Entropies of Activation and Mechanisms of Reactions in Solution

Abstract

Publisher Summary This chapter focuses on entropies of activation and mechanisms of reactions in solution. Entropy of activation is implied in the transition state theory. An underlying principle of the theory is that there exists along the reaction path of any reaction a state of critical energy, the minimum energy of which must be supplied to the reactants in order to cause reaction to occur. This state is termed the transition state or activated complex, and the basic Eyring proposal is that it can be treated as a normal molecule with respect to its thermodynamic properties. Determination of both the energy (and enthalpy) of activation and the entropy of activation involves measurement of the temperature coefficient of the rate constant. Although possessing certain inherent limitations, transition state theory seems adequate to permit the quantitative computation of kinetic parameters from first principles. Practical application of the theory is impeded by incomplete information about the molecular properties of the activated complex and, for reactions in solution, the lack of a quantitative description of molecular interactions in condensed phases. Because transition state theory is essentially an equilibrium theory, one basis for comparison is thermodynamic data for solution equilibria. From the inception of transition state theory, entropies of activation are from the twin aspects of molecular structure and reaction mechanism in this chapter.