Thesis (Ph. D.)--University of Michigan, 1921.

Metastable, electronically excited atoms (²Dº , ²Pº ) of phosphorus, arsenic and antimony have been observed following the isothermal flash photolysis of Group VA hydrides and trihalides. Several mechanisms for the production of these atoms are discussed. The decay of the excited atoms was observed to be rapid due to reactions with the transients produced in the flash photolysis of the parent compounds. Flash photolysis of the Group VA hydrides and trichlorides has yielded new electronic absorption spectra of the AsH and AsH₂, SbH and SbH₂, PC1, AsC1, and SbC1 free-radicals. Vibrational analysis on some of these spectra have been carried out. In the isothermal flash photolysis of cyanogen with Group VA hydrides, it is proposed that the following reactions of the cyanogen radical occur rapidly: CN + AH₃ → AH₂ + HCN (1) CN + AH₂ → AH + HCN (2) CN + AH → ACN + H (A=N,P,As) (3) → HCN + A* (A=P,As, Sb) (4) (formula omitted) HACN (A=N,P) (5) where A, unless specified, is N, P, As or Sb and * denotes electronic excitation. Three of the new electronic absorption spectra observed are tentatively attributed to the PCN, HPCN and AsCN free-radicals produced in reactions (3) and (5). The assignment of the other spectra is discussed. Reactions of CN with NF, PC1 and AsC1, corresponding to (3), have also been shown to occur rapidly. The reactions of the cyanogen radical in the flash photolysis of cyanogen with nitrous oxide, oxygen, water, and methyl isocyanate have also been studied and discussed. / Science, Faculty of / Chemistry, Department of / Graduate

The photolysis of azomethane, di-isopropyl ketone and azoisobutane has been examined briefly in the gas phase and these compounds have been found to be convenient sources of the methyl, isopropyl and tert-butyl radicals respectively. The photolysis of the mixed vapours of cyclohexadiene-1,4 with each of azomethane, di-isopropyl ketone and azoisobutane has been examined over a series of temperatures. These studies afforded the Arrhenius parameters for the abstraction of the methylenic hydrogen atom from cyclohexadiene-1,4 by the methyl, isopropyl and tert-butyl radicals. There was found no significant difference in the reactivities of these radicals towards the cyclohexadiene-1,4 substrate. The rate constants measured were [formula omitted]. The cyclohexadienyl radical is generated in this metathetical reaction, and the interaction of the cyclohexadienyl radical with the various mentioned initiator radicals was examined kinetically. It was found that the interaction of alkyl radicals with the cyclohexadienyl radical produced either benzene and the hydrocarbon, RH, (disproportionation) or 1-alkylcyclohexadiene-2,4 (combination, I) or 1-alkylcyclohexadiene-2,5 (combination, II). The ratio of the rates of formation of the two combination products (I/II) has been found to have the constant value 0.77 ± 0.17 within the experimental error for all the alkyl radicals studied. The ratio of the rate of disproportionation to the combined rates of combination was found to vary systematically over the values 0.27 ± 0.07, 0.52 ± 0.09, and 1.33 ± 0.24 for the methyl, isopropyl and tert-butyl radicals respectively. A previous study of the ethyl radical's reactions with the cyclohexadienyl radical in this laboratory had shown that this ratio for the ethyl radical was 0.38 ± 0.03. The measured values of the termination rate ratios for the various systems are consistent with the expectation that the product of greater entropy should form preferrentially and the results are considered to support the disproportionation transition state model of Bradley and Rabinovitch. During the photolysis of azomethane-cyclohexadiene-1,4 mixtures at lower intensisties, there was observed the formation of cyclohexene and greater than the expected amount of benzene. This was considered to arise from the decomposition reaction C₆H₇→C₆H₆ + H˙. Kinetic analysis of this system has afforded an estimate of the heat of formation of the cyclohexadienyl radical, (45 ± 5 kcal./mole), and consequently of its resonance energy, (24 ± 5 kcal./mole). This has been considered to be evidence that there is an interaction of the delocalized system across the methylenic carbon bridge, since the resonance energy is substantially greater than that measured in another laboratory for the straight chain pentadienyl radical (15.5 kcal./mole). The reactions of the isopropyl radical with the cyclohexadiene-1,3 molecule have been studied in the gas phase. The isopropyl radical adds to the unsaturated linkages with a rate constant [formula omitted]. The abstraction of a methylenic hydrogen atom procedes with a rate governed by the rate constant [formula omitted]. Thus the metathetical reaction procedes more slowly for the conjugated cyclohexadiene than for the unconjugated system by a factor of 1.9 at 100°. This behavior was also found for the reactions of the ethyl radical with the cyclohexadiene isomers in a previous study, and probably arises from a slightly lower free energy of the cyclohexadiene-1,3 molecule. The ratio of addition to abstraction between isopropyl and cyclohexadiene-1,3 is low, (4.3 at 100°) and degradative chain transfer has been suggested as the reason for the very low tendency of the cyclohexadiene-1,3 molecule to polymerize under homogeneous, free radical conditions. / Science, Faculty of / Chemistry, Department of / Graduate

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

Over the last forty years the steady use of radical reactions as the key steps in syntheses has increased. The most commonly used radical reagent is tributyl tinhydride. However such tin based radical reagents are toxic and often contaminate the product as they are difficult to remove. As an alternative to these tin reagents, a novel NaBH4/U.V. system was developed. This system was successfully used to effect the radical reduction of various aromatic halides. In light of these results it was thought that other useful transformations such as C-C bond formation could be achieved. Radical cyclisation onto unsaturated bonds, halogen atom transfers radical cyclisation (HATRC) and 1-5 hydrogen atom translocations were explored. This, 1-5 hydrogen atom translocations, methodology has been successfully applied to the synthesis of the spirocyclic natural products (±) horsfiline and coerulescine. With this success the use of the NaBH4/U.V. system on pyridine substrates was explored. Unfortunately this was not achieved with our current understanding of this reaction. However the use of tributylgernamium hydride, which is considered a ‘green’ radical reagent when compared to tin based reagents, proved successful. The novel application of this reagent in the 1-5 hydrogen atom transfer reaction on pyridine substrates was successfully demonstrated. Its use was successfully employed in the synthesis of a pyridine based bioisostere derivative of horsfiline.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--York University, 1999. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 151-163). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pNQ39292.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

No description available.