The cleavage of C-C bonds in oxidized lignin model compounds is a highly effective methodology for achieving lignin depolymerization, as well the generation of N -substituted aromatics. Here, density functional theory calculations were performed to understand the mechanism of the transformation of an oxidized lignin model compound (ligninox) and hydroxylamine hydrochloride to N -substituted aromatics. The reaction was proposed to proceed via an energetically viable mechanism featuring the initial production of HOAc acting as proton bridge. According to our calculations, Z -type oxime is the major intermediate of the reaction, with an energy barrier of 22.9 kcal mol -1 , owing to the weak interactions between methoxy and oximino groups being stronger than that of E -type oxime. Additionally, the hydroxy addition is the rate-determining step, with an energy barrier of 27.0 kcal mol -1 . Moreover, the huge net energy change of Beckmann and abnormal Beckmann rearrangements is the main overall thermodynamic driving force for producing N -substituted aromatics from oximes. The theoretical results have provided a clear picture of how ligninox transforms into N -substituted aromatics and are expected to provide valuable theoretical guidance for lignin depolymerization.