Dimroth-Reichardt

Another solvatochromic polarity measure, (30), is the transition energy for compound 8, which is 2,6-diphenyl-4-(2,4,6-triphenylpyridinio)phenolate, also referred to as Dimroth-Reichardt s betaine. 

The pyridine ylide of la is the parent compound of the Dimroth-Reichardt betaine dyes used to probe solvent polarity.71,72 These dyes show a very pronounced solvatochromism, and the shifts of the absorption maxima as a function of the solvent polarity has been used to establish the quantitative ET30 scale. 

The Dimroth-Reichardt betaines are synthesized by reactions of p-aminophenols with pyrylium salts bearing aryl substituents in ortho position. 

Dimroth. Reichardt Siepmann Bohlmann Liebigs Ann. Chem. 1963, 661, 1 Dimroth Reichardt Liebigs Ann Chem. 1969, 727. 93. See also Haak Engbcrts Reel. Trav Chim. Pays-Bas 1986, 105, 307. 

The correlation between the Dimroth-Reichardt ET(30) and the Kosower Z solvent polarity parameters, Eq. (4.8), both in kcal mol 1... 

The correlation between the Gutmann-Mayer AN scale and the Dimroth-Reichardt i T(30)/kcal mol"1 polarity/Lewis acidity scales, Eq. (4.14)... 

Oxygenation of 2-substituted adamantanes with methyl(trifluoromethyl)dioxirane showed a reaction constant, p = -2.31, consistent with a strongly electron-demanding transition state. Analysis of the effect of solvents on the rate yielded a positive regression coefficient with Dimroth-Reichardt Ej solvent polarity parameter. A mechanism involving an electrophilic O atom insertion has been postulated for the formation of alcohols and carbonyl compounds.201... 

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... 

Et polarity scale. A solvent polarity scale proposed by Dimroth, Reichardt and coworkers [Dimroth et al., 1963 Reichardt, 1965] based on the solvatochromic band shifts of the 4-(2,4,6-triphenylpyridinium)-2,6-diphenylphenoxide and its trimethyl derivative. This scale is one of the most comprehensive for the number of considered solvents and is widely used. 

Dimroth-Reichardt ET parameter A measure of the IONIZING POWER (loosely polarity) of a solvent, based on the maximum wave number of the longest wavelength electronic absorption band of... 

See also Dimroth-Reichardt et parameter Grunwald-Winstein equation. 

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. 

Solvatochromic effects occur then the color of a solute depends on the nature of the solvent in which it is dissolved. Two such systems were discussed in section 4.9. The first is the betaine dye, 4-(2,4,6-triphenylpyridinium)-2,6-diphenylphen-oxide, which is used to define the Dimroth-Reichardt parameter Ej. This molecule undergoes a ti ti transition in the visible region whose wavelength is very solvent dependent. In the strongly acidic solvent water it is equal to 453 nm which corresponds to an energy gap of 264kJmoH. In the very weakly acidic solvent diphenylether, the wavelength for the same transition is 810 nm. This corresponds... 

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

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. 

Dimroth-Reichardt t(30) solvatochromic polarity parameter in kJ/mol taken from [145]. 

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