Synergistic hydrogen bonded interaction of alkyl benzimidazoles and thiosemicarbazide (TSC) and its corrosion protection properties on mild steel in hydrochloric acid at different temperatures have been studied using polarization, EIS, adsorption, surface studies and computational methods. The extent of synergistic interaction increases with temperature. Quantum chemical approach used to calculate some electronic properties of the molecules and to ascertain the synergistic interaction, inhibitive effect and molecular structures. The corrosion inhibition efficiencies and the global chemical reactivity relate to some parameters, such as total energy, E-HOMO, E-LUMO and gap energy (Delta E) thiosemicarbazide (TSC) interacts with benzimidazoles derivatives up to a bond length of approximately 1.99 angstrom. This interaction represents the formation of a hydrogen bond between the thiosemicarbazide (TSC) and benzimidazoles. This synergistic interaction of thiosemicarbazide (TSC) and benzimidazole derivatives offer extended inhibition efficiency towards mild steel in hydrochloric acid. (C) 2014 Elsevier B.V. All rights reserved.