Abstract
Cyclopropyl type radicals\(X - _\triangledown \cdot (X = \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} C, \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} Si, \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} Si---O)\) were identified on a surface of activated silica by ESR. The possibility of their preparation by two methods,i.e., by photocyclization of substituted allyl radicals and by interaction of cyclopropane molecules with particular surface defects, was demonstrated. The effects of β-substituents on radiospectroscopic characteristics and thermal stabilities of the radicals were studied. Rate constants and activation energies of decomposition of substituted cyclopropyl radicals were estimated. The experimental data obtained were compared with the results of quantum-chemical calculations of model systems. The mechanism of photocyclization of allyl radicals was discussed. The transition states of decomposition of cyclopropyl and β-fluorine-substituted cyclopropyl radicals were calculated. Electronegative substitution was found to result in a considerable decrease in the activation energy of the cyclopropane ring opening.
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The authors are grateful to E. G. Baskir for calling their attention to this publication.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2409–2421, December, 1995.
The work was carried out with financial support of the Russian Foundation for Basic Research (Project code 94-03-09137) and the International Science Foundation (Grant No. MK9000).
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Ustynyuk, L.Y., Radtsig, V.A. & Senchenya, I.N. β-Substituted cyclopropyl rádicals grafted to silica surface. Methods of preparation, structure, and properties. Russ Chem Bull 44, 2303–2315 (1995). https://doi.org/10.1007/BF00713599
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DOI: https://doi.org/10.1007/BF00713599