Naphthalene Peri Annelated N, N‐ and N, O‐Heterocycles: The Effect of Heteroatom‐Guided Peri‐Fusion on Their Structure and Reactivity Profiles‐A Theoretical Endoscopy. Issue 33 (6th September 2018) - Tzeli, Demeter
Abstract: 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 2 nd 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. Abstract : Peri ‐fusion triggers a lower "outward" stretching and an upper "inward" compression π‐delocalization, is mainly concentrated over the more aromatic carbocycle The heterocycle is virtually "isolated" from the rest of the molecule We have coined the term "ring α‐effect" for structures with an inherent α‐effect Heteroring reactivity guides reactivity profile of peri ‐annelated structures