Ab Initio Study of the Isomerization of Substituted Benzenes and [6]Paracyclophanes to the Dewar Benzene Isomers

Publikation: Beitrag in FachzeitschriftArtikelForschungPeer-Review

Autoren

  • Irmgard Frank
  • S. Grimme
  • S. D. Peyerimhoff

Externe Organisationen

  • Rheinische Friedrich-Wilhelms-Universität Bonn
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Details

OriginalspracheEnglisch
Seiten (von - bis)5949-5953
Seitenumfang5
FachzeitschriftJournal of the American Chemical Society
Jahrgang116
Ausgabenummer13
PublikationsstatusVeröffentlicht - 1 Juni 1994
Extern publiziertJa

Abstract

The energy differences (ΔE) between the benzene and the corresponding Dewar benzene forms of seven substituted benzenes and three [6]paracyclophanes were calculated by ab initio methods with basis sets ranging from split valence type to triple-ζ plus polarization type. Correlation effects were taken into account using second-order M⊘ller-Plesset perturbation theory (MP2). The results show that among all the investigated molecules the isomerization energy is largest for benzene itself; that is, benzene is 79 kcal/mol more stable than its Dewar form. Both, electron-accepting substituents and electron-donating substituents lower ΔE. Steric repulsion between substituents in the ortho position additionally destabilizes the benzene form relative to the Dewar form. [6]Paracyclophanes are influenced by substitution effects in the same way as the unbridged compounds. This finding can be interpreted as a further criterion for the aromaticity of the strongly deformed benzene ring in [6]paracyclophanes. Due to the deformation of the benzene ring, the ΔE values for the investigated [6]paracyclophanes are found to be considerably lower than those of the corresponding benzenes (about 25 kcal/mol). Our results are found to agree with the experimental isomerization enthalpies of hexamethylbenzene and perfluorohexamethylbenzene to within 5 kcal/mol, while a large discrepancy between theory and experiment is obtained for 8,9-dicarbethoxy[6]paracyclophane.

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Ab Initio Study of the Isomerization of Substituted Benzenes and [6]Paracyclophanes to the Dewar Benzene Isomers. / Frank, Irmgard; Grimme, S.; Peyerimhoff, S. D.
in: Journal of the American Chemical Society, Jahrgang 116, Nr. 13, 01.06.1994, S. 5949-5953.

Publikation: Beitrag in FachzeitschriftArtikelForschungPeer-Review

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abstract = "The energy differences (ΔE) between the benzene and the corresponding Dewar benzene forms of seven substituted benzenes and three [6]paracyclophanes were calculated by ab initio methods with basis sets ranging from split valence type to triple-ζ plus polarization type. Correlation effects were taken into account using second-order M⊘ller-Plesset perturbation theory (MP2). The results show that among all the investigated molecules the isomerization energy is largest for benzene itself; that is, benzene is 79 kcal/mol more stable than its Dewar form. Both, electron-accepting substituents and electron-donating substituents lower ΔE. Steric repulsion between substituents in the ortho position additionally destabilizes the benzene form relative to the Dewar form. [6]Paracyclophanes are influenced by substitution effects in the same way as the unbridged compounds. This finding can be interpreted as a further criterion for the aromaticity of the strongly deformed benzene ring in [6]paracyclophanes. Due to the deformation of the benzene ring, the ΔE values for the investigated [6]paracyclophanes are found to be considerably lower than those of the corresponding benzenes (about 25 kcal/mol). Our results are found to agree with the experimental isomerization enthalpies of hexamethylbenzene and perfluorohexamethylbenzene to within 5 kcal/mol, while a large discrepancy between theory and experiment is obtained for 8,9-dicarbethoxy[6]paracyclophane.",
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Download

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AU - Frank, Irmgard

AU - Grimme, S.

AU - Peyerimhoff, S. D.

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N2 - The energy differences (ΔE) between the benzene and the corresponding Dewar benzene forms of seven substituted benzenes and three [6]paracyclophanes were calculated by ab initio methods with basis sets ranging from split valence type to triple-ζ plus polarization type. Correlation effects were taken into account using second-order M⊘ller-Plesset perturbation theory (MP2). The results show that among all the investigated molecules the isomerization energy is largest for benzene itself; that is, benzene is 79 kcal/mol more stable than its Dewar form. Both, electron-accepting substituents and electron-donating substituents lower ΔE. Steric repulsion between substituents in the ortho position additionally destabilizes the benzene form relative to the Dewar form. [6]Paracyclophanes are influenced by substitution effects in the same way as the unbridged compounds. This finding can be interpreted as a further criterion for the aromaticity of the strongly deformed benzene ring in [6]paracyclophanes. Due to the deformation of the benzene ring, the ΔE values for the investigated [6]paracyclophanes are found to be considerably lower than those of the corresponding benzenes (about 25 kcal/mol). Our results are found to agree with the experimental isomerization enthalpies of hexamethylbenzene and perfluorohexamethylbenzene to within 5 kcal/mol, while a large discrepancy between theory and experiment is obtained for 8,9-dicarbethoxy[6]paracyclophane.

AB - The energy differences (ΔE) between the benzene and the corresponding Dewar benzene forms of seven substituted benzenes and three [6]paracyclophanes were calculated by ab initio methods with basis sets ranging from split valence type to triple-ζ plus polarization type. Correlation effects were taken into account using second-order M⊘ller-Plesset perturbation theory (MP2). The results show that among all the investigated molecules the isomerization energy is largest for benzene itself; that is, benzene is 79 kcal/mol more stable than its Dewar form. Both, electron-accepting substituents and electron-donating substituents lower ΔE. Steric repulsion between substituents in the ortho position additionally destabilizes the benzene form relative to the Dewar form. [6]Paracyclophanes are influenced by substitution effects in the same way as the unbridged compounds. This finding can be interpreted as a further criterion for the aromaticity of the strongly deformed benzene ring in [6]paracyclophanes. Due to the deformation of the benzene ring, the ΔE values for the investigated [6]paracyclophanes are found to be considerably lower than those of the corresponding benzenes (about 25 kcal/mol). Our results are found to agree with the experimental isomerization enthalpies of hexamethylbenzene and perfluorohexamethylbenzene to within 5 kcal/mol, while a large discrepancy between theory and experiment is obtained for 8,9-dicarbethoxy[6]paracyclophane.

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