Solvent effect on the association equilibria of 1,4-benzosemiquinone—Li+ system

Association constants between 1,4-benzoquinone radical anion and lithium cation in organic solvents have been estimated by studying the variation in the polarographic half-wave potential for the reduction of 1,4-benzoquinone with solution composition. The ion pairs of contact type were identified in acetonitrile, propylene carbonate, dimethylformamide, dimethylacetamide, dimethylsulphoxide and diethylformamide using uv-vis spectrophotometry and esr technique. The association constant was observed to decrease with increase in the Lewis basicity of a solvent. It is shown that the logarithm of the association constant is a linear function of Gutmann's donicity; consequently the variation in association constant is discussed in terms of solvation of the cation. Structural aspects of the ionic interaction were computed according to the restricted LHP method in the π-approximation.