A Theoretical Investigation on the Corrosion Inhibition of Copper by Quinoxaline Derivatives in Nitric Acid Solution

In the present work, a theoretical study of two quinoxaline-type organic compounds, (2Z)-2-[(3E)-3-(2-oxo-2-phenylethylidene)-3, 4-dihydroquinoxalin-2(1H)-ylidene]-1 phenylethanone (Q5) and (Z)-2-((E)-3-(2-oxo-2-phenylethylidene)-3, 4-dihydroquinoxalin-2(1H)-ylidene)-1-phenylethanone (Q6), has been performed using density functional theory (DFT) at the B3LYP/6-31G(d) level in order to elucidate the different inhibition efficiencies and reactive sites of these compounds as corrosion inhibitors. The efficiencies of corrosion inhibitors and the global chemical reactivity relate to some parameters, such as highest occupied molecular orbital energy (E-HOMO), lowest unoccupied molecular orbital energy (E-LUMO), energy gap (Delta E), dipole moment (mu), electronegativity (chi), electron affinity (A), global hardness (eta), softness (sigma), ionization potential (I), the fraction of electrons transferred (Delta N), the global electrophilicity (omega) and the total energy (TE), were calculated. All calculation has been performed by considering Density Functional Theory (DFT) using the GAUSSIAN03W suite of programs. The calculated results are in agreement with the experimental data on the whole.