On the aromaticity and Meisenheimer rearrangement of strained heterocyclicamine, phosphine, and arsine oxides

A theoretical investigation (AIM and ELF analyses together with NMR chemica l shifts) has been conducted far three-membered heterocycle (N, P, and As) oxides. An aromatic stabilization was found for the P and As rings. However , the N derivatives displayed a net negative hyperconjugation in the N-O bo nd formation, without ring aromaticity observed for their electronic proper ties. The calculated delta (C) and delta (H) shifts also supported the ring delocalization for the P and As unsaturated heterocycle oxides (delta (C) x 165 and delta (H) approximate to 9 ppm). In addition, these values for 1H -azirine oxide resembled standard C = C: double bond values (delta (C) appr oximate to 130 and delta (H) approximate to 7 ppm). The different behavior for the N oxides was also observed in their Meisenheimer rearrangement (MR) . All the reaction paths, yielding the corresponding hydroxyl structures, w ere exothermic (G2 method). However, the N derivatives showed the lowest va lues for activation enthalpy, DeltaH double dagger. The C = C bond influenc e in the MR was slight, with the same DeltaH values for the saturated and u nsaturated paths. This rearrangement for the P and As oxides yielded TSs cl oser to the reactives; however, the corresponding TSs resembled the product s for the N-derivatives. The different reaction paths have been examined by their corresponding AIM and ELF analyses at the B3LYP/6-311G* level.