A pulsed N.M.R. spectrometer capable of operating over the frequency range 40 Mhz. to 100 Mhz. has been constructed. It was used to observe the nuclear resonance of Fe⁵⁷ in unenriched iron powder at 4.2°K. and 77°K.. Some preliminary experiments were performed and the results of these experiments are in good agreement with other reported results. This indicates that the spectrometer is suitable for use in future experiments. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A general broad line nuclear magnetic resonance study was made of the ¹⁹F spectra of WF₆ and the adducts IF₇ • AsF₅ and SF₄ • AsF₅ to determine the temperature dependence of the spectra, interpret the line shapes with respect to isotropic and anisotropic chemical shifts and identify non-equivalent fluorine sites in the compounds. The temperature dependence of the second moment at 30 MHz indicated that rigid lattice conditions probably existed at 77°K for WF₆ and IF₇ • AsF₅ but not for SF₄ • AsF₅. The dependence indicated an nmr transition in the vicinity of 200°K for the first two compounds and one commencing below 77°K for the third. From the second moments in the vicinity of the transitions, activation energies mere determined for the average motions involved. The field dependence of the second moments of the compounds was examined, where possible, at 2, 16, 30, 40, 56.4, and 94.1 MHz at 77° and 295°K. The compounds' spectra were resolved, with varying degrees of success, into components. For WF₆ an approximate resolution could be made into two components corresponding to the four equatorial and two axial fluorines in the distorted octahedron at 77°K. The two adducts could both be resolved, especially at 295°K or above, into components which supported the ionic formulations IF⁺₆ AsF⁻₆ and SF⁺₃ AsF⁻₆. Non-equivalent fluorine sites within individual ions could not be detected. From the observed and estimated second moments of the resolved components above and below the transitions, the probable reorientations occuring above the transitions were suggested. The rigid lattice theoretical second moment calculations enabled suggestions to be made for the crystal structures of WF₅ and SF⁺₃AsF⁻₆ and for the bond lengths in IF⁺₆AsF⁻₆ . For the first there had been confusion, at least here, about the space group, while the second has not yet been the subject of reported X-ray studies. Axial symmetry of the chemical shift tensors was assumed. Then, taking account of the relative shifts between the resolved components, averaqe values of the chemical shift anisotropies for each of WF₆ and IF⁺₆ AsF⁻₆ were determined from expressions relating the field squared dependence of the second moment to those quantities. The mean isotropic shifts of the total F spectra for each compound were measured where possible at each field at 77° and 295° K with respect to CF₃. COOH. From those the shifts of the resolved components were calculated relative to HF. Then from the isotropic shifts and the anisotropies, the principal values of the axially symmetric shift tensors were determined. The principal values enabled estimates to be made of I (ionic) and ℓ(double bond) characters, neglecting hybridization, in the M-F bonds of the hexafluoride groups. From these values a prediction was made for I and ℓ in the axial and equatorial bonds in PuF₆ . / Science, Faculty of / Chemistry, Department of / Graduate

In part I of this thesis, orgimotin compounds were investigated, using high resolution proton and tin 119 nuclear magnetic resonance technique. The tin 119 chemical shift of about forty organotin compounds were measured by absorption mode for the first time. The tin chemical shift and tin 119-proton coupling constant in some methyltinhalides wore found, to be solvent and concentration dependent in electron donor solvents. This dependence was attributed to the formation of higher than four coordinated complexes with solvent molecules. Equilibrium constants of the complex formation, the tin chemical shifts, and the tin-proton coupling constants of the complexes, wore obtained in a few solvents. The second-order paramagnetic chemical shifts of methyltinhaiides, methyltin cations, and five coordinated compounds were calculated and compared with the observed tin chemical shifts. Good qualitative agreements between calculated values and observed values confirmed that the second-order paramagnetic term in tin chemical shifts is dominant in the chemical shift changes in those compounds. In part II, X-ray irradiated single crystals of malonamide and cyanoacetamide were studied by electron spin resonance technique. In both cases at least two types of radicals were found. One was the usual π -electron