Quantum Chemical Study on the Corrosion Inhibition of Some Bipyrazoles

A theoretical study for three derivatives of bipyrazole namely ethyl 5,5'-dimethyl-1' H-1,3'-bipyrazole4- carboxylate (Bip1) and 3-(bromomethyl)-5,5'-dimethyl-1' H-1,3'-bipyrazole (Bip3), which are recently used as corrosion inhibitors for steel in 1.0 M HCl medium, was undertaken by Density Functional Theory (DFT) at the B3LYP level. The calculated quantum chemical parameters correlated to the inhibition efficiency are The highest occupied molecular orbital (E-HOMO) and the lowest unoccupied molecular orbital (E-LUMO), the energy difference (Delta E) between E-HOMO and E-LUMO, dipole moment (mu), electronegativity (chi), electron affinity (A), global hardness (eta), global softness (s), ionization potential (I), the global electrophilicity (omega), the fraction of electrons transferred (Delta N) and the total energy (TE). The order of inhibition efficiency of the bipyrazole derivatives was found to be in agreement with experimental corrosion inhibition efficiencies.