Proefschrift--Groningen. / "Stellingen": 2 leaves inserted. Includes bibliographical references.

Proefschrift--Groningen. / "Stellingen": 2 leaves inserted. Includes bibliographical references.

A series of arylformamides and arylthioamides has been synthesized and analyzed using nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), powder and single crystal X-ray diffraction. The work involved the study of hydrogen bonding, weak intermolecular interactions, phase changes and co-crystallization in aryl - formamides and -thioamides resulting in the structure determination of twenty four crystals. Three sets of isomorphic compounds were identified from the 24 solid state structures: set one; 2,6-difluorophenylformamide (1a), 2,6- dichlorophenylformamide (2a) and 2-chloro-6-methylphenylformamide (4a); set two; 2,6-dimethylphenylthioamide (17) and 2-chloro-6- methylphenylthioamide (18) and set three; 2,6-diisopropylphenylformamide (6) and 2,6-diisopropylphenylthioamide (20). In the first two sets, 1a, 2a and 4a, and 17 and 18, there are similar regions of halogen interactions and hydrocarbon interactions with disorder in the chloro-methyl substituents in structures 4a and 18. As for compounds 6 and 20, both the chemical and geometrical effects (size and volume of the isopropyl substituents) play a role in their isomorphism. A mixture of 2,6-dichlorophenylformamide (2a) and 2,6- dimethylphenylformamide (3) yielded a co-crystal 22 in which there was one molecule in the asymmetric unit, same as co-crystal 23 [derived from 2,6- dichlorophenylthioamide (17) and 2,6-dimethylphenylthioamide (18)]. The molecules of the two co-crystals displayed disorder in the substituents on the 2 and 6 positions of the aryl ring as a result of the occurrence of chlorine and methyl groups in the same crystallographic sites. Co-crystal 22 adopted the structure of 2,6-dichlorophenylformamide 2a. Co-crystal 23 also had a ii structure similar to that of 2a and co-crystal 22. Co-crystal 24 derived from a mixture of 2,6-diisopropylphenylformamide (6) and 2,6-diisopropylphenylthioamide (20), and also had one molecule in the asymmetric unit which showed disorder in the position occupied by oxygen and sulfur atoms. The 24 structures studied exhibited a variety of motifs formed from weak intermolecular interactions. Investigation of these weak intermolecular interactions revealed four different categories1 for the arylformamides and only one category for the arylthioamides. The categories were different in their formation of N-H…O/S hydrogen bonds (in which adjacent molecules are related by 21-screw axes, glide planes or by translation) forming chains (as in category 1, 2 and 5), sheets (as in Category 3) or dimers and tetramers (as in category 4). The chains in categories 1, 2 and 5 are in the for form of spirals (molecules along the chain are related by 21-screw axes or glide planes) or stacks (molecules along the chains are related by translation). Compounds from the different categories had certain interactions that contributed most to the stabilizations of their crystals. Apart from the N-H…O/ S hydrogen bonds, π…π, C-H…π, C-F…π, C-H…F, C-H…Cl, C-H…O, Cl…Cl, Br…Br, Cl…O and Br…O interactions also had a role to play in the stabilization of the different structures. Lattice energies and the energies relating to different molecular arrangements were calculated using Gavezzottis’ OPIX program suit. This showed that the N-H…O/S hydrogen bonds and π…π interactions were the most important interactions amongst the 24 structures discussed in this work. The crystal structures, thermal behaviour and phase transformations of all arylformamides and arylthioamides have shown that a phase transformation was only observed when a halogen atom was one of the substituents and only for some of the formamides. 2,6-dichlorophenylformamide 2a and 2-chloro-6-methylphenylformamide 4a transform to a hightemperature form at 155 and 106 °C, respectively. The high-temperature forms 2b and 4b (grown by sublimation) are both monoclinic but not isomorphous, with one short axis of about 4.3 A°, and consist of chains of N– H…O hydrogen-bonded molecules stacked along the short axis, related by translation. 1a and 1b are related to the above polymorphs in their formation of N-H…O hydrogen bonding patterns. Finally, this contribution has analyzed the role of weak interactions on the structural and thermal properties of the compounds studied. In addition, a mechanism for the phase change in 2,6-dichlorophenylformamide has been proposed and rationalized through the examination of the structures themselves together with lattice energy calculations. (1. Category = different types of hydrogen bonding patterns formed by disubstituted phenyl -formamides and -thioamides discussed in this thesis).

