Nucleophilicities of the Anions of Arylacetonitriles and Arylpropionitriles in Dimethyl Sulfoxide

The rates of the reactions of the colored para-substituted phenylacetonitrile anions 1a−c and the phenylpropionitrile anions 2a−c with Michael acceptors (3a−u) were determined by UV−vis spectroscopy in DMSO at 20 °C. The reactions follow second-order kinetics, and the corresponding rate constants k₂ obey the linear-free-energy relationship log k₂(20 °C) = s(N + E), from which the nucleophile-specific parameters N and s of the carbanions 1a−c and 2a−c have been derived. With nucleophilicity parameters from 19 < N < 29, they are among the most reactive nucleophiles which we have so far parametrized. In DMSO, the nucleophilicity of the tert-butoxide anion is comparable to that of the p-cyanophenylacetonitrile anion 1b.