The 2,6-di-tert-butyl-4-methylphenol (1), and its analogues 2,6-di-tert-butylphenol (2), 2,4,6,-tri-tertbutylphenol (3), 2-tert-butylphenol (4), and 4-tert-butylphenol (5), were evaluated with respect to their reactivities with superoxide anion radical (O-2(center dot-)), using a variety of electrochemical methods including cyclic voltammetry and square wave voltammetry. The current intensity associated with anodic peak of O-2(center dot-) oxidation into O-2(-1.16 +/- 0.02 V) was used to measure effectiveness of compounds 1-5. All phenolic compounds reduced the anodic current intensity associated with O-2(center dot-) oxidation into O-2. Compounds 2 and 4 produced reversible oxidation/reduction peaks associated with the corresponding quinones. The C-10% and C-60% values, related to the reduction of anodic O-2(center dot-)/O-2 current to 10% or 60% of its original value, were in 2.2-3.2 and 0.8-1.3 mM range, respectively. Compound 4 exhibited the lowest C-10% and C-60% values and was the most effective radical quencher. Data indicate that compounds belonging to the same class exhibited different radical activity (extent of reactivity with O-2(center dot-)), and that electrochemical methods are extremely useful in analyzing reactivity patterns in antioxidants of similar structures. (C) 2018 Elsevier Ltd. All rights reserved.