Brownstein parameter

Univariate LSERs may possess the conventional LEER form, as exemplified by Eq. (8-67), the Grunwald-Winstein equation, or they may simply be plots of log k against a solvent parameter such as Z, (30), or ir. Brownstein developed an LEER form for the latter type of correlation, writing... 

There are numerous attempts to correlate solvent parameters with the reaction rate of Diels-Alder reactions122. Examples are the Brownstein Polarity Parameter S123, the Solvophobicity Parameter Sp124,125 the D-it parameter (based on the solvent effect on the reaction of tetracyanoethylene and diazodiphenylmethane with benzene as the reference solvent)126 or the Acceptor Number / /V127, l2X (a parameter which describes the ability of a solvent to act as an electron pair acceptor)129. These examples included either reactions that were next to insensitive to solvent effects (like that in Table 9) or reactions in which the reactants mainly interact with the electron pair on the donor atom of the solvent130. 

There are numerous attempts to correlate solvent parameters with the reaction rate of Diels-Alder reactions. Examples are the Brownstein Polarity Parameter 5, the Solvophobicity Parameter the D-n parameter (based on the solvent effect on... 

As a model system for confirmation of the correctness of the above correlation Brownstein used l-ethyl-4-carbomethoxypyridinium iodide, as proposed by Kosower. By definition, the R value relating to this is 1.00, and the S value relating to absolute ethanol is 1.00. The Kosower Z values served as the k values here. On the basis of the experimental data of Kosower, Brownstein calculated S and R for many systems, and found good correlations. Accordingly, he assumed that his equation was of general validity and suitable for the description of the solvent dependence not only of spectral data, but of any solvent-dependent experimental parameter. 

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