Polar Molecules In Nonpolar Solvents Research Articles

Multiparticle orientational correlations are responsible for the nonlinear dielectric effect: Analysis of temperature-dependent measurements for glycerol.

The nonlinear dielectric effect (NDE) is traditionally viewed as originating from saturation of the response of individual dipoles in a strong electric field. This mean-field view, mathematically described by the Langevin saturation function, predicts enhanced dielectric saturation at lower temperatures. In contrast, recent experiments for glycerol have shown a sharp increase of the NDE with increasing temperature. The formalism presented here splits the NDE into a sum of a term representing binary correlations of dipolar orientations and terms referring to three- and four-particle orientational correlations. Analysis of experimental data shows that the contribution of three- and four-particle correlations strongly increases at elevated temperatures. The mean-field picture of dielectric saturation as the origin of the NDE is inconsistent with observations. A positive NDE (increment of the field-dependent dielectric constant) is predicted for low-concentration solutions of polar molecules in nonpolar solvents. The dependence of the NDE on the concentration of the polar component is polynomial.

Direct Measurement of the Selective Microwave-Induced Heating of Agglomerates of Dipolar Molecules: The Origin of and Parameters Controlling a Microwave Specific Superheating Effect.

Agglomerates of polar molecules in nonpolar solvents are selectively heated by microwave radiation. The magnitude of the selective heating was directly measured by using the temperature dependence of the intensities of the Stokes and anti-Stokes bands in the Raman spectra of p-nitroanisole (pNA) and mesitylene. Under dynamic heating conditions, a large apparent temperature difference (ΔT) of over 100 °C was observed between the polar pNA solute and the nonpolar mesitylene solvent. This represents the first direct measurement of the selective microwave heating process. The magnitude of the selective microwave heating was affected by the properties of the agglomerated pNA. As the concentration of the pNA increases, the magnitude of the selective heating of the pNA was observed to decrease. This is explained by the tendency of the pNA dipoles to orient in an antiparallel fashion in the aggregates as measured by the Kirkwood g value, which decreased with increasing concentration. This effect reduces the net dipole moment of the agglomerates, which decreases the microwave absorption. After the radiation was terminated, the effective temperature of the dipolar molecules returned slowly to that of the medium. The slow heat transfer was modeled successfully by treating the solutions as a biphasic solvent/solute system. Based on modeling and the fact that the agglomerate can be heated above the boiling temperature of the solvent, an insulating layer of solvent vapor is suggested to form around the heated agglomerate, slowing convective heat transfer out of the agglomerate. This is an effect unique to microwave heating.

Time domain reflection methods for dielectric measurements to 10 GHz

Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

The rapid synthesis of organic compounds in microwave ovens

This work demonstrates that organic compounds can be synthesized up to 1240 times faster in sealed Teflon vessels in a microwave oven than by conventional (reflux) techniques. It is shown that all polar molecules absorb microwave energy rapidly and that the rate of energy absorption varies with the dielectric constant. The rates of reaction of polar molecules in nonpolar solvents are not increased appreciably by the microwave method. Also, the homogeneity of the reaction does not affect the rate enhancement. The rate enhancement arises predominantly because the oven superheats the solvent rapidly. Finally, pressure (temperature) measurements have shown that the maximum rate enhancement is achieved when the proper power level and volume of solvent are used. It appears that rate enhancements of approximately 200 are possible for many reactions if the reaction conditions are optimized.

On the separation of a broad dispersion curve in two debye contributions.

A new method to separate the absorption curves of very diluted solutions of polar molecules in nonpolar solvents is developed. By taking the slopes of the wings computing an asymmetry-parameter the fit results in two weighted Debye-terms. In the log/log representation graphical methods yield in sufficient results.

An algorithm for computing dimerization constants for polar molecules

Abstract An iterative procedure is described for determining association constants of polar molecules in nonpolar solvents from dielectric permittivity and concentration measurements. An algorithm is described for use with the TI-59 programmable calculator to carry out the computation.

Snowballing effect for electron solvation in dilute solutions of polar molecules in nonpolar solvents

Electron solvation in dilute solutions of polar molecules in nonpolar solvents involves a formation of a localized state by electron attachment to a pre-existing cluster, followed by subsequent attachment of polar molecules to that charged cluster. We studied the effect of subsequent attachment of polar molecules on the transition energy of the solvated electron by use of the continuum model, and found that subsequent attachment has a negligible effect on the transition energy. An implification of this finding is that the snowballing effect cannot probably be observed by means of optical methods. The relative importance of short-range and long-range interactions in electron solvation is also discussed.

Dielectric Absorption of Microwave in Dilute Solutions of Polar Molecules in Non-polar Solvents

Dielectric Absorption of Microwave in Dilute Solutions of Polar Molecules in Non-polar Solvents

Dielectric Absorption of Microwave in Dilute Solutions of Polar Molecules in Non-polar Solvents

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Fluctuations in the vicinity of probes in solutions, as indicated by the induction contribution to dielectric relaxation

Formal analysis of dielectric data on dilute solutions of rigid polar molecules in non-polar solvents yields a second (high frequency) absorption regio

On the dielectric constant of dilute solutions of polar molecules in non-polar solvents

Summary. — The dielectric constant e of an extremely dilute solution of a polar substance in a non-polar solvent is studied for the following model system : a simple cubic lattice with each site occupied either by an A molecule with polarizatbiliy αA or by a B molecule with polarizability αB and permanent dipole µ. This model is solved exactly to the first order in the mole fraction xB of B, leading to the quantity (dε/dxB)0. This same quantity is evaluated by means of the approximate theories of Debye and Onsager, and it is observed that, on replacing a lattice sum by a continuum integral, the exact formula for (dε/dxB)0 reduces to the Onsager expression. For the particular model system studied here, the Debye and Onsager approximations deviate in opposite directions from the exact value of (dε/dxB) o but the discrepancies are however slight in both cases. This suggests that permanent dipole moments evaluated from the dielectric constant of dilute solutions by means of the approximate formulae of either Debye or Onsager, are reliable within a few percents.

