Revisiting the Radical Trapping Activity of N-H and O-H in N-Phenylhydroxylamine: A DFT Study

Abstract

Hydroxylamines have been identified as promising antioxidants that can effectively scavenge free radicals primarily through a hydrogen transfer mechanism. Specifically, for N-phenylhydroxylamines, it is believed that both N-H and O-H bonds serve as two hydrogen- donating centers responsible for this task. M06-2X/6-311++G(d,p) and CBS-QB3 methods were used to re-evaluate the bond dissociation enthalpies of N-H and O-H and the results were found to be in agreement with each other. The revisited BDE(N-H) values in the gas phase, DMSO and water media are 74.8, 77.1, and 78.9 kcal/mol, respectively, while the BDE(O-H) values are about 5.0, 7.6, and 6.0 kcal/mol lower in comparison. Additionally, the effect of substitution with halogen, electron-donating, and electron- withdrawing groups at the para site of the aromatic ring of ArNHOH on the BDEs of both N-H and O-H bonds was evaluated. In addition to examining the role of O-H and N-H bonds in the trapping of radicals, the current study incorporated a kinetic aspect to insight the comprehension of the implicated mechanisms. Moreover, an evaluation of the N-phenylhydroxylamine's antioxidant capability was carried out through the execution of a DPPH assay.