A study of the hydrolysis of the ester, methyl benzoate, shows that the discovery of a reaction mechanism includes a determination of the chemical equation, the structures of the reactants and products, the fate of each atom of the reactants, and the structures of the intermediate molecules. The concepts of bond polarity and the effect of varying the structure of the ester also provide valuable hints. The use of oxygen-18 and its detection in a mass spectrometer provide critical experimental data for the mechanism of the hydroxide-catalyzed hydrolysis of methyl benzoate. Science Consultants: Professor Henry Rapoport, University of California, Berkeley, and Dr. Philip Eaton, Department of Chemistry, University of Chicago. Wardâs Volume 16, CHEM Study #4166, 20 1/2 minutes. In color, 1989.