Formation of solvated electrons in dilute solutions of polar molecules in nonpolar solvents

Formation of solvated electrons in dilute solutions of polar molecules in nonpolar solvents

On the theory of the dielectric constant of dilute solutions of polar molecules in non-polar solvents

The dielectric constant of even a very dilute solution of polar molecules in non-polar solvents depends upon the geometry of how the non-polar molecules are arranged and how the polar molecules are placed relative to them. These are topological effects which the usual semi-macroscopic theories employing continuum approximations are inherently incapable of revealing. Their existence is demonstrated by making a microscopic calculation with classical mechanics in which for simplicity the non-polar molecules are treated as forming a cubic lattice, and in which isotropic harmonic oscillators are used to describe the polarizability. When the dipolar interaction between molecules is included in the second order, different formulas are obtained depending on whether the lattice is simple, body-centred or face-centred cubic, and whether the polar molecule goes in interstitially or at a regular lattice point. In the latter case, the formulas of Onsager and Buckingham are recovered if a lattice sum is arbitrarily rep...

Dielectric Absorption of Microwaves in Dilute Solutions of Polar Molecules in Non-Polar Solvents

Article Dielectric Absorption of Microwaves in Dilute Solutions of Polar Molecules in Non-Polar Solvents was published on May 1, 1972 in the journal Zeitschrift für Physikalische Chemie (volume 78, issue 3_4).

Dielectric studies. Part XIX. Molecular relaxation of some rigid molecules

The dielectric absorption at five microwave frequencies of solutions of seven rigid polar molecules in nonpolar solvents has been examined as also has cyclohexanone. Furan, pyridine, and thiophene have their dipole moments along the major axis and their dielectric absorption should be characterized by a single relaxation time. Unlike the monohalobenzenes, camphor, pentamethylene sulfide, tetrahydropyran, and s-trioxan, however, furan, pyridine, and thiophene have non-zero distribution coefficients at 25 °C, whereas for pyridine at 50 °C and cyclohexanone at 25 °C the value is zero. The non-zero distribution coefficients are to be related to either weak solute-solute or solute-solvent interactions, resulting in the polar molecule experiencing a variety of local environments. The observed relaxation times of furan, pyridine, and thiophene are comparable with those of other rigid molecules of similar shape and size. For such cases, even though the distribution parameters are not zero, it is not feasible to analyze the dielectric data into contributions from more than one relaxation process.

Calculation of infrared band shapes in liquid solutions of diatomic polar molecules in nonpolar solvents

The calculation of the infrared band shapes of a polar diatomic molecule in a nonpolar solvent is performed by using a cell model to represent the solution and by introducing the torque on its rotational motion due to the simultaneuous influence of the surrounding molecules. The average deformation of rotational wave functions is taken into account in zero order of the calculation. The fluctuation of the solute-solvent interaction potential energy around this average value is found to be responsible for the broadening of the these discrete components. The resulting spectral band shape is compared with the experimental data nd some conclusions are discussed.

Dielectric properties of polar solutes in non-polar solvents at microwave frequencies

The dielectric loss and permittivity of solutions of polar molecules in non-polar solvents have been measured at frequencies 9.2 × 109 c/s and 3.5 × 1010 c/s. At the lower frequency independent determinations of absorption and wavelength were made on solutions of benzophenone over the temperature range 10 to 30° C. At the higher frequency the solute investigated was nitromethane and the temperature range was 10 to 40° C. Values of dipole moments obtained were 2.95 Debye units and 2.855 Debye units for benzophenone and nitromethane respectively.

POLARIZATION MEASUREMENTS ON CARBOXYLIC ACIDS IN DILUTE SOLUTION IN NON‐POLAR SOLVENTS

The effective use of dielectric polarization measurements in investigating the association of polar molecules in non-polar solvents has been largely confined to a study of the association of alcohols. These show significant changes in their state of aggregation in a range of concentrations sufEiciently high so that the equipment and methods hitherto available for dielectric constant measurements in solutions can be successfully applied to the investigation of their extent of association. The case of the carboxylic acids in non-polar solvents is quite different. Freezing point determinations show that extremely low concentrations must be attained before significant changes in the state of aggregation occur. This range of concentrations in the case of many of the acids lies below 2 X mole fraction. As a consequence it has been difficult to make sufficiently accurate measurements by most of the methods for molecular weight determination in solution to yield quantitative information about the molecular state of these acids in dilute solution in non-polar solvents. While it has been possible to use the freezing point method, this is applicable only a t a single temperature and so gives information about temperature coefficients and energies of association only through the use of estimates made at other temperatures by other methods. In this paper a description will be given of some of the improvements which were made in apparatus and methods in order to carry out dielectric polarization measurements in very low concentrations in non-polar solvents under anhydrous conditions. In view of the low concentrations involved it is necessary to include a comprehensive statement of the errors of the method. A detailed discussion of the methods employed for interpreting and analyzing the results from the standpoint of the association of the solutes is aIso incIuded.