The highly trans-stereoselective reaction of ammonium salt (AS 2) toward (E)-Nbenzylidene-4-methylbenzenesulfonamide (IM 4) in the presence of Na 2 CO 3 leading to an aziridine derivative, trans-Az 6, was theoretically studied using Molecular Electron Density Theory (MEDT) at the B3LYP/6-31G(d) computational level to probe energy transformation, selectivities, and molecular mechanism. The reaction starts by a nucleophilic substitution reaction between 1,4diazabicyclo [2.2.2]octane (DABCO) and phenacyl bromide (PB) to form AS 2 which undergoes a proton abstraction by Na 2 CO 3 to produce Ammonium Ylide (AY 3). Subsequently, nucleophilic addition of AY 3 to the double bond in IM 4 leads to form a betaine-like intermediate, namely, IN-Ta which named IN-Ta. Finally, trans-Az 6 is produced as a result of the nucleophilic attack of the negatively charged nitrogen atom on the carbon atom bearing DABCO in IN-Ta.Analysis of the relative Gibbs free energies shows that the ring closure step is the rate-determining step (RDS). By an investigation of the conceptual density functional theory, CDFT reactivity indices AY 3 and IM 4 are classified as a strong nucleophilic molecular system and as a strong electrophilic molecular system, respectively, which implies that the addition step of AY 3 to IM 4 has a high polar character. An analysis of the calculated electrophilic and nucleophilic Parr functions at the reactive sites of reagents clarifies the regioselectivity observed experimentally within the C 1 -C 2 bond creation process.

In this work, using density functional theory, the kinetic effects of the substitution of a t‐butyl group and\or the incorporation of an oxygen atom, and both, at the aziridine ring moiety were investigated for N‐inversion in N‐phenylaziridine. Then, for N‐inversion in 3‐t‐butyl‐N‐phenyloxaziridine, the kinetic Hammett substituent effects were studied using the different para‐substituted groups on the N‐phenyl ring moiety. The natural bond orbital (NBO) study was the last case in this work. The calculations were performed in the gas phase and solution (in carbon tetrachloride and dichloromethane). The incorporation of an oxygen atom in the aziridine ring strongly weakens the N‐inversion process. In addition, while both t‐butyl substituent and solvent slightly reinforce the N‐inversion of N‐phenyloxaziridine, in N‐phenylaziridine, they decrease the N‐inversion rate to some extent. In both phases, more pronounced in solution and especially in dichloromethane, and in agreement with the NBO results, the electron‐withdrawing groups on para position of the N‐phenyl ring strongly increase the rate of N‐inversion of 3‐t‐butyl‐N‐phenyloxaziridine molecule.