The reaction of methoxide ion with 2-nitro-4-trifluoromethylsulfonylanisole, 4-nitro-2-triftuoromethylsulfonylanisole and 2,4- bis(trifluoromethylsulfonyl)anisole in DMSO has been studied by1H and19F nmr. Evidence for the transient formation ofgem-dimethoxy σ-adducts arising from nucleophilic attack at the aromatic C1 carbon is given. Concurrent methoxide ion attack occurs at the sulfur atom of the SO2CF3group to give the aryl methyl sulfonates ArSO3CH3, which are slowly converted into aryl sulfonates ArSO3−. The1H chemical shifts of the anisoles are consistent with a greater electron-withdrawing effect of the SO2CF3group compared to the nitro group. In contrast, a 4-nitro group appears to be more efficient than a 4-SO2CF3group in delocalizing the negative charge of the σ-adducts.