Nucleophilicity scales Edwards

In Eq. (10-17), parameters a and b measure the sensitivity of the reaction to these nucleophilic parameters. Since H measures proton basicity and En the electron-donation ability, this treatment models nucleophilicity as a combination of electron loss and electron pair donation. The Edwards equation is thus an oxibase scale of nucleophilic reactivity. Table 10-5 summarizes the nucleophilic parameters. 

Various scales of nucleophilic reactivity for anions have been in use for several years (Swain and Scott, 1953 Edwards, 1956 Pearson et al., 1968 Ritchie, 1972 see also Bunnett, 1963 Ibne-Rasa, 1967 Hartshorn, 1973b), but quantitative scales of solvent nucleophilicity have only recently been developed. Peterson and Waller (1972) derived a scale of solvent nucleophilicity (APW) based on the... 

Verploegh and coworkers have attempted to be more critical. Using a variety of nucleophiles with 1-iodo or l-bromo-(2-thienyl)acetylene they have shown that good correlations may be obtained with the oxibase scale of Edwards, log Ar(Nu)/A (H20) = [Pg.409]

A scale of nucleophilicity, therefore, requires at least two parameters, and these were first provided empirically by Edwards with Equation 4.1.256... 

Broadly speaking, nucleophilicity correlates with reduction potential. Thus, stronger reducing agents tend to make better nucleophiles, which makes sense because both properties are related to electron donation. The correlation, however, is best limited to a set of structurally closely related nueleophiles. For a broader correlation, Edwards and Ritchie proposed an oxibase scale, which afforded a linear correlation of the reactivity of a nucleophile with the reduction potential of its oxidized form and the of its conjugate acid. Although space doesn t permit a more detailed discussion of this scale, redox potentials are broadly important for the subject matter of this book. 

Edwards scale of nucleophilicity is based on a combination of the reduction potentials of nucleophiles and their basicity ... 

Edwards (1954, 1956 Edwards and Pearson, 1962) has extended Foss s original suggestion by including both the oxidative dimerization potential and the basicity of the nucleophile in his empirical double basicity scale ... 

In Table IV the E and H values have been listed for numerous nucleophiles from the papers of Edwards (1954, 1956). In Table V the a and values are listed. The usefulness of the scale, illustrated in this article by estimation of the rate of reaction of iodide with (3-propiolactone will be great. Increased research activity in this area surely will be forthcoming. 

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