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This study aims to explore the inhibitory action of certain derivatives of Schiff's base, namely 4-(pyridin-2-ylimino) pentan-2-one (CE5),4-(pyrimidin-2-ylimino) pentan-2-one (CE4) and 4-((1H-tetrazol-5-yl) imino) pentan-2-one (CE20) against mild steel (MS) corrosion in 1 M HCl by the gravimetric, stationary and transient method. For additional information on the inhibitory properties of the studied compounds, scanning electron microscopy (SEM) and functional density theory (DFT) calculations were also performed. The effectiveness of the Schiff's base derivatives studied follows the order: CE20 > CE4 > CE5. The electrochemical impedance curves show that the corrosion reaction is controlled by a charge transfer process, while the potentiodynamic polarization curves indicate that the synthesized compounds act as a mixed-type inhibitor. The adsorption process follows the Langmuir isotherm. Kinetic, as well as thermodynamic parameters, were calculated and discussed. The increase in EHOMO and decrease in gap energy ΔEgap lead to an increase in the inhibition efficiency. Results obtained from quantum chemical studies are in good agreement with quantum chemical parameters and experimental inhibition efficiencies. [ABSTRACT FROM AUTHOR]