Hydration of Carbonyl Compounds, an Analysis in Terms of No Barrier Theory:  Prediction of Rates from Equilibrium Constants and Distortion Energies

“No Barrier Theory” postulates that when only one thing happens there is a quadratic relation between energy and reaction progress, with no kinetic barrier. The kinetic barrier seen with essentially all real chemical processes results from the need for more than one thing to happen simultaneously. This approach permits calculation of free energies of activation for covalent hydration of carbonyl compounds, over the range of reactivity for which data are available, from formaldehyde to carboxamides. Acid- and base-catalyzed and uncatalyzed reactions can be treated with no adjustable parameters, with root-mean-square errors of 1.41, 1.30, and 1.50 kcal/mol in free energy of activation. The method requires equilibrium constants and distortion energies. The latter can be calculated by molecular orbital theory using relatively low levels of theory. The calculations can be inverted to calculate equilibrium constants from experimental rate constants.