Analysis of molecular electronic structure of imidazole- and benzimidazole-based inhibitors: A simple recipe for qualitative estimation of chemical hardness

The effect of methyl, phenyl, and mercapto substituents on electronic structure of imidazole type inhibitors was characterized by density-functional-theory calculations. The most coherent trend is observed for chemical hardness. It is demonstrated that, in general, larger molecules are chemically softer provided they belong to the same chemical type. The electronegativity is reduced by methyl and mercapto substituents and increased by phenyl substituent. It is further shown that phenyl substituent reduces the solvation free energy thus increasing the relative tendency of the molecule to get adsorbed on the surface, which may contribute to the increased inhibition effectiveness against corrosion of copper.

Research highlights
► Electronic structure of imidazole and benzimidazole type corrosion inhibitors is assessed by quantum chemical calculations.
► Simple recipe for estimating chemical hardness trend of chemically similar inhibitor molecules is presented.
► Effect of various substituents on the molecular electronic structure and solvation free energy is explained.
► Possible implications to adsorption and consequent inhibition of corrosion are discussed.