Thesis (M.S.)--Tennessee Technological University, 2009. / Title from title page screen (viewed on Feb. 25, 2010). Bibliography: leaves 140-144.

Thesis (Ph.D.)--Murdoch University, 2002. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 228-238.

Thesis (Ph. D.)--University of Chicago, 1909.

Thesis (Ph. D.)--University of Chicago, 1909.

The photochemical generation of several novel quinone methide-type intermediates has been observed upon photolysis of pyridoxine (150-Vitamin B₆) and its derivatives 151 and 152, hydroxybiphenyl alkenes 153 and 154, and hydroxybiphenyl alcohols 159 and 160. Mechanistic investigations, utilizing product, fluorescence and laser flash photolysis studies, have suggested two distinct pathways for the formation of these reactive intermediates, depending upon the functional groups present on the progenitor. Formal excited state intramolecular proton transfer (ESIPT) between the phenol and the alkene led to quinone methides upon irradiation of the hydroxybiphenyl alkenes, while excited state proton transfer (ESPT) to solvent followed by dehydroxylation was responsible for formation of these intermediates from the hydroxybiphenyl alcohols. The quinone methide-type intermediates obtained from the pyridoxine systems arise from formal loss of water, although it is not certain whether this is through ESIPT or ESPT from the phenol at neutral pH. Studies of the photogeneration of quinone methide-type intermediates from the pyridoxine systems are important due to their biological relevance. Formation of such reactive intermediates in vivo may explain some of the toxicological properties associated with the intake of large doses of the vitamin. Irradiation of 150 or 151 in 1:1 CH₃OH/H₂O gave the corresponding methyl ethers (Φp = 0.18 and 0.21, respectively), consistent with formation of quinone methide-type intermediates. Similarly, photolysis in aqueous CH₃CN with ethyl vinyl ether resulted in the regioselective formation of the respective chroman products through [4+2] cycloaddition. LFP spectra pointed to formation of two quinone methide-type intermediates upon irradiation of both 151 and 152 in neutral aqueous solution, only one of which is present at pH 12. Previous studies on m-hydroxystyrene have suggested that m-quinone methide formation occurs via formal ESIPT between the phenol and the alkene, mediated by a bridging water trimer. Studies on 153 and 154 were undertaken to determine whether this solvent-mediated ESIPT can occur over longer distances. The photochemistry of the related hydroxybiphenyl alcohols (159 and 160) was also investigated, as quinone methides have been observed upon photolysis of similar systems. Irradiation of 153 and 154 in 1:1 CH₃CN/H₂O gave photohydration products (Φp = 0.013 and 0.1, respectively) via attack of water on the respective quinone methides. pH studies implicated formal ESEPT in formation of these reactive intermediates. Photolysis of the analogous methyl ethers of the phenols suggested the intermediacy of carbocations in the observed photohydration reaction, as quinone methides cannot be generated in these systems. Hydroxybiphenyl alcohols 159 and 160 yielded the corresponding photomethanolysis products (Φp = 0.04 and 0.22) in aqueous methanol, through attack of CH₃OH on the respective quinone methides. In this case, pH studies indicated that quinone methide formation occurs via ESPT and dehydroxylation. Significant quenching of fluorescence firom the hydroxybiphenyl alkenes with small amounts of added water implied that H₂O is directly involved in reaction from the singlet excited state. Loss of fluorescence firom 154 was found to depend on [H₂O ]³, however, the distance required for ESIPT in these systems is too large to be bridged by a water trimer. As such, the non-linear quenching has been attributed to deprotonation of the phenol by a cluster of one or two water molecules, with concerted protonation at the alkene by another molecule of water not associated with the cluster. Fluorescence quenching of the hydroxybiphenyl alcohols required much larger [H₂O], and implied a different mechanism of reaction, consistent with the proposal of ESPT and dehydroxylation. LFP studies indicated the assistance of water is required for formation of a long-lived transient (600 nm, t = 150 μs) upon irradiation of 153, however, it cannot be definitively assigned to the quinone methide. Although no evidence was found for quinone methide formation in LFP studies of 154 and 160 due to its suspected short lifetime, the respective carbocation (420 nm, t =8.5 μs) has been observed upon irradiation in 2,2,2-trifluoroethanol. / Graduate

The photosolvolysis of a series of hydroxy-substituted benzyl alcohols (ArCH₂OH) has been studied. Photomethanolysis of these alcohols showed exceptionally higher efficiencies for methyl ether formation (in 1:1 H₂O-MeOH) than the corresponding methoxybenzyl alcohols. UV-Vis absorption spectra of photogenerated transients were recorded in aqueous solution and had similar appearance to the carbocations that are observable from the methoxybenzyl alcohols, but with much longer lifetimes. These transients were also observable in neat organic solution for the ortho isomers. The yields of all these transients increased with increasing water content. The highest yields were observed in basic aqueous solution when pH > pKₐ(S₀) (of the phenol moiety). In addition, photolysis of the appropriate coumaranones gave the same transient absorption as that from the corresponding o-hydroxybenzyl alcohols. Since photolysis of coumaranones are known to give o-quinone methide, (o-QM) intermediates (via loss of CO), the transients observed for the o-hydroxybenzyl alcohols are assigned to o-QMs. The transients observed for the m and p-isomers are assigned to the corresponding m and p-QMs. The quantum efficiencies for QMs generation from hydroxybenzyl alcohols are in the order as o > m >> p, in agreement with Zimmerman's orthoctivation theory. The mechanism proposed at pH < pKₐ(S₀) involves adiabatic deprotonation of the ArOH moiety in the first excited singlet state (S₁) followed by heterolytic cleavage of the C-O bond of the hydroxymethyl group. In basic media, direct excitation of the phenolate ion results in the loss of hydroxide ion to generate QMs. Subsequent nucleophilic trapping of these QMs by solvent results in the observed solvolysis product. o-QMs were also generated in neat organic solution. The proposed mechanism involves adiabatic deprotonation of phenol moiety facilitated by either intermolecular or intramolecular hydrogen bonding with a benzylic OH group. This Thesis has demonstrated that a simple and general method is available for the photogeneration of all the QM isomers. Notably, the method is applicable to m-QMs, which have previously required more elaborate methods for their generation. A polymerization reaction of m-QMs has been discovered in basic media during investigations of their chemistry. / Graduate

From the culture medium of Shanorella spirotricha Benjamin, four p-benzoquinones have been isolated and identified. The major pigment is shanorellin (2,6-dimethyl-3-hydroxymethyl-5-hydroxy-1,4-benzoquinone). The other three pigments are the acetate, the ethyl ether and the dimer of shanorellin. Shanorellin was found to be synthesized via the acetate-polymalonate pathway by tracer experiments with ¹⁴C-labelled compounds and by chemical degradation of the labelled shanorellin produced. A study was made of the optimal conditions required for the production of these benzoqulnones. Significant factors were pH, temperature and sources of nitrogen and vitamins of the nutrient medium. / Science, Faculty of / Botany, Department of / Graduate

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