Quantitative aspects of the solvation of semiquinones in water + HMPA mixtures

Abstract

The e.s.r. spectra of semiquinones generally vary smoothly with the molar ratio of water to hexamethylphosphoramide (HMPA). Detailed analysis of this variation leads to equilibrium constants which are a measure of the affinity of a radical for HMPA compared to that for water. When there is sufficient HMPA in the solution, the dianions of hydroxysemiquinones give way to the corresponding singly-charged species, providing additional evidence for the formation of a stable complex between the two solvents, of the form HMPA. 2H₂O.