5,8-Quinolinedione Attached to Quinone Derivatives: XRD Diffraction, Fourier Transform Infrared Spectra and Computational Analysis

Quinoline and isoquinoline moieties occur in many natural and synthetic compounds exhibiting high biological activity. The purpose of this study was to analyze the chemical structures of 5,8-quinolinedione and 5,8-isoquinoline derivatives using FT-IR spectroscopy supplemented with theoretical DFT calculations. Spectroscopic measurements were conducted using the attenuated total reflection (ATR) mode in the frequency range of 4000–400 cm−1. An analysis of FT-IR spectra was carried out, assigning the characteristic vibration frequencies of various functional groups to individual peaks. It was found that the experimental and calculated FT-IR spectra showed a good correlation for all the compounds under study. The most significant difference in the spectra occurred in the region of carbonyl bands. For compounds with the 5,8-quinolinedione moiety, two separated C=O vibration peaks were observed, while for compounds with the 5,8-isoquinolinedione moiety, the carbonyl vibrations created only one peak. This difference makes it possible to distinguish between the 5,8-quinolinedione and 5,8-isoquinolinedione derivatives.