Exploring the validity of the Glidewell–Lloyd extension of Clar’s π-sextet rule: assessment from polycyclic conjugated hydrocarbons

Bakouri, Ouissam El; Poater, Jordi; Feixas, Ferran; Solà, Miquel

doi:10.1007/s00214-016-1970-1

Cited by 34 publications

(39 citation statements)

References 49 publications

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“…The resonance energies of the planar structures of azepine and oxepines obtained through extended Hückel MO theory and early Hartree‐Fock computations suggested antiaromatic character, later supported by NICS calculations . However, the dibenz[ b,f ]annelated derivatives were found to have positive resonance energies associated with some aromatic character as their benzene rings keep their Hückel aromaticity in line with Glidewell‐Lloyd's extension of Clar's rule . Still, dibenzo[ b,f ]oxepin, similarly to oxepin, adopts a saddle‐shaped structure in the S 0 state .…”

Section: Introductionmentioning

confidence: 83%

“…[14,22] However, the dibenz[b,f]annelated derivatives were found to have positive resonance energies associated with some aromatic character as their benzene rings keep their Hückel aromaticity in line with Glidewell-Lloyd's extension of Clar's rule. [23,24] Still, dibenzo[b,f]oxepin, similarly to oxepin, adopts a saddle-shaped structure in the S 0 state. [4] Also dibenzannelated 8π-electron six-membered ring (6MR) compounds such as phenothiazine and phenoxepine adopt nonplanar conformations in S 0 .…”

Section: Introductionmentioning

confidence: 99%

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Is Excited‐State Aromaticity a Driving Force for Planarization of Dibenzannelated 8π‐Electron Heterocycles?

et al. 2019

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Compounds with dibenzannelated heterocycles with eight π‐electrons are found in a range of applications. These molecules often adopt a bent structure in the ground state (S0) but can become planar in the first excited states (S1 and T1) because of the cyclically conjugated 4nπ central ring, which fulfils the requirements for excited state aromaticity. We report on a quantum chemical investigation of the aromatic character in the S1 and T1 states of dibenzannelated seven‐ and six‐membered heterocycles with one, two, or three heteroatoms in the 8π‐electron ring. These states could have ππ* or nπ* character. We find that compounds with one or two heteroatoms in the central ring have ππ* states as their S1 and T1 states. They are to a significant degree influenced by excited state aromaticity, and their optimal structures are planar or nearly planar. Among the heteroatoms, nitrogen provides for the strongest excited state aromaticity whereas oxygen provides for the weakest, following the established trend of the S0 state. Yet, dibenzannelated seven‐membered‐ring compounds with N=N bonds have non‐aromatic nπ* states with strongly puckered structures as their S1 and T1 states.

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Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Is Excited‐State Aromaticity a Driving Force for Planarization of Dibenzannelated 8π‐Electron Heterocycles?

et al. 2019

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“…Amidst them, one of the most prominent model was Clar's aromatic π‐sextet rule, which claims that the Kekulé structure with the largest number of disjoint aromatic π‐sextets, that is, the so‐called Clar valence structure, is the one that offers the best description of benzenoid polycyclic aromatic hydrocarbons (PAHs). This model was extended by Glidewell and Lloyd to polycyclic conjugated hydrocarbons having rings with any even number of carbon atoms in their structure . Several studies among the years provided support to Clar's π‐sextet model .…”

Section: Introductionmentioning

confidence: 92%

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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“…Let us now discuss the case of molecules I and II in Figure with a cyclobutadiene ring fused to each cyclooctatetraene ring of octalene . The most stable structure for these molecules in their closed‐shell singlet state is shown in blue in Figure .…”

Section: Combining Rulesmentioning

confidence: 99%

Connecting and combining rules of aromaticity. Towards a unified theory of aromaticity

Solà

2018

WIREs Comput Mol Sci

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Most of the archetypal aromatic compounds present high symmetry and have degenerate highest‐occupied molecular orbitals. These orbitals can be fully occupied resulting in a closed‐shell structure or can be same‐spin half‐filled. This closed‐shell or same‐spin half‐filled electronic structure provides an extra stabilization and it is the origin of several rules of aromaticity such as the Hückel 4N + 2 rule, the lowest‐lying triplet excited state 4N Baird rule, the 4N rule in Möbius‐type conformation, the 4N + 2 Wade–Mingos rule in closo boranes or the 2(N + 1)2 Hirsch rule in spherical aromatic species. Combinations of some of these rules of aromaticity can be found in some particular species. Examples of these combinations will be discussed and the validity of some of these rules will be assessed. Moreover, it is possible to establish connections with some of these rules of (anti)aromaticity and, therefore, they can be partially generalized, which represents a step forward to a future unified theory of aromaticity. This article is categorized under: Electronic Structure Theory > Ab Initio Electronic Structure Methods Electronic Structure Theory > Density Functional Theory Software > Quantum Chemistry

show abstract

Exploring the validity of the Glidewell–Lloyd extension of Clar’s π-sextet rule: assessment from polycyclic conjugated hydrocarbons

Cited by 34 publications

References 49 publications

Is Excited‐State Aromaticity a Driving Force for Planarization of Dibenzannelated 8π‐Electron Heterocycles?

Is Excited‐State Aromaticity a Driving Force for Planarization of Dibenzannelated 8π‐Electron Heterocycles?

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

Connecting and combining rules of aromaticity. Towards a unified theory of aromaticity

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