Reactions of Carbanions with Electron Acceptors

Article abstract of DOI:10.1021/jo00208a001

Second-order rate constants for reactions of families of 9-substituted fluorenide ions, 9-R-Fl(-), and related carbanions in Me2SO solution with the electron acceptors PhSO2CH2Br, PhSO2CH(Ph)Br, PhSO2C(Me)(Ph)Br, Me2CBr2, Me2C(NO2)X, PhS(O)CH2Cl, Me2C(SO2Ph)2, and Ph2I(+)Cl(-) have been measured.The carbanions used varied in basicity over a range of about 20pK_HA units.For a given family, Broensted plots of log k vs. pK_HA were linear, with slopes usually near unity.The relative order of rate constants correlated for the most part with the order of reduction potentials of the electron acceptors.The carbanions were converted by the electron acceptors to dimers, i.e., 9-R-Fl^- -> (9-R-Fl)2, by way of a single electron transfer (e^-_T) mechanism.The Broensted lines for the e^-_T reactions of the GC6H4C(Me)CN^- ion family (G = p-Cl, H, and p-Me) and the 9-t-BuFl^- ion family were displaced below that of the 9-MeFl^- ion family (slower rates); the kinetic points for PhC(Me)SO2Ph^- and Ph2CSO2Ph^- ions fell near the 9-t-BuFl^- ion family line.It is demonstrated that carbanions too weakly basic to undergo thermal e^-_T with a given electron acceptor can be made to undergo comparable e^-_T reactions under photostimulation.