The goals of this thesis were to design and synthesize new stable radicals and to study their properties. The attempted synthesis of new stable thioaminyl, verdazyl, and dioxadiazinyl radicals is described. Successfully prepared radicals were characterized by spectroscopic methods. The synthesis of new thioaminyl radicals and diradicals was attempted. Preparation of thioaminyl precursors, the sulfenamides, was accomplished with sulfenyl chlorides and amines. Oxidation with DDQ yielded radicals which decomposed back to the sulfenamides within 1–2 minutes. A bis(sulfenamide) was synthesized using a sulfenyl chloride and an appropriate bis(amine). The structure of the bis(sulfenamide) was confirmed by NMR spectroscopy and x-ray crystallography. Oxidation of the bis(sulfenamide) to the thioaminyl diradical was unsuccessful. New phosphaverdazyl radicals were prepared and studied using EPR spectroscopy. The phosphaverdazyl precursors, the tetrazines, were prepared from the corresponding bis(hydrazides). The tetrazines were oxidized with benzoquinone to yield phosphaverdazyls. The phosphaverdazyls prepared do not share the same level of stability as the parent carbon-based verdazyls; they slowly decompose back to tetrazines. Incorporation of phosphorus into the verdazyl core has several effects on the properties of the radical relative to the parent verdazyl system. Through a combination of EPR and computational studies, it was concluded that the geometry of the verdazyl ring and the electronic nature at phosphorus appear to be sensitive to the nature of the substituents attached to phosphorus. Exocyclic “spin-leakage” was observed for one phosphaverdazyl, which can be rationalized using a spiroconjugative mechanism. The phenomena of spiroconjugation was further explored through the synthesis of a phosphaverdazyl derivative attached to phosphazene in a spirocyclic manner. Synthetic routes to the hitherto unknown dioxadiazinyl system were explored. An intermediate hydroxyamidoxime was synthesized and fully characterized. Cyclization reactions of the hydroxyamidoxime to putative dioxadiazines were carried out using aldehydes and a ketone. The cyclization products could not be unambiguously assigned. The cyclization products can be rationalized as the desired dioxadiazine or the 5-membered oxadiazolidine. One derivative was oxidized to a persistent radical, the EPR of which is consistent with a nitroxide structure. / Graduate

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The products from a gaseous r.f. electric discharge in ammonia have been studied using electron spin resonance spectroscopy. A paramagnetic species from the discharge was detected and the results were consistent with it being the imine (NH) free radical. The E.S.R. Spectrum fitted the theoretical treatment and was similar to that observed for NH in a frozen matrix. No other radicals could be detected in the discharge except for the atomic species. The low pressure gas phase E.S.R. spectrum of (formula omitted) was also studied. The results showed that at low pressures the spectrum becomes exceedingly complex. A partial assignment of lines was made from the results of a simplified treatment of the theory. The work served a further purpose in developing experimental techniques for the study of unstable free radical species in the gas phase. / Science, Faculty of / Chemistry, Department of / Graduate

The Arrhenius parameters have been measured for the addition of the ethyl radical to methyl acrylate and its mono-methyl derivatives, methyl methacrylate, methyl cis-crotonate and methyl trans-crotonate. The energy of activation for each of these derivatives is significantly greater than for methyl acrylate, probably because of the adverse polar effect introduced by the methyl group. The activation energy for the addition to methyl methacrylate appears to be lower than for either the cis- or trans- methyl crotonate. This can probably be attributed to the fact that the ∝-methyl group can more effectively stabilise the adduct radical resulting from the addition of the ethyl radical to the methyl methacrylate, than the β-methyl group can in the case of crotonates. The pre-exponential factor is significantly smaller for each of the methyl crotonate isomers than for methyl methacrylate; partial shielding of the β-carbon atom of methyl crotonate is thus expressed by a steric factor rather than by an energy term. In terms of the rate constant for the addition reaction over the range 70°C to 160°C, methyl trans-crotonate is significantly more reactive than methyl cis-crotonate, and each isomer is only about one tenth as reactive as the vinyl compounds, methyl acrylate and methyl methacrylate, in which the site of radical attack is comparatively unobstructed. The cis-trans isomerisation of methyl crotonate is photo-sensitised by diethyl ketone illuminated by 3130 Å radiation in the gaseous phase; a mechanism of triplet state energy transfer is proposed for the process below 200°C; above 200°C an alternative mechanism involving the reversible addition of the ethyl radical to the double bond becomes the predominant process of isomerisation. / Science, Faculty of / Chemistry, Department of / Graduate

