We have calculated the reactions enthalpies (ΔHr) of hydroxyl with different functional groups at the edges of graphene, at its basal plane, or at defect sites, which corresponds to the difference between the total energies of reagents and products (Tables and). A negative value indicates energy release. To respect charge balance, some reactions require the transfer of an electron either to the graphene or to a defect. Thus, we have modelled some of the reactions in the presence of either an epoxy or a hydroxyl radical, both of which can become negatively charged. When negatively charged, the epoxy relaxes to a carboxyl configuration. Table . Reactions on finite graphene flakes (F) and respective reaction enthalpies, calculated using DFT calculations.