Reactive oxygen species (ROS) are capable of oxidizing cellular proteins, nucleic acids and lipids, contributing to cellular aging, mutagenesis, carcinogenesis, coronary heart and neurodegenerative diseases. Free radicals-scavenging by phenolic compounds occurs by the transfer of one electron followed by the H-abstraction. In order to evaluate the antioxidant activity of a series of seventeen phenolic compounds extracted from Brazilian flora (Chimarrhis turbinata and Arrabidea samydoides), some physicochemical parameters (heat formation of the neutral, radical, and cationic compounds; orbitals' energies; ClogP; ΔH OX ; and ΔH f) were calculated. Considering the results from the calculated descriptors, the molecules 10a-f can be classified as having a higher antioxidant activity. these targets against the effects of free radicals and they can be enzymatic or non-enzymatic agents, histidine-peptides and iron-binding proteins. Phenolic antioxidants such as vitamin E, hydroxytyrosol, gallic acid, caffeic acid, chicoric acid, flavonoids and epicatechin are extremely important. The radical-scavenging potentials of these compounds have been extensively investigated, but the exact molecular mechanisms radical-quenching reaction has not been explored enough (Lien et al., 1999; Del Rio et al., 2002).