Br0nsted equation

The rates of proton transfer reactions cover a wide spectrum, from exasperatingly slow to diffusion controlled. Any theory which can rationalize this range has obvious merit. Such a rationalization is in fact accomplished, to a large degree, by Br nsted and Pedersen s (1923) relationship between rate (kinetic acidity) and p/sTa (thermodynamic acidity). The relationship, known as the Br0nsted equation, has the form (8) where B is the catalytic rate constant. The... 

The Br0nsted equations relate a rate constant k to an equilibrium constant K. In Chapter 6, we saw that the Marcus equation also relates a rate term (in that case AG ) to an equilibrium term AG°. When the Marcus treatment is applied... 

The purpose of this chapter is to give an introduction to the subject of nucleophilicity. The chapters of the present volume are collected into five groups (1) Marcus theory, methyl transfers, and gas-phase reactions (2) Br0nsted equation, hard-scft acid-base theory, and factors determining nucleophilicity (3) linear free-energy relationships for solvent nucleophilicity (4) complex nucleophilic reactions and (5) enhancement of nucleophilicity. The present chapter is divided in the same way, giving an introduction to each of the five topics followed by a description of key points in each chapter as they relate to current studies of nucleophilicity and the other chapters of the book. 

Br0nsted Equation, Hard-Soft Acid-Base (HSAB) Theory, and Factors Determining Nucleophilicity... 

The Br0nsted equation, which is empirical, can be viewed as being a special case of the Marcus equation, which was derived from first principles. The latter theory has the important added feature of defining intrinsic activation barriers. 

The following data give the dissociation constants for several acids that catalyze hydration of acetaldehyde. Also given are the rate constants for the hydration reaction catalyzed by each acid. Treat the data according to the Br0nsted equation, and comment on the mechanistic significance of the result. 

The relationship between thermodynamics and kinetics in chemical reactions is usually expressed by the Br0nsted equation (Eq. 3.70 in Section 3.4) k =gK, where k is the rate constant, fCis the equilibrium constant of the elementary stage, and and a (Polanyi parameter) are constant values for a series of reactions. These constants are determined by parameters characterizing the elementary mechanism (composition and structure ofthe activated complexes, etc.), thus allowing for the existence of an optimum catalyst, on which the rate of catalytic reaction per unit of surface has a maximum value. Equations of the type (Eq. 3.70) were used for the explanation of volcano-curves, when catalytic activity as a function of thermodynamic characteristics follows a curve with a maximum. An example for a volcano curve in methanation of CO is given in Fig. 7.6. 

Constants of elementary reaction and can be expressed using the Br0nsted equation... 

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