The corrosion inhibition of mild steel in 0.5 M hydrochloric acid by six synthesized heterocyclic compounds was studied using weight loss measurements. The inhibition efficiency exceeded 95%. The excellent inhibitor performance was attributed to the formation of protection adsorption films on the steel surface. The structures of compounds were confirmed by Fourier transform infrared and nuclear magnetic resonance analysis. The adsorption of inhibitor on steel surface followed the Langmuir adsorption isotherm. Quantum chemical calculations were also adopted to clarify the inhibition mechanism.

A series of pyranopyrazoles, namely, 7-(2-aminoethyl)-3,4-dimethyl-1-phenyl-1H-pyrazolo[3,4-b]pyridin-6(7H)-one (2), (Z)-3,4-dimethyl-1-(4-((4-nitrobenzylidene)amino)phenyl)pyrano[2,3-c]pyrazol-6(1H)-one (5), 1-(4-(3,4-dimethyl-6-oxopyrano[2,3-c]pyrazol-1(6H)-yl)phenyl)-3-(naphthalen-1-yl)urea (6), (Z)-ethyl 4-((3,4-dimethyl-6-oxo-1,6-dihydropyrano[2,3-c]pyrazol-5-yl)diazenyl)benzoate (8) and 3,4-dimethyl-N-(naphthalen-1-yl)-6-oxopyrano[2,3-c]pyrazole-1(6H)-carboxamide (9) were synthesized and characterized by means of their UV-VIS, FT-IR, 1H-NMR and 13C-NMR spectral data. Density Functional Theory calculations of the synthesized pyranopyrazoles were performed using molecular structures with optimized geometries. Molecular orbital calculations have provided detail description of the orbitals, including spatial characteristics, nodal patterns, and the contributions of individual atoms.

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A series of novel 5-amino-1,3,4-thiadiazole-2-thiol and 1,3,4-thiadiazole-2,5-dithiol derivatives of benzimidazole were synthesized through nucleophilic substitution reaction of 5-substituted-2-(chloromethyl)-1H-benzimidazole, structures of the synthesized compounds were proved by spectral methods of analysis ( FT-IR, 1 H and 13 C NMR ). All the target compounds were screened for their antibacterial activity toward gram-negative (E.coli, P. aeruginosa) and Gram-positive (B. subtilis, S. aureus) bacteria, most of the synthesized derivatives exhibited good to moderate activity toward both Gram-positive (B. subtilis, S. aureus) and Gram-negative (E.coli, P. aeruginosa) bacteria.

Serious of some novel bis benzimidazole derivatives were designed and synthesized by nucleophilic substitution reaction of 5-(un)substituted-2-chloromethyl-1H-benzimidazole and 5-(un)substituted-2-mercapto-1H-benzimidazole in the presence of sodium in methanol. Spectral methods of analysis (FT-IR, 1H-NMR, and 13C-NMR) were used to confirm the structures of the synthesized compounds. Antibacterial activity were evaluated for most of the target compounds against four strains of bacteria including ( E.coli, P. aeruginosa ) as gram-negative bacteria and ( B. subtilis, S. aureus ) as gram-positive bacteria, the tested compounds showed various activity against both gram-negative and gram-positive bacteria used.