Photochemical reactivity of several dibenzannelated systems has been investigated to demonstrate that the driving force inherent in many of their reactions is the attainment of a 4n π-electron system or intermediate in S1. It has been shown that the inherent driving force for the benzylic C-H bond ionization in 9H-xanthene (125) and 9H-thioxanthene (136) is the formation of 8π-electron cyclically conjugated carbanion intermediates 130 and 137, respectively, in S1. Formation of deuterium incorporated products when 125 and 136 are photolyzed in NaOD-EtOD solutions and protium incorporation in products when photolysis of 123 and 134 is carried out in NaOH-EtOH is consistent with the intermediacy of carbanions in these reactions. Fluorescence quenching of 123 and 125 by ethanolamine in CH3CN gave linear Stern-Volmer plots, with kq = (2.16 ± 0.05) x [special characters omitted] for 125 and (1.12 ± 0.05) x [special characters omitted] for 123, which corresponds to an isotope effect for quenching by ethanolamine, of [special characters omitted] = 1.92 ± 0.04. Enhanced stability of 8π carbanions in S1 is further evidenced in the photodecarboxylation of xanthene-9-carboxylic acids (142 and 145) and thioxanthene-9-carboxylic acids (147 and 148) in aqueous solution. The intermediacy of carbanions has been demonstrated in the product studies carried out in 80% [special characters omitted] solution. A mechanism has been proposed which involves heterolytic bond cleavage of the carboxylate ion in S1 to give intermediate carbanions. Additional support for the excited state stability of 4n systems comes from the studies of 155. Photoexcitation of bent 155 results in its planarization to give planar 155 in S1. The driving force for this change of conformation of 155 is believed to be the attainment of a conjugated 8π-electron internal cyclic array in S1. Photolysis of substituted suberenes in aqueous [special characters omitted] results in benzylic C-H bond cleavage in these systems in S1 the efficiency of which is greatly affected by the nature of substituent present. Results obtained in this study are consistent with benzylic C-H bond cleavage, with H2C acting as the base, to give intermediate carbanions in S1. Quantum yields of exchange in [special characters omitted] (L = H or D) and in a variety of other solvent mixtures have been measured. The photochemistry of xanthenium (99 and 114) and thioxanthenium (219) cations has been studied in aqueous [special characters omitted] in the presence of di- and trimethoxybenzenes. It has been shown that the primary photochemical step is electron transfer from methoxybenzenes to singlet excited 99 and 114. The radical intermediates thus generated subsequently react with 02 to give peroxy compounds as final products. These and other results of the photochemistry of dibenzannelated systems show that there is much interesting photochemistry to be discovered in these molecules. / Graduate

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Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thèse de doctorat : Chimie organique : Lille 1 : 2000. / Résumé en français et en anglais. Notes bibliogr.

Various nucleophiles were subjected to SRNl (nucleophilic substitution via a radical chain mechanism) conditions with representative carboaromatic and heteroaromatic substrates. Upon 5-25 min of near-UV irradiation, the carbanions of 2-benzyl-4,4-dimethyl-2-oxazoline, ethyl phenylacetate, t-butyl acetate, N,N-dimethylacetamide and dimethyl methylphosphonate underwent reactions with both 2-bromopyridine and iodobenzene in an S_R_N1 manner to give yields of good substitution products. The S_R_N1 reaction between N,N-dimethylacetamide enolate ion and 2-chloroquinoline occurred even without photostimulation. Due to incomplete ionization and the lack of homogeneity of the reaction mixture, potassio-2,4,4-trimethyl-2-oxazoline reacted with 2-bromopyridine to give low yield of the substitution product through a photostimulated S_R_N1 pathway. However, the reaction of this carbanion with iodobenzene afforded moderate yield of the substitution product, which was found to be formed via both S_R_N1 and AE mechanisms. The dimethyl phosphite anion reacted slowly with 2-bromopyridine and failed to react with 2-chloroquinoline and chloropyrazine under the influence of near-UV light. This unusual trend of reactivity was attributed to the inability of the product radical anion to restore an electron to the aromatic substrate, a necessary step in the propagation of the S_R_N1 cycle. Treatment of t-butyl α-trimethylsilylacetate with KNH₂ caused cleavage of the C-Si bond. t-butyl acetate and hexamethyldisiloxane were obtained upon quenching. Methylene triphenylphosphorane, sulfur and selenium stabilized carbanions of 1,3-dithiane, 2-phenyl-1,3-dithiane, dimethyl sulfone, t-butyl α-phenylthioacetate, bisphenylthiomethane and t-butyl α-phenylselenoacetate, failed to react with 2-bromopyridine and iodobenzene. The carbanion of dimethyl sulfone remained unreactive towards iodobenzene even upon attempted entrainment by a catalytic amount of acetone enolate. The dianion of phenylacetic acid reacted with iodobenzene to give biphenylacetic acid and benzene upon irradiation. Similar results were obtained with p-bromotoluene as substrate where substitution occurred only at the para position of the dianion. A non-chain mechanism was proposed to described both of these reactions. The dianion of phenylacetic acid also reacted with 2-bromopyridine to give a complex mixture under photostimulated conditions. 2-Benzylpyridine, bis(2-pyridyl)phenylmethane, p-(2-pyridyl)phenylacetic acid, potassio α-bis(2-pyridyl)phenylacetate, and 2-aminopyridine were found as products. Based on experiments performed with several probable intermediates of this reaction, and S_R_N1 mechanism can account for formation of all products. Preliminary results showed that the reaction of phenylacetamide dianion with iodobenzene also gave rise to the para substituted product. The dianion of 1,3-phenylacetone was found to react with iodobenzene to give 1,1,3-triphenylacetone via a mechanism other than an S_R_N1 pathway. / Ph. D.

Thèse doctorat : Instrumentation et analyses avancées : Lille 1 : 2000. / Résumé en français et en anglais. Bibliogr. p. 173-189.