Quantum mechanical study of the structure and spectroscopic (FT-IR, FT-Raman, 13C, and 1H) and HOMO–LUMO analysis of 2,4-dimethoxy benzaldehyde (DMBA) and 4-methoxy-3-methyl benzaldehyde (MMBA)

The present communication is aimed at comparing the molecular structural properties, vibrational and energetic data of 2,4-dimethoxy benzaldehyde and for 4-methoxy-3-methyl benzaldehyde, due to their commercial importance. The ground state properties of the title molecules have been calculated employing DFT/B3LYP level of theory using the 6-31G (d) basis set. In order to obtain a complete description of molecular dynamics, vibrational wavenumber calculation along with the normal mode analysis, have been carried out at the DFT level. The calculated spectra of both the molecules agree well with the experimental data. The 1H and 13C NMR spectra have been simulated using the gauge independent atomic orbital (GIAO) method. The electronic properties, such as HOMO, LUMO energies, absolute electronegativity X and absolute hardness η were performed by DFT approach. The first order hyperpolarizability (βo) of these novel molecular system and related properties (β, αo and Δα) of DMBA and MMBA are calculated using DFT/6-31G (d) method on the finite-field approach.

► Spectroscopic properties of DMBA and MMBA were examined by FT-IR, FT-Raman and NMR techniques by DFT method.
► Simulated and observed vibrational spectra are agreed well.
► 1H and 13C NMR chemical shifts have been compared with experimental values.
► HOMO and LUMO energies showed the charge transfer.
► The first static hyperpolarizability have been calculated and compared.