The kinetics of the ethanolysis of three triphenylmethyl chlorides, the 4-nitro, 4,4′-dinitro, and 4,4′,4″-trinitrophenylmethyl compounds, have been studied. The effect of change in substrate and solvent composition on the activation parameters, ΔH≠ and ΔS≠, has been determined. For these compounds, ΔH≠ appears to be controlled by substrate structure while ΔS≠varies predominantly with solvent composition.The attempted reaction of pyridine with 4,4′,4″-trinitrophenylmethyl chloride to form the quaternary ammonium salt is also reported.The reactions are interpreted to be proceeding via a carbonium ion-pair mechanism.