INDEX solvatochromic parameters

The dielectric constant and refractive index parameters and different functions of them that describe the reactive field of solvent [45] are insufficient to characterize the solute-solvent interactions. For this reason, some empirical scales of solvent polarity based on either kinetic or spectroscopic measurements have been introduced [46,47]. The solvatochromic classification of solvents is based on spectroscopic measurements. The solvatochromic parameters refer to the properties of a molecule when its nearest neighbors are identical with itself, and they are average values for a number of select solutes and somewhat independent of solute identity. 

X0 is the value of the property in the gas phase. (In practice, X and X0 are often the logarithm of the property in question.) The parameters a and p are measures of a solvent s ability to donate and accept hydrogen bonds, respectively, and tt is an index of its polarity/polarizability. They were initially assigned on the basis of ultraviolet spectral shifts of certain dyes in a variety of solvents, and hence were labeled solvatochromic parameters.186"188... 

Three major approaches to the prediction of aqueous solubility of organic chemicals using Quantitative Structure Activity Relationship (QSAR) techniques arc reviewed. The rationale behind six QSAR models derived from these three approaches, and the quality of their fit to the experimental data are summarized. Their utility and predictive ability are examined and compared on a common basis. Three of the models employed octanol-water partition coefficient as the primary descriptor, while two others used the solvatochromic parameters. The sixth model utilized a combination of connectivity indexes and a modified polarizability parameter. Considering the case of usage, predictive ability, and the range of applicability, the model derived from the connectivity- polarizability approach appears to have greater utility value. 

The solvatochromic parameters are derived from spectroscopic and other measurements specifically designed to measure only a single interaction. In addition, the values are averages of the results from several solutes for each parameter and somewhat independent of solute identity. The most comprehensive solvatochromic treatment of solvent selectivity are the Tti, ai and Pi parameters of Kamlet and Taft, Table 4.15 [568-570, 578]. The rti value is an index of solvent dipolarity/polarizability, normalized to dimethyl sulfoxide = 1. The i scale of hydrogen-bond acidity measures the... 

Problems Eacouutered in Determining a Values. Considerably greater difHculties were encountered in the formulation of the a scale than with the other solvatochromic parameter indexes. Complications were of three main types ... 

Autoignition temperature Explosive limits in air CAS registry number Exposure limits Solubility parameter, 5 Hydrogen bond index, % Solvatochromic a Solvatochromic p Solvatochromic k ... 

Some mathematical treatments are considered useful to predict a wide range of physicochemical properties in addition to solute solubility. This commonality may more likely result from mathematical treatment than be based on chemistry. For example, the Jouyban-Acree model, which was involved from the equation treating nearly idea binary solvents (NIBS), has been applied to predict the physicochemical properties such as density, viscosity, relative permittivity, surface tension, solvatochromic parameter, refractive index, etc., of mixed solvent systems. For solute solubility, the model takes the form ... 

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