The effect of p-p stacking between substituted benzene and benzamide on the properties of -CONH 2 functional group, as an important unit in the drugs activities, was studied at the M06-2X/6-311??G(d,p) level of theory. All substituents enhanced the p-p interaction energies, where a reasonably good correlation was found between the interaction energies and Hammett constants of substituents. A linear correlation is observed between the sum of electron charge density at the cage critical point P q ccp obtained from the atoms in molecules (AIM) analysis and the interaction energies, where both values grow up with electron-withdrawing substituents (EWSs). The electrostatic potential around the O and N atoms, the natural charges, and the dipole moment of C=O bond have been calculated to predict the ability of functional group on the electrophilic and nucleophilic attacks. The charge transfer increases the electrostatic potential around the benzamide functional group in the presence of electrondonating substituents (EDSs). EWSs increase the acidity of the N atom of the -NH 2 group; a linear relationship is observed between the acidity calculated with the molecular electrostatic potential around the N atom and the natural valence orbital energies.

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