Effects of fused benzene rings on tautomerizations and inversions of benzo, azabenzo, and oxabenzocycloheptatrienes at theoretical levels |
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Authors: | M Z Kassaee M R Momeni F A Shakib M Ghambarian S M Musavi |
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Institution: | (1) Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran;(2) Faculty of Chemistry, University of Tabriz, 5166616471 Tabriz, Iran |
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Abstract: | Biologically important bicyclic species, including 6H-, 6H-6-aza-, and 6-oxabenzocycloheptatrienes (in which the benzene moiety is fused meta with respect to the tetrahedral constituents: –CH2–, –NH–, and –O–, respectively), show strong shifts of tautomerizations in favor of the corresponding tricyclic benzonorcaradienes
(with ΔH values of −11.49, −14.55, and −19.20 kcal mol−1, respectively), at B3LYP/6-311++G**//B3LYP/6-31G*, and MP2/6-311++G**//MP2/6-31G* levels, and at 298 K. In contrast, such
shifts are strongly disfavored by the isomeric bicyclic species in which the benzene moieties are fused ortho or para with respect to –CH2–, –NH–, and –O–, respectively. Hence for species with ortho benzene rings including 5H-, 5H-5-aza- and 5-oxabenzocycloheptatrienes, tautomerization ΔH values are 30.76, 31.89, and 25.27 kcal mol−1, respectively, while for species with para fused benzene moieties including 7H-, 7H-7-aza-, and 7-oxabenzocycloheptatrienes, tautomerization ΔH values are 24.12, 26.00, and 19.55 kcal mol−1, respectively. NICS calculations are successfully used to rationalize these results. The calculated energy barriers for inversion
of the seven-membered rings of bicyclic species predict a dynamic nature for all the structures except for the virtually planar
6H-6-aza- and 6-oxabenzocycloheptatrienes. Finally, our theoretical data are compared to the experimental results where available.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Benzocycloheptatriene Tautomerization Inversion DFT Ab initio NICS |
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