Theoretical study of 2-guanidinobenzimidazole.: HF, MP2 and DFT calculations

In this paper, the 2-guanidinobenzimidazole molecular structure is analysed by ab initio (HF and MP2) and density functional theory (DFT) calculations; and the neutral, cationic, and radical forms are studied by ab initio theory. The HF calculations with the 3-21G and 6-31G basis sets provide good geometric features according to available experimental data. The percentage of p-character of the natural atomic hybrids and the charge distribution in the molecule were analysed with the natural bond orbital method (NBO). Calculations of the enthalpy and Gibbs free energies for the protonation reactions of 2-guanidinobenzimidazole were carried out at the HF level. In accordance with the experimental data, UHF/3-21G showed a delocalised free radical. (C) 2003 Elsevier B.V. All rights reserved.