Strain-Free Sextet-Resonant Benzenoids and Their Antisextet Dualists

Balaban, Alexandrù T.; Schmalz, Thomas

doi:10.1021/ci060007l

Cited by 28 publications

(14 citation statements)

References 99 publications

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“…Balaban and Klein used the expression “claromatic” for such fully benzemoids . Dias provided solution of such systems, and an enumeration procedure was published by Balaban and Schmalz . Clar and Zander compared the reactivity of two isomeric polycyclic systems shown in Figure .…”

Section: Introductionmentioning

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: Introductionmentioning

confidence: 99%

Local aromaticity and aromatic sextet theory beyond Clar

Randić

Balaban

2018

Int J of Quantum Chemistry

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“…This has been shown using various measures of p-electron delocalization (generally known as aromaticity indices). 10,[13][14][15][16][17][18][19][20][21][22][23][24][25][26] The references mentioned lead to the well-documented conclusion that rings in a given molecule of a benzenoid hydrocarbon may have strongly different p-electron delocalization. To some degree, it may be said that, depending on the kind of benzoannulation (i.e.…”

Section: Introductionmentioning

confidence: 99%

The effect of benzoannulation on the transition state and the proton transfer equilibrium in di(2-pyridyl)methane derivatives

et al. 2011

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The tautomeric properties of di(2-pyridyl)methane and its benzoannulated derivatives were studied using a computational approach (M05/6-31G(2d,p)). Our analysis showed that the degree of cyclic p-electron delocalization in benzene and pyridine rings is directly connected to the effect of resonance present in quasi-rings formed by intramolecular hydrogen bonds of the N-HÁ Á ÁN type. This direct relation can be explained using two concepts, namely, the concept of Clar's aromatic sextet and the Leffler-Hammond concept originally developed for the explanation of the energy relation between ground-state and transition-state structures corresponding to proton transfer in H-bridges. Application of these two different concepts allows us to explain in detail the role of intramolecular hydrogen bonding in polycyclic aromatic hydrocarbons containing N heteroatoms. w Electronic supplementary information (ESI) available: Cartesian coordinates, computed total energies of optimized structures, aromaticity indices, densities of total electron energy at the ring critical points, and definitions of aromaticity indices. See

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“…This triangular correlation for the isomer numbers in Table PAH6(sextet) 35 has been structurally explained by the correlation of the empty ring configuration (antisextet dualist graphs) 36 which coincides with the excised internal structure of the retro-leapfrog. 37 To illustrate consider the TRS isomer numbers for C 30 H 16 , C 36 H 20 , and C 42 H 24 all having r(empty) = 3 in Fig.…”

Section: Leapfrog Algorithmmentioning

confidence: 83%

“…According to Harary and Harborth [their eqn (36) and eqn (39)], 52 benzenoid hydrocarbons (which they called hexagonal animals) exist if and only if n (number of vertices), and r (number of rings) are integers within the ranges of 2r + 1 + J(12r À 3) 1/2 n r n r 4r + 2…”

Section: Some Analytical Expressions For Deriving the First Generatio...mentioning

confidence: 99%

The polyhex/polypent topological paradigm: regularities in the isomer numbers and topological properties of select subclasses of benzenoid hydrocarbons and related systems

Dias

2010

Chem. Soc. Rev.

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The informatics on benzenoid hydrocarbons and related systems is reviewed. This informatics involves a collection of algorithms used to discover, process, and analyze patterns in structure/formula data sets. The unique organizational structure that emerges will be useful to chemists with an interest in polycyclic aromatic compounds, environmental chemists, material scientists, and other scientists wishing for a greater understanding of the formation of carbonaceous materials. This tutorial review will show that isomer enumeration can lead to significant chemical insights. The isomer number regularities will be shown to have a structural origin referred to as the polyhex/polypent topological paradigm.

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Strain-Free Sextet-Resonant Benzenoids and Their Antisextet Dualists

Cited by 28 publications

References 99 publications

Local aromaticity and aromatic sextet theory beyond Clar

Local aromaticity and aromatic sextet theory beyond Clar

The effect of benzoannulation on the transition state and the proton transfer equilibrium in di(2-pyridyl)methane derivatives

The polyhex/polypent topological paradigm: regularities in the isomer numbers and topological properties of select subclasses of benzenoid hydrocarbons and related systems

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