Validity and limitations of the annulene-within-an-annulene (AWA) model for macrocyclic π-systems

Aihara, Jun‐ichi

doi:10.1039/c3ra45874a

Cited by 19 publications

(28 citation statements)

References 52 publications

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“…In 2011, however, we noticed that the sequential line plot of TRE against N π for any PAH molecule is similar with the same number of extrema as that for benzene (1). 79,80 For example, the TRE-vs-N π plots for naphthalene (3), benzo[a]pyrene (12), coronene (19), and zethrene (20) are shown in Figure 14. Similar to that for 1 (Figure 13b), these plots exhibit three major maxima and two major minima.…”

Section: Extension Of the Tre Conceptmentioning

confidence: 99%

“…TREs for four annulenes are plotted in Figure 13, each as a function of the number of π-electrons (N π ). 79,80 These plots clearly show that all annulenes and annulene ions are aromatic if they have 4n+2 π-electrons and otherwise antiaromatic. For example, the molecular ions of [18]annulene (28) are predicted to be aromatic whenever they have 4n+2 π-electrons (n = 18).…”

Section: Extension Of the Tre Conceptmentioning

confidence: 99%

“…79,80 TREs for these polycyclic π-systems and their molecular ions can again be interpreted by reference to those for the monocyclic species of the same ring size. As a different type of TRE-vs-N π plots, those for pentalene (41) and dicyclopenta[a,e]pentalene (52) are shown in Figure 15.…”

Section: Extension Of the Tre Conceptmentioning

confidence: 99%

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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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Section: Extension Of the Tre Conceptmentioning

confidence: 99%

Section: Extension Of the Tre Conceptmentioning

confidence: 99%

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Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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“…Since their introduction, altan ‐molecules have attracted a considerable interest in the chemical and mathematical communities . Their topological definition has been extended, and limitations of the altanisation protocol have been investigated.…”

Section: Introductionmentioning

confidence: 99%

The intriguing class of altan‐molecules

Zanasi

Porta

Monaco

2016

J of Physical Organic Chem

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-molecules are formed from parent molecules with outgoing C-H bonds by substituting the C-H bonds with C-C bonds to alternating carbon atoms of an annulene. If the outgoing C-H bonds are even, which happens for totally fused aromatic hydrocarbons, the altan-molecule has a 4n perimeter expected to hold a paratropic circulation, in consideration of its poor coupling with the inner part of the molecule. This qualitative expectation is borne out in many systems by ab initio and tight-binding calculations, but it breaks down when the perimeters of the parent molecule and its altan derivative are of close dimensions. The theoretical design of these molecules is reviewed. The possible importance of their anions and their openshell singlet ground states is also briefly discussed.

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“…This pattern reminds us of the annulene-within-anannulene model, which has been referred to in section 3.4 in conjunction with the macrocyclic aromaticity of kekulene (3). 104 Coronene may be viewed as [6]annulene (i.e., benzene) within [18]annulene. If this bonding model holds true, diatropic currents must be induced both along the periphery and along the central ring.…”

Section: Limitations Of Familiar Magnetic Criteriamentioning

confidence: 99%

Graph Theory of Ring-Current Diamagnetism

Aihara

2017

Bulletin of the Chemical Society of Japan

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Various magnetic criteria of aromaticity have been proposed so far, because they are easily calculated and applicable to a variety of cyclic π-systems. Many researchers, however, are reluctant to accept all or some of them. Our graph theory of ring-current diamagnetism revealed serious flaws in familiar magnetic criteria of aromaticity. Physically meaningful information on aromaticity can nevertheless be extracted from the ring-current diamagnetism. In particular, magnetic resonance energy (MRE), derived from the ring-current diamagnetic susceptibility, is interpretable as a kind of aromatic stabilization energy (ASE) and helps in consistently interpreting energetic and magnetic criteria of aromaticity. MRE and related quantities can be determined without reference to any hypothetical polyene-like structure but with a reasonable assumption that, when a magnetic field is applied to a cyclic π-system, a current is induced in each circuit in proportion to the ASE arising from the circuit. Unlike other conventional magnetic indexes, they are independent of the size and shape of the π-system.

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Validity and limitations of the annulene-within-an-annulene (AWA) model for macrocyclic π-systems

Cited by 19 publications

References 52 publications

Graph Theory of Aromatic Stabilization

Graph Theory of Aromatic Stabilization

The intriguing class of altan‐molecules

Graph Theory of Ring-Current Diamagnetism

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