BETA-SUBSTITUTED CYCLOPROPYL RADICALS GRAFTED TO SILICA SURFACE - METHODS OF PREPARATION, STRUCTURE, AND PROPERTIES

Cyclopropyl type radicals [GRAPHICS] were identified on a surface of a ctivated silica by ESR. The possibility of their preparation by two me thods, i.e., by photocyclization of substituted allyl radicals and by interaction of cyclopropane molecules with particular surface defects, was demonstrated. The effects of beta-substituents on radiospectrosco pic characteristics and thermal stabilities of the radicals were studi ed. Rate constants and activation energies of decomposition of substit uted cyclopropyl radicals were estimated. The experimental data obtain ed 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 beta-fluorine-substituted cyclopropyl radicals were calculated. Electr onegative substitution was found to result in a considerable decrease in the activation energy of the cyclopropane ring opening.