type radical the proton coupling tensor of which had been studied, quite extensively in the past. In this study, besides the proton coupling and in the case of cyanoaecetamide, the coupling tensor for the cyano-nitrogen was also measured and discussed. The second radical found both in X-ray irradiated malonamide and cyanoacetamide was a Ϭ-electron type radical which was produced by the loss of one of the amide protons (-COṄH). The proton hyperfine coupling constant was found to be almost isotropic and very large, more than 80 gauss in both compounds. The nitrogen coupling tensor for the amide- nitrogen was found to be axially symmetric with the unique principal value equal to 36.6 gauss in the one (malonamide) and 25.4 gauss in the other (cyanoacetamide). The principal value in perpendicular direction was found to be very small but could not be determined conclusively. A semi-empirical molecular orbital calculation was performed on the fragment of Ϭ-electron radical together with perturbation through configuration interaction; the large isotropic proton coupling constants were explained theoretically. / Science, Faculty of / Chemistry, Department of / Graduate

The work reported here is: 1) a detailed study of the ¹⁹F nuclear magnetic resonance (n.m.r.) spectra of KPO₂F₂. The temperature dependence of the second moment and line width is interpreted in terms of reorientation of the PO₂F₂⁻ anion in the crystal lattice. A detailed analysis of the line shape at low temperatures is used to yield the interatomic spacings of the PF₂ fragment in the PO₂F₂⁻ anion. 2) an investigation of the n.m.r. adiabatic rapid passage technique as a quick and simple method for determining nuclear Zeeman spin-lattice relaxation times, T₁. The limitations of the experiment are examined and correction formulae are presented. The temperature dependence of T₁ is observed for the globular molecules, exo- and endo-pentadienyl maleic anhydride, for the fatty acid soap, lithium stearate, and for the inorganic salt, KPO₂F₂. The data are interpreted to yield some of the kinetics of molecular motion in these solids. 3) a ¹⁹F nuclear magnetic resonance investigation of polycrystalline K₂NbF₇ and K₂TaF₇, yielding some of the kinetics of molecular motion. The crystal structures, as seen by n.m.r., are found to be essentially identical. 4) an investigation of the ¹⁹F n.m.r. spectra of paramagnetic RhF₅. and IrF₅. This study has been reasonably successful in elucidating the molecular configuration of these substances, a problem uniquely suitable to the n.m.r. technique and insoluble to most other methods of structural analysis. The very large resonance shifts are interpreted in terms of unpaired electron density at the fluorine atoms. 5) a brief examination of the electron spin resonance spectra of X-irradiated polycrystalline KPO₂F₂ and Na₂PO₃F. Two anion radicals, PO₃⁼ and PO₂F⁻ , are identified and, within certain approximations, the nearly isotropic hyperfine coupling constants are evaluated and interpreted in terms of unpaired electron spin densities at the magnetic nuclei. Presentation of Data The organization of this dissertation differs from the form usually found. The justification offered in its behalf is that the topics covered can more easily be listed in a horizontal rather than a vertical array. Therefore, the presentation, theoretical comparison and discussion of the data have been grouped together for each topic. The order in which topics are considered depends on their priority in common discussion and their interdependences. The first to be considered is the n.m.r. line shape of the fluorine resonance in KPO₂F₂. Then, using experimental results as a guide, a determination of the interatomic distances is attempted. The temperature dependences of the n.m.r. line shape is presented and a model describing the type of molecular motion is sought. An explanation of the adiabatic rapid passage technique is then considered because it is used to obtain the spin-lattice relaxation time data. The spin-lattice relaxation time data of ¹⁹F in CaF₂ and KPO₂F₂ and of the ¹H in lithium stearate and endo- and exo-pentadienyl maleic anhydride are then considered. The limits of applicability of the adiabatic rapid passage technique are considered. The n.m.r. line shape of the fluorine resonance in K₂NbF₇ and K₂TaF₇ and its variation with temperature are interpreted in terms of molecular motion. A modified line width-correlation frequency equation first derived by Bloembergen, Purcell and Pound is used to derive an activation energy describing the hindered reorientation of the NbF₇⁼ and TaF₇⁼ anions in the low temperature solids. The n.m.r. line shape of the fluorine resonance in IrF₅- and RhF₅ is used to elucidate the molecular structure, a problem uniquely suitable to n.m.r. The large resonance shifts of the fluorine resonances may be used to obtain the unpaired electron density at the fluorine nuclei. The e.s.r. line shape observed for X-irradiated polycrystalline KPO₂F₂ and Na₂PO₃F is interpreted in terms of the •PO₂F⁻ and the •PO₃⁼ radicals, respectively. The hyperfine coupling constants are obtained and the electron density at the phosphorous and fluorine atoms are estimated. / Science, Faculty of / Chemistry, Department of / Graduate

