Physicochemical properties, NMR, Ab initio calculations and the molecular interactions in a binary mixture of N-methylimidazole and water

For a binary mixture of xN-methylimidazole (hereafter abbreviated to N-mim) + (1-x) water, over a full molar fraction range, the mass density, sound velocity, refractive index, viscosity, mixing enthalpy, conductivity, and pH at (298.15, 308.15, 318.15) K and 0.1 MPa, and 1H NMR and 13C NMR at room temperature combined with Ab initio calculations, were measured and carried out. The excess molar volume (VmE), sound deviation (∆u), refractive index deviation (∆nD), viscosity deviation (∆η), excess Gibbs energy of activation of viscous flow (∆G⁎E), molar mixing enthalpy (∆mixHm), 1H NMR chemical shift changes of N-mim and water protons (∆δH), 13C NMR chemical shift change of N-mim (∆δC), sum of the chemical shift changes (∑∆δH(N-mim), ∑∆δC), and the interaction energy, hydrogen bond length, second-order perturbation stabilization energy, electron density, and the electronic energy density of the trimer hydrogen-bonded complexes were calculated. The values of VmE, ∆u, ∆nD, ∆η, ∆G⁎E, and ∆mixHm were fitted to a Redlich-Kister equation. The extreme positions of these quantities and the chemical shift changes were compared and discussed with regard to the intermolecular interaction between N-mim and water, and a possible molecular interaction scheme was suggested for N-mim added to water. There occurs an ionization process and hydrogen-bonded interactions between N-mim and water. The ionization process may not be neglected at an infinite dilution of water, and hydrogen bonds predominate the primary interaction in the mixture. The predominant hydrogen-bonded complex in the mixture transforms with increasing x, which is consistent with the calculation results.