ON THE INFLUENCE OF MOLECULAR-STRUCTURE ON THE ORIENTATION AND THE OCCURRENCE OF PHASE-TRANSITIONS IN ORGANIC ADSORBED LAYERS AT THE MERCURY WATER INTERFACE

All seven monomethyl isomers of isoquinoline have been investigated, by examining the effect of the electrode potential (scanned or stepped according to the circumstances) on the differential double-layer capacity, the charge. density and the interfacial tension at a mercury surface in aqueous 0.5 M Na2SO4 solutions. The position of the methyl group plays a determinant role, by controlling the molecular orientation and the extent of molecular interactions. For the 3-, 6- and 7-methyl compounds (as well as for isoquinolines) a condensation process is observed, leading to the formation of compact layers, which are described in terms of structure and kinetics of formation. The process is entirely controlled by nucleation and growth, which proceed at rates which have been evaluated. The contrasted orientations between the two groups of isomers also explains the variable extent of inhibition towards faradaic concomitant processes, presenting dioxygen as test depolarizer.