Oxibase scale

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. 

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]

R.E. Davis et al.. The Oxibase Scale and Displacement Reactions. XVII. The Reaction of Nucleophiles with Ethyl Tosylate and the Extension of the Oxibase Scale, J. Am. Chem. Soc., 1969, 91, 91. 

Equation 8.38 has been called an oxibase scale, since the E term is an oxidation term, while the H term is a basicity term Davis, R. E. in Janssen, M. J., Ed. Organosulfur Chemistry Wiley-Interscience New York, 1967 pp. 311-328. 

Ethyl 3-acyl-2-thioxo-l,3-oxazolidine-4-carboxylates are acylated (32) and phosphorylated (33) at N and alkylated (34) at S. The various reactions of benzothiazole-2-thiolate ion has been analyzed (35) using the oxibase scale. 

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. 

It is profitable to give a concrete example of the oxibase scale. 

The oxibase scale has been discussed by Edwards (1956 Edwards and Pearson, 1962) who now favors the equation written... 

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