Gas phase carbon and deuterium isotope effects on electron affinity of benzophenone: A combined experimental and theoretical study

Article abstract of DOI:10.1021/ja00126a022

Carbonyl-¹³C, ¹⁷O, and C₆D₅ isotope effects (IEs) on the electron transfer equilibrium between benzophenone and benzophenone radical anion were determined by means of fourier transfer ion cyclotron resonance (FT-ICR) measurements and the ab initio MO calculations (UHF/6-31G*). The experimental and theoretical IEs are in excellent agreement with each other (K₁₂/K₁₃ = 1.03 (50°C, ICR), 1.026 (50°C, MO) and K_D5/K_H5 = 1.35 (50°C, ICR), 1.325 (50°C, MO)). The carbonyl-¹³C, ¹⁷O, ring ¹³C₁₂, and D₁₀ IEs were calculated as 1.044, 1.025, 1.206, and 2.812, respectively, at -75°C. The carbonyl-¹³C and ¹⁷O IEs disagree with the reported IEs in liquid NH₃ (K₁₂/K₁₃ = 2.0, K₁₆//K₁₇ = 0.26, at -75°C, Stevenson et al. J. Phys. Chem. 1988, 92, 3687) and are close to unity as generally expected. The present results do not support the explanation in terms of an ion association effect in the liquid phase.