It was determined that N-(4-nitrophenyl)perfluorononanamide (1) forms a stable monolayer which suffers a liquid expanded (LE)--> liquid condensed (LC) phase transition upon compression. The surface pressure of the transition was linearly dependent on the temperature indicating a diffuse first-order transition process. The transition was ascribed to rotation of the C-N bond of the amide. In the LE state, 1 has an "L" conformation and in the LC state the phenyl group is aligned with the perfluoroalkyl chain. The pK of 1 is about 2 units higher than the value expected in the water solution. The surface potential of 1 at the air-water interface is negative at all measured pH values, indicating that the molecule on the surface can be considered as a vector having its air end negative. In solution, 1 is in an aggregated form even at 2 x 10(-6) M concentration and these aggregates are destroyed in solutions containing 0.01 M of sodium dodecyl sulfate (SDS) or 7 x 10(-3) M of perfluorononanoic acid 2. The kinetics of deaggregation occurs with two characteristic times with values of tau(1) 74.6 and 21.7 s and tau(2) 294 and 83 s for SDS and 2, respectively, at 25 degrees C.