Ab initio, DFT, HOMO–LUMO and Natural Bond Orbital analyses of the electronic structure of 2-mercapto-1-methylimidazole

The Fourier transform Raman and Fourier transform infrared spectra of 2-mercapto-1-methylimidazole have been recorded. Ab initio and density functional computations of the vibrational spectrum, the molecular geometry, highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gaps were studied. On the basis of the comparison between calculated and experimental results and the comparison with related molecules, assignments of the fundamental vibrational modes are examined. The observed and simulated spectra were found to be well comparable. The molecular stability and bond strength were investigated by applying the Natural Bond Orbital analysis (NBO). The other molecular properties like Mulliken population analysis, thermodynamic functions and polarizabilities of the title compound have been reported. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with electrostatic potential (ESP).

► Vibrational spectra of 2-mercapto-1-methylimidazole were analyzed.
► The calculations were carried out for MMI at HF/B3LYP/6-31+G(d).
► The donor and acceptor atoms of MMI were identified by HOMO-LUMO energy surfaces.
► The derived point charges of atoms were compared with MEP surface.