Universidad de Granada
Facultad de Ciencias


Abstract: (Chemical Abstract 2001, 134: 131605)

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 dC and dH shifts also supported the ring delocalization for the P and As unsaturated heterocycle oxides (dC ca. 165 and dH ca. 9 ppm). In addition, these values for 1H-azirine oxide resembled standard C=C double bond values (dC ca. 130 and dH ca. 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, DH#. The C=C bond influence in the MR was slight, with the same DH 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.ding a net electron delocalization compatible with the 3c-4e bond model.
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