On π-electron conjugation in the five-membered ring of fluoranthene-type benzenoid hydrocarbons

Gutman, Iván; Djurdjevic, Jelena

doi:10.2298/jsc0907765g

Cited by 22 publications

(14 citation statements)

References 16 publications

(13 reference statements)

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“…The effect of benzo-annelation on cyclic conjugation in various polycyclic conjugated systems was much studied: in acenaphthylene and fluoranthene congeners, [1][2][3][4][5][6][7][8] in other non-alternant conjugated molecules, 9,10 and in benzenoid hydrocarbons, [11][12][13][14][15][16][17] and a general theory thereof was developed. 18 The analogous effect of benzocyclobutadieno-annelation has until now not been examined at all.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8] Within these studies, the following five generally valid regularities could be established: Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

“…19,20 For additional details see an older paper, 21 more recent articles, 16,17,22,23 and elsewhere. 4,11 For the present considerations it is sufficient to recall that the ef-values are expressed in units of the HMO carbon-carbon resonance integral β. Therefore, positive ef-values indicate thermodynamic sta-____________________________________________________________________________________________________________________________ bilization caused by cyclic conjugation, and the greater is ef, the stronger is the cyclic conjugation in the considered ring.…”

Section: Introductionmentioning

confidence: 99%

“…In these works, [1][2][3][4][5][6][7][8] RuAle 1 was referred to as the "PCP rule" or the "PCP effect". Since in the present work, we are going to consider benzocyclobutadieno-annelation will be considered, the term "PCP" would be misleading, and, therefore, the more plausible term "angular" is used (cf.…”

Section: Introductionmentioning

confidence: 99%

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Effect of benzocyclobutadieno-annelation on cyclic conjugation in fluoranthene congeners

Gutman

Furtula

Balaban

2011

JSCS

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Earlier studies revealed that benzo-annelation has a peculiar effect on the intensity of cyclic conjugation in the five-membered ring of fluoranthene congeners. Now, the analogous effect of benzocyclobutadieno-annelation was examined and it was found show it is opposite to the effect of benzo-annelation: a benzocyclobutadiene fragment in angular (resp. linear) position with regard to the five-membered ring, decreases (resp. increases) the intensity of cyclic conjugation in the five-membered ring.

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Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8] Within these studies, the following five generally valid regularities could be established: Fig. 1.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Effect of benzocyclobutadieno-annelation on cyclic conjugation in fluoranthene congeners

Gutman

Furtula

Balaban

2011

JSCS

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“…In a series of recent papers, [26][27][28][29][30][31][32][33][34][35] we studied various π-electron properties of fluoranthenes were studied including also their Kekulé structures. 33,34 Based on the observations made in, 33,34 some triplet-ground-state Kekuléan fluoranthenes were recognized.…”

Section: Introductionmentioning

confidence: 99%

Diradical character of some fluoranthenes

Marković¹,

Djurdjevic²,

Jeremić³

et al. 2010

J Serb Chem Soc

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It is shown that some Kekuléan fluoranthenes are diradicals and that their ground state is a triplet. In the energetically less favorable singlet state, these hydrocarbons also exhibit pronounced diradical character. The diradical character y of the compounds under investigation was estimated using the unrestricted symmetry-broken (yPUHF) and complete active space (yNOON) methods. It was found that the yPUHF values better reproduce the diradical character of the investigated hydrocarbons. It was shown that singly occupied molecular orbital (SOMO) and SOMO-1 of a diradical structure occupy different parts of space with a small shared region, resulting in a spin density distribution over the entire molecule. The spatial diradical distribution in the singlet diradical structures was examined by inspecting the HOMOs and LUMOs for α and β spin electrons. It was shown that the α-HOMO and the β-LUMO (as well as the β-HOMO and the α-LUMO) occupy practically the same part of space. In this way, there are no unpaired electrons in a singlet diradical structure, yet two of them occupy different parts of space, thus allowing the π-electrons to delocalize.

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Local aromaticity and aromatic sextet theory beyond Clar

Randić

Balaban

2018

Int J of Quantum Chemistry

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Recently assigned numerical expressions to qualitative benzenoid formulas of Clar have transformed Clar's theory into a quantitative model that allowed a structural characterization of aromaticity in benzenoid polycyclic hydrocarbons and construction of aromaticity maps for benzenoid polycyclic hydrocarbons. The key structural elements of the novel quantitative aromatic sextet theory of Clar are (1) Kekul e valence structures, (2) Pauling bond orders, and (3) Clar's aromatic sextet benzenoid rings. In the present contribution we go beyond Clar and consider local aromaticities of benzenoid rings in benzenoid polycyclic hydrocarbons. We have characterized each benzenoid ring by two descriptors: (1) their content of C 5 C bonds in the set of Kekul e valence structures, which is reflected in the ring bond orders, and by (2) the variations of CC bond orders within rings, which are zero for benzene. This allows us to introduce for any set of benzenoid hydrocarbons local aromaticity map, which allows one to graphically view similarities and dissimilarities of local aromaticity of different benzenoid rings. For such map, one can calculate the "distance" of each ring from the benzene, with coordinates (3.00, 0) for benzene RBO and variations in CC bonds, respectively. We show that the central ring in peropyrene is visibly less aromatic that the terminal sextets, as has been claimed by Gutman and Agranat, and similarly we show that the central ring of anthracene is unexpectedly more aromatic than the terminal rings, in having greater similarity in bond lengths to benzene ring than the terminal rings. This suggests limitations of the assumption of the Clar model that migrating sextets have equal local aromaticities.Finally, we examined a pair of non benzenoid hydrocarbons related to peropyrene, built from terminal benzenoid rings and naphthalene fragments. Surprisingly, we have found the terminal benzene rings in the two non benzenoid compounds to have unusually high ring bond orders, approaching that of benzene.

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On π-electron conjugation in the five-membered ring of fluoranthene-type benzenoid hydrocarbons

Cited by 22 publications

References 16 publications

Effect of benzocyclobutadieno-annelation on cyclic conjugation in fluoranthene congeners

Effect of benzocyclobutadieno-annelation on cyclic conjugation in fluoranthene congeners

Diradical character of some fluoranthenes

Local aromaticity and aromatic sextet theory beyond Clar

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