Molecular structure and vibrational spectra of 2- and 5-methylbenzimidazole molecules by density functional theory.

The FT-IR and FT-Raman spectra of 2-methylbenzimidazole (2-MB) and 5-methylbenzimidazole (5-MB) molecules have been recorded between 400-4000 cm(-1) and 50-3500 cm(-1) region, respectively. The molecular geometry and vibrational frequencies of 2- and 5-MB molecules in the ground state have been calculated by using the density functional methods (B3LYP) with 6-311++G(d,p) and 6-31 G(d,p) as basis sets. The total energy distributions (TEDs) for the normal modes were computed for the minimum energy structure of the molecules. Comparison of the observed fundamental vibrational frequencies of 2- and 5-MB molecules with calculated results by density functional B3LYP approach will give better result for our studied molecular vibrational problem.