This work is devoted to examine the effectiveness of pyrazoles 4-(4,5-dihydro-1H-pyrazol-5-yl)-N,N-dimethylaniline (D) on corrosion of mild steel in a 1 M HCl solution, using weight loss measurement at concentration effects. The inhibitor (D) was synthesized in our laboratory. The formation of this pyrazole was carried out with hydrazine and α-unsaturated aldehydes, and the structure was checked by spectroscopic means, such as FT-IR, 1H NMR and 13C NMR. Polarization curves and electrochemical impedance spectroscopy (EIS) methods were used to assess both the corrosion rate and inhibition efficiency. Potentiodynamic polarization showed that D behaved as a mixed-type inhibitor. The Nyquist plots showed that, while D concentrations increased, charge-transfer resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. Adsorption of the inhibitor molecules corresponds to Langmuir adsorption isotherm. Quantum chemical calculations showed that the inhibitor was prone to be protonated in the acid, and the results were in full agreement with experimental observations.

Results of a theoretical study devoted to comparing NLO (non-linear optics) responses of derivatives of tetracene, isochrysene, and pyrene are reported. The static hyperpolarizability β, the dipole moment μ, the HOMO and LUMO orbitals, and their energy gap were calculated using the CAM-B3LYP density functional combined with the cc-pVDZ basis set. The para-disubstituted NO2-tetracene-N(CH3)2 has the highest NLO response, which is related to a large intramolecular charge transfer. Adding vinyl groups to the para-disubstituted NO2-tetracene-N(CH3)2 results in an increase in the NLO responses. We further investigated the effect of the intercalation of various push–pull molecules inside an armchair single-walled carbon nanotube. The intercalation leads to increased NLO responses, something that depends critically on the position of the guest molecule and/or on functionalization of the nanotube by donor and attractor groups.

In this work we made a synthesis of two molecules of the same family, the pyrazole 4-(4,5-dihydro-1H-pyrazol-5-yl)-N,N-dimethylaniline D and N,N-dimethyl-4-(3-methyl-4,5-dihydro-1H-pyrazol-5-yl)aniline D10. These two molecules have a good inhibiting activity against the corrosion of mild steel in 1 M HCl. This activity has been confirmed by gravimetric and electrochemical studies; we use a potentiodynamic polarization and the impedance spectroscopic technique. From this investigation, we observe that the integration of a methyl group in the pyrazole D allows decreasing slightly the corrosion of steel. For more information about the action mode of our inhibitors, we launched theoretical calculation by DFT method. We used these calculations to discuss the stability, the reactivity, and the adsorption of our pyrazolic inhibitors with iron in acid medium.