Small free radicals trapped in solid argon, krypton and carbon tetrachloride at 4.2°K have been studied using electron spin resonance (ESR). An attempt was made to determine whether the methylene radical, produced by the photolysis of diazomethane and ketene trapped in the solid matrix, has a triplet ground state. No signal definitely attributable to the methylene radical was observed. It is postulated that the zero field splitting due to the spin-spin coupling of the unpaired electrons broadened any ESR signal beyond detectability„ The ESR signal of trapped methyl radicals was observed in some experiments, and it is suggested that they were formed by abstraction of hydrogen atoms from another deposited material by methylene radicals. An experiment in which diazomethane was photolysed in the presence of D₂O in an argon matrix at 4.2°K yielded an ESR signal which may possibly have been due to the CH₂D radical. An investigation has been carried out of the populations of the rotational levels of methyl radicals produced by the photolysis of trapped methyl iodide and dimethyl mercury at 4.2°K. For thermal equilibrium freely rotating radicals should populate only the ground state at this temperature, but it was found that the lowest two levels were both populated. It is suggested that either there was not thermal equilibrium, or, more likely, the methyl radicals were undergoing hindered rotation. Room temperature equilibrium mixtures of N₂F₄ - NF₂ were trapped in the three matrices at 4.2°K, and ESR absorption due to the trapped NF₂ radicals was observed. Three lines were observed at this temperature, with the centre one of greater amplitude and smaller line width than the outer two. During warmup the amplitudes and widths of these lines became approximately equal and two further triplets appeared, symmetrically distributed about the centre line. From the warmup spectra the isotropic hyperfine splitting constants for fluorine and nitrogen have been deduced to be 168 and 48 mc./sec. respectively. It is suggested that the radicals underwent slow isotropic rotation at 4.2°K. The degree of s-character of the molecular orbital containing the unpaired electron is discussed in the light of the isotropic hyperfine splitting constants. An unsuccessful attempt to find hyperfine and rotational structure in the ESR signal of the NF₂ radical in the gas phase was carried out. The photolysis of CF₃I in krypton and carbon tetrachloride matrices at 4.2°K yielded a very complicated ESR spectrum. A phase reversal of some of the lines was observed. A broad single line was observed when CF₃I in carbon tetrachloride was irradiated at 77°K. At the time of writing no definite interpretation of the spectra can be suggested. / Science, Faculty of / Chemistry, Department of / Graduate

The technique of electron-nuclear double resonance spectroscopy (ENDOR) has been used to determine the identity and structure of radicals trapped in x-irradiated single crystals of cytosine monohydrate and caffeine hydrochloride dihydrate. The radical studied in cytosine mono-hydrate had previously been observed by several workers using electron paramagnetic resonance (EPR) but its identity was in question. All intramolecular and several intermolecular proton hyperfine couplings were analyzed in detail. The experimentally determined coupling parameters were compared with ones obtained by theoretical means for several possible radical species. The agreement between the observed and calculated parameters fit best for the radical formed by net addition of a hydrogen atom to 0(2) of cytosine, with the hydroxyl proton lying in the nodal plane of the π-system. The appearance of twice the number of certain ENDOR lines than expected from the crystal symmetry was interpreted by postulating that the radical was stabilized in two different conformations at 77°K. The assignment of the hyperfine couplings to specific protons was supported by an ENDOR study of a partially deuterated cytosine monohydrate crystal, grown from heavy water. Three different radical species were identified in caffeine hydrochloride dihydrate x-irradiated at room temperature. The EPR spectrum of this system, which had not previously been reported, was too complex to be analyzed. Furthermore, the EPR spectra of two of the radicals studied by ENDOR could not be distinguished in the overall EPR lineshape. One of these radicals had a lifetime of only a few hours and was tentatively identified as the methyl radical, primarily on the basis of the observed isotropic proton hyerpfine coupling constant of -62.65 MHz. The other radical was indefinitely stable and was identified as that formed by net abstraction of a hydrogen atom from N(9) of the caffeine moiety. This radical is equivalent to that which would be produced by the loss of an electron from a neutral caffeine molecule, the caffeine cation; as such, it is the first reported cation radical in a purine derivative. The radical which dominated the EPR spectrum was identified as that resulting from net addition of a hydrogen atom to C(8) of the protonated caffeine molecule. The identification of this radical was based on the analysis of four different proton hyperfine couplings. Nitrogen (¹⁴N) hyperfine and quadrupole coupling tensors were also obtained from the ENDOR spectra and were attributed to N(7). The observation of ¹⁴N-ENDOR lines, which had not previously been reported in any pyrimidine or purine derivative, provided a second, independent estimate of the unpaired spin density centred on N(7). An indirect second-order effect, giving rise to a non-crossing phenomenon, was observed between the methylene protons, which were also found to be non-equivalent. The structure of this radical was found to agree with those determined previously by EPR and by molecular orbital calculations for the analogous species in other purine derivatives. / Science, Faculty of / Chemistry, Department of / Graduate

The decomposition of nitrosyl disulfonate ion was studied in strongly alkaline solution of 10-2 to 5 m sodium hydroxide. The decomposition was found to be first-order in both hydroxide and nitrosyl disulfonate ions. A multi-step mechanism involving sulfite ion, sulfite ion radical and nitrosyl monosulfonate ion radical as intermediates was proposed, with the initiating step being the SN2 replacement of a sulfite ion by a hydroxide ion. The rate constant for the initiating step ranged from 1.2 x 10-7 to 2.25 x 10-5 M-1s-1 for the solution concentration range of the study. The products of the decomposition were identified as hydroxylamine disulfonate ion, hydroxylamine trisulfonate ion, and nitrite ion. The proposed mechanism was applied to the previously studied decomposition in mildly alkaline to slightly acidic, and nonaqueous solutions and found to explain all the reported observations if the side reactions involving the hydrolysis and reversion of hydroxylamine disulfonate ion were included.