Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5418537 | Journal of Molecular Structure: THEOCHEM | 2007 | 10 Pages |
Abstract
The effects of substituents on the rate of intramolecular cyclization of the 2,5-hexadienyl radicals have been investigated computationally with DFT theory, using the UB3LYP functional. Various substituents - CN, NO2, CH3, NH2, and t-butyl - at various positions - C1, C5 and C6 - were considered in the calculations. An electron-donating substituent on the C1 position raises the radical SOMO energies to increase the interaction with the alkene LUMO, whereas an electron-withdrawing counterpart lowers the SOMO and increases the interaction with the alkene HOMO. Both interactions decrease the activation energies, by 0.9-10.2Â kcal/mol, and increase the rate of reaction rate, from 3 to 2.7Â ÃÂ 107 times. Similar results were obtained for the substituents at the C6 position, and the activation energies for the intramolecular cyclization were decreased by 0.2-4.8Â kcal/mol and the reaction rate increased from 2 to 2.8Â ÃÂ 103 times. The substituent at the C5 position favors the formation of a 6-endo product because of a steric effect. The effects of disubstituents at both C1 and C6 positions were also investigated; the results showed that the electron-withdrawing groups decrease most effectively the activation energies. The so-called captodative effect was also investigated.
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Authors
Ching-Wen Wu, Hui-Lung Chen, Jia-Jen Ho,