Superaromatic Stabilization Energy as a Novel Local Aromaticity Index for Polycyclic Aromatic Hydrocarbons

Aihara, Jun‐ichi; Makino, Mitsunori; Sakamoto, Kenkichi

doi:10.1021/jp406932m

Cited by 24 publications

(94 citation statements)

References 59 publications

(183 reference statements)

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“…Highly aromatic rings with large SSE(LA) values correspond to the locations of sextet rings in the Clar formulas. 122 PAHs 1, 11, and 21 are fully benzenoid hydrocarbons, in which all carbon atoms belong to sextet rings at the same time. In contrast, all benzene rings in polyacenes 36 tend to become less aromatic in accord with the dilution of the only aromatic sextet in higher members.…”

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confidence: 99%

Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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Aromaticity is very sensitive to the geometry of the π-system. Topological resonance energy (TRE), defined graphtheoretically, represents an aromatic stabilization energy (ASE) arising from cyclic conjugation in the π-system. TRE can be calculated for not only ground-state but also excited-state species. The TRE concept has since been extended analytically to solve many different problems concerning aromaticity and reactivity. Bond resonance energy (BRE), defined in harmony with TRE, is an excellent probe for exploring kinetic stability of cyclic π-systems. It represents the contribution of individual π-bonds to global aromaticity. The well-known isolated pentagon rule (IPR) for fullerenes was verified in terms of BRE. Superaromatic stabilization energy (SSE) defined for macrocyclic π-systems finally confirmed the absence of macrocyclic aromaticity in kekulene. A novel local aromaticity index for polycyclic aromatic hydrocarbons (PAHs) was devised by reinterpreting the definition of SSE. We then found that aromatic properties of some PAHs are not compatible with Clar's aromatic sextet rule. We now feel that many fundamental problems with regard to aromatic stabilization and related phenomena have been solved conceptually.

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confidence: 99%

Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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“…Thus, Equation excludes the contributions of these circuits from the coefficients of the characteristic polynomial, defining the reference π‐system for estimating the local aromaticity of the ring C. Circuits that pass through any 2 of the 3 π‐bonds are not excluded from the characteristic polynomial, because they are not macrocyclic but local circuits. We justified SSE(LA) as an indicator of local aromaticity finally by observing a nice correlation with HOMA and bond order index of aromaticity values for relatively small PAHs …”

Section: Theorymentioning

confidence: 96%

“…In this case, a given benzene ring is viewed as an alternative cavity of a macrocyclic π‐system. We can design a hypothetical π‐system devoid of local aromaticity supposed to arise from all circuits around ring B of 1 by modifying the resonance integrals for the C a C b and C c C d bonds in the following manner:

β_{ab} = β_{cd} = i β and β_{ba} = β_{dc} = - i β

…”

Section: Theorymentioning

confidence: 99%

“…As will be seen later, we defined a new local aromaticity index, SSE(LA), which is almost free from this type of overestimation or ambiguity . SSE(LA) is a kind of superaromatic stabilization energy (SSE) modified to estimate the degree of local aromaticity (LA) for benzene rings in PAHs.…”

Section: Introductionmentioning

confidence: 99%

“…SSE(LA) is a kind of superaromatic stabilization energy (SSE) modified to estimate the degree of local aromaticity (LA) for benzene rings in PAHs. SSE(LA) arises from all circuits that enclose the benzene ring in question; it does not take into account the stabilization due to length‐6 circuits chosen along the adjacent benzene rings . This quantity can readily be calculated even for polycyclic π‐systems with hundreds of conjugated atoms .…”

Section: Introductionmentioning

confidence: 99%

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Critical evaluation of HOMA and MBL as local aromaticity indices

Makino

Nishina

Aihara

2017

J of Physical Organic Chem

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The harmonic oscillator model of aromaticity (HOMA) index is an excellent structural indicator of aromaticity. We found that HOMA values for internal benzene rings in large pericondensed polycyclic aromatic hydrocarbons are often overestimated because of the local aromaticity of adjacent benzene rings. The occurrence of this phenomenon was confirmed by comparing the HOMA with the corresponding SSE(LA) values; SSE(LA) is a graph‐theoretical index of local aromaticity not disturbed by the aromaticity of the adjacent benzene rings. Mean bond length values were likewise assessed by comparing them with the corresponding HOMA and SSE(LA) values.

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Is coronene better described byClar's aromatic π‐sextet model or by the AdNDP representation?

2017

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The bonding patterns in coronene are complicated and controversial as denoted by the lack of consensus of how its electronic structure should be described. Among the different proposed descriptions, the two most representative are those generated by Clar's aromatic π-sextet and adaptative natural density partitioning (AdNDP) models. Quantum-chemical calculations at the density functional theory level are performed to evaluate the model that gives a better representation of coronene. To this end, we analyse the molecular structure of coronene, we estimate the aromaticity of its inner and outer rings using various local aromaticity descriptors, and we assess its chemical reactivity from the study of the Diels-Alder reaction with cyclopentadiene. Results obtained are compared with those computed for naphthalene and phenanthrene. Our conclusion is that Clar's π-sextet model provides the representation of coronene that better describes the physicochemical behavior of this molecule. © 2017 Wiley Periodicals, Inc.

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Superaromatic Stabilization Energy as a Novel Local Aromaticity Index for Polycyclic Aromatic Hydrocarbons

Cited by 24 publications

References 59 publications

Graph Theory of Aromatic Stabilization

Graph Theory of Aromatic Stabilization

Critical evaluation of HOMA and MBL as local aromaticity indices

Is coronene better described byClar's aromatic π‐sextet model or by the AdNDP representation?

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