Chlorine kinetic isotope effects. Application of the transition state model to thermolysis of secondary and tertiary alkyl chlorides

Abstract

Chlorine kinetic isotope effects in the thermolysis of 2-chloropropane and 2-chloro-2-methyl-propane have been measured at temperatures between 250 and 441 °C. The isotope effects are primary and they show normal temperature dependence. They increase with increasing methyl substitution on the central carbon atom. Model calculations using the heavy atom approximation theory show satisfactory agreement with the experimental data and with the observed temperature dependence. The participation of chlorine in the activated complex is the same for primary, secondary and tertiary alkyl chlorides and involves a combination of C—Cl stretching (3 %), C—C—Cl bending (2.7 %) and C—CH₃ shortening (4 %) from the ground state values.