Impact of electron-withdrawing and electron-donating substituents on the corrosion inhibitive properties of benzimidazole derivatives: A quantum chemical study

The role of substituents in the enhancement of corrosion inhibition effectiveness in some organic compounds has been the subject of several studies in recent years. Understanding the relationship between corrosion inhibition performance and electronic properties of the molecule shall facilitate the design of efficient inhibitors and reduce the burden of experimental trials involved. In this study, quantum chemical calculations using density functional theory (DFT) method were performed on benzimidazole and its derivatives involving various electron-withdrawing and electron-releasing substituents. Several reactivity indicators, such as frontier orbitals, energy gaps, electronegativity, electrophilicity and global hardness were calculated and correlated with available experimental data. Frontier orbital energy gap predicted 2-nitrobenzimidazole to possess higher anti-corrosion properties, while electronegativity, electrophilicity and global hardness predicted 2-aminobenzimidazole to exhibit higher corrosion inhibition tendency. Results of molecular level interaction studies predicted that the adsorption of the molecules over the iron surface would take place preferentially through the nitrogen atoms of the imidazole ring and the carbon atoms of the benzene ring, resulting in the formation of Fe–N and Fe–C bonds with 2.00–2.40 Å bond distances which lie within the range of the chemisorption interaction.