<P> Solving the electronic Schrodinger equation for the molecular wavefunction is the central problem in theoretical chemistry. From these wavefunctions (possibly with relativistic corrections), one may completely characterise the chemical reactivity and physical properties of atoms, molecules, and materials. Unfortunately, there are very few systematic approaches for obtaining highly-accurate molecular wavefunctions. The approaches that do exist suffer from the so-called curse of dimensionality: their computational cost grows exponentially as the number of particles increases. Furthermore, even after obtaining an accurate wavefunction, partitioning the molecule into atoms is not straightforward. This is because the kinetic energy operator is a differential operator in spatial coordinates. This is a source of ambiguity in the definition of an atom-in-a-molecule and the associated atomic properties. Even after selecting an appropriate definition of an atom and obtaining the atoms from the wavefunction, the atom's intrinsic reactivity cannot be completely characterised without considering every possible reaction partner. This is because each set of two molecules produces a new wavefunction that is more complicated than the products of the wavefunctions of the separate molecules. </p> <P> This thesis presents methods for addressing the three challenges raised in the previous paragraph: computing atomic properties (e.g. chemical reactivity), partitioning molecules into atoms, and computing accurate molecular wavefunctions. The first challenge is addressed by developing a general-purpose reactivity indicator to quantify the reactivity of an atom within a molecule. This indicator quantifies the reactivity of any point of the molecule using only the electrostatic potential and Fukui potential at that point. The key idea is to include only a vague description of an incoming molecule and compute an approximate interaction with the incoming object; this ensures that the general-purpose reactivity indicator is simple enough to be useful. Practically, this indicator is most useful when it is used to compute the reactivity of the atomic sites in the molecule of interest. </p> <P> Partitioning a molecule into atoms is not straightforward because of the inherent nonlocality of quantum mechanics. In the context of molecular electronic structure, this nonlocality arises from the nature of the kinetic energy operator. The quantum theory of atoms in molecules (QTAIM) is a popular method that partitions molecules into atoms. QT AIM resolves the problem of ambiguity for all permissible forms of the kinetic energy operator. In this thesis the characterisation of an atom provided by QT AIM is extended to include relativistic contributions in the zero-order regular approximation (ZORA). The intrinsic ambiguity arising from the kinetic energy operator is also examined in detail. </p> <P> Computing atomic or molecular properties (including computing the general-purpose reactivity indicator) almost always requires a wavefunction. For this reason, obtaining accurate wavefunctions is the central hurdle of quantum chemistry. This thesis proposes algorithms for finding high-accuracy molecular wavefunctions without exponentially exploding computational cost. To do this, tools for exploiting the smoothness of electronic wavefunctions are crafted. Computational methods that use these tools can break the curse of exponential scaling without sacrificing accuracy. Specifically, the computation cost of these new methods grows only as some polynomial of the electron number. The wavefunctions obtained from these methods are much simpler than those from conventional approaches of similar accuracy, and are therefore ideal for computing the electron density and atomic properties. </p> / Thesis / Doctor of Philosophy (PhD)

<p> 1,1-Bis(4-(trifluoromethyl)phenyl)germacyclobutane and 1,1-bis(3,5-bis(trifluoromethyl)phenyl)germacyclobutane have been prepared, and their photochemistry studied by steady state and nanosecond laser flash photolysis (NLFP) techniques. Photolysis of the two compounds in the presence of methanol leads to the formation of products resulting from reaction of the alcohol with two germanium-containing reactive intermediates, the germenes and germylenes.</p> <p> The reactivities of the two germenes with nucleophiles such as alcohols, carboxylic acids, and amines have been examined by NLFP techniques, and the results are compared to analogous data for 1,1-diphenylgermene and 1,1-diphenylsilene. Germene reactivity is shown to increase with increasing electron-withdrawing power of the substituents, consistent with a mechanism initiated by nucleophilic attack at germanium. The increased electrophilicity of the substituted 1,1-diarylgermenes results in kinetic behavior indistinguishable from that of 1,1-diphenylsilene, indicating that germenes and silenes form a mechanistic continuum in their reactions with nucleophiles.</p> / Thesis / Master of Science (MSc)

