QUANTUM CHEMICAL CALCULATION OF THE ASSOCIATE OF TWO ETHYL ALCOHOL MOLECULES AND THREE WATER MOLECULES BY THE DFT METHOD

This article presents the results of quantum chemical calculations of the associate of two ethyl alcohol molecules and three water molecules using the DFT-PBE0/6-311g** method. The gradient method was used to optimize the geometry in all parameters. In the process of obtaining aqueous alcohol solutions, heat is released and the volume of the solution is compressed. This phenomenon is called a contract. The amount of compression initially increases with increasing alcohol concentration, reaches a maximum when it contains 45-48% by weight in solution, and then decreases again. This phenomenon is explained by the hydration of alcohol, i.e. its interaction with water to form chemical compounds [1]. To obtain an optimized geometric and electronic structure of the studied associate, two molecules of ethyl alcohol + three molecules of water, that is, to determine the conformer - stereoisomeric structure with the maximum negative energy of the studied compound, one of the authors of this article developed a special program for calculating the configuration interactions of the ingredients included in the associate. Previously, a conformer of the molecular system was found, consisting of two ingredients: alcohol - alcohol, then three: alcohol - alcohol - water, etc. Ultimately, all possible combinations of the interaction of the associate two alcohol molecules and three water molecules were investigated, and a conformer was found for all five components for which the DFT calculation was performed. As a result, an optimized geometric and electron structure of the studied associate (conformer) was obtained and the acidic strength of this compound was theoretically calculated (pKa=15, pKa is a universal indicator of acidity). It has been established that this associate belongs to the class of weak acids (pKa>14). The obtained data from quantum chemical calculations can be used to explain the phenomenon of contraction at the quantum level.