CHED 358 |
| Using coupled cluster and density functional theory, calculations pertaining to degenerate bond shifting and conformational changes of [10]annulene isomers 1-5 were conducted. Our results (CCSD(T)/cc-pVDZ//BHandHLYP/6-311+G**) support that bond shifting in the twist (1) proceeds via a two step mechanism by way of the bond equalized heart (2) minimum. The transition state for 1 to 2 (Ea=11.7 kcal/mol) is bond localized. In comparison, a mechanism for degenerate bond shifting proceeds through a double-twist, bond equalized (but not aromatic) transition state (Ea=16.1 kcal/mol). Pseudorotation in the all-cis, boat conformation (3) was found to have a negligible barrier in agreement with the observed single peak NMR spectra at various temperatures. While the naphthalene-like isomer (4) and the azulene-like isomer (5) were found to have low bond shifting and conformational automerization barriers (<5 kcal/mol), the barrier for conformational change of 5 to 4 was approximately 13 kcal/mol, ruling them out as candidates for the observed spectra. Further investigation of the mechanisms for valence isomerization of [10]annulene to bicyclic compounds is underway. This computational study supports Masamune's original assignments of 1 and 3 for the two [10]annulene isomers isolated.
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Undergraduate Research Poster Session: Organic Chemistry
11:00 AM-1:00 PM, Monday, 27 March 2006 Georgia World Congress Center -- Ex. Hall B4, Poster
Division of Chemical Education |
