Ground states of conjugated molecules. XI. Improved treatment of hydrocarbons

Dewar, Michael J. S.; Llano, Carlos De

doi:10.1021/ja01032a001

Cited by 490 publications

(273 citation statements)

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“…Since each bond in VB is described by a singlet coupled pair of orbitals, the reference points 1,3,5-cyclohexatriene in the benzene geometry (D 6h symmetry) and in its optimized geometry (D 3h symmetry) with double bonds between the carbonatoms (1,2), (3,4) and (5,6), is described by the following wavefunction:…”

Section: Methodsmentioning

confidence: 99%

“…Since 1,3,5-cyclohexatriene as such does not exist, it was proposed to compare the energy of benzene with that of a polyene-like 1,3,5-cyclohexatriene with D 3h symmetry [4]. In this case also a change in geometry ðD 6h !…”

Section: Introductionmentioning

confidence: 99%

“…This gives the theoretical resonance energy (TRE) [5]. The energy of the hypothetical reference compound is now estimated by taking thrice the C@C and CAC increment [4]. We note in passing that the name 1,3,5-cyclohexatriene has been given to compounds that possess a benzene moiety distorted to a D 3h geometry; illustrative examples are tris(benzocyclobutadieno)-(bond alternation DR 0.159 A A [6]) and tris(bicyclo[2.1.1]hexeno)-benzene (bond alternation DR 0.089 A A [7]).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

1,3,5-Cyclohexatriene captured in computro; the importance of resonance

Lenthe

Havenith

Dijkstra

et al. 2002

Chemical Physics Letters

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The geometry and energy of 1,3,5-cyclohexatriene, the reference molecule for the determination of the extra stabilization of benzene, have been calculated using an Ab Initio Valence Bond method. The theoretical resonance energy, according to Dewar, calculated as the energy difference between two-structure benzene and single-structure 1,3,5-cyclohexatriene, both with completely optimized geometries and orbitals, is only )12.05 kcal/mol. Resonance energies of )25.37 (local orbitals), )19.82 (delocal orbitals) and )44.13 (breathing orbitals) kcal/mol are found using the Pauling definition. The concept of the vertical resonance energy, however, is proven to be not tenable beyond a minimal basis. Ó

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

1,3,5-Cyclohexatriene captured in computro; the importance of resonance

Lenthe

Havenith

Dijkstra

et al. 2002

Chemical Physics Letters

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“…benzene, compared to their non-aromatic counterparts is a subject of considerable interest in chemistry. Many approaches for its calculation have been suggested in the literature, both empirical [1][2][3] and employing Ab Initio quantum chemistry [4][5][6][7][8]. Historically, Pauling and Wheland [9] have defined the resonance energy of an aromatic compound as the difference in energy between the resonating multi-structure valence bond wave function and the lowest contributing structure.…”

Section: Introductionmentioning

confidence: 99%

A comparison of approaches to estimate the resonance energy

et al. 2010

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We discuss Ab Initio approaches to calculate the energy lowering (stabilisation) due to aromaticity. We compare the valence bond method and the block-localised wave function approaches to calculate the resonance energy. We conclude that the valence bond approach employs a Pauling-Wheland resonance energy and that the block-localised approach employs a delocalisation criterion. The latter is shown to be more basis set dependent in a series of illustrative calculations.

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“…In fact, it shows a minimum between 1.52 and 1.53 Å, which agrees well with the expected equilibrium bond length for a σ bond between two sp 2 carbon atoms. 62 In comparison, the corresponding triplet state in the two-electron system of H 2 is purely repulsive since the underlying potential is just the repulsion between the bare nuclei. In semiempirical applications of the Hubbard model, the underlying bond potential is most often modeled as a spring, in other words as a harmonic expansion about a minimum.…”

Section: The V C Parametermentioning

confidence: 99%

A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

Schmalz

Serrano‐Andrés

Sauri

et al. 2011

The Journal of Chemical Physics

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The Hubbard model, which is widely used in physics but is mostly unfamiliar to chemists, provides an attractive yet simple model for chemistry beyond the self consistent field molecular orbital approximation. The Hubbard model adds an effective electron-electron repulsion when two electrons occupy the same atomic orbital to the familiar Hückel Hamiltonian. Thus it breaks the degeneracy between excited singlet and triplet states and allows an explicit treatment of electron correlation. We show how to evaluate the parameters of the model from high-level ab initio calculations on twoatom fragments and then to transfer the parameters to large molecules and polymers where accurate ab initio calculations are difficult or impossible. The recently developed MS-RASPT2 method is used to generate accurate potential energy curves for ethene as a function of carbon-carbon bond length, which are used to parameterize the model for conjugated hydrocarbons. Test applications to several conjugated/aromatic molecules show that even though the model is very simple, it is capable of reasonably accurate predictions for bond lengths, and predicts molecular excitation energies in reasonable agreement with those from the MS-RASPT2 method.

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Ground states of conjugated molecules. XI. Improved treatment of hydrocarbons

Cited by 490 publications

References 1 publication

1,3,5-Cyclohexatriene captured in computro; the importance of resonance

1,3,5-Cyclohexatriene captured in computro; the importance of resonance

A comparison of approaches to estimate the resonance energy

A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

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