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Updated: Jun 25, 2026
Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Systematic repression of beta-silyl carbocation stabilization
Xavier Creary1, Elizabeth D Kochly
1Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA. creary.1@nd.edu
Abstract:
Solvolysis of 1-(trimethylsilylmethyl)cyclopropyl mesylate in CD(3)CO(2)D gives ring-opened products as well as methylenecyclopropane. The rate enhancement due to the beta-trimethylsilyl group is a factor of about 10(6). The large stabilizing effect of a beta-silyl group (which can cause rate enhancements of up to 10(12)) on the intermediate cation has been repressed. B3LYP/6-31G* computational studies indicate a carbocation stabilization energy of 16.6 kcal/mol. Rates of solvolyses of 1-phenyl-2-trimethylsilylcyclopropyl chlorides are enhanced by a factor of 10(3)-10(4). The intermediate cyclopropyl cation undergoes substantial ring opening since beta-silyl stabilization is not large (calculated stabilization energy of 12 kcal/mol). Solvolysis rates of 2-trimethylsilylbenzocyclobutyl derivatives are not significantly enhanced by the beta-trimethylsilyl group. Beta-silyl stabilization of benzocyclobutenyl carbocations generated in solution has been effectively eliminated due to antiaromatic considerations (calculated stabilization energy of 3.7 kcal/mol when R = Ph). While computational studies parallel solvolytic rate studies, they overestimate the extent of beta-trimethylsilyl stabilization of solvolytically generated carbocations.
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