Model calculations of isotope effects. VI. The structure of the transition state for hydrogen atom transfer from ethane to methyl radicals

Abstract

Kinetic hydrogen isotope effects for the reaction

C₂H₆ + CD_B → C₂H₅ + CHD₃

have been calculated for a large number of transition state models, bond orders being based on an ab initio structure for the ethyl radical. Various empirical relationships for transition state force fields in terms of partial bond orders were examined for each model structure. No transition state model reproduced the experimental intermolecular and intramolecular isotope effects over the temperature range, but when an Eckart tunnel correction was applied a single model gave satisfactory agreement.