Broensted Correlations for Electron Transfer from Carbanions to Halomethyl Phenyl Sulfone and 1,1-Dinitroalkane-Type Acceptors

Article abstract of DOI:10.1021/jo00134a003

9-Substituted fluorenyl carbanions, 9-G-Fl(1-), with G = Ar or Me, have been dimerized to (9-G-Fl)2 by reaction in Me2SO solution with PhSO2CH2X and R2C(NO2)X electron acceptors.Rate measurements revealed the following electron-accepting abilities: c-C6H10(NO2)2 > Me2C(NO2)2 > PhSO2CH2Br, PhSO2CH2I > c-C6H10(NO2)CN > c-C6H10(NO2)SO2C7H7 > Me2C(NO2)SO2C7H7 > PhSO2CH2Cl.The rate-limiting step in these reactions is electron transfer from 9-G-Fl(1-) to the electron acceptor.Plots of log k vs. pK_a of 9-G-FlH are linear with a slope near unity for all seven electron acceptors studied.We conclude that a Broensted β of unity is characteristic of electron transfer from carbanions to electron acceptors in Me2SO solution.This is interpreted to mean that the changes in ΔG⁰ brought about by changes in the basicity of the carbanion are matched by changes in ΔG(excit.), which correspond to the difference in the energy gap between the HOMO of the donor and the LUMO of the acceptor.