Nuclear magnetic resonance lock-in absorption mode and dispersion mode spectra of polycrystalline samples of CaF₂ potassium caproate (KC₆), and lithium stearate (LiC₁₈) have been obtained at various levels of saturation. The line widths narrow and the line shapes change in both the absorption and dispersion mode spectra on saturation. This behaviour is not predicted by previous theories of saturation, but is predicted by the new magnetic resonance saturation theory of Provotorov. The effects of modulation saturation have also been demonstrated. They are in agreement with Goldman's extension of Provotorov theory to include the audio modulation field. An Important prediction of Provotorov-Goldman theory is that saturation narrowing and modulation saturation do not affect the signal at the centre of resonance (within certain limiting conditions) and so the signals at this point are expected to saturate with the normal saturation factor: Z(O) = [ 1 + ɤ²H₁²T₁f(O)/2]⁻¹, where H₁ is the rf field amplitude, f(Δ) is the absorption line shape function normalized to 2π, and Δ is in rad/sec. Therefore the progressive saturation of the lock-in dispersion signal, u₁(0), has been studied in the CaF₂ KC₆, and LiC₁₈ samples at room temperature. The results verify the above prediction and yield the spin lattice relaxation times (T₁) of the samples. The CaF₂ result of 0.385 ±0.03 sec compares well with 0.45 ± 0.05 sec, the value found by adiabatic rapid passage. A modified Linder signal decay technique has also been used to measure T₁ values in KC₆ and LiC₁₈. The innovation being that the signal u₁(0) was used instead of the lock-in maximum absorption signal. The results are in good agreement with the progressive saturation results. It is concluded that one is finally in a position to measure correct T₁ values in solids by CW techniques. A technique for recording the true shapes of rapid passage signals has been developed. Using the shape of the rapid passage signal as a criterion of whether or not the passage was also adiabatic, it was found that the Bloch adiabatic condition, dH₀/dt « ɤH₁² , is also applicable to solids. The inequality, however, must be larger for solids than for liquids. The width at half its peak height of an adiabatic rapid passage (Arp) signal in a solid was shown to be [12(H₁²+HL²)]⅛, where HL² = <ΔH²>/3, is called the local magnetic field, and <ΔH²> is the Van Vleck second moment. ARP signals were used to find local field and second moment values in polycrystalline and single crystal forms of CaF₂ and also in polycrystalline LiC₁₈, all at room temperature. The results are in excellent agreement with theory and CW measurements. It is believed that this is the first time this method has been used. The ARP technique was also used to measure T₁ values. A symmetric sweep method was used for the above samples and a two pass method (equivalent to the π- π/2 sequence used in pulse spectrometry) was used for a very pure crystal of maleic anhydride. A value of 76 min was found for this sample at room temperature. This is a particularly good example of the usefulness of the ARP technique since it is difficult to measure such a long T₁ by the usual pulse method. Normal and saturation narrowed lock-in absorption spectra of LiC₁₈ have been obtained over the temperature range 25° to 193°C. There are two phase transitions in this region. They were revealed by both the normal and saturation narrowed spectra. / Science, Faculty of / Chemistry, Department of / Graduate

