Molecular structure analysis and spectroscopic characterization of carbimazole with experimental (FT-IR, FT-Raman and UV–Vis) techniques and quantum chemical calculations

• FT-IR and FT-Raman spectra of CBZ in solid phase were recorded and analyzed.
• The vibrational wavenumbers were computed using B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) methods.
• The complete vibrational assignment and spectroscopic analysis have been carried out.
• The first order hyperpolarizability and HOMO, LUMO energy gap were theoretically predicted.
• The NBO/NLMO analysis explained the intramolecular hydrogen bonding.

The complete vibrational assignment and analysis of the fundamental modes of carbimazole (CBZ) was carried out using the experimental FTIR, FT-Raman and UV–Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT–B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO–LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of CBZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.