydrogen bond donor. Several linear relationships were found between binding energies of different halogen bond donors. The main conclusion of this study is that the XB inverts the tautomeric equilibrium while an HB does not.