Rates of proton abstraction from 4-nitrobenzyl halides

The rates of proton abstraction and carbanion protonation for 4-nitrobenzyl halides in aqueous and methanolic dimethyl sulphoxide have been determined. In addition, measurements have been made on some benzylidene and bis-(4-nitrophenyl)methyl halides in aqueous dimethyl sulphoxide. The effects of introducing a second halogen atom or a 4-nitrophenyl group upon both kinetic and thermodynamic acidities are discussed in terms of carbanion structure and solvent effects.