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

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 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.

N,N‐ and N,O‐6‐membered Ring peri‐Annelation in Naphthalene. Is it a Heteroring or merely a peri‐ Heterobridge?

“…More importantly, the latter shows a steeper orientation while the former one is more or less sensitive to the number and arrangement but not the nature of ring heteroatoms. Overall, a sharper fusion angle is observed in 3 , 4 , 7 and 8 , a markedly larger in 5 and 6 whereas no change is found in 2 and 9 [44] . In other words, an “outward” stretching of their lower part and a corresponding “inward” compression of their upper one has been detected.…”

“…The aromaticity of azines [41] and other 5‐ and 6‐membered heterorings [15,18,25,42,43] has been and still is a research theme. Intriguing features of the structure of peri ‐fused N,O− heterorings 3 – 9 (Figure 2), reflecting their reactivity profile, have been recently reported [44] . It is the implications of peri fusion on their structure that sparked our interest to explore their aromatic character.…”

“…Peri ‐fusion distorts the geometry of 3 – 9 (Figure 2) and further their reactivity profile [44] . C atoms of the peri ‐fused ring in the parent structure 2 are replaced (in part or in full) by N and O heteroatoms in a varying arrangement, i. e., contiguously bonded, as in 4 , 6 and 8 , those one C unit apart, such as 5 and 9 and those with one heteroatom, like 3 and 7 .…”

“…Geometry changes (bond lengths and angles, peri H−H distance) have shown [44] only a weak π‐perturbation but a notable σ‐ one of the structure. Dihedral angles [44] reveal that 2 , 5 and 7 – 9 are entirely planar, 3 and 4 are virtually planar (variation in the range of ca . 0.01–0.05°) and it is only 6 notably deviating from planarity of ca .1–6°.…”

Aromaticity and Chemical Bonding of Chalcogen‐Bonded Capsules Featuring Enhanced Magnetic Anisotropy

“…The magnitude of the computed values correspond to NICS values at the center of common aromatic rings, i. e., NICS(0) of phenalene, oxo-and/or azaphenalene. [33] The calculation of the NICS values at the same locations in the encapsulation complexes revealed an increase in the negative NICS values, see NICS contour plots Figure 16S of SI.…”