Dimroth-Reichardt value

Dimroth-Reichardt values (kcal/mol) for the longest-wavelength solvatochromic absorption based on a pyridinium- -phenoxide betaine dye no. 30. 

Physical organic chemists have tended to examine parameters based on shifts in the absorption peaks in the spectra of various dyes or indicator molecules. The a and P scales of Taft and Kamlet, the ET(30) scale of Dimroth and Reichardt, the 7t scale of Taft and co-workers and the Z value of Kosower are all examples of this type of parameter. The definitions and measurement means for these parameters, as well as important references, are shown in Table 5. An alternative definition of the Dimroth-Reichardt parameter is the dimensionless, ETN, which is now preferred by some organic chemists (for a discussion see Ref. 15). The Z value is important in that it led to the scale of Dimroth and Reichardt, which overcomes many of the limitations of the earlier scale. Several workers have shown that relationships exist, with good correlation coefficients, between similar parameters. Thus, DN is linearly related to p, both parameters being designed to measure the donor properties (or Lewis basicity) of solvent molecules. Also, Lr(30) is related to a as well as to AN all three parameters purport to measure the electron acceptor properties (or Lewis acidity) of solvent molecules. It has been found that different solvent types have different coefficients in linear relationships between n and the dipole moment. The Taft and Dimroth-Reichardt parameters, in particular, have been found to correlate with free energies and... 

The Kosower parameter (Z = //v) is derived from the effect of the solvent on the charge transfer spectrum of the pyridinium iodide (5) excitation. A high value of Z (the energy of the charge transfer transition) corresponds to highly polar solvents. Similar parameters have been obtained for other reporter molecules and the charge transfer system of 6 generates the Dimroth-Reichardt scale. 

C, Pc = 73.83 bar, = 0.467 g mL , ought to be utilized. [5] In terms of polarity, SC-CO2 [Dimroth-Reichardt t(30) value of 32 [6]] is roughly comparable to carbon tetrachloride. However, differences remain when the Kamlet-Taft n solvatochromicity parameter n = -0.2) [7] is taken into account. Thus, SC-CO2 could be used as a replacement for commonly used organic solvents. Until 1994 it appears that most experiments have been primarily governed by academic curiosity, however, interest has largely increased since. 

On the basis of these considerations, the wave-lengths of the absorption maxima of the above model, measured in various solvents, were used to calculate [Di 63, Re 69, Re 81, Di 73] the Dimroth-Reichardt Ej values, which were expressed in... 

The Gutmann acceptor numbers (AN) of some solvents are listed in Table 4.9, together with the Kosower Z values and the Dimroth-Reichardt Ej values characterizing the acceptor strengths. 

The phenomenological theory has been applied by Skwierczynski to the Et values of the Dimroth-Reichardt betaine, a quantity sensitive to the polarity of the medium. The approach is analogous to the earher development. We need only consider the solvation effect. The solute is already in solution at extremely low concentration, so solute-solute interactions need not be accoxmted for. The solvent cavity does not alter its size or shape dining an electronic transition (the Franck-Condon principle), so the general medium effect does not come into play. We write Ej. of the mixed solvent as a weighted average of contributions from the three states ... 

It is generally well understood that values of E1/2 can vary markedly as a function of solvent. Numerous papers have been published in this area and they often include correlations between E1/2 and one or more solvent parameters such as the Gutmann donor number, the Gutmann acceptor number, or the Dimroth-Reichardt parameter [14]. In general, values of E1/2 have been shown to correlate with the Gutmann donor number for electrode reactions of the type where n is a... 

The normalized Dimroth-Reichardt polarity index is preferably used, because its values are dimensionless and with values between zero and unity for the sake of comparison with other solvent property indexes used in LSER expressions ... 

The curves of the polarity and donicity indices as functions of the cosolvent mole fractions are generally nonlinear. The deviations AT in terms of Equation 3.42, where Y represents the Dimroth-Reichardt E/30) and the Kamlet-Taft %, a, and p (see Section 3.3.2), then express the properties of the solvent mixture that depend on the self- and mutual-interactions of its molecules. Expressions similar to (3.43) may then be used to fit the experimental AT values. The coefficients of this expression for j.(30) and x are shown in Table 3.17 and those for p and a are shown in Table 3.18, the values being adapted from data in compilations by Marcus [56, 87],... 

AN is known to show good correlations with the solvation energies of anions. Also, AN has good correlations with other solvent parameters defined in different reaction systems, e.g., Grunwald and Winstein s T-value [24], Kosower s Z-value [25], Dimroth and Reichardt s T Value [26,27], etc. 

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].

Then, Dimroth and Reichardt proposed a solvent polarity parameter, Ey(30), based on transition energy for the longest-wavelength solvatochromic absorption band of the pyridynium N-phenolate betaine dye, which is dye No. 30 in a table constructed by these authors. The x(30) values have been determined for more than 360 pure organic solvents and many binary solvent mixtures. 

Dimroth, K. Reichardt, C. Liebigs Ann. Chem. 1969, 727, 93. Values based on other ions have also been reported See, for example, Reichardt, C. Harbusch-Gornert, E. Schafer, G. Liebigs Ann. Chem. 1988, 839. 

The extraction (and hence the transport) efficiency depends on several diluent factors such as Schmidt empirical diluent parameter [124,125], the Swain s acity and basity parameters along with the Dimroth and Reichardt polarity indices [126], dielectric constant [127], refractive index [127] and viscosity [127], and the Hildebrand s solubility parameter [128]. The permeability coefficients (Paio) were computed from the Wlke-Chang, Scheibel, and Ratcliff [129,130] equations, which compared reasonably well with the experimentally determined values as shown in Table 31.10. Efiiassadi and Do [131] have, on the other hand, taken into account only the viscosity and solubility effect of the diluent and the carrier immobilized in SLM. They have reported that these two factors influenced the transport rates significantly. 

A number of solvent parameters such as the Z values (Kosower, I9S8) or By values (Reichardt and Dimroth, 1968 Reichardt and Harbusch-Gdmert, 1983 Buncel and Rajagopal, 1990) have been proposed. These characterize solvent polarity inclusive of all kinds of solvent-solute interactions. 

Dimroth and Reichardt devised a scale based on the solvatochromic behavior of the pyridinium-V-phenoxide betaine dye shown in Figure 1(a).5 The UV spectrum varies over several hundred nanometers according to the solvent in which it is dissolved. The wavenumber observed relates to T(30) or normalized f TN values. At one end of the TN scale is cyclohexane with a value of 0.006, and water lies at the other end with a value of 1.000. 

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