Comparisons between Crystallography Data and Theoretical Parameters and the Formation of Intramolecular Hydrogen Bonds: Benznidazole

The conformational preferences of benznidazole were examined through the application of DFT, PCM and QTAIM calculations, whose results were compared with crystallography data. The geometries were fully optimized with minimum potential energy surface by means of the Relaxed Potential Energy Surface Scan (RPESS) at AM1, followed by the B3LYP/6-311++G(d,p) theoretical level. As a result, the s-cis conformation (1C) was shown to be more stable (4.78 kcal ̈mol ́1) than s-trans (1T). The Quantum Theory Atoms in Molecules (QTAIM) was applied in order to characterize the (N–H ̈ ̈ ̈O=N) and (C–H ̈ ̈ ̈=N) intramolecular hydrogen bonds. The simulation of solvent effect performed by means of the implicit Polarized Continuum Model (PCM) revealed great results, such as, for instance, that the conformation 1W is more stable (23.17 kcal ̈mol ́1) in comparison to 1C. Our main goal was stressed in the topological description of intramolecular hydrogen bonds in light of the QTAIM approach, as well as in the solvent simulation to accurately obtain an important conformation of benznidazole.