The surface behavior of 2- and 3-(1-octadecynyl)aniline (2ODA and 3ODA) was studied in Langmuir films and compared to that of 2- and 3-pentadecylaniline (2PDA and 3PDA), which was previously reported. Surface pressure (Jr) and potential (DeltaV) vs mean molecular area (A) isotherms of these substituted anilines were generated, and the results were, in part, attributed to the orientation of the aromatic rings at the interface. Using well-established methods, 2ODA and 3ODA were polymerized at the air-aqueous interface, and the reactivities of the aniline derivatives were studied at different surface pressures. It was found that the initial rate constant (k') for the polymerization of 2ODA was significantly greater than that of 2PDA, but autoacceleration was not detected. The reaction rates are explained in part by molecular orientational differences at the air-aqueous interface. The polymerization rates of 3ODA and 3PDA were comparable, which is probably due to similar headgroup orientation at the air-aqueous interface.