Linear free energy relationships in the electron-transfer reactions between Ph2COH and electron acceptors

The rates of the electron-transfer reaction between Ph2ĊOH and 40 electron acceptors (π) have been determined by ns laser flash photolysis to give a uniquely comprehensive set of such data for an important transient organic radical. The rate data have been correlated successfully with various measures of the electron-accepting power of π, depending on the availability of thermodynamic data, viz. the redox potential at pH 7 in water (E71), the polarographic half-wave potential in MeCN (E½), the Hammett σ constant, and the energy of the lowest unoccupied MO (ELUMO); thus the rate of reduction of XC6H4CO2H by Ph2ĊOH varies 103-fold with change in X, yielding ρ 3.11 ± 0.21.