Quantum mechanical analysis of donor-acceptor interactions in organometallic complexes and comparative analysis of class size and teacher experience on student experience satisfaction and learning

The first five chapters of this thesis use modern density functional and ab initio methods to analyze donor-acceptor complexes of transition metals. Chapter 1 gives background for the theories used in this work.;In chapter 2, density functional theory (DFT) is used to investigate the geometries and metal-ligand bonds in nickel complexes of bidentate phosphines. The net donor/acceptor properties of the phosphine ligands can be deduced from the computed frequency of the symmetric CO stretch of the Ni(CO) 2(R2P(CH2)nPR 2) complexes. This frequency can be estimated from the empirical expression nu(CO) = 1988 + Sigma chiB -- 4 n, where the sum is over the four phosphorus bound substituents; chiB is a substituent-dependent parameter; and n is the number of carbon atoms in the backbone (1 ≤ n ≤ 3). The calculated frequencies also show that the phosphine appears to be a better donor (or weaker acceptor) as the number of carbon atoms in the backbone increases.;In Chapter 3, density functional theory and ab initio methods have been used to calculate the structures and energies of minima and transition states for the reactions of methane coordinated to a transition metal. The reactions studied are reversible C-H bond activation of the coordinated methane ligand to form a transition metal methyl/hydride complex, and dissociation of the coordinated methane ligand. Three-center metal-carbon-hydrogen interactions play an important role in this system. Both basis sets and functionals have been benchmarked in this work, including new correlation consistent basis sets for a third transition series element, osmium. Double zeta quality correlation consistent basis sets yield energies close to those from calculations with quadruple zeta basis sets, with variations that are smaller than the differences between functionals. The energies of important species on the potential energy surface, calculated by using ten DFT functionals, are compared both to experimental values and to coupled cluster CCSD(T) single point calculations.;In Chapter 4, M05-2X and BB1K were used to analyze the effect of ancillary ligands on the hydrogen exchange reaction of (C5HxR 5-x)Os(Y2PCZ2PY2)(CH3)H +, where R = Me, F, CF3, SiH3, SiMe3, or H; x = 1-5; Y = H, Me, Ph, or F; and Z = H or F. Three points on the potential energy surface are studied: the methyl hydride 1, the methane tautomer 2, the transition state 1‡ between 1 and 2, and the fragment molecule 3. We find that the steric and electronic effects of the ligands affect the relative energies of these structures on the potential energy surface.;In Chapter 5, we use M05-2X, B3LYP, and PBE0 methods to analyze a possible agostic interaction in the compound Ti2Cl6[N(t-Bu) 2]2. The crystal structure of Ti2Cl6[N(t-Bu) 2]2 shows very close contact (2.634 Angstroms) between the electron poor titanium atom and a methyl group. Short distances between an electron deficient metal center and carbon-hydrogen bonds are often assigned to be agostic, i.e., attractive interactions involving 3-center-2-electron bonds. To ascertain whether or not this close contact is due to an agostic interaction between the Ti and C-H atoms, the gas phase structure of the complex and related model compounds were optimized with dispersion corrected density functional methods, which have been shown to be capable of accurately describing agostic interactions. These calculations reveal that decreasing the steric bulk of the amido ligand (by replacing the non-interacting tert-butyl ligand with a smaller alkyl group) caused the Ti-H distances to increase significantly. Natural bond order (NBO) analysis of the gas phase structure showed that there are no bonding interactions between titanium and hydrogen. We conclude that close contacts between electron deficient metal centers and nearby C-H bonds are not always attractive, and that some agostic interactions are repulsive and are consequences of steric repulsions between the ligands in the inner coordination sphere.;Chapter 6 discusses the results of a year long research project studying student perceptions and success in two types of general chemistry courses. This study uses three ways to determine if student performance and satisfaction were different between the two types of sections: exam scores, attrition rates, and student happiness in the class (as measured by effectiveness ratings). On average, students in the small discussion performed worse on exams, left the course in higher numbers than large lecture students and rated their instructor less effective than students in the large lecture course. However, students in sections with experienced TAs performed significantly better than students in the large lecture course, suggesting that small classes with TAs can be effective provided that TAs are trained and motivated. (Abstract shortened by UMI.)...