Mechanisms of Proton Transfer between Oxygen and Nitrogen Acids and Bases in Aqueous Solution

Abstract

This chapter reviews that acid and base catalysis of a chemical reaction involves the assistance by acid or base of a particular proton-transfer step in the reaction. Many enzyme catalyzed reactions involve proton transfer from an oxygen or nitrogen centre at some stage in the mechanism and often the role of the enzyme is to facilitate a proton transfer by acid or base catalysis. Proton transfer at one site in the substrate assists formation and/or rupture of chemical bonds at another site in the substrate. It discusses that an increasing number of categories of proton transfer of oxygen and nitrogen acids are being discovered that do not fit this simple picture and many of these more complex proton transfers have been proposed as components of multi-step mechanisms. In a sense, the more complex proton transfers are of greater chemical interest than processes controlled by the rate of encounter between reactant molecules. The chapter highlights that the presence of an intramolecular hydrogen bond in an acid considerably modifies the acid–base behavior and rates of proton transfer are different from the diffusion-limited values.