| Περίληψη: | An endoscopy of the little known peri-fused N,N and N,O-heterocycles is described herein using the density functional theory (DFT/B3LYP), the 2nd order Møller–Plesset perturbation theory (MP2) and the 6–311++G(d,p) basis set. Their salient structure features, their reflection onto aromaticity, depicted by means of certain aromaticity indicators (HOMA, IA, ABO, PDI, FLU, NICS) and their reactivity profiles are the theme of this investigation. N and O atom(s) and their relative arrangement in the ring perturb the σ and π frames of the structures and ultimately introduce peri strain. The incorporation of N and O atoms in the annelated ring causes a limited π-delocalization over the whole structure, a relatively low aromatic character and a weakly polarized double bond of the heteroring. Bond length variation, in the range of 0.01-0.05 Å, dihedral angles deviating from planarity by 1.2-4.1 Å and compressed fusion bonds, particularly peri ones, indicate a σ frame–triggered ring distortion of 0.6-2.6° as an “outward” stretching of the lower part of a still planar structure except one. The heteroring, as a masked enamine, hydrazone, imine, vinyl ether, oxime or imino ether, clamped onto naphthalene scaffold, appears to be the best description of this type of structures. The nature of the heteroring dictates their reactivity profile. Those housing the masked hydrazine and oxime entities exhibit a “ring α-effect”-guided reactivity, consistent with preliminary experimental findings. |
