Aromaticity and conjugation

Randić, Milan

doi:10.1021/ja00444a022

Cited by 403 publications

(232 citation statements)

References 7 publications

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“…77,78; and with different physical consequences -as in Refs. [38][39][40]62,[79][80][81]38. On the other hand, from a molecular-orbital perspective, there are relevant spanning subgraphs (identified with Sachs subgraphs, 23 supplemented with single-site components to make the result spanning), for which forcing ideas might somehow also be relevant.…”

Section: Resultsmentioning

confidence: 99%

“…It is realized that e is chemically relevant in Pauling's work, 35,36 and C is relevant in "conjugated-circuits" theory. [37][38][39][40][41][42][43] Next, our initial view of "forcing" is indicated. 6 S of conjugated 6-cycles of G is 6-forcing if no other Kekule structure κ of G manifests the same subset of conjugated 6-cycles with the same conjugation pattern within each of these cycles.…”

Section: Forcing For Kekule Structuresmentioning

confidence: 99%

See 1 more Smart Citation

Forcing, Freedom, & Uniqueness in Graph Theory & Chemistry

Klein

Rosenfeld

2014

Croat. Chem. Acta

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Abstract. Harary's & Randić's ideas of "forcing" & "freedom" involve subsets of double bonds of Kekule structure such as to be unique to that Kekule structure. Such forcing sets are argued to be greatly generalizable to deal with various other coverings, and thence forcing seems to be fundamental, and of notable potential utility. Various forcing invariants associated to (molecular) graphs ensue, with illustrative (chemical) examples and some mathematical consequences being provided. A complementary "uniqueness" idea is noted, and the general characteristic of "derivativity" of "forcing" is established (as is relevant for QSPR fittings). Different ways in which different sorts of forcings arise in chemistry are briefly indicated.(doi: 10.5562/cca2000)

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Section: Resultsmentioning

confidence: 99%

Section: Forcing For Kekule Structuresmentioning

confidence: 99%

Forcing, Freedom, & Uniqueness in Graph Theory & Chemistry

Klein

Rosenfeld

2014

Croat. Chem. Acta

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“…In the quantitative evaluation of aromaticity, experimentally determined or theoretically calculated, parameters currently used include: magnetic properties, 2-12 geometry, [13][14][15][16][17][18] bond orders, [19][20][21][22][23][24][25][26][27][28] isodesmic energy, 29 combustion energy, 30 (topological) resonance energy, [31][32][33][34][35][36][37][38] bond lengths [40][41][42][43][44][45][46] etc.…”

Section: Introductionmentioning

confidence: 99%

“…[33][34][35] Almost simultaneously, "topological resonance energy" TRE was put forward by Aihara 31 and Gutman et al 32 The values of aromaticity (Randić) and TRE (Gutman) are computed using very different formulas. These two models, used in the quantitative computation of aromaticity, use the "limit" Kekulé structures, in fact non-existent.…”

Section: Introductionmentioning

confidence: 99%

Aromatic molecular zones and fragments

Tarko¹

2008

Arkivoc

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An edge on the weighted molecular graph is aromatic if the bond order B value is within [α, β] range. A certain "non-conjugated topological path" includes minimum two adjacent "single" edges (B < α). The topological paths that are not "non-conjugated" are "conjugated topological paths". An aromatic zone is a collection of contiguous aromatic edges. An aromatic fragment is a topological path within aromatic zone. The proposed aromaticity formula measures the aromaticity of zones and any "conjugated paths" via two variables that gauge deviations of bond orders from a reference value and of atom hybridization from sp 2 character. The aromaticity of "non-conjugated paths" is, conventionally, null. The analysis of organic/inorganic molecules, ions and radicals, including those having cyclic, non-cyclic, planar and non-planar geometries, uses a unique set of parameters. The larger the deviation from Hückel rules, the smaller (even negative) is the computed aromaticity value. The paper presents a few non-aromatic Hückel and aromatic non-Hückel structures. After geometry optimization by PM6 method, one can compute the value of some aromaticity molecular descriptors, useful in QSPR computations. The paper includes a list of some descriptors that are measurements of the aromaticity of zones and aromatic "conjugated topological paths".

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“…The concept of k-resonance originates from Clar's aromatic sextet theory [3] and Randić's conjugated circuit model [18,19,20]. In the former Clar found that various electronic properties of polycyclic aromatic hydrocarbons can be predicted by defining mutually resonant sextets [7] (i.e., disjoint hexagons that are all alternating with respect to a Kekulé structure).…”

Section: Introductionmentioning

confidence: 99%

k-resonance in Toroidal Polyhexes*

2005

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This paper considers the k-resonance of a toroidal polyhex (or toroidal graphitoid) with a string (p, q, t) of three integers (p ≥ 2, q ≥ 2, 0 ≤ t ≤ p − 1). A toroidal polyhex G is said to be k-resonant if, for 1 ≤ i ≤ k, any i disjoint hexagons are mutually resonant, that is, G has a Kekulé structure (perfect matching) M such that these hexagons are M -alternating (in and off M ). Characterizations for 1, 2 and 3-resonant toroidal polyhexes are given respectively in this paper.

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Aromaticity and conjugation

Cited by 403 publications

References 7 publications

Forcing, Freedom, & Uniqueness in Graph Theory & Chemistry

Forcing, Freedom, & Uniqueness in Graph Theory & Chemistry

Aromatic molecular zones and fragments

k-resonance in Toroidal Polyhexes*

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