Adan Effio

Electric dipole moments in polar solvents. I. Audiofrequency measurement with slightly conducting solutions

Audiofrequency methods were used to measure dielectric constants of dilute solutions containing electrolytes up to free-ion concentrations of 10−4M. Using a calibrated transformer bridge, capacitance was measured with an accuracy of 0.03 pF at a conductance of 100 μmho and within 0.3 pF at 800 μmho. Evaluation of the double-layer capacitance from the frequency dependence of the data is discribed. The effect of the free ions on the dielectric constant is found to be relatively large and in reasonable agreement with the prediction of the Debye-Falkenhagen theory. The calculation of the electric dipole moment for polar solutes, including ion pairs, is discussed in terms of Kirkwoods theory. Experimental tests are described for finding out whether possible deviations of Kirk-woods correlation factors from unity may be neglected. These tests involve changing the solvent and the temperature. The tests were satisfied for the ion pairs of tetraisoamylammonium nitrate and for nitrobenzene in chlorobenzene and acetic acid.

Electric dipole moments in polar solvents. II. Tetraisoamylammonium nitrate ion pairs in chlorobenzene. Effect of mutual polarization of the ions

The dielectric constant and conductivity of dilute solutions of tetraisoamylammonium nitrate in chlorobenzene are measured between −34.6° and 99.0°C to give association constants for the formation of ion pairs (KA) and triple ions, and electric dipole moments. The quantityKA as a function of temperature is reproduced by the Denison-Ramsey-Fuoss treatment for unolarized ion pairs [Eq. (2)] with a distance of closest approach of 4.90 Å. The dielectric data are reproduced by Onsagers equation with an inherent (gas-phase) dipole moment of the ion pairs of 14.2±0.3 D. Other methods of calculation lead to consistent dipole moments, confirming that the mutual polarization of the ions is important. The energetics of ionic association is considered on the basis that the ion pair may be treated as a polarizable dipole in a spherical cavity.