Abstract
We have calculated the geometry and energy of the valence tautomers benzene oxide and oxepin using the semiempirical AM1 model and the 6–31G and 6–31G* basis sets utilizing full geometry optimization. In the oxide the folding angleα, the angle between the epoxide ring and the adjacent plane containing four carbon atoms, is about 106°. The carbon skeleton is almost planar, the folding angleβ, the angle between the two four-carbon atom planes being about 175°. In contrast, oxepin is found to have a marked boat-shaped structure with the correspondingα andβ angles about 137° and 159°, respectively. The AM1, 6–31G, and 6–31G* calculations give −11.4, −10.8, and −2.9 kcal mol−1 for the energy change that accompanies the valence tautomerism, oxide-oxepin, compared to an experimental value of about +0.3 kcal mol−1. Single point calculations of the energies at the 6–31 G* geometry using Møller-Plesset perturbation theory to second order (MP2/6–31 G*) and third order (MP3/6–31G*) give ΔE T =+3.3 and +0.8 kcal mol−1. The values for the energy change in the transfer of epoxide oxygen from ethylene oxide to benzene using AM1, 6–31G, and 6–31G* are in good agreement, viz., +31.1, +34.5, and +33.6 kcal mol−1, respectively. A large positive energy change is to be expected in view of the loss of benzene aromaticity.
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Bock, C.W., George, P., Stezowski, J.J. et al. Theoretical studies of the benzene oxide—oxepin valence tautomerism. Struct Chem 1, 33–39 (1990). https://doi.org/10.1007/BF00675782
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DOI: https://doi.org/10.1007/BF00675782