In Part I of this thesis an irradiated single crystal of dipotassium difluoromalonate monohydrate has been studied by Electron Spin Resonance. On X-irradiation the crystal yields CF(COO¯)2 radical with a highly anisotropic hyperfine tensor, characteristic of a (19)F nucleus. In addition, some other lines were also observed which were too weak to be analyzed. On γ-irradiation, the crystal yields mainly the same radical in addition to two types of CF(2)COO¯ radicals. In one type, the carboxyl group was found to be nearly coplanar with the CF(2) fragment while in the other, it was nearly perpendicular. A broad central line in each spectrum indicated also the possibility of the presence of CO(2)¯ radical. An unrestricted Hartree-Fock calculation, using the approximation of Intermediate Neglect of Differential Overlap was carried out on a number of fluorinated radicals to correlate the (19)F hyperfine tensors obtained in the present study with those obtained previously. The theory was used to calculate the theoretical hyperfine tensors for various radicals and was found to give a reasonably good agreement with the experimental results. On this basis the hyperfine tensor for CHFCOO¯ radical was predicted. The calculation also showed that one of the carboxyl groups in CF(COO¯)2 radicals is co-planar with the radical plane while the other makes an angle of 85°. In Part II, a crystal of zinc trifluoroacetate dihydrate, containing small amounts of Cu++ has been studied at 77°K and it was found that the Cu++ ion resides in an approximately tetragonal environment with the ground state consisting of mainly d(z2) orbital which is coupled to d(x2)-(y2) orbital, perhaps through vibronic interactions. Also a solution of copper trifluoroacetate in trifluoroacetic acid was studied at room temperature and at 77°K and the results were interpreted by assuming a tetragonal symmetry with the ground state being pure d(x2)-(y2). / Science, Faculty of / Chemistry, Department of / Graduate

<p dir="ltr">This dissertation investigates novel approaches for modifying cellulose nanofibers (CNFs) to develop sustainable alternatives to petroleum-based plastics. As plastic production continues to rise dramatically – from 2 million tons in 1950 to a projected 1231 million tons by 2060 – the need for renewable, biodegradable alternatives has become increasingly urgent. This work presents three interconnected studies exploring different aspects of CNF modification and application.</p><p dir="ltr">The first study introduces an innovative method for developing superhydrophobic (SHP) coatings using CNFs lyophilized from a 10 wt% <i>tert</i>-butyl alcohol slurry. Through solvent-free mechanochemical modification, we successfully produced oleic acid-modified CNFs (OL-CNFs), which exhibited exceptional SHP properties, demonstrating high contact angles, low hysteresis, and remarkable durability. Suspensions of OL-CNF were utilized in various spray coating applications, including moisture barriers and atmospheric water harvesting systems.</p><p dir="ltr">The second study explores the trifluoroacetylation of CNFs using trifluoroacetic anhydride (TFAA) without additional base. By employing glucopyranosides as small molecule models to guide reaction optimization, we developed a method for controlled trifluoroacetylation while preserving CNF crystallinity. Notably, we introduce a novel approach for quantifying the degree of substitution using ¹⁹F NMR spectroscopy of saponified trifluoroacetylated CNFs (TFA-CNFs) in methanol-<i>d4</i>, offering improved accuracy over traditional methods.</p><p dir="ltr">The third study examines the potential of TFA-CNFs as reinforcing materials in biodegradable polymer composites, particularly with poly(butylene adipate-co-terephthalate) (PBAT). We investigate the dispersibility of TFA-CNFs in various organic solvents and explore methods for creating PBAT/TFA-CNF blends. The research reveals promising aspects of TFA-CNFs, including their compatibility with biodegradable polymers and rapid ester hydrolysis in soil, while also identifying key challenges and opportunities for future development.</p><p dir="ltr">Together, these studies advance our understanding of sustainable CNF modification strategies and their applications in developing eco-friendly materials. This work contributes to ongoing efforts to address environmental challenges posed by conventional plastics while maintaining high performance standards for material applications.</p>

The β-acyloxyalkyl radical rearrangement has been known since 1967 but its mechanism is still not fully understood, despite considerable investigation. Since the migration of a β-trifluoroacetoxy group generally proceeds more rapidly and with more varied regiochemistry than its less electronegative counterparts, this reaction was studied in the hope of understanding more about the subtleties of the mechanism of the β- acyloxyalkyl radical rearrangement. The mechanism of the catalysed rearrangement of Nalkoxy- 2(1H)-pyridinethiones was also explored because preliminary studies indicated that the transition state (TS) for this process was isoelectronic with TSs postulated for the β-acyloxyalkyl radical and other novel rearrangements. ¶ A kinetic study of the rearrangement of the 2-methyl-2-trifluoroacetoxy-1-heptyl radical in solvents of different polarity was undertaken using a radical clock method. Arrhenius equations for the rearrangement in each solvent were: hexane, log10[kr (s-1)] = 11.8±0.3 – (48.9±0.7)/ θ; benzene, log10[kr (s-1)] = 12.0±0.2 – (43.7±0.8)/ θ; and propionitrile, log10[kr (s-1)] = 11.9±0.2 – (42.0±0.3)/ θ. Rate constants at 75˚C were: hexane, kr = 2.9 × 104; benzene, kr = 2.8 × 105; and propionitrile, kr = 4.0 × 105 s-1. The equilibrium constant for the reversible rearrangement at 80°C in benzene was 15.1 <K < 52.9. ¶ A regiochemical study with oxygen-labelled radicals revealed that trifluoroacetoxy group migration occurs with 66-83% label transposition (3,2 shift). The proportion of 3,2 shift is decreased by polar solvent, high temperature and low concentration of the reducing agent. Results of labelling experiments were consistent with cooperative 1,2 and 3,2 shifts, the former having Ea 9.5 kJmol-1 higher than the latter in benzene solution. ¶ An esr study of nine β-oxygenated radicals revealed that the temperaturedependent equilibrium conformation is controlled by a balance between steric and stereoelectronic effects. The influence of the latter is increased by electron-attracting β- substituents. Barriers to C α–C β rotation in β-oxyethyl radicals are approximately the same as for the propyl radical. Consequently, there is no significant through-space interaction between the β-substituent and the unpaired electron. ¶ Experimental results were consistent with a mechanism involving a combination of polarized 1,2 and 3,2 concerted shifts. The results may also be rationalised by the intermediacy of a contact ion pair, as well as combinations of the three options. ¶ The rearrangement of N-alkoxy-2(1H)-pyridinethiones is catalysed by oxidants, Lewis acids and protic acids. Pseudo first order kinetics are observed and there are moderate solvent effects. The migration of a 1,1-dideuteroallyl group occurs almost exclusively in a 1,4 sense. Migration of an enantiomerically enriched 1-phenylethyl group proceeds with predominant retention of configuration in chloroform, but with virtual racemisation in acetonitrile. Migrating groups do not become diffusively free during the rearrangement. Substituents which stablise positive charge at C1 migrate more rapidly. The bulk of evidence indicates that a catalyst activates the pyridinethione for rearrangement by promoting aromatisation. Mass-spectrometric analysis of an isolated intermediate and kinetic results are consistent with an intermolecular mechanism.