Assistance d'un groupe voisin pour des tosylates secondaires β substitues diequatoriaux dans l'hexafluoroisopropanol 97% |
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| Authors: | J Laureillard E Casadevall |
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| Institution: | Laboratoire de Chimie Bioorganique et Organique Physique, ERA CNRS No. 685, Ecole Nationale Supérieure de Chimie de Paris, 11 rue Pierre et Marie Curie, 75321 Paris Cedex 05, France |
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| Abstract: | Solvolysis rates in methanol and 97% hexafluoroisopropanol (HFIP) for four β-methyl and β-phenyl bicyclic tosylates, show that solvent nucleophilic assistance is operating in the former solvent. However, in 97% HFIP, for three of the mentioned compounds, the mechanism involves π or σ neighboring group assistance. The factors influencing the occurrence of these processes are discussed. Owing to these possible neighbouring group assistances in non-nucleophilic solvents used to obtain kc reference mechanisms, it is concluded that the ka/kc ratio which was proposed as a quantitative evaluation of solvent nucleophilic assistance must be used with caution. |
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