Concert along the Edge: Dynamics and the Nature of the Border between General and Specific Acid-Base Catalysis.

Reactions that involve a combination of proton transfer and heavy-atom bonding changes are normally categorized by whether the proton transfer is occurring during the rate-limiting step, as in the distinction between general and specific acid-base catalysis. The experimental and computational study here of a β-ketoacid decarboxylation shows how the distinction between the two mechanisms breaks down near its border due to the differing time scales for proton versus heavy-atom motion. Isotope effects in the decarboxylation of benzoylacetic acid support a transition state in which the proton transfer is complete.