Thesis--Catholic University of America.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also in an electronic version.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Vita. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, 1943. / Includes bibliographical references.

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

The work described in this thesis is an investigation into the reactivity and possible synthetic applications of aziridinylcarbinyl radicals. These radicals rapidly rearrange via β cleavage, which can proceed by breakage of either the CoN or C-C bond. Cleavage of the latter has been found when the molecule has a phenyl stabilising group attached to the aziridine ring. Chapter I is a review of the known radical reactions involving aziridines whilst chapter 2 discusses the various methods of aziridine syntheses. Chapter 3 outlines the project aims with reference to the potential of directed cleavage of aziridinylcarbinyl radicals in synthesis. Chapter 4, the main body of the work, describes the synthetic routes to aziridines derived from 3-phenyl-2-cyclohexen-I-one and indenone. The radical mediated β-cleavage reactions of these is reported and the selectivity of C-C v. CoN bond homolysis has been investigated. Two successful approaches to the target aziridines were involved. I) Conversion of 3-azido-3-phenylcyclohexan-I,2-diol, derived from the epoxide of 3- phenyl-2-cyc1ohexen-I-ol, to the aziridine via reaction with triphenylphosphine. Subsequent methylation and formation of the thiocarbonylimidazolide gave the radical precursor Nmethyl- 5-[imidazol-I-yl(thiocarbonyl)oxy]-I-phenyl-7-azabicylo[4.1.0]heptane. In the course of this work, several unusual cyclic thiocarbonates resulting from the reaction of 3-azido-3- phenylcyclohexan-I,2-diol and 2-azido-3-phenylcyclohexan-I,3-diol with I, I 'thiocarbonyl diimidazole were isolated. 2) Formation of N-(2-ethylquinazolinonyl)-I-phenyl-7-azabicyclo[4.1.0]heptan-5-01 from the reaction of 3-amino-2-ethyl-4(3H)-quinazolinone with 3-phenyl-2-cyc1ohexen-I-ol in the presence of lead tetraacetate. These aziridines show interesting acid-catalysed rearrangements to diazadioxabicyclo[2.2.2]octanes. Formation of the thiocarbonylimidazolide then gave the radical precursor. A number of other aziridines have been prepared using this methodology. It has been found that in all cases the precursors undergo CoN bond homolysis under radical conditions. These results are discussed and conclusions are drawn. Suitable future work is also suggested.

This work expands the investigation into the behaviour of verdazyl radicals and N-alkylated tetrazines as ligands. These new ligands were coordinated to various metals as a means of exploring new properties in the metal-verdazyl and metal-tetrazine products. The synthesis of N,N’-diphenyl Kuhn and 6-oxo verdazyl radicals bearing a 2-pyridyl group at the C3 position was accomplished. Palladium(II) dichloride complexes of each of these radicals were prepared in order to study the differences in the structural, electronic, and electrochemical properties compared to corresponding complexes of the previously reported N,N’-dialkyl-6-oxoverdazyl ligands. The N,N’-diphenyl verdazyl ligands are structurally bulkier than their dialkyl counterparts resulting in increased interaction between the ligand and palladium as observed in the solid state. The radical complexes were investigated by EPR and shown to exhibit a small amount of spin density on the palladium atoms with most of the spin density remaining on the ligands. The UV-Visible spectra had a noticeable red-shift in the absorbance maxima of the complexes compared to the free ligands. The electrochemistry of the new palladium-verdazyl complexes showed that there was a positive increase to the reduction and oxidation potentials when compared to the free ligands. An N-benzyl tetrazine and its Ru(hfac)2 complex were synthesized from their corresponding radical species utilizing Mn2(CO)10 to photogenerate benzyl radicals. This method was found to give high yields of the tetrazine and its metal complex. Spectroscopic, structural, and electrochemical properties of the tetrazine and its Ru(hfac)2 complex are reported. These compounds were investigated in regards to the activation energy associated with the homolytic cleavage of the C-N bond in the inert solvent, tert-butylbenzene. The activation energy of C-N bond of the tetrazine was 155 kJmol-1 while its Ru(hfac)2 complex was 138 kJmol-1; this resulted in the rate of dissociation being a factor of ~40 greater for the Ru(hfac)2 complex at 393 K. This work presents the potential of coordination compounds in tuning the properties of molecules associated with the stable free radical polymerization process. / Graduate / 0488 / 0485 / cooper_johnston@hotmail.com

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

Pages 154 and 155 were not included in the thesis. / <p> The post-irradiation annealing of highly converted styrene-polystyrene systems was explored. Experimental conditions necessary for the entrapment of high concentrations of free radicals in such systems were investigated. They were found to bear a relation to the glass transition temperature of the system.</p> <p> The concentration of free radicals formed by subjecting the polymer-monomer systems to Gamma rays, at room temperature, was measured, and the subsequent GM and GP values were calculated. The structure of the formed radical was found to be in agreement with that suggested by previous investigators. The free radicals decay was examined at varied temperatures above and below Tgs, and was found to follow a second order mechanism. The activation energy of decay was found to increase by raising the temperature above Tgs.</p> <p> When irradiation was executed at temperatures below Tgs, post-irradiation annealing led to high rates of polymerization when carried out at temperatures above Tgs. </p> <p> The number average molecular weight was practically unchanged during the polymerization of the last few percent monomer.</p> / Thesis / Master of Engineering (MEngr)