Structural and spectroscopic investigation of the chalcones (E)-1-(4-aminophenyl)-3-(4′-ethoxyphenyl)-prop-2-en-1-one and (E)-1-(aminophenyl)-3-(4′-methoxyphenyl)-prop-2-en-1-one

[Display omitted] •Spectroscopic characterization of synthetic chalcones.•Raman and infrared studies.•DFT studies were done.•The internal and symmetrical coordinates were defined.•The assignment of the vibrational modes was presented.•A comparative analysis of the structural and vibrational properties was carried out. In this study, two 4′-aminochalcones with structural similarity were structurally characterized using the NMR technique of 1H and 13C. Polycrystalline samples of these chalcones were analyzed by FT-Raman and ATR-FTIR spectroscopy at room temperature in the regions 40-4000 cm-1 and 400-4000 cm-1, respectively. The DFT calculations using the B3LYP functional with 6-311 G(d,p) basis set were performed, revealing the optimized molecular geometry and the vibrational wavenumbers for these chalcones. Conformational analysis was done from the optimized structures to obtain different conformers. The calculated harmonic vibrational wavenumbers were scaled to improve the agreement between theoretical and experimental wavenumbers. A complete vibrational assignment using Potential Energy Distributions (PED) was provided for the observed Raman and infrared spectra. The scaled wavenumbers were found to be in good agreement with experimental wavenumbers. Furthermore, a comparative structural and vibrational analysis was performed. The structural analysis allowed us concluding that in addition to differences in the position 4′ – where one chalcone has a methoxy group and the other, an ethoxy group – the molecular conformation of them is significantly different, especially regarding the torsion angles linking the enone chains with the rings of these chalcones. The vibrational analysis allowed us to identify all Raman and infrared bands of the two chalcones, highlighting the main differences and correspondences between them.