Structural, vibrational, and electronic properties of 2-methyl-5-nitro-1 <i>H</i> -benzimidazole-6-amine: An experimental and theoretical approach

The structural, vibrational, and electronic properties of 2-methyl-5-nitro-1H-benzimidazole-6-amine (MNBA) were analyzed using experimental and theoretical approaches. Density Functional Theory (DFT) simulations utilizing the B3LYP functional and 6-311++G(d,p) basis set were performed to optimize the geometry, predict vibrational frequencies, and analyze the frontier molecular orbitals (HOMO-LUMO) of the MNBA molecule. FT-IR and UV-Vis spectroscopy were used to empirically validate the results, which were subsequently compared to theoretical predictions in both gaseous and aqueous phases. The study highlights the critical role of intramolecular hydrogen bonding between the nitro and amine groups, which forms an intramolecular O···H interaction, that may contribute to the stabilization of the molecular structure. Solvent effects substantially affected molecular shape and electronic distribution, with aqueous phase calculations showing improved concordance with experimental results. Mulliken charge analysis together with molecular electrostatic potential (MEP) mapping provides qualitative insight into the charge distribution and possible reactive regions of MNBA. A reduced HOMO–LUMO gap in aqueous solution suggests enhanced electronic reactivity of the molecule in polar environments, providing insight into the structural and electronic characteristics of MNBA. This study demonstrates the effective integration of DFT simulations and experimental methodologies to elucidate the physicochemical properties of benzimidazole derivatives under diverse environmental conditions.