Substitution effects in kinetically controlled reactions

Abstract

A simple method for determination of relative reactivity of functional groups of polyfunctional substances in the form of a kinetic rate constant ratio is shown to be defective especailly for reactions carried out to a high degree of substitution. A general scheme of kinetic rate equations implying substitution effects by functional groups upon reactivity of unsubstituted ones is developed for an irreversible reaction of a trifunctional substance. The method is exemplified for Kuhn methylation of methyl β-D-xylopyranoside. Good agreement of the proposed model with experimental results is shown, which facilitates the expression of substitution effects by virtue of free activation energy changes. A convenient method of numerical analysis of experimental results is developed which simplifies complicated least squares procedures considerably.