The radical-anion of thioxanthen SS-dioxide is non-planar. The spectra of the 9-methyl and 9-phenyl derivatives show that in these radical-anions the substituent, contrary to the situation in the neutral parent, is in the boatequatorial position. These radicals are unstable and the solutions, at low temperature in contact with potassium give fluorene or biphenyl radical-anions or their derivatives.