E Dielectric constant

Solvent Effects on the Rate of Substitution by the S l Mechanism Table 8 6 lists the relative rate of solvolysis of tert butyl chloride m several media m order of increasing dielectric constant (e) Dielectric constant is a measure of the ability of a material m this case the solvent to moderate the force of attraction between oppositely charged par tides compared with that of a standard The standard dielectric is a vacuum which is assigned a value e of exactly 1 The higher the dielectric constant e the better the medium is able to support separated positively and negatively charged species 8olvents... 

The 2eta potential (Fig. 8) is essentially the potential that can be measured at the surface of shear that forms if the sohd was to be moved relative to the surrounding ionic medium. Techniques for the measurement of the 2eta potentials of particles of various si2es are collectively known as electrokinetic potential measurement methods and include microelectrophoresis, streaming potential, sedimentation potential, and electro osmosis (19). A numerical value for 2eta potential from microelectrophoresis can be obtained to a first approximation from equation 2, where Tf = viscosity of the liquid, e = dielectric constant of the medium within the electrical double layer, = electrophoretic velocity, and E = electric field. 

T critical temperature density viscosity surface tension, P, compressibility at 1 atm, nj, refracuve index,e dielectric constant... 

The central role of the concept of polarity in chemistry arises from the electrical nature of matter. In the context of solution chemistry, solvent polarity is the ability of a solvent to stabilize (by solvation) charges or dipoles. " We have already seen that the physical quantities e (dielectric constant) and p (dipole moment) are quantitative measures of properties that must be related to the qualitative concept of... 

Becker and Israel (1979) have studied the influence of the solvent in more detail. They determined the constant KD of the equilibrium between free ions and ion pairs (Schemes 10-12 and 10-13) conductometrically in five solvents (H20, MeCN, MeOH, EtOH, and Me2CO). An inverse linear relationship was found between the ratio of products [ArOS]/[ArF] (where ArOS is the product of heterolytic solvolysis) and Kd/e (e = dielectric constant). This result indicates that solvolysis products are formed mainly from free diazonium ions, whereas fluoro-de-diazoniation takes place in the ion pair. Of the solvents used, acetone gives the lowest value of KD, and thus the yield of the fluorinated product is highest in this solvent. 

It follows from the depth of penetration of the nucrowaves, which is calculated from the formula d = -—= frequency, e = dielectric constant of the adsorb-... 

Note Oxygen activity +, ESR signal disappeared upon addition of oxygen —. ESR signal did not change upon addition of oxygen, d. Average diameter of particles e,. dielectric constant. (From Ref. 

Table 1.4 Solvent descriptors of organic solvents commonly used for biocatalysis. Sw/o (solubility of water in solvent, wt%) So/w (solubility of solvent in water, wt%) and e (dielectric constant) values from [78], log P (P = partition coefficient between octanol and water), ET (empirical polarity parameter by Reichardt-Dimroth) and HS (Hildebrand solubility parameter, )l, cm J, ) from [79].

Note e = electron charge NA = Avogadro s number z, = charge of ion of type Mt = molar concentration of ions in the bulk e = dielectric constant of the medium 4 = energy of attraction A = Hamaker constant d = distance between the surfaces 4 = energy of repulsion = ionic concentration (in number/volume) T0 1 17 = viscosity of the liquid u = electrophoretic mobility... 

De Kreuk [2] made the first systematic study of the various physical constants of nitric esters, i.e. dielectric constant (e20), refractive index (n ), density (df) and viscosity (r]20), (Table 2). Figures for tribromohydrin and triacetin are given for comparison. 

The influence of the polarity of solvents on their ability to dissolve nitrocellulose has been also demonstrated by Wo. Ostwald [50], who has introduced the value fi2/e as an expression characterizing the strength of solvent ( —dipole moment, e-dielectric constant). Good solvents of acetyl celluloses are characterized by a high iM2/s value. The physical significance of /i2/e is not clear, however, and its introduction has not helped to clarify the process of dissolution. 

The a carbon shifts of haloalkanes depend on temperature and solvent. Strong solvent effects are observed for the iodinated carbon atoms in iodoalkanes, as shown in Table 4.18 [253]. As expected from theory [254], carbon-13 solvent shifts are linearly dependent on (e — l)/(2e + n2) (e dielectric constant n refractive index) [253]. 

All attempts (74,89) to find a sensible, quantitative relation between the wavelength of maximum absorption ( max) and typical macroscopic properties of the solvent (i.e., dielectric constant) have so far failed (146). However, the size of the solvent cavity in which the electron is trapped also plays a decisive role (101) in determining the transition energy [Eqs. (2), (3)], and the solvent dependence of A.max might well indicate a variation in cavity size from solvent to solvent. In this spirit, Dorfman and Jou (48) have evaluated cavity radii on the basis of the simple Jortner model for the solvated electron. The values are shown in Fig. 3, which shows a plot of the optical transition energy max versus... 

Hi concentration of ionic species / (ion/cm3) radial flux of particles (particle cm 2 s ) e dielectric constant (dimensionless)... 

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