Hydration and Intermolecular Interactions in Carboxylic Acids

Abstract

At the moment, the most accurate and reliable information about intermolecular interactions in low-molecular compounds and their polymer analogues can be obtained by means of combined UV, visible, and IR spectroscopy. However, this combination is not always used when interpreting the results of intermolecular interactions in carboxylic acids. Therefore, the aim of our study was to investigate the intermolecular interactions in carboxylic acids and their hydration properties using the UV, visible, and IR spectroscopy. The article presents the results of the investigation of intermolecular interactions and hydration in carboxylic acids by means of UV, visible, and IR spectroscopy, and the microscopic study of the swelling/contraction curves of the beads of the sorbents with slightly acidic –СООН groups in exchange reactions of R–COOH + NaOH ↔ R–COO–Na+ + H2O. The study revealed a H-bond in the water dimers formed due to the Coulomb, exchange, charge transfer, polarisation, and dispersion components of the total energy of the hydrogen bonds. In our study we also tested the formulas for the calculation of the energy of the H-bond, enthalpy, the force constants of the Н-bond, and the elongation of the covalent bond. The article suggests a formula for calculating the distance RCH2…O, i.e. the length of the H-bond between the donor and the acceptor of the proton, based on the information about stretching vibrations in the IR spectra of carboxylic acids. We also specified the characteristic frequencies of the stretching and deformation vibrations of certain H-bonds and functional groups in fatty acids. The article demonstrates the possibility of the formation of five- and six-membered cycles, resulting from the formation of Н-bonds between СН2 groups of the chain and –СООН end groups of carboxylic acids. The characteristic electron and vibrational frequencies in the UV and IR spectra were used to determine the intermolecular interactions in ion exchangers CB-2 and CB-4. The microscopic and microphotographic study of the swelling of certain beads of carboxylic cationites helped to register the presence of the outer shell R–COO–…Me+ and the inner shell R-COOH during the exchange reactions: R–COOH + Me+ + OH– ↔ R–COO–…Me+ + H2O.

Keywords

• uv spectroscopy
• ir spectroscopy
• visible spectroscopy
• carboxylic acids
• intermolecular interactions