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

A photon asymmetry measurement in radiative muon capture (RMC) on ⁴⁰Ca has been carried out in order to determine a value for the induced-pseudoscalar coupling constant (ցƿ), thereby allowing us to investigate the possible renormalisation effect for this coupling constant inside nuclear matter. Negative muons from the M20A channel at TRIUMF were stopped in a ⁴⁰Ca target. The resulting RMC photons were then converted by a 5 cm thick Nal converter placed immediately in front of our main detector, a Nal crystal of size 46 cm∅x51 cm. The purpose of the converter was to provide discrimination against the prolific high energy neutron background. From a fit to our time spectrum for the high-energy (57 MeV< E⋎ <95 MeV) photons, we were able to extract a value for the RMC photon asymmetry (⍺⋎). This time spectrum, with 5200 "clean" photons and a signal to noise ratio of ~7, showed the photon asymmetry quite clearly. With our measured value for the photon asymmetry: ⍺⋎ = 1.00±0.23, the predicted value of the induced-pseudoscalar coupling constant becomes: ցƿ = (0.0±⁸‧⁰₆․₇) ցA;, this range contains the (theoretical) unrenormalised value of Goldberger-Treiman: ցƿ ≈ 7 ցA⋅ / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The photon asymmetry (⍺⋎) and partial branching ratio (Rk>57), for radiative muon capture on ⁴⁰Ca, have been measured in order to determine the magnitude of the induced-pseudoscalar coupling constant, gp. A large Nal(Tl) crystal (46cm ϕ x 51cm) was used with an active Nal(Tl) converter (36cm x 30cm x 5cm) as the photon detector. The combined system had an energy resolution of 15% at 70 MeV; a factor of two improvement over previous similar experiments. Simultaneous measurements of the photon asymmetry and the partial branching ratio have been performed twice in the past. From a theoretical stand-point the photon asymmetry measurement is of greater interest as it represents the least nuclear model-dependent way of extracting gp. In the present experiment we have observed 3100 photons with energies greater than 57 MeV, after background subtraction. Of these, 2500 could be used in the determination of ⍺⋎. A value of ⍺⋎ = 1.32+⁺⁰֗⁵⁴˗₀․₄₇ is obtained from a fit to the photon time distribution. For the first time in such measurements the photon asymmetry was visible in the time spectrum and an unconstrained fit is able to reproduce its known frequency and phase. The extracted asymmetry allows for the first time a meaningful limit to be placed on gp which is free of the uncertainties associated with the extraction of gp from the partial branching ratio. Our asymmetry result implies gp < 5Agp, favouring a renormalization of the induced-pseudoscalar coupling constant. The partial branching ratio determined in this experiment is consistent with previous measurements. A model-dependent extraction of gp from Rk>57 yields gP ~ (7 ± 2)gA. As a consequence of this work an improved experiment has recently been successfully performed at TRIUMF with increased statistics, improved energy resolution, and an improvement of approximately a factor of 15 in the signal-to-noise ratio. We have also identified a potential systematic error of as large as 15% in the normalization of the photon asymmetry in past experiments. Such an error occurs from the use of the V—A asymmetry distribution rather than a bound decay asymmetry distribution when performing Monte Carlo calculations of the decay electron asymmetry. This error affects the estimation of the residual muon polarization which is used to normalize the photon asymmetry. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. Description based on print version record. Includes bibliographical references.