The adsorbability of a wide series of aromatic derivatives (38) on mercury from aqueous solution at constant potential (E(pzc) or close to it) cannot be simply accounted for by the " aromaticity " of the compounds, at any rate modulated by substituent groups on the aromatic moiety, even if the adsorbates show a common planar disposition on the surface in the adsorbed state. The interfacial activity can be successfully related to the process of formation of a "soft-soft" couple (in the Pearson’s concept) between mercury and the organic, in competition with the ’hard-soft" couple between the metal and water. Desorption is then explained with a higher ’hard" character of mercury at increasing negative potential. In this view, the feasibility of a partial charge transfer, as expressed by lambda, calculated for neutral organic adsorbates, corresponding to a positive DELTAN value (DELTAN, fractional number of electrons transferred from the adsorbate to the mercury) can be confirmed. A simple relation between adsorbability and "bulkyness" of the compounds, in relation to the dislodgement of water molecules from the surface occurring in the adsorption process is proposed and discussed.