Spectroscopic investigation (IR and NMR) and HOMO-LUMO analysis of aromatic imines using theoretical approach

In this work, the theoretical studies on the structure, FT-IR, NMR, and UV–Vis spectroscopy of (E)-N-benzylidenebenzenamine (A1) and (E)-N-(2, 4′-dichlorobenzylidene) propan-1-amine (A2) are presented. The optimized structure of the molecules, NMR and UV–Vis spectra analysis were determined by the Density Functional Theory (DFT) method using B3LYP/6-311G (d, p) basis set. For FT-IR analysis, both the HF and DFT methods were used in order to determine their accuracy and reliability in theoretical calculations. The computed result of DFT calculations in comparison with the experimental results showed that the DFT method gives a more accurate prediction. The infrared (IR) spectra for the imine molecules have been recorded in the region of 500–4000 cm^?1. The gauge-independent atomic orbital (GIAO) method has been used to evaluate the ¹³C and ¹H nuclear magnetic resonance (NMR) chemical shifts of the molecules. The computed results of NMR spectra of the molecules was found to be in good agreement with the experimental data. The UV–Vis spectra of the molecules were computed to determine the HOMO-LUMO energies in order to gain insight into their electronic properties. Mulliken population analysis on atomic charges of the molecules was also calculated using the HF (Hartree-Fock) and B3LYP method. All the computed results indicated that the B3LYP method provides satisfactory results and, therefore, can be employed to support experimental data. It also demonstrated a reliable approach towards characterization of molecules in chemical science.