Abstract: Beckmann rearrangement is a classical reaction in the courses of organic chemistry. However, mainstream textbooks often lack detailed explanations of its reaction mechanism, leaving students with a superficial understanding. This study investigates the Beckmann rearrangement mechanism of three types of ketoxime structures under two different proton sources using quantum chemical calculations. The detailed comparison and analysis provide insights into rearrangement process, including the migration rules of cis- and trans-ketoxime structures. Additionally, the electronic structures of the σ-type and π-type nitrilium ion intermediates are analyzed through frontier molecular orbital theory. This work aims to deepen students’ understanding of Beckmann rearrangement and introduce them to the application of theoretical computational chemistry in studying chemical reactions and their underlying mechanisms.

Key words: Beckmann rearrangement, DFT calculations, Reaction mechanism