OBSERVATION OF A LINEAR CORRELATION BETWEEN DIMETHYL-SULFOXIDE SOLUTION REDUCTION POTENTIALS AND EQUILIBRIUM ACIDITIES FOR SUBSTITUTED METHYLANTHRACENES

With the aid of cyclic voltammetric techniques that utilize a platinum working electrode, we have determined reduction potentials for 15 variously substituted methylanthracenes in dimethyl sulfoxide (DMSO) solution. An excellent correlation is observed between reduction potentials for 10 10-substituted-9-methylanthracenes and absolute DMSO phase C-H acidities for the same 10-substituted-9-methylanthracenes: a plot of E(red) vs pK(a) for these species is linear (r = 0.989) with slope 0.77. 9-Methylanthracenes in which an anthrylic hydrogen atom has been replaced with SPh, CN, or NO2 substituent deviate from the E(red)/pK(a) correlation established by the 10-substituted-9-methylanthracenes. These results complement published gas-phase results (Fukuda, E. K.; McIver, R. T. J. Phys. Chem. 1983, 87, 2993-2995) and allow direct comparison of substituent effects on the stabilities of radical anions and carbanions derived from substituted 9-methylanthracenes when dissolved in DMSO.