<p> 2-Trifluoromethylnorbornene has been synthesized from norbornene. The UV photoelectron spectra and optical UV absorption spectra of norbornene, 2-methylnorbornene and 2-trifluoromethylnorbornene have been studied, and indicate that the π,π* state is the lowest excited singlet state. Direct photolysis of 2-trifluoromethylnorbornene with 193 nm light yields 1-trifluoromethyl-2-norcarene (in 90% yield) by formal [1,3]-sigmatropic rearrangement. Chlorobenzene-sensitized photolysis affords the photoreduction products, exo-and endo-2-trifluoromethylnorbornane, decane isomers, and several products of higher molecular weight.</p> <p> By comparing the photochemistry of 2-trifluoromethylnorbornene to those previously reported for norbornene and 2-cyanonorbornene as well as on the basis of spectroscopic evidence, it is proposed that the π,π* state is the lowest energy excited singlet state in 2-trifluoromethylnorbornene. Trifluoromethyl substitution has the effect of significantly raising the energy of the π,R(3s) Rydberg state in simple alkenes without altering the high energy or the localized character of the π,π* state.</p> <p> 7-Trifluoromethylbicyclo[4.2.0]oct-7-ene (86) was synthesized from bicyclo[4.2.0]oct-7-ene (84). By comparing the UV photoelectron spectroscopy and optical spectra of 86, 84, 97, it is concluded that the π,π* state is the lowest excited singlet state in 86. Direct photolysis with 193 nm light yields three diene isomers derived from formal electrocyclic π,π* ring opening, and cyclohexene derived from fragmentation. Comparison of spectroscopic and photochemical results for this compound to those of bicyclo[4.2.0]oct-7-ene (84) and 7-methylbicyclo[4.2.0]oct-7-ene (97) indicate that ring-opening is non stereospecific and arises largely from the π,π* singlet state. Fragmentation arises largely from the Rydberg excited state.</p> / Thesis / Master of Science (MSc)

<p> This thesis provides examples of new Si-based polymeric materials in three parts. The rapid evolution of hydrogen gas was observed after the combination of an α- or β-hydroxy carboxylic acid with an alkoxyhydrosilane. This unusual reactivity is interpreted to arise from the cooperative nucleophilic attack of the hydroxy group at silicon and the electrophilic attack of the acid proton at the Si-H bond. These systems further react to produce modified sol-gel materials in which the acid units were incorporated into the matrix.</p> <p> The reactions of tetraethoxysilane, (TEOS) and α-hydroxy acids similarly produced modified sol-gels (in solution, DMSO) and solids (precipitated from THF). The reaction kinetics were followed in these systems using 29Si NMR. Extensive characterisation of our sol-gels was carried out by the use of various NMR techniques, FT-IR, elemental analysis and thermal methods of solids characterisation (TGA, DTA, and DSC).</p> <p> Silicones containing vinylsilane units were prepared in order to examine the silicon β-effect in a polymeric system for the first time. The addition of bromine to these systems unexpectedly resulted in no reaction unless vigorous conditions were used. Steric factors as shown by molecular modeling are attributed to this lack of reactivity. Although many silicone systems were studied where more sterically "open" vinylsilanes were present these steric problems could not be overcome.</p> / Thesis / Master of Science (MSc)

One of two project reports. The other one is designated PART A: McMASTER (ON-CAMPUS) PROJECT / <p> A reactivity meter code based on point kinetics was developed. Rod-drop experiments performed in the ZED-2 reactor tested the code for various detector and rod-drop positions. A delayed neutron hold-up effect was observed whenever a rod was dropped close to a detector. A better understanding of this effect was obtained through a theoretical analysis of the pertinent experiments. The three-dimensional kinetics code, CERBERUS, was used for the theoretical analysis. </p> / Thesis / Master of Engineering (MEngr)

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Stress is one of life’s greatest health threats and increases susceptibility to mental illness. Physical activity and mindfulness are lifestyle factors that are protective against mental health concerns. Critically, those with high levels of physical activity also tend to have high levels of trait mindfulness—the tendency to be more mindful in everyday life. However, the relationship between physical activity and mindfulness, and their impact on acute stress and mental health, remains unclear. The current study aimed to explore this association between physical activity and mindfulness, and their relative impact on acute stress reactivity and mental health. Specifically, we examined whether trait mindfulness accounted for unique variance after controlling for physical activity. In a sample of young adult participants (N = 50) we first assessed their physical activity, trait mindfulness, and mental health and then exposed them to the Trier Social Stress Test, during which we recorded using heart rate, blood pressure, salivary cortisol samples, and state anxiety. Hierarchical linear regression revealed a distinct pattern, such that physical activity was more strongly associated with acute stress (heart rate and state anxiety reactivity), whereas trait mindfulness was more strongly associated with mental health even after controlling for physical activity. The results suggest that physical activity and trait mindfulness may work via synergistic mechanisms to enhance wellbeing with physical activity reducing stress reactivity and trait mindfulness improving overall mental health. / Thesis / Master of Science in Kinesiology