Lifetimes in water as short as 10-11 s have been determined forcarbocations and carbanions by referencing the rate of theirreaction with solvent species to that for the appropriate "clock"reaction, and equilibrium constants have been determined as theratio of rate constants for their formation and breakdown. Rate-equilibrium correlations for these organic ions are often poor andsometimes even defy the simple generalization that reactivityincreases with decreasing stability. This seemingly confusing bodyof data can be understood through consideration of the both theMarcus intrinsic barrier and the thermodynamic driving force toreaction of these organic ions.