Non-covalent interactions of N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives—a case of intramolecular N-oxide hydrogen bonds

Abstract

The crystal structures of new N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives are reported. The results of X-ray diffraction showed the existence of intramolecular hydrogen bonding between carboxamide nitrogen donors and N-oxide oxygen acceptors. The use of Quantum Theory of Atoms in Molecules allowed its classification as a strong interaction, with energy about 10 kcal/mol, and of intermediate character between closed shell and shared bonds. Comparison of experimental data and quantum theoretical calculations indicated that a substituent attached to the phenyl ring in the para position influences the strength and geometry of the title hydrogen bonding. Stronger π-electron-withdrawing properties of the higher energy substituent of the intramolecular hydrogen bond are observed. Among other intermolecular contacts in the studied crystals are C–H…O/C–H…N hydrogen bonds of imidazole carbon atoms and some π…π stacking interactions between aromatic molecular fragments. Their importance in stabilization of the crystal structure was confirmed by the results of Hirshfeld surface analysis.