The reactions of a ketone surface oxide group have been studied on two forms of the zigzag edge and the armchair edge of a model char using density functional theory at the B3LYP/6-31G(d) level of theory. Rearrangement and surface migration reactions were found to occur much more rapidly than desorption reactions on both the zigzag and armchair edges. A number of desorption pathways characterized here go some way toward explaining the experimentally observed broad activation energy profile for CO desorption. Three separate desorption processes were characterized; on the zigzag surface two were found with activation energies of 275 and 367 kJ mol(-1), while on the armchair surface one was found with an activation energy of 296 kJ mol(-1). The activation energies for these processes were found to be insensitive to increasing the size of the char fragment. On a larger char fragment, however, an extra desorption process was found to be possible, with an activation energy of 160 kJ mol(-1).