ORGN 621 |
| In contrast to the long-held view that bond shifting in annulenes occurs via planar or nearly planar structures, we present computational evidence that certain annulenes can undergo bond shifting via highly nonplanar conformations. The known isomers of [12]annulene (1) and [16]annulene (2) undergo bond shifting via Möbius-topology transition states, resulting in facile configuration change. The BH&HLYP/6-311+G** computed barriers for these two systems are ca. 20 and 10 kcal/mol, respectively, in good agreement with early experimental results of Oth. In addition, the transition states are Möbius aromatic annulenes. Other [4n]annulene isomers have Möbius bond shifting barriers as low as 3 kcal/mol. Results for bond shifting in [10]- and [12]annulene isomers with two half-twists will also be reported.
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
8:00 AM-12:00 PM, Thursday, 30 March 2006 Georgia World Congress Center -- C303, Oral
Division of Organic Chemistry |
