An AM1 study of the molecules of [10]annulene and [12]annulene

Hernando, José M.; Enríquez, F.; Quirante, J.J.

doi:10.1016/0166-1280(93)87214-x

Cited by 2 publications

(2 citation statements)

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“…The BHandHLYP/TZ optimized geometry of 1a is shown in Figure , along with two other conformations, 1b and 1d (vide infra). In agreement with earlier studies, , we find that the most stable conformation of tri- trans -[12]annulene is that in which two inner hydrogens lie on one face of the average ring plane (Table ). Conformations 1b and 1d are ca.…”

Section: Resultssupporting

confidence: 92%

“…Loos and Leska's semiempirical results contradicted those obtained by Allinger, in that 1b was found to be the most stable conformation . Later, Hernando and co-workers concluded, based on AM1 calculations, that the most stable conformation of 1a was that in which two of the internal protons are on one face of the carbon skeleton and the other is on the opposite face …”

Section: Introductionmentioning

confidence: 85%

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Computational Evaluation of the Evidence for Tri-trans-[12]Annulene

Castro

Karney

et al. 2005

J. Org. Chem.

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[reaction: see text] Automerization in tri-trans-[12]annulene (1) was investigated by DFT, MP2, and coupled-cluster methods. Using the highest level of theory employed here, CCSD(T)/cc-pVDZ//BHandHLYP/6-311+G(d,p), we located two low-energy pathways for degenerate conformational change from the lowest-energy conformer of 1 (1a): one with E(a) = 4.5 kcal/mol that interconverts the three inner trans hydrogens with the three outer trans hydrogens and one with E(a) = 2.7 kcal/mol that interconverts the three inner hydrogens with each other. These results are consistent with the experimental results of Oth and co-workers on [12]annulene 1a (Oth, J. F. M.; Röttele, H.; Schröder, G. Tetrahedron Lett. 1970, 61). The conformational exchange of the inner trans hydrogens with the outer ones is predicted to occur via a one-step process involving a C(2)-symmetric transition state and not via the D(3)-symmetric transition state (1b) that was postulated earlier. Conformer 1b was found to be a shallow minimum 6.7 kcal/mol above 1a with a barrier of 0.4 kcal/mol for conversion to 1a. Finally, GIAO-B3LYP/6-311+G(d,p) and BHandHLYP/6-311+G(d,p) computed (1)H NMR chemical shifts of 1a and three other low-lying isomers support Oth's original assignment of observed (1)H NMR peaks to 1a at both low and high temperature.

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Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 85%