A survey of hydrogen bonding in imidazole and its 4-nitro derivative by ab initio and DFT calculations of chemical shielding

Using restricted Hartree-Fock (RHF) and density functional theory (DFT) methods at gauge invariant atomic orbital (GIAO) condition, chemical shielding of C-13 and N-15 nuclei of imidazole and its 4-nitro derivative at different temperatures were calculated. Since we have used the realized structures determined by X-ray and neutron diffraction methods, accuracy of calculated results is improved. By partially optimization of structures of 4-nitroimidazole, determined by X-ray crystallography, the obtained results of these structures are also better than nonoptimized structures. Additionally, we have obtained an optimized geometry for hydrogen bond in structures mentioned above. (c) 2006 Elsevier B.V. All rights reserved.