IGLO Study of Benzene and Some of Its Isomers and Related Molecules. Search for Evidence of the Ring Current Model

Fleischer, Ulrich; Kutzelnigg, Werner; Lazzeretti, Paolo; Muehlenkamp, V.

doi:10.1021/ja00091a039

Cited by 263 publications

(274 citation statements)

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“…Thus, in line with the findings of Shaik et al [34], benzene ðD 6h -2Þ can easily distort towards the 1,3,5-cyclohexatriene geometry ðD 3h -2Þ. This, however, is not a sign that resonance is unimportant, but should instead be attributed to the fact that resonance is still an important factor even in deformed benzene ðD 3h -2Þ [9,10] (see also [35]). …”

Section: Resultssupporting

confidence: 74%

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: Resultssupporting

confidence: 74%

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

Lenthe

Havenith

Dijkstra

et al. 2002

Chemical Physics Letters

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“…In the literature, numerous quantum-chemical data have been reported from which completely different conclusions have been derived. For example, in 1994 Kutzelnigg and coworkers [46], using the IGLO (Individual Gauge for Localized Orbitals) method, found only little reduction of aromaticity when benzene was deformed to a 1,3,5-cyclohexatriene geometry. Two planar structures with all angles equal to 120° were considered for cyclohexatriene, one structure with alternating single and double bond lengths equal to 1.501 and 1.336 Å, and the other one with the C−C and C=C bond lengths equal to 1.479 and 1.323 Å, respectively.…”

Section: Original Homa Index (Ohoma)mentioning

confidence: 99%

On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems

et al. 2010

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Abstract:The HOMA (Harmonic Oscillator Model of Aromaticity) index, reformulated in 1993, has been very often applied to describe π-electron delocalization for mono-and polycyclic π-electron systems. However, different measures of π-electron delocalization were employed for the CC, CX, and XY bonds, and this index seems to be inappropriate for compounds containing heteroatoms. In order to describe properly various resonance effects (σ-π hyperconjugation, n-π conjugation, π-π conjugation, and aromaticity) possible for heteroatomic π-electron systems, some modifications, based on the original HOMA idea, were proposed and tested for simple DFT structures containing C, N, and O atoms. An abbreviation HOMED was used for the modified index.

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“…their cisdi-epoxides and trans-di-epoxides obtained by diepoxidation of CP-PAH 2-4, respectively, their 1 H [␦( 1 H)] and 13 C NMR [␦( 13 C)] chemical shifts were computed using the direct version of the reliable ab initio individual gauge for localized orbitals (IGLO) method with the implemented basis set III [37,38] using ab initio RHF/6-31G** geometries of the cis-and trans-stereo-isomers of 6-8 optimized with GAMESS-UK [39]. All RHF/6-31G** optimized geometries were characterized as genuine minima by Hessian calculations; in all cases no imaginary vibrations were found.…”

Section: Appendix Bmentioning

confidence: 99%

“…1) using the S. typhimurium strain TA98, with and without exogenous metabolic activation mixture (±S9-mix) following standard protocols [22,23] Concentration ( g/plate) 5 Lack of background lawn; toxicity was observed. [21]) [37,38]. All other computed quaternary ␦( 13 C) chemical shift values for 6-8 are available upon request from the corresponding author (LWJ).…”

Section: Appendix Bmentioning

confidence: 99%

See 1 more Smart Citation

Di-epoxides of the three isomeric dicyclopenta-fused pyrenes: ultimate mutagenic active agents

Otero-Lobato

Kaats-Richters

Havenith

et al. 2004

Mutation Research/Genetic Toxicology and Environmental Mutagene

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To rationalize the high bacterial mutagenic response recently found for the (di-) cyclopenta-fused pyrene congeners, viz. cyclopenta[cd]-(1), dicyclopenta[cd,mn]-(2), dicyclopenta[cd,fg]-(3) and dicyclopenta [cd,jk]pyrene (4), in the presence of a metabolic activation mixture (S9-mix), their (di-)epoxides at the externally fused unsaturated five-membered rings were previously proposed as the ultimate mutagenic active forms. In this study, cyclopenta[cd]pyrene-3,4-epoxide (5) and the novel dicyclopenta[cd,mn]pyrene-1,2,4,5-di-epoxide (6), dicyclopenta[cd,fg]pyrene-5,6,7,8-di-epoxide (7) and dicyclopenta[cd,jk]pyrene-1,2,6,7-di-epoxide (8) were synthesised from 1 to 4, respectively, and subsequently assayed for bacterial mutagenicity in the standard microsomal/histidine reverse mutation assay (Ames-assay with Salmonella typhimurium strain TA98). The di-epoxides 6-8 are present as a mixture of their cis-and trans-stereo-isomers in a close to 1:1 ratio ( 1 H NMR spectroscopy and ab initio IGLO/III//RHF/6-31G** calculations). The direct-acting mutagenic activity and the strong cytotoxicity exerted by 5-8 both in the absence or presence of an exogenous metabolic activation system (±S9-mix) demonstrate that the ultimate mutagenic active forms are the proposed (di-)epoxides of 1-4.

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IGLO Study of Benzene and Some of Its Isomers and Related Molecules. Search for Evidence of the Ring Current Model

Cited by 263 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

On the Harmonic Oscillator Model of Electron Delocalization (HOMED) Index and its Application to Heteroatomic π-Electron Systems

Di-epoxides of the three isomeric dicyclopenta-fused pyrenes: ultimate mutagenic active agents

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