Substituent effects on the antioxidant capacity of monosubstituted diphenylamines: a DFT study

There are undesirable effects leading to considerable changes in the properties of polymers and plastics since exposing to oxygen undergo oxidative degradation. Therefore, investigation of the bond dissociation enthalpies (BDEs) of N-H bond for a series of monosubstituted diphenylamines is great interest. In this study, DFT-based method B3P86/6-311G was employed to perform this task. In comparison with the available experimental data, this method could reproduce the BDE(N-H)s values more accuracy. Effects of substituents and substitution positions on the BDE(N-H)s were also examined. Moreover, there is a good correlation of BDE(N-H)s with the Hammett's substituent constants. Depending on the nature of substituents, electron withdrawing groups increase the BDE(N-H)s but electron donating ones reduce the BDE(N-H)s. The hydrogen atom transfer processes from N-H bond of these diphenylamines to the peroxyl radical (CH3OO center dot) were also analyzed via potential energy surfaces and kinetic calculations.