ORGN 667 |
| Electronic structure calculations predict that cyclization of the radical anion of 2,5-dicyano-1,5-hexadiene to form the corresponding cyclohexane-1,4-diyl radical anion is exothermic by 16.2 kcal/mol (B3LYP/6-31+G*). Gas-phase experimental studies have confirmed that cyclization does occur upon reduction, providing the first example of electron catalyzed Cope cyclization. In continuation of this work we investigate the effects of substituents in the 2- and 5- positions of 1,5-hexadienes on the potential energy surface of electron catalyzed Cope cyclization. Based on the observed reactivity from ion-molecule reactions and study of reaction rates we found that the ion of 2,5-di(4,4′-trifluoromethylphenyl)-1,5-hexadiene and 2,5-di(3,3′-trifluoromethylphenyl)-1,5-hexadiene undergo Cope Cyclization, whereas the radical anions having substituents such as the fluoro-, nitro-, chloro- and acetyl- groups do not. The chemical reactivity is consistent with a simple potential energy surface picture based on the energetics of model systems (Figure 1).
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Physical Organic Chemistry: Calculations, Mechanisms, Photochemistry, and High-Energy Species
1:00 PM-4:40 PM, Thursday, 30 March 2006 Georgia World Congress Center -- C303, Oral
Division of Organic Chemistry |
