Theoretical vibrational spectroscopy (FT-IR), PED and DFT calculations of chromones and thiochromones

Abstract

Chromones are heterocyclic compounds having a benzoannelated γ-pyrone ring and recognized as privileged structures and useful templates for the design of novel compounds. For the first time, this protocol presents a combined experimental and theoretical studies aiming at the vibrational properties and density functional theory (DFT) calculations of chromone and thiochromone analogs. The calculated HOMO and LUMO energies illustrate that charge transfers within the molecule. The effects on these energy gaps due to the substitution of different functional groups were investigated. The molecular geometries calculated using DFT was compared with available experimental data. The FT-IR spectra of the title compounds were recorded in the region 4000-400 cm−1. The vibrational spectra calculated at the B3LYP/6-31G(d,p) level were compared with the experimental spectral data, and thus each vibrational frequency was assigned on the basis of potential energy distribution (PED). The comparative experimental and theoretical 1H and 13C-NMR analysis of representative compounds 1d and 2d was also carried out to evaluate the effect of corresponding oxo and thio groups on the chemical shift values. The structural and spectral results obtained from DFT are in good agreement with the experimental data.