Evaluation of a 4 MHz integrated circuit oscillator for the measurement of solute dipole moments in dilute solution

A simple device for the measurement of solute dipole moments in dilute solutions of nonpolar solvents is described and evaluated. The device is based on an integrated circuit radio frequency oscillator and is demonstrated to be capable of measuring changes in solution dielectric constant of less than one part in 10 000. This allows the measurement of solute dipole moments using solutions in the 0.0001–0.005 molar range. Solute–solute interactions are shown to be minimized within this concentration range, and a simple means of extracting the solute dipole moment from concentration-dependent dielectric constant measurements is described. Dipole moments of para-(dimethylamino)benzonitrile, nitrobenzene, para-(nitro)anisole, and para-(nitro)aniline are measured, and are shown to compare favorably with previously reported values. The device is demonstrated to be capable of distinguishing solution dielectric constant changes associated with solute concentration changes as low as 3×10−5 M. It is therefore well suited to the measurement of dipole moments of polar compounds whose solubility in nonpolar solvent is low.