Theoretical study on intermolecular interactions of 2,4-dinitroimidazole with methanol

Nine optimized conformers of 2,4-dinitroimidazole with methanol have been obtained at B3LYP/6-31++G(2d,p) level. The intermolecular interaction energies are predicted by using MP2/6-31++G(2d,p), B3LYP/6-31++G(2d,p) and B3LYP/aug-cc-pVTZ methods with basis set superposition error (BSSE) and zero-point energy (ZPE) correction, and natural bonding analysis has also been carried out. The four main types of hydrogen bonds, which are N-H⋯O, C-H⋯O, O-H⋯O and O-H⋯π, are investigated. The results indicate that only two of the conformers are the stable ones with the intermolecular interaction energies of 42.39 and 26.27 kJ/mol at B3LYP/aug-cc-pVTZ level, respectively. For these two conformers, the N-H⋯O or C-H⋯O hydrogen bonding interaction is dominant and the hydroxyl oxygen offers lone pairs to the contacting σ(N-H)* or σ(C-H)* antibond orbital of 2,4-dinitroimidazole and electrons transfer from methanol to 2,4-dinitroimidazole, while for the other conformers, the O-H⋯O or O-H⋯π hydrogen bonding interaction is dominant and the nitro oxygen offers p electrons or imidazole ring offers part of the π electrons to the σ(O-H)* antibond orbital and the electrons transfer reversely. Intermolecular binding interaction between the nitro oxygen and hydroxylic hydrogen is relatively weak, as is in accordance with the literature.