Molecular orbital theoretical studies of some organic corrosion inhibitors

Molecular orbital theoretical calculations based on the modified neglect of differential overlap (MNDO) method were performed on some substituted methyl pyridines and substituted ethane derivatives in common use as corrosion inhibitors for iron in acid media. New correlations of corrosion rates with the energy of the highest occupied molecular orbital (E-HOMO), the energy gap or difference between the lowest unoccupied molecular orbital and the highest occupied molecular orbital (E-LUMO-E-HOMO), and Hammett's parameter (sigma) were presented. Absolute electronegativity (chi) values and the fraction of electrons (Delta N) transferred from substituted pyridine and ethane compounds to iron in the bulk metal were calculated and correlated with corrosion rates for the first time.