Hydrogen-atom abstractions: a semi-empirical approach to reaction energetics, bond lengths and bond-orders

ion at any point of the reaction coordinate. However, in this approximation, some systems present spurious negative activation energies. Johnston and Parr 3 addressed this problem by introducing an anti-Morse function to describe the triplet repulsion between the end atoms of the three-atom fragment involved in the reactive bonds. A recent evaluation of the BEBO method, involving 97 gas-phase reactions for which experimental activation energies are available, presented an average error of 6.4 kJ mol with a standard deviation of 8.2 kJ mol.