The nuclear magnetic resonance spectra of a number of organosilieon compounds are examined. The 7.95 Mcs. silicon-29 spectra are obtained for these compounds and the chemical shifts are considered in detail. It is proposed that the trends observed are the result of a competition between two opposing effects; a paramagnetic shift influenced by changes in the effective nuclear charge on silicon and a diamagnetic shift influenced by (p→d)π bonding. The concept of the competitive shift mechanism rationalizes the chemical shifts observed for series of the type MexSiX₄₋x (where: X = 0Me,0Et, 0Ac, Cl, F and C₆H₅) but does not explain the shifts of silicon hydrides. This concept also rationalizes the trends observed in ¹¹⁹Sn chemical shifts but, logically, does not apply to ¹³C chemical shifts where the d-orbital contribution must vanish. None of the observed coupling constants correlate with the ²⁹Si chemical shifts. Available theories are found to be inadequate to describe the coupling constants in these molecules. A new long range coupling is observed between the methyl groups on silicon attached to oxygen and chlorine with J[subscript]HCSiCH of about 0.35 c.p.s. / Science, Faculty of / Chemistry, Department of / Graduate

The study of pulsed n. m. r. in single crystal metallic samples, initiated by McLachlan, has been extended to liquid helium temperatures with special emphasis on Sn¹¹⁹ . Contrary to McLachlan's belief it was found that cooling to 4. 2°K and lower afforded significant improvements to the signal to noise ratio and in many cases the n. m. r. signals (including spin echoes in Sn¹¹⁹ ) could readily be seen on an oscilloscope without the use of a signal averager. The theory of magnetic resonance in metallic samples was studied in some detail with particular emphasis on the experimental situation where matters are complicated by the high conductivity which modulates both the amplitude and the phase of the exciting r.f. magnetic field as it penetrates into the sample. It is shown theoretically that several assumptions must be made to show that the conventional methods of pulsed n. m. r. used to measure T₂ (by either spin echo or free induction decay) and T₁ yield true meaningful results. In particular it is found that the spin lattice relaxation time T₁ is obtained by the conventional two pulse sequence only when the magnetic field is exactly on resonance; this was observed to be the case experimentally as well. In sharp distinction to McLachlan's findings for Sn¹¹⁹, the spin-spin relaxation time T₂ obtained by FID methods (175 ± 18μsec) was much smaller than that obtained by spin echo techniques (390 ± 48μsec) in the present research on Sn¹¹⁹. The spin-lattice relaxation time was also measured at liquid helium temperatures and yielded a value of 56 ± 4 millisec deg for T₁, in excellent agreement with Dickson although twice as large as McLachlan’s value. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A gas of atomic hydrogen confined at and below 1K in a sealed cell has been studied by magnetic resonance at the zero-field hyperfine transition frequency of 1420 MHz. A review is presented of magnetic resonance theory for a two level system, with emphasis on determination of the absolute magnetization by two methods: calibration of the spectrometer sensitivity and by use of the radiation damping time constant. Measurements at 1K on a gas at low density, 10¹¹<n[sub=H]<5x10¹² cm⁻³, in the saturated ⁴He vapour density have yielded the rate for the reaction H+H+He￫H₂+He, the diffusion constant and pressure shift of the hyperfine transition for H interacting with the He gas, and the cross-section for spin exchange relaxation. At temperatures below 1K, measurements of the frequency shift and effective recombination rate for H adsorbed on the He film have yielded values of the binding energies for H on ³He and for H on ³He as well as the hyperfine transition frequency shift and surface recombination rate for H adsorbed on each of these surfaces. The binding energies are found to be 1.15(5) K for H on ³He and 0.42(5) K for H on ³He. Measurements have been carried out at temperatures as low as 162 mK for H on ³He and 65 mK for H on ³He. lineshape for H atoms undergoing occasional sticking events on the helium surface. This model has been applied to frequency shift and transverse relaxation data at low temperatures to yield sticking probabilities of 0.046(5) for H on ³He and 0.016(5) for H on ³He. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The work described herein falls into three major categories: synthesis of model glycolipids, NMR studies on'model glycolipid'micelles, and application of 2D-NMR spectroscopy in spectral assignment. Three synthetic routes, namely the glycosidation reaction, reductive amination reaction, and amide bond formation have been investigated in relation to their efficiency and convenience in coupling carbohydrates with aliphatic chains. The reaction of amide bond formation was found to be a superior method over the others for the preparation of long alkyl chain derivatives. ¹H-NMR spectroscopy has been utilized to study and detect the micelle formation by the model glycolipids. The studies described illustrate that the ¹H spin-lattice relaxation rate (R-₁) is well suited for the determination