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|Título:||Supramolecular catalysis by cucurbituril and cyclodextrins: similarity and differences|
Moreira, José A.
|Editora:||American Chemical Society|
|Citação:||Basilio, Nuno; García-Río, Luís; Moreira, José A.; Pessêgo, Márcia. Supramolecular Catalysis by Cucurbituril and Cyclodextrins: Similarity and Differences, The Journal of Organic Chemistry, 75, 3, 848-855, 2010.|
|Resumo:||To understand the analogies and differences between the cucurbituril and cyclodextrin cavities different solvolytic reactions have been studied in the presence of cucurbituril, CB7, and β-CD or its methylated derivative, DM-β-CD. Solvolysis of 1-bromoadamantane has been used as a test to evaluate the ability of the cavities to solvate the Br- leaving group. Obtained results show that in both cases the polarity inside the cavity is similar to that of a 70% ethanol:water mixture. Solvolysis of substituted benzoyl chlorides shows a great difference between the CB7 and DM-β-CD cavity. Solvolysis of electron withdrawing substituted benzoyl chlorides (associative mechanism) is catalyzed by DM-β-CD and inhibited by CB7. However, solvolysis of electron donating substituted benzoyl chlorides(dissociative mechanism) is catalyzed by CB7 and inhibited by DM-β-CD. These experimental behaviors have been explained on the basis of different solvolytic mechanisms. Participation of the hydroxyl groups of the cyclodextrin as a nucleophile can explain the catalytic effect observed for solvolysis of benzoyl chlorides reacting by an associative mechanism. Solvolysis of benzoyl chlorides reacting by a dissociative mechanism is catalyzed by CB7 due to the ability of the CB7 cavity to stabilize the acylium ion developed in the transition state by electrostatic interactions.|
|Versão do Editor:||http://pubs.acs.org/doi/pdf/10.1021/jo902398z|
|Aparece nas colecções:||FCT2-Artigos (em revistas ou actas indexadas)|
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|The Journal of Organic Chemistry 2010 Basilio.pdf||1,13 MB||Adobe PDF||Ver/Abrir Acesso Restrito. Solicitar cópia ao autor!|
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