On NMR prediction of the antioxidant effectiveness of p-substituted diphenyl amines

NMR shifts of a series of ten p-substituted diphenyl amine antioxidants in DMSO have been measured as well as evaluated by B3LYP calculations. At 25 °C no correlation between Molar Antioxidant Effectiveness (AEM) and NMR chemical shifts of relevant atoms is evident. AEM at 130 °C increases with NMR chemical shifts of nitrogen atoms between aromatic rings and hydrogen atoms bonded to them with very good statistical parameters (except nitro- and nitroso-compounds). This treatment might aid to a very simple estimation of high-temperature AEM values based on NMR shifts (experimental or calculated by quantum-chemical methods) of relevant atoms. Our results confirm that the essential mechanism of the antioxidant action is temperature-dependent.