1972 Volume 45 Issue 7 Pages 2083-2087
The effect of a solvent on the ultrasonic relaxation of propionic acid has been studied. The relaxation frequency is affected a little in hydrophilic solvents, while in non-hydrophilic solvents it shifts to a higher-frequency side. The activation enthalpy in a reaction from open to cyclic dimers decreases with dilution in the non-hydrophilic solvents; the magnitude of the change in the hydrophilic solvents is less than in the non-hydrophilic solvents. This means that the open dimer is destabilized by non-hydrophilic solvents. The sequence of the magnitude of the solvent effect on the relaxation frequency is consistent not with that estimated from the magnitude of the dielectric constant of the solvent, but with that estimated from the magnitude of the non-hydrophilic strength of the solvent. The stability of an open dimer in a hydrophilic or polar solvent is attributed to the interaction of the free OH group on the open dimer with the solvent.
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