Coumarin and coumarin derivatives are bioactive compounds that have an important role in medicinal chemistry, for example in the development of anti-inflammatory, anticancer and antiviral drugs. These compounds arealso very powerful antioxidants that successfully scavenge free radicals and prevent or aleviate oxidative stress. The antioxidant potential of selected heterocyclic compounds containing coumarin core was investigated theoretically, the focus of this study was on hydrogen atom transfer mechanism (HAT) and sequential electron transfer followed by proton transfer mechanism (SET-PT). Using MOPAC2012 PM7, reaction enthalpies related to the cleavage of O–H, N–H and C–H bonds via selected mechanisms of free radical scavenging were studied and calculated. The effect of the position of the hydroxyl group, as well as other functional groups, on the antioxidant activity was examined. Based on obtained results, Schiff bases, thiosemicarbazides, oxadiazoles and 4-thiazolidinones containing one or more OH– groups exhibit higher radical scavenging properties.