Topological Ring Currents and Bond Currents in Some Neutral and Anionic <i>Altans</i> and Iterated <i>Altans</i> of Corannulene and Coronene

Dickens, Timothy K.; Mallion, R. B.

doi:10.1021/acs.jpca.8b06862

Cited by 19 publications

(87 citation statements)

References 38 publications

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“…The problem also arose in some recent calculations (not yet published) in which, following the ab initio calculations of Monaco and Zanasi, [28,29] we attempted to extend our earlier studies of the neutral altans and multiple ('iterated') altans of corannulene and coronene, [30] and their dianions, [31] to the tetra-anions and hexa-anions of the same parent species.…”

Section: Introductionmentioning

confidence: 99%

Some Observations on Triplet Ground-States in the Context of ‘Topological’ (HLPM) Ring-Currents in Conjugated Systems

Dickens¹,

Mallion²

2019

Croat. chem. acta (Online)

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When the quasi graph-theoretical Hückel–London–Pople–McWeeny (HLPM) approach is used to calculate ‘topological’ π-electron ring-currents and bond-currents in conjugated hydrocarbons, a problem is identified that occurs whenever application of the Aufbau process gives rise to a π-electronic ground-state configuration that is a triplet. This circumstance seems to occur only occasionally and, even when it does, the generally somewhat outré molecular graphs in question appear unlikely to represent extant or viable conjugated systems. The molecular graphs of four examples are used to illustrate this ‘triplet ground-state problem’, only one of which represents a hydrocarbon that has actually been synthesised. It is pointed out that the ‘triplet ground-state problem’ does constitute an intrinsic limitation of the HLPM approach. It is, though, a limitation that is also necessarily inherent in other equivalent (though ostensibly different) methods of calculating magnetic properties due to π-electron ring-currents — methods that are likewise founded on the Hückel molecular-orbital conventions. When a triplet ground-state arises, topological ring-currents and bond-currents cannot be calculated by the HLPM method and its equivalents. Infinite paramagnetism is formally to be predicted in such situations.

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Section: Introductionmentioning

confidence: 99%

Some Observations on Triplet Ground-States in the Context of ‘Topological’ (HLPM) Ring-Currents in Conjugated Systems

Dickens¹,

Mallion²

2019

Croat. chem. acta (Online)

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“…In general, in monocyclic aromatic compounds, magnetically induced diatropic and paratropic RC are associated with their aromaticity and antiaromaticity, respectively [55]. The Hückel-London theory was used here to derive RC patterns of the above compounds [36][37][38][39][40][41]. In order to better understand the role of the diatropic and paratropic contributions of the different circuits to the RC, we investigated the trend of the magnetic properties of the different circuits.…”

Section: The Rc Resultsmentioning

confidence: 99%

“…TRE, BRE and CRE are given in units of |β|, where β is the standard resonance integral in Hückel theory. RC strength herein has been obtained using the Hückel-London model [36][37][38][39][40][41]. Van-Catledge's set of Hückel parameters have been used for nitrogen [42].…”

Section: Methods Of Calculationmentioning

confidence: 99%

A study on the aromaticity and magnetic properties of N-confused porphyrins

Tuersun

Kerim

2020

R. Soc. open sci.

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In this paper, topological resonance energy (TRE) methods were used to describe the global aromaticity of nitrogen confused porphyrin (NCP) isomers. The TRE results show that all NCP isomers exhibit lower aromaticity than the normal porphyrins, and their aromaticity decreases as the number of confused pyrrole rings in the molecule increases. In the NCPs, global aromaticity decreases as the distance between the nitrogen atoms increases. The bond resonance energy (BRE) and circuit resonance energy (CRE) indices were applied to study local aromaticity and conjugated pathways. Both the BRE and CRE indices revealed that individual pyrrolic subunits maintain their strong aromatic character and are the main source of global aromaticity. Ring currents (RC) were analysed using the Hückel–London model. RC results revealed that the macrocyclic electron conjugation pathway is the main source of diatropicity. As the number of confused pyrrole rings in the molecule increases, its diatropicity gradually decreases. In the confused pyrrole rings of the NCP isomers, the diatropic RC passing through the β -positions is always weaker than that passing through the inner sections. This is unrelated to the location of the protonated or non-protonated nitrogen atom at the periphery of the molecule and must be ascribed to the unique properties of the confused pyrrole rings.

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“…RCs have been calculated using the Hückel-London model. [37][38][39][40][41][42][43] The standard set of Hückel heteroatom parameters proposed by Van-Catledge has been used here in order to calculate the TRE, BRE, and CRE aromaticity values. [46] In general, positive values for TRE, BRE, and CRE indicate aromaticity, whereas negative values indicate the antiaromaticity of those molecules.…”

Section: Methods Of Calculationmentioning

confidence: 99%

“…[28][29][30][31][32][33][34] In the present paper, we describe the global aromaticity of diheterodiazuliporphyrins and their dications utilizing the TRE method (an energetic index) [35,36] and the ring current (RC) method (a magnetic index). [37][38][39][40][41][42][43] The effect of the azulene units on the global aromaticity of the porphyrinoid macrocycle is investigated. The origin of global and local aromaticities as well as the main conjugation pathways have been identified using the bond resonance energy (BRE) [44] and circuit resonance energy (CRE) indices.…”

Section: Introductionmentioning

confidence: 99%

A study on the aromaticity and conjugation pathways of diheterodiazuliporphyrins and their dications

Tuerhong

Kerim

2020

J of Physical Organic Chem

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The aromaticity of a series of diheterodiazuliporphyrins, both in the neutral and the dicationic states, has been investigated using the topological resonance energy (TRE) method. Our TRE results show that in each of the dicationic states, all the diheterodiazuliporphyrin isomers have greater aromaticity than when in their corresponding neutral states. An evaluation of the local aromaticity and of the main aromatic conjugation pathways has been carried out through the use of the bond resonance energy (BRE) and circuit resonance energy (CRE) indices, both in the neutral and dicationic states. Our BRE and CRE results show that the local aromaticity arising from the small rings is much larger and is a greater contributor to global aromaticity than the aromaticity which arises from the main aromatic conjugation pathway. In their neutral states, the azulene units are the main contributors to global aromaticity and the compounds themselves are stabilized primarily by their 10π‐electron peripheral structures. In their dicationic states however, it is the 6π‐electron tropylium unit structures which are the main contributors to the global aromaticity. The strength of the magnetically induced ring current (RC) has been calculated using the Hückel‐London model. The RC results show that current strength and the direction of the induced RC of the macrocyclic circuit play a crucial role in determining the paratropicity or diatropicity of the compound. The correlation between the observed 1H NMR chemical shift and the RC strength is discussed, and good correlation is obtained. Finally, the main impact factors upon aromaticity and the RCs are clarified.

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Topological Ring Currents and Bond Currents in Some Neutral and Anionic Altans and Iterated Altans of Corannulene and Coronene

Cited by 19 publications

References 38 publications

Some Observations on Triplet Ground-States in the Context of ‘Topological’ (HLPM) Ring-Currents in Conjugated Systems

Some Observations on Triplet Ground-States in the Context of ‘Topological’ (HLPM) Ring-Currents in Conjugated Systems

A study on the aromaticity and magnetic properties of N-confused porphyrins

A study on the aromaticity and conjugation pathways of diheterodiazuliporphyrins and their dications

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