Π-Electron CONTENTS OF RINGS IN THE DOUBLE-HEXAGONAL-CHAIN HOMOLOGOUS SERIES (PYRENE, ANTHANTHRENE AND OTHER ACENOACENES)

Gutman, Iván; Randić, Milan; Balaban, Alexandrù T.; Furtula, Boris; Vučković, Veselin

doi:10.1080/10406630591007080

Cited by 18 publications

(11 citation statements)

References 23 publications

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“…There have been numerous approaches to characterization of local aromaticity of benzenoid hydrocarbons, which include the work of Polansky and Derflinger from 1967, who considered partitioning of HMO (Hückel molecular orbitals) into ring contributions, and an early work of Randić from 1980 in which as a measure of local aromaticity is considered the count of how many times each benzenoid ring in all Kekulé valence structure of a molecule has three C = C bonds. Our interest in characterization of benzenoid rings continued well over 35 years, until finally through evolution we arrived at the current local aromaticity map ( vide infra ). In Figure we show local aromaticities of benzene rings obtained by counting occurrence C = C bonds in benzene rings for the 27 benzenoid hydrocarbons of Table .…”

Section: Local Aromaticity—going Beyond Clar's Aromatic Sextet Theorymentioning

confidence: 99%

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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Section: Local Aromaticity—going Beyond Clar's Aromatic Sextet Theorymentioning

confidence: 99%

Local aromaticity and aromatic sextet theory beyond Clar

Randić

Balaban

2018

Int J of Quantum Chemistry

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“…In this approach the “empty” rings are indeed empty of π-electrons. Recent comparisons of these approaches have shown minor differences in the distribution of π-electrons within different rings . It has yet to be better established in which cases these schemes give significantly different results.…”

Section: Modified Approach: Superposition Of Clar Structuresmentioning

confidence: 99%

Partitioning of π-Electrons in Rings for Clar Structures of Benzenoid Hydrocarbons

Randić¹,

Balaban²

2005

J. Chem. Inf. Model.

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Resonance structures of polycyclic aromatic hydrocarbons can be associated with numerical formulas by assigning pi-electrons of C=C double bonds to individual benzenoid rings. Each C=C double bond in a resonance structure assigns two pi-electrons to a ring in a fused-benzenoid system if it is not shared by adjacent rings and one pi-electron when it is common to two rings, obtaining thus a "local" characterization of rings in polycyclic conjugated hydrocarbons. In the present contribution we extend this approach to the aromatic pi-sextet model of Clar, which offers an alternative description of benzenoid hydrocarbons. In this model local characteristics of individual benzenoid rings are based on partitioning of pi-electrons but only for those resonance structures (fewer in number) that contribute to Clar's formula of benzenoid hydrocarbons.

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“…The concept of the π -electron content of a ring of a polycyclic conjugated molecule was put forward by Randić and Balaban (11) and was eventually further elaborated and applied to a variety of aromatic hydrocarbons (12)(13)(14)(15)(16)(17)(18)(19)(20) and heteroatom-containing species (21)(22)(23).…”

Section: Methodsmentioning

confidence: 99%

Testing the Y–rule in Clar Theory

Gutman

Stanković

2007

Polycyclic Aromatic Compounds

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A recently proposed modification of the basic postulates of the Clar aromatic sextet theory, called the Y-rule, is tested on a suitably chosen homologous series of benzenoid hydrocarbons. For these benzenoid systems the original Clar theory predicts a significantly different distribution of π -electrons than the Y-rule. It was found that both the π -electron contents of rings as well as their energy effects agree with the predictions of the original Clar theory, failing to corroborate the Y-rule.

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Π-Electron CONTENTS OF RINGS IN THE DOUBLE-HEXAGONAL-CHAIN HOMOLOGOUS SERIES (PYRENE, ANTHANTHRENE AND OTHER ACENOACENES)

Cited by 18 publications

References 23 publications

Local aromaticity and aromatic sextet theory beyond Clar

Local aromaticity and aromatic sextet theory beyond Clar

Partitioning of π-Electrons in Rings for Clar Structures of Benzenoid Hydrocarbons

Testing the Y–rule in Clar Theory

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