Kamlet-Taft analysis

FIGURE 19. The good correlation found between the fluorescence maximum of 2N and solvent polarity using Kamlet-Taft analysis in 22 solvents. In this case no level crossing is evident and the emitting state is assumed to be Z-i, in all solvents (from Reference 91)... 

This problem may be tackled by a more systematic analysis of the Stokes shift. Pines and coworkers assumed that the first absorption transition of 1-naphthol and the two absorption transitions of 2-naphthol may be described by Pekarian functions. These functions were analyzed by the Kamlet-Taft analysis (Figures 25 and 26). 

Correlation analysis of solvent effects on the heterolysis of p-methoxyneophyl tosyl-ate has been performed by using the Koppel-Palm and Kamlet-Taft equations. The reaction rate is satisfactorily described by the electrophilicity and polarity parameters of solvents, but a possible role for polarizability or nucleophilicity parameters was also examined. 

The Kamlet-Taft scheme [189, 203, 204] represents a LEER for the analysis of a solvent environment via solvatochromic effects. The Kamlet-Taft model is similar to the form of Eq. (10), but is simplified... 

A number of studies have attempted to characterize ionic liquids through their dielectric constant, and all have observed inconsistencies between the measured dielectric constant and the solvation properties of the liquid. Recent experiments making use of dielectric reflectance spectroscopy [214] indicate dielectric constants in the range of 10-15 for a series of imidazolium-based ILs, substantially lower than those for molecular solvents observed to possess comparable polarities as estimated by solvatochromism. Weingartner [215] has recently published a series of static dielectric constants obtained from dielectric reflectance spectroscopy, and compared them with those of common molecular liquids. The analysis includes comparison with the Kamlet-Taft ji parameter for the liquids from Eq. (11) we have prepared a plot of n versus dielectric constant in Fig. 6. The relationship between n and e for molecular liquids... 

In 1994, a review on the further development and improvement of the n scale was given by Laurence, Abboud et al. [227], They redetermined n values for a total of 229 solvents, this time using only two (instead of seven) solvatochromic nitroaromatics as indicator compounds, i.e. 4-nitroanisole and A,A-dimethylamino-4-nitroaniline, for good reasons see later and reference [227] for a more detailed discussion. A thermodynamic analysis of the n scale [and the t(30) scale] has been reported by Matyushov et al. [228]. Using six novel diaza merocyanine dyes of the type R-N=N-R (R = N-methylpyridinium-4-yl or A-methylbenzothiazolium-2-yl, and R = 2,6-disubstituted 4-phenolates or 2-naphtholate) instead of nitroaromatics as positively solvatochromic probe compounds, an analogous n azo scale was developed by Buncel et al., which correlates reasonable well with the n scale, but has some advantages for a detailed discussion, see references [333], Another n scale, based solely on naphthalene, anthracene, and y9-carotene, was constructed by Abe [338], n values are mixed solvent parameters, measuring the solvent dipolarity and polarizability. The differences in the various n scales are caused by the different mixture of dipolarity and polarizability measured by the respective indicator. The n scale of Abe is practically independent of the solvent dipolarity, whereas Kamlet-Taft s n and Buncel s n azo reflect different contributions of both solvent dipolarity and polarizability. 

Dealing with this type of multiparameter correlation analysis, a series of twelve articles entitled Solubility Properties in Polymers and Biological Media was published by Kamlet, Taft, Abraham et al. (Part 1 [273]...Part 12 [274]), as well as another series entitled Solute Solvent Interactions in Chemical and Biological Systems (Part 4 [358]... Part 7 [359]). The application of the LSER equation (7-58) to the prediction of solubilities of organic nonelectrolytes in water, blood, and other body tissues has been reviewed [286],... 

The relative strength of the hydrogen-bonding interactions may also be estimated indirectly by correlating their effect on the optical transition frequencies of the chromophore. In the Kamlet-Taft (K-T) analysis , any solvent-influenced property of the solute... 

The decarboxylation rate of 3-carboxybenzisoxazoles depends on the substituent and strongly on the solvent, which is evidenced by the use of the empirical Kamlet-Taft-Abraham solvatochromic parameter set in a multilinear correlation analysis based on LSER, along with a theoretical computational set of molecular parameters <94JCS(P2)1641>. The effect of temperature and evaluation of thermodynamic parameters for the polarographic behavior of 3-methyl-4-(2 substituted benz-eneazo)-2-isoxazol-5-ones are reported <94Mi 303-02). 

