Item – Thèses Canada

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Numéro d'OCLC
36341045
Auteur
Froese, Robert D. J.(Robert David J.),1964-
Titre
Theoretical studies of organic systems
Diplôme
Ph. D. -- University of Guelph, 1996
Éditeur
Ottawa : National Library of Canada = Bibliothèque nationale du Canada, 1996.
Description
3 microfiches.
Notes
Includes bibliographical references.
Résumé
Ab initio quantum chemical methods have been used to predict aspects of chemical reactivity for selected organic systems. For the most part, the Hartree-Fock self-consistent-field method with the 6-31G* basis set was used as a starting point, and then electron correlation effects were included by Moller-Plesset perturbation theory. The structures and reactivities of these organic systems have been compared with experiment where possible. The four organic systems considered were: (I) Thiirane S-oxides. The structure and energetics of different isomers of methyl and silyl substituted thiirane S-oxides were compared at the MP2/6-31+G$\sp{*}$ level of theory. Anti-substituted methyl thiirane S-oxides and gem-substituted silyl thiirane S-oxides are predicted to be formed. These intermediates would lead to the experimentally observed products. (II) Pyramidalization in dioxinones. The pyramidalizations at the carbons of the enone moiety of 1,3-dioxinone, dihydropyrone, $\alpha,\beta$-unsaturated-$\delta$-lactone, and 2-cyclohexenone were compared. The pyramidalization of these carbons is greatest in 1,3-dioxinone and decreases as the oxygen atoms are replaced by methylene groups. This pyramidalization correlates well with the experimentally observed face selectivity in ground state reactions. (III) Diels-Alder dimerizations. The relative rates of Diels-Alder dimerizations of spiro-substituted heptadienes were predicted to increase in the order spiro (2,4) hepta-4,6-diene, cyclopentadiene, and 1-oxaspiro (2,4) hepta-4,6-diene in agreement with experiments. Of the four possible transition states for the dimerization of 1-oxaspiro (2,4) hepta-4,6-diene, the lowest energy one led to the minimum which corresponded to the same structural isomer observed by X-ray crystallography. (IV) Photochemistry. The photochemical cycloaddition reaction of triplet allene with ground state cyclopentenone has been studied. The head-to-head: head-to-tail ratio of cycloadducts was estimated from the transition state data, the relative energies of the intermediate biradicals, the spin-orbit coupling constants, and the singlet-triplet energy gaps. The estimate agreed well with the experimental data. Triplet-triplet energy transfer between enones and alkenes in photochemical reactions was examined. The lower triplet energies for the alkenes which we have predicted make such energy transfer a clear thermodynamic possibility. Experiments leading to trans-fused adducts at the cyclohexene side, certain quenching rate constants, and the cyclohexene isometrization of and sensitized dimerization of alkenes all can be reconsidered in light of triplet-triplet energy transfer.
ISBN
0612085864
9780612085862