Proton and fluorine nuclear magnetic resonance spectroscopy was used to investigate the favoured forms of several furanosyl fluorides. The low energy barrier to pseudo-rotation in these systems precludes the assignment of only one favoured conformation for each molecule. A systematic study of five membered ring sugar conformations was undertaken by examining three types of systems, varying from a relatively rigid molecule involving three fused rings, to more flexible molecules involving a "free" furanosyl fluoride ring. The spectral assignment was greatly facilitated by heteronuclear fluorine decoupling and computer analysis. 5-fluoro-3,6-anhydro-α-L-idofuranose was synthesized in good yield from several precursors and the molecule's furanose ring conformation of ₂T³was assigned on the basis of vicinal ¹H-¹H coupling constants. Using the values for vicinal ¹H- ¹⁹F couplings obtained from this molecule, together with data from other workers, a partial Karplus type curve was constructed relating vicinal ¹H- ¹⁹F couplings to dihedral angles. This curve - which was found to be more asymmetric than the Karplus relationship for vicinal ¹H-¹H couplings - was then used, together with the known Karplus curve for vicinal ¹H-¹H couplings, to determine the conformations of the triester furanosyl fluorides of ribose, arabinose and xylose. Assuming pure sp³ hybridization and maximum ring puckering, the conformations for most of the sugars studied were found to involve the displacement of C₂ and/or C₃ positions out of the plane of the ring formed by the other atoms. The conformation for α-fluoro-ribo-furanosyl triester ( ₃T⁴ ) was found to be different than that of the β-fluoro-ribofuranosyl triester (₃T⁴). A significant and apparently stereospecific long-range ⁴J[subscript H].₄,F coupling through oxygen of ca. 6.5 Hz, is observed when H₄ and F are in a trans arrangement, while a much smaller coupling for ⁴J[subscript H].₄,F of ca. 1.0 Hz. is observed when these two nuclei are in a cis or approximately "planar M" arrangement. On the other hand, ⁴J[subscript H].₃,F couplings were found to have a value of ca. 2.2 Hz. in the cis or "planar M" geometry, while in the trans geometry, ⁴J[subscript H].₄,F is ca. 0.5 Hz. / Science, Faculty of / Chemistry, Department of / Graduate

Resonance absorption spectra have been observed which may be interpreted as many-quantum transitions where the axis of quantization is along the effective magnetic field in the rotating frame. By this description, resonances which required up to five quanta were observed. The spin system used was that of conduction electrons of lithium metal in neutron irradiated lithium fluoride crystals. An analysis of the experimental results using a modified Bloch equation under the assumption that Ƭ₁= Ƭ₂= Ƭ 1.5x10 ̄⁷sec. and that the spin system relaxes toward the instantaneous field is presented. A brief outline of the concept of spin temperature is included. A comparison is made between some of the predictions of the spin temperature concept and the simple Bloch theory used in analyzing the experimental data. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Wave-particle interaction in the ionosphere is studied theoretically for wave frequencies around the lower hybrid resonance (LHR) frequency. Expressions are derived by two methods for the growth rate of whistler-mode waves propagating in a magneto-active plasma penetrated by a tenuous beam of nonthermal particles. The first method employs the electrostatic dispersion equation; the second uses the full-wave dispersion equation which reduces to the electrostatic one for large values of refractive index. The equilibrium distribution function for the plasma is Maxwellian, and that for the diffuse streaming particles is also Maxwellian, but is shifted by a streaming velocity parallel to the background magnetic field. The first method assumes that the temperatures are isotropic, while the second assumes that the distributions are characterized by the perpendicular and parallel temperatures, T[subscript: I] and T[subscript: II] . The growth-rate expressions are fairly general, but numerical calculations are performed for the case of a cold plasma consisting of electrons, H⁺ , He⁺ , and 0⁺ ions and a beam of nonthermal electrons. The growth-rate expression obtained using the electrostatic dispersion equation shows that waves propagating slightly off the direction perpendicular to the background magnetic field can grow due to the Landau instability process which is excited by high energy (∼ 10 keV) electrons streaming along the direction of the magnetic field of the earth. The growing wave thus triggered is shown to have a frequency band with a sharp lower cutoff at the LHR frequency and an upper limit at the electron cyclotron frequency or electron plasma frequency, whichever is lower. The previous growth-rate expression is generalized by making use of the full-wave dispersion equation. It is shown that there are two regions in propagation angle 6 where the Landau instability may occur. The "electrostatic" region lies just below the resonant angle and, separated by a region of damping, the "low-θ" region lies above θ = 0 . The growth-rate values calculated in the "electrostatic" region correspond to the values obtained