The direct spectrophotometric analysis for carbanions was considered as a method for measuring the kinetics of proton transfer reactions. It was applied to the reaction of 2-nitropropane with piperidine in water and 50% acetonitrile-water solvents. A large solvent effect on the equilibrium was found. Deuterium isotope effects in both solvents were measured and a correlation with the work of Bell and Goodall, which says that kH/kD should be a maximum when delta pi kappa is zero, was shown. This method was considered to be useful over a very wide range of reactivities, but with the disadvantage that a very large number of kinetics runs are required to obtain a rate constant for one reaction.