The single electron transfer (SET) reactions from the neutral and anionic forms of 27 edaravone derivatives to 11 free radicals have been studied using density functional theory and the Marcus theory. All of the studied compounds were found to be able to efficiently scavenge at least some of the studied radicals. More than half of them were found to be excellent free radical scavengers, via SET, under physiological conditions. Their SET reactions with all the studied radicals were found to have rate constants ranging from 10(6) to 10(9) M-1 s(-1) (diffusion limited). Therefore, they are predicted to be versatile scavengers, able to deactivate free radicals of different nature. Functionalizing the R1 and R3 sites of the pyrazol-5-one ring with the NO group is not recommended for edaravone derivatives designed as free radical scavengers through the SET mechanism. In general, this family of compounds was found to be exceptionally good for scavenging free radicals by transferring one electron. Moreover they are predicted to be outstanding scavengers, even if they would only react by SET. In addition, the acid-base equilibrium was found to play an important role in their activity.