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

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.