DISSOCIATION ROUTES OF TRIHYDROXYBENZENES. QUANTUM CHEMICAL AND UV RESEARCHES

10.25712/ASTU.1811-1416.2026.02.008

Abstract

The interest in the behavior of flavonoids in solution is due to various reasons. The dissociative properties of flavonoids, as representatives of the polyphenol class, are complicated by the occurrence of independent dissociation processes of hydroxyl groups in various positions of the carbon skeleton. Experimental methods of dissociation research show a generalized picture, hiding individual stages and not revealing different dissociation routes. The paper considers the modeling of dissociative properties of flavonoids by reduced analogues – triatomic phenols (trihydroxybenzenes, triphenols). The choice is due to the fact that it is only starting from triphenols in the series of polyatomic phenols that a structural isomerism appears in the molecule of the compounds of interest. When alkalis are introduced into the solution, anions with different dissociation constants are formed. Characteristics such as absorption spectra (UV spectra) are also changing. The set of dissociation products indicates the existence of various dissociation routes with the manifestation of averaged dissociation constants. Quantum chemical modeling was carried out in the Gaussian-09 software package, B3LYP/6-311+G**, TDDFT, influence of the solvent medium – PCM model. UV spectroscopic examination was performed on an SF-200 spectrophotometer, wavelength range 190-600 nm, quartz cuvette 10 mm. The working concentration of triphenol C = 5*10-5 M. The study is based on the original software: the description of experimental UV spectra with model ones was carried out using the LSM method. The results of the study for phloroglucin show the correspondence of the stages of anion formation and the sequence of ionization reactions of phloroglucin; the observed stages of dissociation of pyrogallol and hydroxyhydroquinone describe a set of internal processes of ionization and interconversion of various anionic forms of the named triphenols. It was shown the multiplicity of tryphenol dissociation routes.