Modelling the mechanism and kinetics of the radical scavenging activity of iminostilbene

•Iminostilbene (IS) exhibits excellent HO• and TBO• scavenging activity.•The radical scavenging activity against HOO• is moderate (koverall = ~ 104 M−1 s−1).•The rate constant of the HO• antiradical activity in benzene is 7.20 × 109 M−1s−1.•For TBO• scavenging activity in benzene, the rate constant is 2.10 × 108 M−1 s−1.•Comparison with experimental data in benzene yields kcalculated/kexperimetal = 0.3.•Consistently IS is a promising artificial scavenger. Iminostilbene (IS) (5H‐dibenz[b,f]azepine) is frequently used as a polymerization inhibitor to stop the reactions of radical polymerization. The compound itself is considered an antioxidant; however, little is known about the mechanism and kinetics of its activity. In this study, the antiradical activity of IS against typical radicals i.e. HO•, HOO• and TBO• (tert-butoxy radical) has been evaluated by computational methods. It was found that IS exhibits excellent HO• and TBO• scavenging activity in gas phase and in lipid-mimetic environment (benzene), whereas its activity against HOO• is moderate with koverall = ~ 104 M−1 s−1. The overall rate constants of the HO• antiradical activity are koverall = 7.06 × 1011 and 7.20 × 109 M−1 s−1 in gas phase and benzene, respectively, whereas for the TBO• antiradical activity in benzene it is 2.10 × 108 M−1 s−1. Comparison with the experimentally determined rate constant in benzene (k(BTO•) = 7.8 × 108 M−1s−1) yields the kcalculated/kexperimetal ratio of 0.3; thus, the computed kinetic data are reasonably accurate. It was shown that the TBO• and HOO• radicals scavenging of IS mostly follows the FHT mechanism at the NH bond; however, in case of the HO• radical both FHT (at NH bond) and RAF (at C10 position) mechanisms contribute to the observable activity. [Display omitted]