RELATIVE SOLUTION ELECTRON-AFFINITIES OF SELECTIVELY DEUTERIATED PYRENES - CORRELATIONS BETWEEN VOLTAMMETRIC, ELECTRON-PARAMAGNETIC-RESONANCE, AND SEMIEMPIRICAL PM3 DATA

The equilibrium isotope effects (EIE) for the one-electron transfer be tween pyrene and seven regioselectively deuteriated pyrene isotopic is omers in dimethylformamide with 0.1 M tetrabutylammonium hexafluoropho sphate were measured electrochemically. These data correlate linearly with the free energies (Delta G(o)) obtained in tetrahydrofuran using electron paramagnetic resonance (EPR) techniques. However, the slope o f the resulting line is not unity, and it indicates that the EIE in th e DMF system is only two-thirds of that in the THF system. PM3 calcula ted Delta G(o,)s, which would correspond to the gas phase electron tra nsfers, also correlate linearly with both sets of experimental data, b ut the predicted magnitudes of the EIE's are smaller than those observ ed experimentally by either technique. The nonunity slopes probably re flect slight differences in ion solvation and/or ion association param eters between the anion radicals of the isotopic isomers. No general r elationship between the EIE and the charge on the hydrogen/deuterium s ubstituted carbon atom was found.