Möbius Aromaticity and Delocalization

S., Rzepa Henry

doi:10.1021/cr030092l

Cited by 338 publications

(297 citation statements)

References 87 publications

(147 reference statements)

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“…The NICS(0) values of the COT ring (-22.0 at the PW91/IGLOIII//B3LYP/6-311+G**) and superphane center of symmetry (-35.5) predicts the strong diatropicity of the system. From these results as well as the results for other ring size, the authors concluded that "stacking, along with triplet [42] and Möbius strategies [89,90], is the third way to render 4nπ electron system aromatic." CTOCD-DZ calculations [91] supported the conclusion, whereas an analysis based on energetic criteria using graph theory concluded that the stacking of antiaromatic ring does not bring about aromatic stabilization energy even though the original antiaromaticity is reduced [92].…”

Section: Stacking Of Planar Cot Ringsmentioning

confidence: 86%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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Cyclooctatetraene (COT), the first 4nπ-electron system to be studied, adopts an inherently nonplanar tub-shaped geometry of D 2d symmetry with alternating single and double bonds, and hence behaves as a nonaromatic polyene rather than an antiaromatic compound. Recently, however, considerable 8π-antiaromatic paratropicity has been shown to be generated in planar COT rings even with the bond alternated D 4h structure. In this review, we highlight recent theoretical and experimental studies on the antiaromaticity of hypothetical and actual planar COT. In addition, theoretically predicted triplet aromaticity and stacked aromaticity of planar COT are also briefly described.

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Section: Stacking Of Planar Cot Ringsmentioning

confidence: 86%

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

2010

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“…It is very difficult to synthesize relatively small Möbius annulene molecules because of heavy steric strain. 86 π-Orbital energies of any Möbius annulene can be calculated simply by changing the sign of two matrix elements for one of the CC bonds (e.g., C i C j bond) that form a Möbius strip, namely,…”

Section: Extension Of the Tre Conceptmentioning

confidence: 99%

“…We noticed that Clar's sextet formula fails to reproduce the SSE-based aromaticity pattern for some irregular-shaped large PAHs. 124 For example, Clar formulas of circumcoronene (84), C 72 H 26 (85), C 48 H 18 (86), and C 84 H 24 (87) can be written uniquely (Figure 32), even though three of them (84, 86, and 87) are not fully benzenoid hydrocarbons. The positions of sextet rings in 84 and 85 agree exactly with those of highly aromatic benzene rings in the aromaticity patterns (Figure 33).…”

Section: Failure Of Clar's Sextet Formulamentioning

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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“…In this section, we briefly summarize the results obtained for the series [X n Y 4 clusters is D 4h square planar [119]. For X 2 Y 2 there are two possible planar structures corresponding to the cis-and trans-configuration [22,120].…”

Section: Nics and MCI Assessment In A Series Of Inorganic Clusters Wimentioning

confidence: 99%

“…The proliferation of new aromatic compounds compelled to reconsider the traditional definition based on the Hückel's (4n + 2)π electrons rule. Thus, species considered as Möbius aromatic [3,4] disobeyed the (4n + 2)π electrons rule while spherical aromatic compounds such as certain fullerenes added a third dimension to aromaticity [5,6]. Both descriptions broke down the well-established relation between aromaticity and planarity.…”

Section: Introductionmentioning

confidence: 98%

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

et al. 2010

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Abstract:The lack of reference aromatic systems in the realm of inorganic aromatic compounds makes the evaluation of aromaticity in all-metal and semimetal clusters a difficult task. To date, calculation of nucleus-independent chemical shifts (NICS) has been the most widely used method to discuss aromaticity in these systems. In the first part of this work, we briefly review our previous studies, showing some pitfalls of the NICS indicator of aromaticity in organic molecules. Then, we refer to our study on the performance of some aromaticity indices in a series of 15 aromaticity tests, which can be used to analyze the advantages and drawbacks of aromaticity descriptors. It is shown that indices based on the study of electron delocalization are the most accurate among those analyzed in the series of proposed tests, while NICS(1) zz and NICS(0) πzz present the best behavior among NICS indices. In the second part, we discuss the use of NICS and electronic multicenter indices (MCI) in inorganic clusters. In particular, we evaluate the aromaticity of two series of all-metal and semimetal clusters with predictable aromaticity trends by means of NICS and MCI. Results show that the expected trends are generally better reproduced by MCI than NICS. It is concluded that NICS(0) π and NICS(0) πzz are the kind of NICS that perform the best among the different NICS indices analyzed for the studied series of inorganic compounds.

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Möbius Aromaticity and Delocalization

Cited by 338 publications

References 87 publications

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Graph Theory of Aromatic Stabilization

A Critical Assessment of the Performance of Magnetic and Electronic Indices of Aromaticity

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