The effect of electron-withdrawing substituents on ion-ion interactions is exemplified by conductivity studies on dimethyl sulfoxide solutions of lithium acetate and fluoroacetates. Association constants decrease upon increasing fluorine substitution by a factor of 50. They are correlated with mean oxygen charges calculated with the help of semiempirical quantum mechanical methods. The distance parameters from such calculations prove to be good estimates for the liquid state. Non-Coulombic contributions of the CH3COO- ion to the ion-ion interactions show stronger competition with solvent molecules in the solvation shell of the Li+ ion than the CF3COO- ion, which is a weak ligand in comparison to the dimethyl sulfoxide molecule.