Chlorine kinetic isotope effects. Theramal decomposition of 1-chloroethane and evaluation of possible models of activated complex

Abstract

Chlorine kinetic isotope effects have been investigated for the pyrolysis of 1-chloroethane in a static system in the temperature range 395–482°C. The temperature dependence of the kinetic isotope effects has been determined. The mass spectrometric isotope ratio analysis was made on the hydrogen chloride produced. A model for the chlorine involvement in the four-centre activated complex is advanced and various alternative geometries are evaluated in terms of heavy-atom approximation and first-order high temperature kinetic isotope effects. Best agreement with the experimentally determined values of k³⁵/k³⁷ is given by a model of the activated complex which involves chlorine participation in the reaction coordinate with three degrees of freedom. The effect of the individual geometric parameters that includes the C—Cl stretching, the C—C—Cl bending and the C—CH₃ stretching and their combination, is evaluated.