A study of the aromaticity of heteroannelated cyclooctatetraene derivatives

J of Physical Organic Chem

2021

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In this study, topological resonance energy (TRE) methods and ring current (RC) methods were used to describe the global aromaticity of a series of polycyclic neutral oxocarbon isomers. The observed trends in aromaticity are explained. Our results obtained using the TRE method are compared with those obtained using the nucleus independent chemical shift (NICS) method as reported in the literature. The bond resonance energy (BRE) and circuit resonance energy (CRE) indices were applied to study the local aromaticity of oxocarbons. The aromaticity of the individual rings of each of the polycyclic neutral oxocarbon isomers studied was assessed using the Hückel–London ring current (RC) model. The results regarding the local aromatic and antiaromatic states of the individual rings as obtained using the BRE and CRE indices show direct correspondence with the RC results, which indicate the strength of the diatropic and paratropic currents within those rings.

Section: Methods Of Calculationmentioning

confidence: 99%

A study on the aromaticity and ring currents of polycyclic neutral oxocarbon isomers

Yusufujiang

J of Physical Organic Chem

2021

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“…24,25 Both the BRE and CRE can be used to predict the local aromaticity of polycyclic p-bond systems. [26][27][28][29][30][31] The TRE, BRE, and CRE are given in units of |b|, where b is the standard resonance integral in Hückel theory. RCs are analyzed by means of the Hückel-London model.…”

Section: Methods Of Calculationmentioning

confidence: 99%

A study on the aromatic conjugation pathways and the ring currents of bridged [18]annulenes

Tuoheti

2019

RSC Adv.

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In this article, the topological resonance energy (TRE) method was used to investigate the global aromaticity of a set of [18]annulene-derived compounds which were obtained by replacing either two, four, or all six of the inner hydrogen atoms of [18]annulene with bridges (oxygen, imino-, sulfur, or combinations of the three). Our TRE results show that all the mono-bridged, di-bridged, and tri-bridged [18]annulenes are globally aromatic systems with positive TREs and show relatively larger aromaticity in comparison with the [18]annulene. The aromaticity of each compound was explained using the topological charge stabilization (TCS) rule. The bond resonance energy (BRE) and circuit resonance energy (CRE) methods were used to evaluate local aromaticity. Our BRE and CRE results show that incorporation of fivemembered heterocyclic rings changes the main conjugation pathway of the bridged [18]-annulenes. The local aromaticities arising from the five-membered heterocyclic rings (6p) contribute strongly to global aromaticity. However, the ring current (RC), which arises from the 18p annulene-like pathway structures, is the primary determinant of the magnetic properties of the molecule. Our RC results are in good agreement with available 1 H-NMR chemical shift data.Fig. 3 The p-electron circuits in mono-bridged (2-4), di-bridged (5-16), tri-bridged (17-26) [18]annulenes (X ¼ O, NH and S) and the related species (27-30).This journal is

“…The CRE value can be used to measure the contribution of the resonance energy of each circuit to the TRE . Both the BRE and CRE can be used to predict the local aromaticity of polycyclic π bond systems . The TRE, BRE, and CRE are given in units of | β |, where β is the standard resonance integral in Hückel theory.…”

Section: Methods Of Calculationmentioning

confidence: 99%

A study of the aromaticity and ring currents of azaacepentalenes

Liu

J of Physical Organic Chem

2019

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Using the topological resonance energy (TRE) method, a computational study has been carried out on the aromaticity of an acepentalene (cyclopenta[cd] pentalene) molecule upon the replacement at different positions of some of its carbon atoms by two pyrrole-like nitrogen atom isomers and by one or more pyridine-like nitrogen atom isomers. The relative aromaticity of the isomers was explained by the topological charge stabilization rule. Each of the resultant azaacepentalene isomers shows lower aromaticity relative to the acepentalene dianion. We found that the magnitudes of the global aromaticity of these azaacepentalenes are solely determined by the position of the two substituted pyrrole-like nitrogen atoms. Bond resonance energy (BRE) and circuit resonance energy (CRE) indices were used to evaluate the local aromaticity of each of the distinct azaacepentalenes. Our BRE and CRE results show that all of these compounds are primarily stabilized by the 6π electron conjugated system.Our global and local aromaticity results are compared with the other aromaticity indices as reported in the literature. Regarding the order of aromaticity, some discrepancies were found between the magnetic and energic criteria for aromaticity. The ring current (RC) analyses were made using the Hückel-London model. The RC results revealed that all of the compounds were diatropic, and the quantitative differences in their degrees of diatropicity were quite consistent with the experimental data on 1 H NMR chemical shifts.