Abstract
The signal response of an EPR active species is attenuated by the medium it is in. Keeping all other parameters the same, the higher the dielectric constant of the medium, the lower the EPR signal response. This behavior is problematic in studying EPR active species in high dielectric media but can be capitalized upon to monitor changes in the dielectric constant or estimate the dielectric constant of the medium. Using a coaxial EPR cell design, the EPR signal of a stable nitroxyl radical compound (2,2,6,6-tetramethyl-piperidin-1-oxyl radical) in a low dielectric constant solvent in an inner tube is attenuated by the solvent present between the inner and outer tubes (jacket medium). The attenuation increases monotonically with an increase in the dielectric constant of the jacket medium. Calibration curves can be constructed using jacket media of known dielectric constants ranging from 2 to 80 and the dielectric constant of a sample used as the jacket medium can be estimated by interpolation. This technique is applied to estimate the dielectric constants and/or composition of mixed solvents and to monitor the rate of a reaction.
Highlights
A static dielectric constant is a fundamental property of matter that reflects its ability to be polarized in an electric field
Using a coaxial electron paramagnetic resonance (EPR) cell design to eliminate any problems due to paramagnetic species differentially interacting with the medium being measured, we have shown that the EPR signal of a stable nitroxyl radical compound (2,2,6,6-tetramethyl-piperidin-1-oxyl radical) in a low dielectric constant solvent in an inner tube is attenuated by the solvent present between the inner and outer tubes
The use of this technique to measure dielectric constants requires the construction of a calibration curve for each set of experiments
Summary
A static dielectric constant is a fundamental property of matter that reflects its ability to be polarized in an electric field. 108−9 Hz) and there are no electrodes per se, frequency dependence and polarization phenomena are not as big a problem for ionic conductors Such microwave cavity equipment is often not readily available in chemistry laboratories, and special cavities are needed if corrosive or hygroscopic materials are to be measured. Keeping all other parameters the same, the higher the dielectric constant of the medium, the lower the EPR signal response This behavior is problematic in studying EPR active species in high dielectric media and generally such media are avoided or special thin cells designed to minimize the attenuation are used. Using a coaxial EPR cell design to eliminate any problems due to paramagnetic species differentially interacting with the medium being measured, we have shown that the EPR signal of a stable nitroxyl radical compound (2,2,6,6-tetramethyl-piperidin-1-oxyl radical) in a low dielectric constant solvent in an inner tube is attenuated by the solvent present between the inner and outer tubes (jacket medium). We report here initial studies of the use of this EPR technique to measure changes in dielectric constants of solvent mixtures, to measure solvent mixture compositions, to monitor reactions, and to determine dielectric constants
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