in the previous calculation. Generally, the maximum growth rate is larger in the "electrostatic" than in the "low-θ" region. It is also seen that with increasing frequency the "electrostatic" maximum growth rate increases monotonically and the cyclotron instabilities become important at frequencies above about ten times the LHR frequency. The influence of the following parameters on the growth rate is also examined: temperature ratio T[subscript: II]/T[subscript: I], streaming velocity of the nonthermal particles, and the ratio of the kinetic energy in the streaming motion to the thermal energy of the streaming electrons. The theory presented is applied to LHR noise bands discovered by the Canadian Alouette I satellite. It is shown that many features are in good agreement. Other observations, such as auroral hiss, also have features which suggest that the theoretical work may be relevant to these types of ionospheric noise. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Spin-lattice relaxation times have been measured in metal single crystals with a pulsed nuclear magnetic resonance apparatus at both room and liquid nitrogen- temperatures. The values obtained for aluminum and vanadium agreed well with the values given in the literature for powdered samples. The niobium value was slightly lower than the most reliable powder value, possibly because of impurities. Measurements were made on isotopically pure tin to see if any anisotropy could be detected in the spin-lattice relaxation time. No anisotropy could be detected, but the crystal orientation used was so unfavourable that an anisotropy of less than about 50% could not be detected. The spin-spin relaxation time was measured in the isotopically pure tin for five different magnetic field orientations. These showed that exchange narrowing occurred. With a suitable choice of operating conditions, the apparatus measured the equivalent of the absorption mode in steady state nuclear magnetic resonance as a function of magnetic field orientation. This was combined with the spin-spin measurements to give the complete orientation dependence of the latter. These measurements gave a value of (2.1±0.3)Kc/s. for the pseudo-exchange constant in tin. The pseudo-dipolar second moment was found to be twice the dipolar second moment. Spin echoes were observed in the isotopically pure tin and were used to measure the spin-spin relaxation time. These gave values which were much shorter than those measured by free induction decays. The reason for this was not determined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The object of this work was to produce and identify reaction intermediates in systems containing group I and group II halides treated with fluorine. The systems which are studied in detail are the NaCl and KCl/F₂ and SrCl₂/F₂ systems. In accordance with predictions from kinetic studies, ESR has shown that treatment of vacuum-sublimed NaCl with F₂ at room temperature produces a defect containing an unpaired electron, and that the decay of this defect is retarded by Cl₂. The ESR spectrum indicates an anisotropic g-factor and unresolved hyperfine structure. In KCl, a spectrum is obtained which is closely similar except that the hyperfine structure is partly resolved. The spectra appear consistent with interactions of the unpaired electron with Cl atoms, rather than with F or such impurities as 0 or Br, and can be accounted for adequately by a model of the defect as linear Cl[formula omitted], i.e., an H center or something very similar. For NaCl, the spectra indicate that the vacuum-sublimed material is sometimes partly oriented. It is suggested that centers with one-electron deficiency are observable at such high temperatures in vacuum-sublimed material because this consists of essentially perfect crystals devoid of sites which could accept a second electron from the centers. The reaction of SrCL₂ powder or single crystal with fluorine at room temperature produces a defect, stable after removal of fluorine but located close to the reaction interface only, which has an electron spin resonance absorption. The ESR spectrum is consistent with a model of the defect as a chlorine atom displaced from an anion site towards a neighbouring anion vacancy. The principal directions of the hyperfine tensor and g-tensor are two two-fold axes and a four-fold axis of the SrCl₂ lattice. The tensor components indicate that the unpaired electron is localized on the Cl atom, and suggests that the atom is subject to a strong crystal field determind chiefly by two nearest-neighbour cations which define a two-fold axis of the crystal. The unpaired electron is in an orbital mainly of p-character and aligned along a two-fold axis which is probably the one perpendicular to the line of the cations. The single-crystal spectrum, although haying orientation-dependent line positions, has line shapes and intensities resembling those of a powder spectrum. This suggests a range of relative displacement of Cl atoms and neighbouring cations along a "reaction co-ordinate" which is probably a four-fold axis of the crystal. / Science, Faculty of / Chemistry, Department of / Graduate

