The reaction of O-2 with an adlayer of the oligopyridine 2-pheny1-4,6-bis(6-(pyridine-2-yl)-4-(pyridine-4-yl)pyridine-2-yl)-pyrimidine (2,4'-BTP), adsorbed on the (111) surfaces of silver and gold and on HOPG - which can be considered as a model system for inorganiclorganic contacts - was investigated by fast scanning tunneling microscopy (video STM) and dispersion corrected density functional theory (DFT-D) calculations. Only on Ag(111), oxidation of the 2,4'-BTP adlayer was observed, which is related to the fact that under the experimental conditions O-2 adsorbs dissociatively on this surface leading to reactive 0 adatoms, but not on Au(111) or HOPG. There is a distinct regiospecifity of the oxidation reaction caused by intermolecular interactions. In addition, the oxidation leads to a chiral ordering. The relevance of these findings for reactions involving organic monolayers is discussed.