Scavenging of O-2(.-) and OH. by urea, thiourea, selenourea and their derivatives in both gas phase and aqueous medium has been investigated using density functional theory. It has been found that O-2(.-) would be scavenged efficiently by single hydrogen abstraction from thiourea and selenourea but not from urea and by addition to pairs of carbon sites of thiourea and selenourea derivatives but not to those of urea derivatives, in agreement with experiment. Further, OH. is found to be scavenged efficiently by hydrogen abstraction from thiourea and selenourea but not from urea and by addition to carbon sites of the derivatives. (C) 2017 Elsevier B.V. All rights reserved.