Proton affinities (PAs) and basicities (GBs) of substituted benzamides in gas phase have been calculated at the DET/B3LYP level with a 6-311++G(2df,2p)//6-311+G(d,p) basis set. The influence of environment on PAs has been studied by means of SCRF solvent effect computations using PCM solvation model for water solvent. Results reveal that benzamides behave as oxygen base. Theoretical results show a good agreement with the experimental data. A good linear correlations between these quantities and the molecular electrostatic potential and the valence natural atomic orbital energies have been obtained. Substitution effect on PAs, GBs and structural properties has been considered. (C) 2014 Elsevier B.V. All rights reserved.