Electron paramagnetic resonance techniques have been used to investigate the nature and possible effects of adsorption of gaseous species on several adsorbents, in particular several synthetic zeolites, at temperatures from 77°K upwards. Analysis of the spectra obtained has been aided through computer simulation of the various spectra and comparison of these to the actual observed spectra. The molecule chlorine dioxide ( C10₂ ) has been studied in various low temperature matrices but little has been published for C10₂ in the adsorbed state. An attempt was made to find an adsorbent such that an inert matrix might be approximated, to give a base from which to make comparisons. To this end, adsorbents including silica gel, synthetic zeolites 13X, 10X, 4A, 5A, Na-mordenite and H-mordenite were investigated. The results vary between those from silica gel, where spectra yielding EPR parameters similar to other matrices were obtained, to those from 13X where it was evident that two distinct adsorption sites of the C10₂ were present. In the 13X as in the other synthetic zeolites, EPR parameters markedly different from other studies were found and were attributed to the intense electrostatic fields present in these zeolites. Results obtained at room temperature for these adsorbents ranged from C10₂ molecules freely rotating in the cages of the zeolites to other molecules having hindered rotations. Nitrogen dioxide ( NO₂ ) was also investigated with a view to finding similar interactions. Although changes as marked as for C10₂ compared to other studies were not observed, the synthetic zeolite H-mordenite yielded spectra closely approximating those obtained in solid N₂O₄ matrices. It is proposed the NO₂ molecules are caged in the numerous side pockets emanating from the main channels in this zeolite and are effectively isolated from other NO₂ molecules. The resulting spectra are strikingly more resolved than those obtained using other adsorbents and enabled accurate computer simulations to be made. The adsorption of nitric oxide ( NO ) produced an effect not found with the other molecules. A new species was formed from a reaction of the NO with H-mordenite and could not be removed at room temperature, indicating a strong bond to the surface. The new species does not contain nitrogen as identical spectra were obtained from adsorption of ¹⁴NO and ¹⁵NO. Attempts to observe spectra which could be assigned to the difluoroamino radical from adsorption of tetrafluorohydrazine were unsuccessful. The spectra observed were assigned to a species having no hyperfine structure and an anisotropic g tensor. / Science, Faculty of / Chemistry, Department of / Graduate

Paramagnetic impurities containing oxygen were produced in the reactions of KBr, KCl, NaCl and SrCl(2) with fluorine. Molecular oxygen, FOO･ radical and C10(2) were identified by ESR as reaction by-products. The spectra assigned to CIO(2) have predominant powder character even in single crystals of halides. The results are correlated with previous work in this laboratory. The origin of oxygen impurity is suggested to be surface hydroxide ions in KBr and KC1, and entrapped water in NaCl and SrCl(2). Nucleation processes and other anomalous features observed in these reactions by previous workers are explained by the presence of impurities. Oxygen was found to be incorporated into the SrCl(2) crystals by recrystallisation from the melt in the presence of oxygen. It exists in the form of superoxide ion O(2)¯ which occupies an interstitial position between two lattice anions and is associated with two anion vacancies. The molecular axis lies in a [00l] direction of the crystal and the degeneracy of the 2pπ(g) -molecular orbital is lifted by the crystal field. The bonding between the O(2)¯ ion and its neighbouring cations and anions is discussed in terms of a Cl(6)Sr･O(2)¯･SrCl(6) "complex". The orbital angular momentum reduction factor for O(2)¯ in SrCl(2) has been calculated from the experimental g-factors and found to be anomalously large. A survey was made on impurities incorporated into strontium compounds through processes of recrystallisation from melts or from aqueous solutions. Strontium carbonate was identified in melt-recrystallised Sr(NO3)(2) by Infrared Spectroscopy and X-ray powder method. It was produced by partial decomposition of the nitrate in the presence of atmospheric CO(2). NO(3)²¯ ion was identified in the recrystallised material by ESR. ESR and infrared studies suggest that the NO(3)²¯ ion substitutes a carbonate ion in the SrCO(3) lattice. Results from a similar study on Ba(NO3)(2) also support this conclusion. / Science, Faculty of / Chemistry, Department of / Graduate

