Catalytic Activity and Acid-Base Strength

The search for relationships between molecular structure and chemical reactivity, presented in Chapter 7, was instrumental for the development of chemical kinetics in the beginning of the twentieth century. One of the early successes in this area was the relationship suggested by Brbnsted and Pedersen for the acid catalysis. 

Bronsted relationships can only be observed for a limited range of add dissodation constants because as they become larger the reaction eventually becomes diffusion controlled and a must tend to be zero. On the other hand, given the equilibrium constant eq=( f/ r) when a=0 the reaction rate for the reverse reaction must vary inversely with and, consequently, be proportional to (Xg ) . Then, j5= 1. In general, the sum of the Bronsted coefficients must be equal to unity 

When the acid has more than one equivalent proton that can be transferred and the conjugate base has more than one equivalent basic site to be protonated, the above equations can be generalised to 

Acid-Base Catalysis and Proton-Transfer Reactions 

This reaction can be studied under conditions where some of the terms of the general equation can be neglected. For example, in the presence of an excess of OH , eq. (13.58) reduces to 

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