Dielectric constants Table

In addition, a marked influence of solvent polarity on AG was found to be exemplified for triafulvene 227, which showed a decrease of AG when measured in solvents with higher dielectric constants (Table 13). 

When solvated ions migrate within the electrolyte, the drag force applied by the surrounding solvent molecules is measured by solvent viscosity rj. Thus, in a solvent of lower viscosity, the solvated ions would move more easily in response to an applied electric field, as expressed by the Einstein—Stokes relation (eq 3). Solvents of low viscosity have always been considered the ideal candidates for electrolyte application however, their actual use was restricted because most of these solvents have low dielectric constants (Tables 1 and 2) and cannot dissociate ions effectively enough to prevent ion pairing. 

A key requirement for solvents in electrochemical systems is their ability to form conductive electrolyte solutions. The possibility of dissolving salts and separating ions in solution depends on the polarity of the solvent. A primary measure for the polarity of solvents can be properties such as the dielectric constant (Table 1) or dipole moment, which influences electrostatic interactions of solvents with solutes. However, these parameters are not sufficient for an appropriate evaluation of solvents for electrochemistry. The crucial problem with their use is that the solvating power of a solvent is a fairly complex quantity which depends on... 

Not only is water the most plentiful solvent, it is also a most successful and useful solvent. There are several facts that support this description. First, the dissolution of true electtolytes occurs by solvation (Chapter 2) and therefore depends on the free energy of solvation. A sizable fraction of this free energy depends on electrostatic forces. It follows that the greater the dielectric constant of the solvent, the greater is its ability to dissolve true electrolytes. Since water has a particularly high dielectric constant (Table 4.23), it is a successful solvent for true electrolytes. 

Solvents with low dielectric constants have been utilized to stabilize peptide solutions (Brennan and Clarke, 1993). Specifically, the rate of asparagine deamidation for Val-Tyr-Pro-Asn-Gly-Ala (pH 7.4) in water, glycerol, EtOH and dioxane decreased with decreasing dielectric constant (Table 4). Theoretically, the decrease in the rate of deamidation may be due to destabilization of the deprotonated nitrogen anion in the peptide backbone responsible for attack on the asparagine side chain and formation of the succinimide intermediate. Similarly, increasing ratios of organic content decreased the deamidation rate of Boc-Asn-Gly-Gly-NHg due to a decrease in dielectric constant, where deamidation data was collected in water, MeOH, EtOH, dioxane, acetone and acetonitrile (Table 4) (Capasso etal., 1991). 

Accordingly, we identify 12.4 eV as the value of Eg from our bonding model. This closely agrees with Eg = 12.2 eV, found from the dielectric constant. Table 5.6 contains comparisons of the same kind for ionic compounds. The agreement is surprisingly good, since the excited states contributing to the polarizability need not be the same as the lowest excited states in the UV spectrum. 

Table 1 shows the extraction conditions selected to optimize the extraction of antioxidants from Spirulina platensis. As mentioned, different combinations between solvent composition and temperature were tested in order to cover a wide range of dielectric constants. Since dielectric constant of water drops when increasing temperature, approaching to that of an organic solvent (such as medianol), we were interested in knowing if it could be possible to achieve approximately the same antioxidant composition (and activity) using mixtures of similar dielectric constants or if the composition would mainly depend on the selectivity of the solvent used (and therefore not directly dependant on the dielectric constant). Table 1 also shows the ECso values measured at all the conditions tested. 

To the difference of other fluorophores such as TNS or calcofluor, the position of the emission peak of porphyrin does not depend on the medium polarity or dielectric constant (Table 9.4 and Fig. 9.10). 

A rough indication of a solvents polarity is a quantity called the dielectric constant. The dielectric constant is a measure of the solvents ability to insulate opposite charges (or separate ions) from each other. Electrostatic attractions and repulsions between ions are smaller in solvents with higher dielectric constants. Table 6.4 gives the dielectric constants of some common solvents. 

What is special about water A solvent should solubilize all reactants and also absorb excess heat that may be liberated by the reaction. A very important property of a solvent is polarity, which largely determines its abfiity to solvate and separate ions (solvation). A good measure of the ability to separate ions is the dielectric constant. " Table 13.2 shows the dielectric constants for several common solvents, where a high dielectric constant indicates that the solution can conduct a crurent, which is associated with an increase in ion formation (i.e., the solvent facihtates ionization). This table also appears as Table 11.2 in Chapter 11. 

Lorentz-Lorentz molar refractions, Rll> Gladstone-Dale molar refractions, Rq, can be used with Eqs. (58) and (59) to estimate dielectric constants. The estimated dielectric constants (Table 15) are lower than the reported experimental values [60] ... 

Frequency. The dielectric constant of glass decreases very slightly with increasing frequency (see Fig. 2.36). At frequencies above 50 Hz, the relatively long relaxation times typical of sihcate glass structures prevents an increase in the dielectric constant. Table 2.9 lists the dielectric constants at several frequencies for a number of commercial glasses. 

For these applications, one is looking for materials with very low dielectric constant. Table 4-2 lists typical dielectric constant values of various plastics. The dielectric constant of air (or vacuum) is 1 at all frequencies. The dielectric constant of plastics varies from 2 to 20. 

The dielectric constant of water is defined as 80 relative to that of a vacuum. Thus energy of the bond between two point charges separated by two picometres in water would be 80 times less than the eneigy of the bond in a vacuum and have a value of ca. 8 kf moP. Water is the best solvent for ionic compounds because of its high dielectric constant Table 1.4 shows the dielectric constants of some common solvents. Sodium chloride dissolves in water at 1 g in 2.8 mL and in glycerol, which has half the dielectric constant of water 1 g dissolves in 10 mL. Sodium chloride is almost insoluble in ethanol in this case the dielectric constant is too low for the inter-ionic attraction to be overcome. 

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