Nucleophilicities of the Anions of Arylacetonitriles and Arylpropionitriles in Dimethyl Sulfoxide

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