Interaction of dimethyl sulphoxide with chloranil by ESR and optical methods

The molecular charge-transfer absorption bands have been observed in solution of dimethyl sulphoxide (DMSO) and tetrachloro-p-benzoquinone (chloranil) in chloroform and cyclohexanone. The stability constant, the thermodynamic parameter of the complex and the extinction co-efficient of CT bands at 350 nm in chloroform and 360 nm in cylohexanone have been estimated on the assumption of the 1:1 complex formation. Detection of ESR signal of the solution of chloranil in pure DMSO (g ≈ 2) indicates the formation of chloranil radical anion, the precursor being the charge-transfer complex, which dissociates partly in high dielectric constant DMSO.