Grunwald-Winstein relationship

The Hammett equation is not the only LFER." ° Some, like the Hammett equation, correlate structural changes in reactants, but the Grunwald-Winstein relationship (see p. 452) correlates changes in solvent and the Brpnsted relation (see p. 337) relates acidity to catalysis. The Taft equation is a structure-reactivity equation that correlates only field effects. ... 

Other examples of linear free energy relationships include the Brpnsted relation, the Grunwald-Winstein relationship, and the Taft equation. See Rho Value... 

A disturbing feature of the Grunwald-Winstein analysis is that quite often different values of m are obtained for the same complex with different solvent pairs. This has been attributed to variation in the nucleophilicity, N, of the organic component of the solvent and a more complex relationship (10) has been proposed16 to account for the variation of rates in different solvents ... 

The Hammett and Taft equations are not the only linear free-energy relationships known. We shall encounter others—for example, the Bronsted relations, and the Grunwald-Winstein and Swain-Scott equations later in this book. 

There is an enormous amount of information on solvolyses in a variety of solvents, and linear free energy relationships, such as those of Grunwald and Winstein (1948), successfully correlate much of it. The Grunwald-Winstein Y relationship, in terms of solvent activity coefficients, becomes... 

The initial objective of our work was to quantify solvent effects (particularly solvent nucleophilicity) by adapting the Grunwald-Winstein equation (2) (5). In equation 2, k is the rate of solvolysis of a substrate (RX) in any solvent relative to 80% v/v ethanol-water (k0) and Y is the solvent ionizing power defined by m = 1.000 for solvolyses of tert-butyl chloride at 25 °C. In this chapter, a discussion of equation 2 and similar free-energy relationships is presented. At the time our work began (1969), in collaboration with Schleyer, mechanisms of solvolytic reactions were close to a high in controversy (6-8). More recent mechanistic developments (9-13) are not reviewed in detail here, but increased recognition of the importance of nucleophilic solvent assistance should be noted. 

On the other hand, transition-state positions in bromination can be evaluated from solvent effects and their Winstein-Grunwald m-coefficients, since these latter are related mainly to the magnitude of the charge in the activated complexes (p. 274). The p- and m-values for most olefins included either in selectivity relationship A (44) or in B (45) are compared in Table 17. The m-value varies significantly with the reactivity as does p. Since m-variations arise from transition-state shifts, p-variations necessarily come, at least in part, from the same effect. 

Assessments of solvent nucleophilicities are also available, again by comparing the rates of substitution of standard substrates in various media. A useful measure of solvent nucleophilidty is one based on the Winstein-Grunwald relationship... 

The influence of solvents upon the rates and mechanism of Sj l reactions was quantitatively studied by using the linear free energy relationships . Grunwald and Winstein have chosen the rate of solvolysis of f-butyl chloride in a solvent, (k ), relative to the rate, ( o)> of the same substrate in the standard solvent, taken arbitrarily to be ethanol-water at 25 °C, (PetoH 80%, as... 

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