David Andrew

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Part I. The irradiation of 2-cyclopentenone with ultraviolet light in the presence of alkenes results in the formation of 2+2 cycloadducts which contain cyclobutane rings. According to the Corey-de Mayo mechanism, the regiochemistry of the cyclobutane products is controlled by the relative orientation of the alkene and the cyclic enone in an exciplex intermediate which precedes the formation 1,4-biradicals along the reaction pathway.;The biradicals formed in the photocycloaddition reactions of 2-cyclopentenone, 2-methyl-2-cyclopentenone and 3-methyl-2-cyclopentenone with various alkenes were trapped as stable compounds by H{dollar}\sb2{dollar}Se. By determining the structures and relative yields of the trapped products, the structures and relative rates of formation of the biradical intermediates from which the trapped products originated were deduced. These studies indicate that the regiochemistry of the cycloadduct products is not controlled by the relative rates of formation of the isomeric biradical intermediates; rather, the regiochemistry is a result of the way each biradical partitions between closure to form products and reversion to form starting materials. This conclusion is in disagreement with the Corey-de Mayo exciplex mechanism. Therefore, the factors which control the way each biradical partitions between closure and reversion were investigated in detail.;Part II. The Photo-Fries reaction of 1-naphthyl acetate was investigated in supercritical carbon dioxide. This photolysis proceeds via a solvent-caged singlet radical pair to result in the formation of 2-acetyl-1-naphthol, 4-acetyl-1-naphthol, and 1-naphthol. In supercritical CO{dollar}\sb2{dollar} the relative ratios of these products are sensitive to pressure variations in the near-critical region. The relative yield of 1-naphthol decreases dramatically as the pressure is decreased in the region near the critical pressure. Since formation of this product is the result of escape from the solvent cage by the naphthoxyl radical, this observation was interpreted in terms of an increase in the strength of the solvent cage near the critical point. Comparison of the pressure dependence of the relative product ratios with the pressure dependence of the partial molar volume of solute molecules in supercritical CO{dollar}\sb2{dollar} provided strong evidence for the unusual phenomenon of "solvent clustering" near the critical point.



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