Density functional study on the structural conformations, intramolecular charge transfer and vibrational spectra of 4-hydroxy-3-methoxy-5-nitrobenzaldehyde

In this paper, we report a combined experimental and theoretical study on molecular structure; vibrational spectra of 4-hydroxy-3-methoxy-5-nitrobenzaldehyde (HMN) have been recorded using Fourier transform infrared spectroscopy (FT-IR) and FT-Raman measurements in the region of 4000–400 cm−1 and 3500–100 cm−1, respectively. The molecular geometry, harmonic vibrational frequencies, bonding features, total energy, Mulliken atomic charges and thermodynamic properties for most stable conformer of HMN in ground state were obtained by density functional theory (DFT) with the standard B3LYP/6-311++G(d,p) basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule.