Nucleophilicity Parameters of Arylsulfonyl-Substituted Halomethyl Anions

The rates of the reactions of the arylsulfonyl-substituted carbanions carrying α-chloro and α-bromo substituents (1a–e) with quinone methides 2a–g and benzylidenemalonates 2h and 2i in DMSO were determined photometrically at 20 °C. The reactions were performed under pseudo-first-order conditions, and the second-order rate constants were obtained as the slopes of the plots of the pseudo-first-order rate constants versus the concentrations of the reactants used in excess. The second-order rate constants correlate linearly with the parameters E of the reference electrophiles according to the linear free energy relationship log k2(20 °C) = sN(N + E), which allowed us to derive the nucleophile-specific parameters N and sN of carbanions 1a–e. The resulting nucleophilicity parameters N (23 < N < 29) reveal the title compounds to be among the most reactive nucleophiles so far integrated on our comprehensive nucleophilicity scale.