Insights on the mechanism of the reaction between nitric oxide and aziridines with and without CaO catalyst

• First principles investigations of the cycloaddition reactions between NO and aziridines. • Regio selectivity explanation of these reactions. • Formation of the oxadiazolidines is favored over the production of diazetidines in gas phase and using catalysts. • Solvent and substituents effects. The reactions between nitric oxide (NO) and an aziridine in gas phase and using calcium oxide (CaO) surfaces are investigated using Density Functional Theory (DFT) to explore the formation of valuable nitrogen-containing heterocycles. Gas-phase analyses identify CH-side ring opening of aziridine as the most favorable pathway for radical attack by NO, leading to stable intermediates and products such as oxadiazolidines and diazetidines. Solvent effects are found to further enhance the reactivity, with water notably reducing activation barriers. Also, we show that electron-withdrawing groups significantly lower activation energies and improve reaction spontaneity. Besides, the CH cleavage mechanism is confirmed to be energetically preferred while the reaction occurs at the CaO(100) surface or CaO cluster, facilitated by surface basicity and favorable transition state stabilizations. Natural Bond Orbital (NBO) analysis shows the radical character development and charge redistribution during key steps. Further, periodic computations reveal that the oxadiazolidine production over the CaO(100) slab is kinetically favored compared to the diazetidine synthesis, whereas in gas phase this is due to thermodynamical considerations. These results provide insights into the reactivity of NO on oxide surfaces and should help guiding the design of efficient NO capture and transformation strategies for synthetic and environmental applications.