Theoretical DFT, vibrational and structural characterization of 1-propenyl-2-methylbenzimidazole and its isomers

Benzimidazole nucleus is present in many biologically active compounds. The synthesis and characterization of new benzimidazole derivatives is driven by the search for enhanced physiological activity. In this contribution, three 1-propenyl isomeric derivatives of 2-methylbenzimidazole (2-MBZM) prepared from the reaction of 2-MBZM with allyl chloride, using a strong base as a catalyst. Gas chromatography–mass spectrometry (GC–MS) was selected as the method of chemical analysis to identify and quantify the products of the reaction which allowed the characterization of two diastereomers: E-1-(1-propenyl)-2-methylbenzimidazole and Z-1-(1-propenyl)-2-methylbenzimidazole and one constitutional isomer: 1-(2-propenyl)-2-methylbenzimidazole. The structures of the compounds were confirmed by 1H and 13C Nuclear Magnetic Resonance. Also FT-Raman, FT-IR and UV–VIS spectral data in a condensed phase have been included. For the interpretation of the experimental results, the structural and spectral characteristics of 1-propenyl-2-methylbenzimidazole have been studied by performing DFT calculations for energies, geometries, vibrational frequencies and shieldings constants (GIAO method). Using the basis set 6-311+G∗∗ and the hybrid density functional B3LYP, the experimental and calculated results were consistent with each other.