A subsequent multiple linear regression analysis [138] focused on the Kamlet-Taft solvatochromic parameters, employing transfer Gibbs energies and enthalpies AG°t and AH°r) for 26 solvents. Standard molar Gibbs energies of transfer for nine univalent and six divalent small cations correlated well with the Kamlet-Taft parameters via linear solvation energy relationships of the form... 

Kamlet, M. J., Doherty, R. M., Veith, G. D., Taft, R. W., Abraham, M. H. (1986) Solubility properties in polymers and biological media. 7. An analysis toxicant properties that influence inhibition of bioluminescence in Photobacterium phosphoreum (the Microtox test). Environ. Sci. Technol. 20, 690-695. 

RW Taft, MH Abraham, GR Famini, RM Doherty, JL Abboud, MJ Kamlet. Solubility properties in polymers and biological media 5 an analysis of the physicochemical properties which influence octanol-water partition coefficients of aliphatic and aromatic solutes. J. Pharm. Sci. 74 807-814 (1985). 

For reviews of solvent polarity scales, see Abraham Grellier Abboud Doherty Taft Can. J. Chem. 1988,66. 2673-2686 Kamlet Abboud Taft Prog. Phys. Org. Chem. 1981,13,485-630 Shorter Correlation Analysis of Organic Reactivity Wiley New York, 1982, pp. 127-172 Reichardt, Ref. 386 Reichardt Dimroth, Ref. 386 Abraham Prog. Phys. Org. Chem. 1974, II, I -87 Koppel Palm, in Chapman Shorter Advances in Linear Free Energy Relationships, Plenum New York, 1972, pp. 203 280 Ref. 384. See also Chastrette Carrclto Tetrahedron 1962,38, 1615 Chastrette Rajzmann Chanon Purcell J. Am. Chem. Soc. 1965,107, 1. 

There have been other phenomenological approaches to rationalize (or even predict) the experimentally observed solvent effect on the chemical shift. Many chemists use the Kamlet-Abbout-Taft (KAT) set of solvatochromic parameters it, a and 8 [31], KAT parameters can be used together with the multiple linear analysis to describe the variation in the chemical shift of the solute as the solvent is varied. An extensive study of this type was conducted by Witanowski et al. to interpret the solvent effects on the shielding of l4N in a large set of compounds (see ref. [32] and references cited therein). For a nitroso aliphatic and aromatic series, solvent-induced shielding was indeed found to depend on the polarity of the solvent. However, other experience with this model suggests the need for caution. 

An analysis of Winstein s Y and N values and their modifications in terms of Kamlet and Taft s linear solvation energy relationship cf. Section 7.7) has been given by Abraham et al [288]. 

Interestingly, a statistical principal component analysis of the solvatochromic shift data sets previously used by Kamlet and Taft in defining the n scale has shown that, rather than one [n ), two solvent parameters (0ik and 02k) are necessary to describe the solvent-induced band shifts of the studied solvatochromic indicators [236]. This is not unexpected since the n parameters are assumed to consist of a blend of dipolarity and polarizability contributions to the solute/solvent interactions. 

The general SPP scale of solvent dipolarity/polarizability and the specific SB and SA scales of solvent HBA basicity and HBD acidity, respectively, are orthogonal to one another and they can be used in the correlation analysis of solvent effects in single- or, in combination with the others, in two- or three-parameter correlation equations, depending on the solvent-influenced process under consideration see also Section 7.7. Examples of the correlation analysis of a variety of other solvent-dependent processes by means of SPP, SB, and SA values, including those used for the introduction of other solvent polarity parameters, can be found in references [335-337, 340-342]. In particular, comparisons with Kamlet and Taft s n scale [340] and Winstein and Grunwald s Y scale [341] have been made. 

Kamlet, M.J., Doherty, P.J., Taft, R.W., Abraham, M.H., Veith, G.D. and Abraham, D.J. (1987a). Solubility Properties in Polymers and Biological Media. 8. An Analysis of the Factors that Influence Toxicides of Organic Nonelectrolytes to the Golden Orfe Fish Leuciscus idus mela-notus). Environ.ScLTechnol., 21,149-155. 

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