Collect. Czech. Chem. Commun. 2004, 69, 2121-2133

Molecular Basis of LFER. Simple Model for the Estimation of Brønsted Exponent in Acid-Base Catalysis

Robert Ponec

Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Prague 6, Czech Republic


A simple model was proposed allowing to estimate the Brønsted exponents in acid-base catalysis on the basis of the pK values of the species participating in the proton transfer process. The approach was tested using the experimental data on the basically catalyzed halogenation of carbonyl compounds and on the proton removal from nitroalkanes. It has been shown that the model is able to reproduce the Brønsted exponents not only in the case of "ordinary" Brønsted plots with the slope within the expected range 0-1 but also for unusual plots with negative slopes. In addition, the proposed model opens the possibility of calculation of the activation energies of a given proton transfer reaction and also provides straightforward theoretical justification for the validity of the Hammond postulate in these reactions.

Keywords: Acidity; Brønsted acids; Proton transfer; Brønsted equation; Analytic model.

References: 36 live references.