Diminished solution electron affinities of ¹³C- and deuterium-substituted anion radical precursors allow isotopic enrichment

Direct Voltammetric Determination of the Equilibrium Isotope Effect in Naphthalene‐h8/d8, Anthracene‐h10/d10, and Benzophenone‐12CO/13CO

“…The only difference between the studies lies in the identity of the cation used to maintain charge neutrality with the organic radical anion. In Stevenson's work (1,3,7,8), alkali metal reductants are used exclusively. Thus, the alkali metal cations serve as counterions.…”

“…Mechanical stresses that arise during charge-discharge can also lead to structural instability resulting in the fracture of substrate particle-particle bonds. The resulting increase in the resistance of the active material coupled with restructuring of the porous electrode may result in substantial changes in capacity as the electrode is cycled between charged and discharged states (1).…”

“…The possibility that one manifestation of an isotope effect is in the existence of an energy difference for the identical redox transformation between two different isotopically labeled isomers has been suggested by Stevenson and co-workers (1)(2)(3)(4)(5)(6)(7)(8). This is based on their observations that the equilibrium constant (Koq) for the electron selfexchange reaction [1] differs, in some cases dramatically, from unity A-+ *A = A + *A [1] where *A and A are the heavy and light isotopic isomers, respectively, and A-and *A-their corresponding one-electron reduction products.…”

“…This is based on their observations that the equilibrium constant (Koq) for the electron selfexchange reaction [1] differs, in some cases dramatically, from unity A-+ *A = A + *A [1] where *A and A are the heavy and light isotopic isomers, respectively, and A-and *A-their corresponding one-electron reduction products. In the work of Stevenson et al, either chemical separation of the reaction mixture followed by mass-spectral analysis or direct electron pragmatic resonance (EPR) or nuclear magnetic resonance (NMR) curve-fitting analysis of the reaction mixture has been used to determine Keq for [1] and thereby the magnitude of the isotope effect. If, in fact, differences in redox potentials are a manifestation of an isotope effect, then a careful electrochemical determination of the reduction potential for a pure sample of each of the isotopic isomers provides the most unambiguous and unequivocal verification of the existence of the isotope effect.…”

“…If, in fact, differences in redox potentials are a manifestation of an isotope effect, then a careful electrochemical determination of the reduction potential for a pure sample of each of the isotopic isomers provides the most unambiguous and unequivocal verification of the existence of the isotope effect. In addition, the difference in the reduction potential for the isomers provides the most reliable means of determining the equilibrium constant for reaction [1] and thereby the maximum possible isotope separation factor, a. This is because the results from electrochemical experiments are not dependent on or clouded by potential inefficiencies in subsequent chemical separation processes or difficulties inherent in theoretical simulations of complex EPR/NMR spectral patterns.…”