Kinetics of rapid reactions involving two pairs of consecutive second order steps

Abstract

An examination is made of the kinetics of the reaction between A and B, where both reactants are capable of unifunctional behaviour, and A is also capable of bifunctional behaviour, for the general case in which the two reactive sites on A are not equivalent. Solutions are given of the appropriate rate equations for the two pairs of consecutive stages, and it is shown that the final concentrations of reactants and products can be related to given values of the initial concentrations and the velocity constants of the four second order stages. Relatively simple relations are established between the final concentrations and the ratio of the velocity constants for the case in which reaction at one position on A does not affect the reactivity of the other position. Some special cases of interest are considered. The results are related to the authors' earlier treatment of the case In which the initial reactivity of the two positions on A is initially the same. The theory is applied, by way of example, to the coupling of histidine with p-diazobenzenesulphonic acid, which appears to conform to the assumption of the same initial reactivity. The implications of the method in the correlation of molecular structure and reactivity are briefly discussed.