Noncomparative scaling of aromaticity through electron itinerancy

Paul, S.; Goswami, Tamal; Misra, Anirban

doi:10.1063/1.4933191

Cited by 10 publications

(15 citation statements)

References 67 publications

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“…It is interesting to compare the delocalization of the inner cycle of Kekuleńe with that of a D 6h -symmetrical [18]annulene (R values of 1389 and 1.406; BSO values of 1250 and 1.406). The HOMA value is 0.991, suggesting a large aromaticity that is not confirmed by any other investigation of [18]annulenes.…”

Section: The Journal Of Organic Chemistrymentioning

confidence: 99%

“…During the last 80 years since the formulation of the Hückel rules, the concepts of aromaticity and antiaromaticity have been probed with regard to almost every molecular property. A multitude of methods and procedures has been developed to define and measure the degree of aromaticity in polyaromatic hydrocarbons (PAHs), their heteroatomic analogues, − to estimate the influence of substituent effects on aromaticity, − and to determine the degree of aromaticity in nonplanar compounds. − The performance of the different approaches has been tested and compared. − …”

Section: Introductionmentioning

confidence: 99%

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Quantitative Assessment of Aromaticity and Antiaromaticity Utilizing Vibrational Spectroscopy

Setiawan

Kraka

2016

J. Org. Chem.

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Vibrational frequencies can be measured and calculated with high precision. Therefore, they are excellent tools for analyzing the electronic structure of a molecule. In this connection, the properties of the local vibrational modes of a molecule are best suited. A new procedure is described, which utilizes local CC stretching force constants to derive an aromaticity index (AI) that quantitatively determines the degree of π-delocalization in a cyclic conjugated system. Using Kekulé benzene as a suitable reference, the AIs of 30 mono- and polycyclic conjugated hydrocarbons are calculated. The AI turns out to describe π-delocalization in a balanced way by correctly describing local aromatic units, peripheral, and all-bond delocalization. When comparing the AI with the harmonic oscillator model of AI, the latter is found to exaggerate the antiaromaticity of true and potential 4n π-systems or to wrongly describe local aromaticity. This is a result of a failure of the Badger relationship (the shorter bond is always the stronger bond), which is only a rule and therefore cannot be expected to lead to an accurate description of the bond strength via the bond length. The AI confirms Clar's rule of disjoint benzene units in many cases, but corrects it in those cases where peripheral π-delocalization leads to higher stability. [5]-, [6]-, [7]-Circulene and Kekulene are found to be aromatic systems with varying degree of delocalization. Properties of the local vibrational modes provide an accurate description of π-delocalization and an accurate AI.

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Section: The Journal Of Organic Chemistrymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Quantitative Assessment of Aromaticity and Antiaromaticity Utilizing Vibrational Spectroscopy

Setiawan

Kraka

2016

J. Org. Chem.

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“…For example, the impact of the π-electron cyclic delocalization on aromatics stabilization energy was quantitatively accounted for by determining the atom–atom charge transfer, repulsion energy, and spin orbitals population at π-electron sites. 15…”

Section: Introductionmentioning

confidence: 99%

Three Queries about the HOMA Index

Dobrowolski

2019

ACS Omega

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HOMA (Harmonic Oscillator Model of Aromaticity) is a simple, successful, and widely used geometrical aromaticity index. However, HOMA can also be used as a general molecular descriptor appropriate for any type of molecule. It reaches the global maximum for benzene, whereas the potent magnetic aromaticity NICS index has no lower or upper limits. Hence, questions arise and go beyond mere differences between the geometric and magnetic aspects of aromaticity: (1) Does a molecule of aromaticity greater than that of benzene, but undisclosed by the HOMA definition, exist? (2) Can the Kekuléne cyclohexatriene moiety with HOMA = 0 exist as a part of a larger system? (3) Can the geometrical aromaticity index be defined better? Our answer to the first query is “It is not likely enough”, to the second, “Why not define HOMA using a less mysterious molecule than cyclohexatriene?”, and to the third, “It is possible to construct another fair geometrical index, but is it better for evaluating aromaticity?” To find these answers, we have studied: (1) the HOMA and NICS indices of over 50 hexahomosubstituted benzenes, (2) the HOMA, as well as EN and GEO, indices of over 100 triply fused hexasubstituted benzenes, and (3) the HOMA and new Geometrical Auxiliary Index (GAI) , of different unsaturated and saturated, aromatic and aliphatic hydrocarbons including all alkane constitutional isomers composed of up to nine carbon atoms.

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“…The aromatic compounds are associated with extra stabilization due to π electron circulation. The aromaticity observed from NICS and AdNDP analysis provoke us to calculate this stabilization energy which known as Aromatic Stabilization Energy (ASE) using a recently developed phenomenological model [40] . We obtained reasonable values of aromatic stabilization energies for these systems and compared with that of benzene and borazine (Table 5).…”

Section: Figurementioning

confidence: 88%

A New Approach to Design High Spin Organic Systems: Aromatic Stabilization with Exo‐cyclic π Electrons Plays Crucial Role

2020

Self Cite

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Radicals are important because of their diverse applications. Here we have modelled three systems, BC6F2H5, B2C6F4H4 and B2C5F4NH4. Each of them contain −CF2 unit (s) with one pz electron on carbon atom exo‐cyclic to the six membered ring. First two systems have 6π electrons and the last one contains 7π electrons in total. Stability of these systems are computationally investigated through Energy Decomposition Analysis (EDA), Molecular Dynamics Simulation, HOMO‐LUMO energy gap and minimum frequency analysis. Aromaticity is quantified through Nucleus Independent Chemical Shift (NICS), Aromatic Stabilization Energy (ASE), Adaptive Natural Density Partitioning (AdNDP) and Multi‐Centre Bond Order (MCBO). Isolated −CF2 unit can be considered as monoradical entity. From this computational study we observe that the pz electron on exo‐cyclic carbon atom participates in aromatic conjugation which in turn imparts stability to the designed systems. We found that exo‐cyclic conjugation is strong enough to force BC6F2H5 and B2C6F4H4 to be closed shell singlet. On the other hand, B2C5F4NH4 is in doublet state where formation of aromatic sextet of electrons stabilizes the system, and the extra spin is delocalized over the whole ring and thus forming a stable radical.

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Noncomparative scaling of aromaticity through electron itinerancy

Cited by 10 publications

References 67 publications

Quantitative Assessment of Aromaticity and Antiaromaticity Utilizing Vibrational Spectroscopy

Quantitative Assessment of Aromaticity and Antiaromaticity Utilizing Vibrational Spectroscopy

Three Queries about the HOMA Index

A New Approach to Design High Spin Organic Systems: Aromatic Stabilization with Exo‐cyclic π Electrons Plays Crucial Role

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