Understanding the Influence of Electron-Donating and Electron-Withdrawing Substituents on the Anticorrosive Properties of Imidazole: A Quantum-Chemical Approach

The nature and position of electron-donating and electron-withdrawing substituents are believed to play a major role on the corrosion inhibition properties in small organic molecules. In this study, the substituent effect on the imidazoles anticorrosive properties has been explored theoretically using the density functional theory performed at the B3LYP/6-311++G(d,p) level. A wide spectrum of substituents including NH₂, COOH, I, Br, Cl, F, CN, F, OH, OCH₃, NO₂, C₆H₅ and SH groups has been explored in the aqueous medium, and the different possible substitution positions have been investigated. Frontier molecular orbitals and quantum-chemical reactivity descriptors were calculated for the neutral and protonated forms of imidazole derivative. While the energy gaps, electronegativity and global hardness values showed a very good agreement with the corrosion inhibition performance reported from previous experimental work for imidazoles, the electrophilicity and molecular volume parameters were found less consistent. This study concluded that the amino and nitro groups, in particular those at C2 and C4 positions, exhibit prominent corrosion inhibition performance. The electron-releasing phenyl and methoxy substituents could also play a potential role in enhancing the anticorrosive properties of imidazole.