Substituent effects in eight-electron electrocyclic reactions |
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Authors: | Lecea Begoña Arrieta Ana Cossío Fernando P |
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Affiliation: | Farmazi Fakultatea and Kimika Fakultatea, Universidad del País Vasco-Euskal Herriko Unibertsitatea, P.K. 1072, 20080 San Sebastián-Donostia, Spain. |
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Abstract: | The main features of transition structures associated with eight-electron electrocyclic reactions have been studied with Density Functional Theory. It is found that conrotatory electrocyclization reaction of (3Z,5Z)-octa-1,3,5,7-tetraenes takes place via M?bius aromatic transition structures of helical conformation. The reaction is completely periselective. In general, transition structures having outward substituents are preferred with respect to the inward transition structures, irrespective of the pi-donor or pi-acceptor character of the substituent. In contrast with four-electron thermal conrotatory electrocyclic reactions, there is no satisfactory correlation between the difference in energy of activation between inward and outward substituents and the Taft resonance sigma(R) parameter. |
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