On the utility of organotellurium reagents for the determination of relative radical stabilities /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1990.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| Abstract: | A simple and novel protocol for the determination of relative radical stabilities has been developed. This method is based on a bimolecular homolytic substitution of an alkyl radical generated from N-acyloxy pyridine-2- thione (X2) [commonly known as Barton ester], at the tellurium center of a dialkyl telluride (ie., 48). A transient trivalent tellurinyl radical (79) was perceived to be an intermediate of this S[H]2 process. The fragmentation of this species is governed by the stability of the resulting alkyl radical. In the event that the alkyl substituent of telluride 48 is more stable than that of 12, disintegration of 79 leading to a new unsymmetrical telluride (ie., 68) and an alkyl pyridyl sulfide (ie., 36) occurs. Quantification of these products provides an experimental validation of relative stabilities of the radicals involved. The excellent resolution of these products in a normal gas chromatography analysis provides feasibility for determining the product distribution, using cyclododecane as an internal standard. Conclusions from a photolysis experiment were further confirmed by performing a complementary experiment. Using this technique isopropyl and cyclohexyl radicals were compared. The experiments led to the conclusion that isopropyl radcial is the more stable one. The existing thermochemical methods for the determination of radical energies involve uncertain marginal errors. For this reason, the presently developed method would be a significant one for the determination of relative radical stabilities as it provides direct experimental support. Two very similar primary radicals can also be compared using this method. Pentadecyl, docecyl, and octyl radicals were compared in the same manner. The β-stabilization effect of a radical was also studied by comparing β-phenethyl with 1-adamantyl and pentadecyl radicals. The tertiary radical was found to be more stable. An interesting hexenyl radical cyclization leading to the formation of a five-membered ring system was also performed. In principle, a qualitative knowledge of comparative stabilities of radicals can be obtained using this methodology. The outcome of such a comparison could then be applied to the generation of a desired radical. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemistry." |
| Physical Description: | ix, 208 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |