Aniline chemisorption at clean and partially oxidized Cu(110) surfaces at 293 K is compared with the reaction of a 300:1 aniline/dioxygen mixture at the same surface using STM and XPS. Limited dissociation occurs at the clean surface but in the presence of chemisorbed oxygen efficient oxy-dehydrogenation takes place with water desorption and the formation of chemisorbed phenyl imide (C6H5N(a)) with a reaction stoichiometry that changes with coverage. The adsorption site of the phenyl group is identified by STM to be the 2-fold hollow and it is proposed that the nitrogen is situated over the short bridge site. Chemisorptive replacement of oxygen gives a maximum phenyl imide concentration of 2.8 x 10(14) molecules cm(-2) at which coverage the surface is dominated by a mixture of three ordered domains with structures described by (4 0),(4 0), and (4 0) (2 2) (-1 2) (1 2) unit meshes. Adsorption of aniline and dioxygen mixtures however results in phenyl imide concentrations up to 3.4 x 10" cm-' molecules cm(-2) and a highly ordered biphasic structure characterized by (3 0) and (3 0) domains. (-1 2) (1 2) A discrepancy between the concentrations measured by XPS and those calculated from the STM structures is discussed in terms of pi-stacking of the phenyl rings in the adsorbed monolayer. Finally the chemistry of aniline is compared with that of ammonia and the importance of the NH bond strength and the basicity of the amine discussed.