Iron surfaces, chemically modified by n‐decanethiol (n‐DMc), have been investigated in order to get a better understanding of the corrosion protection of reactive metals by organic coatings, as investigations of the phase boundary substrate/organic coating are possible only if just monolayers of an organic monomere are adsorbed onto the metal. Electron spectroscopic (XPS, AES) and electrochemical analyses (cyclovoltammetry, rotating ring‐disc‐electrode) have shown that a stable bond between iron and n‐DMc and a well defined orientation of the organic molecules towards the surface are only observed, if the thiol is adsorbed at an oxid free substrate. In this case the oxidation of the thiol by air to disulfide, sulfenate, and sulfonate is highly inhibited. Similar results are obtained regarding the electrode reactions like metal dissolution/passivation, and H+‐reduction in an Ar‐purged borate buffer (pH = 8.5). Only oxygen can be reduced on the modified surface with high rates, the kinetics being completely different from the one on clean iron surfaces. It is proposed, that as part of the O2‐reduction the thiol is transformed into disulfide, which then catalyses the oxygen reduction but still inhibits the rate of metal dissolution and H+‐reduction. After prolonged O2‐reduction the disulfide is oxidized to sulfonate, which then desorbs from the metal surface.