Dechlorination rate constants on iron and the correlation with electron attachment energies

The correlation between rate constants for dehalogenation of contaminants on iron surfaces and vertical attachment energies (VAEs), a gas phase measure of the ease of reduction, is examined in a series of chlorinated alkanes and alkenes. A recent analysis has shown a good correlation of such rate constants, independent of chemical family, with the computed energies of the lowest unoccupied molecular orbitals (LUMOs) of these molecules. Noting that VAEs are the physical quantities that LUMO energies approximate, we test this result experimentally. We find that the rate constants appear to be satisfactorily correlated with VAE but only within each family. We show that this difference arises because LUMO energies are not relatively consistent in saturated and unsaturated compounds. By shifting and scaling LUMO energies to fit a few measured VAEs in each family, this useful quantum-chemical descriptor can have improved predictive value.