Aromatic Character of Polycyclic π Systems Formed by Fusion of Two or More Rings of the Same Size

Sekine, Rika; Nakagami, Yuto; Aihara, Jun‐ichi

doi:10.1021/jp2033438

Cited by 22 publications

(66 citation statements)

References 32 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: 82%

“…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: 95%

“…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: 82%

Section: Extension Of the Tre Conceptmentioning

confidence: 95%

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Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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“…¹ , polycyclic π-systems with one or more five-membered rings usually have low-lying unoccupied π-orbitals in the neutral state and tend to form stable molecular anions. 130 The ability of fullerenes to accommodate excess negative charge must be related to the presence of 12 pentagonal rings. 131 By contrast, as in the case of 93 + , polycyclic π-systems with one or more seven-membered rings have high-lying occupied π-orbitals in the neutral state and tend to form stable molecular cations.…”

Section: Magnetic Resonance Energies Of Antiaromatic Speciesmentioning

confidence: 99%

“…131 By contrast, as in the case of 93 + , polycyclic π-systems with one or more seven-membered rings have high-lying occupied π-orbitals in the neutral state and tend to form stable molecular cations. 130 Pentalene (81) with two fivemembered rings and heptalene (83) with two seven-membered rings have a nonbonding LUMO and HOMO, respectively. Hence, 81 and 83 tend to form an molecular dianion and dication, respectively, both of which are iso-π-electronic with naphthalene (1).…”

Section: Magnetic Resonance Energies Of Antiaromatic Speciesmentioning

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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The Influence of Benzo‐Fusion on the Aromatic Pathways and Ring Currents of Cycl[3.2.2]azine

Mattursun

Kerim

2017

Journal of Heterocyclic Chem

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The effect of benzene ring fusion on the aromaticity of cycl[3.2.2]azine was studied by calculating topological resonance energy (TRE), the percentage topological resonance energy (%TRE), and magnetic resonance energy (MRE). The bond resonance energy (BRE) and circuit resonance energy (CRE) indices were used to estimate the local aromaticity. Our BRE and CRE results show that the central nitrogen atom plays a significant role both in the global and local aromaticity of the compounds in our study, and contrary to what has been reported in the literature, none of these compounds are peripheral π‐electronic systems. In the case of benzene ring‐fused derivatives, benzene ring(s) exhibit relatively larger local aromaticity and reduce the local aromaticity of the central portion of cycl[3.2.2]azine to a level comparable to a corresponding non‐benzene fused parent system. Ring current results predict that a strong diamagnetic current flows around the whole molecular perimeter. The diatropic bond current results, as computed here, are in good agreement with the observed 1H‐NMR chemical shifts of these compounds.

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Aromatic Character of Polycyclic π Systems Formed by Fusion of Two or More Rings of the Same Size

Cited by 22 publications

References 32 publications

Graph Theory of Aromatic Stabilization

Graph Theory of Aromatic Stabilization

Graph Theory of Ring-Current Diamagnetism

The Influence of Benzo‐Fusion on the Aromatic Pathways and Ring Currents of Cycl[3.2.2]azine

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