The microwave resonator method for studying small amplitude surface waves in liquids has been improved by making the time measurement more accurate and much more convenient. It was used to measure the oscillation frequency of the surface as a function of liquid depth. Discrepancies between the experimentally obtained results and theoretical predictions due to the rigidity of the mercury meniscus where contact is made with the walls of a cylindrical resonator were found. From these an accurate value for the effective reduction in radius of the resonator because of the meniscus effect was obtained. A method was developed for applying strong electrostatic fields (about 20 kV/cm) onto the fluid surface without interfering with the measuring technique. An interesting result of this was the observation that the field cleans the surface from contamination. This phenomenon manifests itself in a marked reduction in the damping of surface waves just after a large field is applied. A resonator of square cross-section was used to demonstrate the Fourier analyzing property of rectangular resonators. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A new method of synthesizing organic fluorides stereospecifically was developed; the elements 'BrF' and 'IF' were added quantitatively across the double bond of simple olefins such as cyclohexene, using elemental halogen and silver fluoride at room temperature in benzene. Application of this reaction to the activated olefin, acenaphthylene, resulted in a variety of products, depending on solvent; with pure acetonitrile solvent, quantitative 'BrF' addition occurs, but with an increasing proportion of benzene various side reactions take place, including difluorination and dimerization. Another series of compounds was synthesized from fluoro- acenaphthylene by various addition and substitution reactions, and all together fifteen acenaphthene fluorides were made, including thirteen new compounds. The ¹H and ¹⁹F N.M.R. spectra of these substances were measured and a set of ³JHF values obtained for a wide variation in the electronegativity of the substituents, and for two values of dihedral angle (0°and 100°). This data showed that the dependence of ³JHF upon electronegativity was far from linear, as had hitherto been supposed, but rather exponential, which is in retrospect more logical. Application of this data on ³JHF to some flexible systems, derivatives of indene and benzofuran, allowed their conformations to be determined. In all cases the pucker of the five-membered ring is small (∼25°), except in the cis-bromofluoride of benzofuran where it is much larger, (45-50°). A separate study was made of the conformational inversion of trans-1-fluoro-2-iodocyclohexane (I) and its specifically deuterated analogue, derived from 3,3,6,6-tetradeutero-cyclohexene. Several methods were employed to measure the position of the conformational equilibrium and this permitted a comparison of the methods themselves. It was found that all chemical shifts and coupling constants were temperature dependent, those involving ¹⁹F being particularly susceptible. The only reliable methods were found to be area measurements (at -90°C), linewidth measurements (at -45°C), and temperature-corrected ¹⁹F chemical shift measurements; thus the compound in question was found to have a preference for the diequatorial form, with ∆G° = 0.650 ± 0.025 kcal./mole (at -90°C to 0°C), and a near zero entropy, ∆S° = 0.0 ± 0.5 e.u. This value of ∆G° is only 0.1 kcal./mole smaller than the sum of the A-values for iodine and fluorine, and indicates that the repulsion between these two halogens in the diequatorial form is quite small, about one tenth that between iodine and chlorine, or between chlorine and chlorine, etc. A kinetic study of I was made by applying the general lineshape equation of Gutowsky and Holm for two-site exchange; calculated line-widths and positions were matched to the experimental ¹⁹F spectra (with all ¹H couplings removed by irradiation) at various temperatures, and thus an Arrhenius plot was made and activation parameters derived. ∆FƗ = 10.38 kcal./mole; ∆SƗ = 2.1 e.u. / Science, Faculty of / Chemistry, Department of / Graduate

X-irradiated cyanoacetylurea CNCH₂CONHCONH₂ and x-irradiated dicyandiaraide NCNC(NH₂)₂ single crystals were studied,by Electron Spin Resonance. Two radical species were formed when cyanoacetylurea, CNCH₂CONHCONH₂, was irradiated with x-rays. One was a π-electron radical, CNCHCONHCONH₂, and the other a σ-electron radical, CNCH₂CONHCONH . The σ electron radical was found to have a large, isotropic proton coupling tensor and an anisotropic nitrogen coupling tensor very similar to those of H₂NCOCH₂CONH . The π-electron radical had similar proton and nitrogen coupling tensors as CNCHCOOH which was formed in γ-irradiated cyanoacetic acid. In x-irradiated dicyandiamide crystals, the main species formed was shown to be NCNC(NH₂)NH, having also a large, isotropic proton coupling tensor, and hyperfine interactions with two nitrogen coupling nuclei were also observed and measured. ESR studies were carried out both at room and at liquid nitrogen temperatures. The effect of temperature on the spectra is discussed. INDO-SCF-LCAO-MO calculations were carried out for a model compound HCONH , with the amide proton assuming different inplane and out of plane positions. The spin density was found to vary over a wide range and could be used to interpret the large proton coupling of the dicyandiamide radical. MO calculations were also performed on the radical NCCHCOO ̄. The calculated results correlate fairly satisfactorily with the observed ones. Comparison of the direction of the unpaired electron p-orbital symmetry axis with bond directions and with normals to the fragment planes showed that while malonamide radical, H₂NCOCH₂CONH was a genuine σ-electron radical, dicyandiamide radical, NCNC(NH₂)NH was most likely a π-electron radical. / Science, Faculty of / Chemistry, Department of / Graduate