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.