title: On the aromaticity and Meisenheimer rearrangement of strained heterocyclic amine, phosphine, and arsine oxides.
abstract: A theoretical investigation (AIM and ELF analyses together with NMR chemical shifts) has been conducted for 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 bond formation, without ring aromaticity observed for their electronic properties. The calculated delta(C) and delta(H) shifts also supported the ring delocalization for the P and As unsaturated heterocycle oxides (delta(C) approximately 165 and delta(H) approximately 9 ppm). In addition, these values for 1H-azirine oxide resembled standard C=C double bond values (delta(C) approximately 130 and delta(H) approximately 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, were exothermic (G2 method). However, the N derivatives showed the lowest values for activation enthalpy, DeltaH(). The C=C bond influence in the MR was slight, with the same DeltaH values for the saturated and unsaturated paths. This rearrangement for the P and As oxides yielded TSs closer to the reactives; however, the corresponding TSs resembled the products for the N-derivatives. The different reaction paths have been examined by their corresponding AIM and ELF analyses at the B3LYP/6-311G level.
authors: Grupo de Modelización y Diseño Molecular, Instituto de Biotecnología, Campus Fuentenueva s/n, Universidad de Granada, 18071-Granada, Spain.
authors: J M
authors: JM
authors: Molina
authors: R
authors: R
authors: El-Bergmi
authors: J A
authors: JA
authors: Dobado
authors: D
authors: D
authors: Portal