The effective dipole moments of isobutyric acid in the liquid state and dilute solutions in methanol |
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Authors: | A. Yu. Osadchev T. P. Stepanova |
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Affiliation: | (1) Institute of Macromolecular Compounds, Russian Academy of Sciences, Bol’shoi pr. 31, St. Petersburg, 199004, Russia |
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Abstract: | The dipole moments of isobutyric acid (I) were determined in the liquid state (μ1) and dilute solutions in methanol (μ1) at 20–50°C. The permittivity of I in the liquid state was found to increase as the temperature grew, and the permittivity of solutions of I was lower than that of pure methanol; it decreased as the concentration of I and the temperature of solutions increased. The effective dipole moments of I were calculated using the Onsager polarization theory for the pure liquid and the Buckingham statistical polarization theory for solutions with various acid concentrations in methanol. The small μ1 (~0.8 D) and higher μ2 (~3.0 D) values compared with the dipole moment of I in the gas phase μ0 (1.9 D) were analyzed as determined by the character of acid-acid, acid-solvent, and solvent-solvent intermolecular interactions, a key role in which was played by H-bonds. An analysis of the dipole moments of I in methanolic solutions led us to conclude that the μ1 and μ2 values corresponded to the dipole moments of associates and solvates comprising like and unlike molecules linked by intermolecular H-bonds. Their stoichiometry changed as the temperature increased. |
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