The solvatochromic parameters are intended for use in linear solvation energy relationships (or, in the case of solute/solute interactions, linear complexation energy relationships) of the generalized form XYZ = XYZ0 + s(x* + dS) + aa + 6/3 + WH + e{. This equation may be reduced to a more manageable form by a judicious choice of solvents and reactants or indicators. One-, two-, and three-parameter correlations involving different combinations of the above parameters and various types of physicochemical properties are demonstrated. A comprehensive and up-to-date collection of x*, a, and ß values is presented.The present paper demonstrates how the solvatochromic comparison method may be used to unravel, quantify, correlate and rationalize multiple interacting solvent effects on many types of physicochemical properties and reactivity parameters. A further purpose is to assemble in one convenient reference an up-to-date (as of Feb 1983) and comprehensive collection of the solvatochromic parameters x*, a, and ß. The x* scale is an index of solvent dipolarity/polarizability, which measures the ability of the solvent to stabilize a charge or a dipole by virtue of its dielectric effect.1'4 56789101112Values of x* for "select solvents", nonchlorinated nonprotonic aliphatic solvents with a single dominant bond dipole, have been shown to be generally proportional to molecular dipole moments.4 The a scale of solvent HBD (hydrogen-bond donor) acidities describes the ability of the solvent to donate a proton in a solvent-to-solute hydrogen bond.1,5-7 The ß scale of HBA (hydrogen-bond acceptor) basicities provides a measure of the solvent's ability to accept a proton (donate an electron pair) in a solute-to-solvent hydrogen bond.1,8-11 The ß scale has also been used to evaluate hydrogenbond-acceptor strengths of solid HBA bases dissolved in non-HBA solvents.Rather than being based on solvent effects on single indicators, as has been the case for most earlier solvent property scales,1,12 the solvatochromic parameters were (1)

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