Kamlet-Taft equation

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. 

Kamlet-Taft Linear Solvation Energy Relationships. Most recent works on LSERs are based on a powerfiil predictive model, known as the Kamlet-Taft model (257), which has provided a framework for numerous studies into specific molecular thermodynamic properties of solvent—solute systems. This model is based on an equation having three conceptually expHcit terms (258). 

This approach to separating the different types of interaetions eontributing to a net solvent effeet has elieited much interest. Tests of the tt, a, and p seales on other solvatochromie or related proeesses have been made, an alternative tt seale based on ehemieally different solvatochromie dyes has been proposed, and the contribution of solvent polarizability to ir has been studied. Opinion is not unanimous, however, that the Kamlet-Taft system eonstitutes the best or ultimate extrathermodynamie approaeh to the study of solvent effeets. There are two objections One of these is to the averaging process by which many model phenomena are eombined to yield a single best-fit value. We eneountered this problem in Section 7.2 when we eonsidered alternative definitions of the Hammett substituent eonstant, and similar eomments apply here Reiehardt has diseussed this in the eontext of the Kamlet-Taft parameters. - The seeond objeetion is to the elaim of generality for the parameters and the eorrelation equation we will return to this eontroversy later. 

The relative importance of the hafide anion - HO - Cell interactions can be inferred from application of the Taft-Kamlet-Abboud equation to the UV-Vis absorbance data of solvatochromic probes, dissolved in cellulose solutions in different solvent systems, including LiCl/DMAc and LiCl/N-methyl-2-pyrrolidinone [96]. According to this equation, the microscopic polarity measured by the indicator, Ej (indicator), in kcalmol is correlated with the properties of the solvents by Eq. 1 ... 

H-bonding is an important, but not the sole, interatomic interaction. Thus, total energy is usually calculated as the sum of steric, electrostatic, H-bonding and other components of interatomic interactions. A similar situation holds with QSAR studies of any property (activity) where H-bond parameters are used in combination with other descriptors. For example, five molecular descriptors are applied in the solvation equation of Kamlet-Taft-Abraham excess of molecular refraction (Rj), which models dispersion force interactions arising from the polarizability of n- and n-electrons the solute polarity/polarizability (ir ) due to solute-solvent interactions between bond dipoles and induced dipoles overall or summation H-bond acidity (2a ) overall or summation H-bond basicity (2(3 ) and McGowan volume (VJ [53] ... 

In this respect, the solvatochromic approach developed by Kamlet, Taft and coworkers38 which defines four parameters n. a, ji and <5 (with the addition of others when the need arose), to evaluate the different solvent effects, was highly successful in describing the solvent effects on the rates of reactions, as well as in NMR chemical shifts, IR, UV and fluorescence spectra, sol vent-water partition coefficients etc.38. In addition to the polarity/polarizability of the solvent, measured by the solvatochromic parameter ir, the aptitude to donate a hydrogen atom to form a hydrogen bond, measured by a, or its tendency to provide a pair of electrons to such a bond, /, and the cavity effect (or Hildebrand solubility parameter), S, are integrated in a multi-parametric equation to rationalize the solvent effects. 

The study of solute-solvent and solvent-solvent interactions in mixed solvents has been gaining significance in recent years61-64, because of the increasing application of these solvents. Casassas and collaborators67 have used the Kamlet-Taft multiparametric equation for the correlation of dissociation constants of acids in 1, 4-dioxane-water mixtures. They found that when the main solvent is retained the property does not involve significant changes in the cavity volumes and, in those cases, the pK in binary solvents can be described by equation 8 ... 

Studies of medium effects on hexacyanoferrate(II) reductions have included those of dioxygen,iodate, peroxodisulfate, - [Co(NH3)5(DMSO)] +, and [Co(en)2Br2]+. Rate constants for reaction with dioxygen depended strongly on the electron-donor properties of the organic cosolvent. Rate constants for reduction of peroxodisulfate in several binary aqueous media were analyzed into their ion association and subsequent electron transfer components. Rate constants for reduction of [Co(en)2Br2] in methanol water and dioxan water mixtures were analyzed by a variety of correlatory equations (dielectric constant Grunwald-Winstein Swain Kamlet-Taft). 

Equations containing a number of solvent parameters in linear or multiple linear regression and expressing the effect of the solvent on the rate of the reaction or the thermodynamic equilibrium constant. See Ej Values Kamlet-Taft Solvent Parameter Koppel-Palm Solvent Parameter Z Value... 

Multiparametric models of solvent effects are the IMF and the Kamlet-Taft-Abraham equations. 

Equation (10) is only one example of several multiparametric equations17 that may be used to forecast the effect of variation of solvent on rates of reaction. One such equation18 that has been applied in organic chemistry is that of Kamlet and Taft (equation 11) ... 

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],... 

GRUNWALD-WlNSTEIN EQUATION IONIZING POWER KAMLET-TAFT SOLVENT PARAMETERS Z-VALUE. 

GRUNWALD-WlNSTEIN EQUATION KAMLET-TAFT SOLVENT PARAMETERS KOPPEL-PALM SOLVENT PARAMETERS SOLVOPHOBICITY PARAMETER Z-VALUE. 

In a series of publications using this approach, a number of equations were developed that increased our understanding of the solvation forces acting in different media. Quantifying the polarity/polarizability contribution solely from solute structural input proved the most difficult. The Kamlet-Taft group, used dipole-moment squared and the symbol H, while Abraham et ai, used polarity (S) and added excess molar refract vity, E. 

A cmcial component of this treatment is the value of P°w for the distribution of the solute molecules between 1-octanol and water. This could be estimated from group contributions (Hansch and Leo 1979) but could also be related to other properties of the solutes, namely, their solvatochromic parameters according to Kamlet et al. (1984,1988). Their equation was tested for 245 solutes of all kinds with a correlation coefficient of 0.996 and a standard deviation of 0.13. Earlier, Kamlet, Taft and coworkers (Taft et al. 1985, Kamlet et al. 1986) applied the LSER concept directly to the solubility of non-electrolytes in water, independently of the octanol/water distribution. Subsequently, important differences between aliphatic and aromatic solutes were stressed (Kamlet et al. 1987). For liquid aliphatic solutes the expression ... 

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