Análisis geométrico, energético y topológico de una heterononámeros de (etanol)8-agua. Una paroximación computacional

Abstract

The present research focused on the study of the ethanol-water azeotropic mixture, in order to provide information that can be used in new low-cost separation techniques. The study was carried out through the computational analysis of the intermolecular interactions responsible for the geometrical preferences and stability of the (ethanol)8-water heterononamers. For this, the Gaussian 09 program was used. It was based on 14 stable heterononamers optimized with the approximation B3LYP/6-31+G(d) which belong to the research line; after reoptimizing those structures, including the Grimme D3 correction and a more robust basis set, (B3LYP/6-311++G(d,p)), the number of stable structures was reduced to 7. The main structural changes were different orientations of the alkyl chains. The most stable heterononamer (Hnon-I) has an isomeric population of 98%, therefore, from this structure, homologous structures of (ethanol)9, (methanol)9, and the (methanol)8-water heterononamer were designed and optimized. The measurements taken include geometrical, energetic, and topological data. The binding energy (nonamerization) is the difference between the energy of the heterononamer and the sum of the energy of each isolated monomer. In the same way, other state functions (ΔH, ΔS, and ΔG) were calculated. As an example, the following are the energy data of Hnon-I: ΔE = -72.58 kcal/mol; ΔH = -81.09 kcal/mol; ΔS = 0.275 kcal/K*mol, and ΔG = 0.99 kcal/mol. These results imply that the formation of Hnon-I is a highly exothermic and no spontaneous process. It was found that the cycles formed by the O-H---O interactions are fundamental for the stability of the heterononamer regardless of its nature. The weakest interactions (C-H---O and H---H) were revealed by means of the molecular graphs calculated through the topological analysis of the electronic density according to the Quantum Theory of Atoms in Molecules.