Theoretical and Experimental Study of the Reaction of 2-Guanidinobenzimidazole on a Series of meta-Substituted Benzaldehydes

The syntheses of a variety of 1,3,5-triazinebenzimidazoles obtained by the cyclocondensation reaction of 2-guanidinobenzimidazole with a series of meta-substituted benzaldehydes were reported. The prepared compounds were fully characterized by IR and NMR spectroscopies. Based on the density functional theory(DFT) calculations method, quantum chemical calculations were performed by Gaussian 09 set of programs. All possible transition states, reactants and products were fully optimized at the hybrid density functional B3LYP level using the 6-311+G(d,p). The geometries of five possible tautomers of 2-amino-4-aryl[1,3,5]triazino[1,2-a]benzimidazoles were optimized in ethanol, using conductor like polarizable continuum(CPCM) in the gas phase. The energetic diagrams of tautomeric equilibrium showed that form A is the most stable tautomer which proved to be in accordance with the X-ray diffraction structure analysis. In order to interpret the reaction mechanism, the chemical reactivity was studied using local and global reactivity indexes.