of critical micelle concentration providing it is sufficiently high. The contrasting behaviour of R-₁ of the anomeric proton (H-1) of n-octyl β-D-glucoside in relation to that of H-2 and w-CH₃ upon micellization, has been tentatively attributed to the conformational changes accompanying micelle formation. The observed upfield shift of the ¹³C resonances of the alkyl chain has been explained as being due to the increased proportion of trans conformers in the micellar state. The question of the downfield ¹³C shift observed for the sugar resonances has been discussed. Study of N-alkyllactobionamides with ¹H-NMR proved to be difficult due to their extremely low critical micelle concentrations. Application of 2D J-resolved spectroscopy and spin-echo correlated spectroscopy (SECSY) in spectral assignment of unprotected sugar derivatives has been demonstrated. Using above techniques, complete assignment of the sugar region of n-octyl β-D-glucoside and N-hexyllactobionamide has been achieved. / Science, Faculty of / Chemistry, Department of / Graduate

Nuclear magnetic resonance absorption and spin-lattice relaxation time measurements have been carried out on the tropolone salt of t-butylamine, (CH₃)₃CN⁺H₃Tr⁻ (Tr ⁻= tropolonate ion, C₇H₅0₂⁻), the choline salts, (CH₃)₃NCH₂CH₂OH. X⁻ (x⁻ = Cl⁻, Br , I , ClO₄ ⁻) and the trimethylamine-phosphorous penta-fluoride adduct, (CH₃)₃NPF₅, in order to study molecular motion and phase transitions in these systems in the solid state. Activation energies and rate parameters associated with the motional processes are reported. Proton magnetic resonance (pmr) absorption second moments and proton spin-lattice relaxation times in the Zeeman frame (T₁) in the temperature range 66K - 425K for the solid (CH₃)₃CNH₃Tr⁻ show that the molecule is rigid on the nmr timescale at the lowest temperature studied, while at higher temperatures rotation of methyls about their C₃ symmetry axes is found to set in first, followed by an additional composite motion involving reorientation of both the t-butyl group and the NH₃ group about the C-N bond. A proton study in the partially deuterated (-ND₃) analogue has enabled the relaxation effects of the latter two motions to be separated, and, by fitting the T₁, data for the two compounds to appropriate relaxation rate expressions, activational energy barriers for the abovementioned motional processes have been determined. It has also been suggested that the t-butyl group and the NH₃ group rotate independently about the C-N bond rather than as one unit. Proton spin-lattice relaxation time measurements in both the Zeeman and rotating frames of reference (T₁ and T₁[sub p]) for the four choline salts and second moments of the pmr absorption for the perchlorate have enabled the following motional processes to be identified: (i) rotation of the methyl groups at low temperatures followed successively by, (ii) the onset of motion of the NMe₃ moiety about the long chain C-N axis (denoted C₃), (iii) general reorientation of the whole choline cation, (iv) additional slow motion of the long chain (CH₂CH₂OH in the case of the chloride and bromide, and (v) diffusion of the choline ion in the case of the iodide and perchlorate. From a quantitative analysis of the and data, activation energies for the above types of motion are determined. A crystal-crystal phase transition known to occur at 353, 364 and 362K in the chloride, bromide and iodide, respectively, has been confirmed. A similar transition has been discovered in the perchlorate, and is found to occur at a much lower temperature (272K). Evidence has also been presented for a further crystal-crystal phase transition in choline iodide at 430K, at which point a "quenching" of the diffusional process is found in this structure. In the adduct (CH₃)₃NPF₅, studies of proton and fluorine nmr absorption spectra and measurements have shown that (i) at 4.2K the molecule is 'rigid1, (ii) C₃ reorientation of one of the methyls and reorientation of the PF₅ group about the P-N bond cause a ¹H and ¹⁹F nmr line narrowing, (iii) this is followed by the C₃ rotation of the other two methyl groups together with the rotation of the (CH₃)₃N group about the P-N bond. These are confirmed by a successful simulation of the observed pmr lineshapes at 4.2K and at 77K. The proton and fluorine T₁ data show the ¹H and ¹⁹F spins to be strongly coupled. A study of fluorine T₁ in the fully deuterated compound, (CD₃)₃NPF₅ has enabled the analysis of the overall T₁ data to be simplified. The observed trends in the T₁ data are seen to be well explained by the theory for a coupled spin system of two unlike spins. / Science, Faculty of / Chemistry, Department of / Graduate