Theoretical study on ionic liquids based on DBUH+: Molecular engineering and hydrogen bond evaluation

The new generation of the ionic liquids (ILs) based on 1,8-diazobicylo [5,4,0] undec-7-ene (DBU) are applied as the solvent in organic reactions. In this work, by using a theoretical procedure, the most probable interactions between the ion pairs of DBUH+ based ILs, including 10 functionalized imidazole anions were investigated. For this purpose, the electrostatic potential surfaces were analyzed to detect the most probable interaction sites of DBUH+. On the basis of the obtained results, hydrogen bond formation between the anions and DBUH+ is influenced by the electronic effect of the substituted functional groups. This means that electron donating groups, such as phenyl has a stabilizing effect on the ion pairs, while electron-withdrawing groups, such as nitro, induces a destabilizing effect. These behaviors are described based on the interaction energy values (Delta E-int). To investigate the dispersion interaction effects in ILs formation, M06-2X-D3 functional was applied in energy analysis. The solvent reaction field was investigated by the polarizable continuum model in ethanol and chloroform as the solvent. The results showed that ethanol has a greater effect on the interaction energy of the ILs. Finally, to have a comprehensive understanding of the charge transfer effect on the stability of the studied ILs and to characterize the most probable interactions, natural bond orbital and quantum theory of atoms in molecules analyses were applied and the obtained results were analyzed.