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

authored by: Irmgard Frank, S. Grimme, S. D. Peyerimhoff
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.
External Organisation(s): University of Bonn
Type: Article
Journal: Journal of the American Chemical Society
Volume: 116
Pages: 5949-5953
No. of pages: 5
ISSN: 0002-7863
Publication date: 01.06.1994
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Catalysis, General Chemistry, Biochemistry, Colloid and Surface Chemistry
Electronic version(s): https://doi.org/10.1021/ja00092a051 (Access: Closed)

BibTeX

@article{a1e8e91b06894d1dbf6e4a3efdd70f24,
title = "Ab Initio Study of the Isomerization of Substituted Benzenes and [6]Paracyclophanes to the Dewar Benzene Isomers",
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.",
author = "Irmgard Frank and S. Grimme and Peyerimhoff, {S. D.}",
year = "1994",
month = jun,
day = "1",
doi = "10.1021/ja00092a051",
language = "English",
volume = "116",
pages = "5949--5953",
journal = "Journal of the American Chemical Society",
issn = "0002-7863",
publisher = "American Chemical Society",
number = "13",
}