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An NMR spectroscopy study of trimethylsilylmethyllilthium, TMSM-Li, indicates that TMSM-Li exists as two different aggregates in cyclopentane solution. Using previously reported colligative properties of TMSM-Li in different solutions in connection with new 13C and 6Li NMR data collected in this study, aggregation states were assigned as octamer and hexamer. Low temperature 13C and 6Li NMR peak intensities indicated an equilibrium exists between the two aggregates that shifts toward the octamer as the temperature decreases. ΔH was calculated to be 5.23 + 0.15 kcal/mol and ΔS was calculated to be 17.9 + 0.6 eu for the hexamer/octamer equilibrium system. Samples of TMSM-Li were mixed with TMSM-OH in attempts to form mixed alkyllithium/lithium alkoxide aggregates. 13C NMR data for these mixtures gave inconclusive results whether or not these compounds formed, which is different from other primary alkyllithium compounds studied in the past. A study of neopentyllithium, NpLi, indicates only one aggregate in solution with the aggregation state unknown using low temperature 13C NMR spectroscopy.

Solvent effects on the chemical exchange of a push pull Ethylenes <p> Chemical exchange rates provide a sensitive probe of solvent effects in solution. The push-pull ethylene methyl 3-dimethylamino-2-cyanocrotonate (MDACC) has three exchange processes E-Z (the same as E' -Z'), E-E', and Z-Z', and we have measured these rates in acetone-d6, chloroform-d, tetrahydrofuran-d8, toluene-d8, methanol-d4, acetonitrile-d3, and methylene chloride-d2 through 1D 1 H.NMR at different temperatures. From this we obtain ΔG+, ΔHt+, ΔS+ of activation for each solvent by employing an Eyring plot. As the solvent changes, ΔH+ is approximately constant whereas ΔS+ follows the solvent polarity. </p> <p> Since the equilibrium constant is less than one, we would expect it to increase with temperature, but it decreases. This is seen in the Van't Hoff plot where the slope is positive indicating that the process of going from the major site to the minor site is exothermic, so not only is the rate governed by entropy effects, but also the equilibrium constant between E and Z. </p> <p> The rotation between the C-N and the C=C bond occurs through a non-concerted mechanism. Two reasons why this occurred was apparent through EXSY, since the intensity of the off diagonal peak varies with different mixing time and second, the rates from C=C rotation (E-Z) and C-N rotations (E-E' and Z-Z') are different at the same temperature </p> / Thesis / Master of Science (MSc)

A series of bicyclic peptides have been designed and synthesized to provide ammonium ion complexation sites via hydrogen bonding in a tetrahedral geometry. Molecular modeling dynamics and electrostatics studies indicate that target compounds 1d-6d may provide better selectivity for ammonium ions over potassium ions than the ammonium ionophore currently used for blood analysis applications, nonactin. Attempts to synthesize 1d, cyclo(L-Glu1�D-Val2�L-Ala3�D-Lys4�D-Val5�L-Val6)-cyclo-(1ã-4å), were unsuccessful due to poor solubility of the synthetic intermediates. This led to the design of 2d-6d in which specific amino acid residues were chosen to provide higher solubility. Compound 2d, cyclo(L-Glu1�D-Ala2�D-Ala3�L-Lys4�D-Ala5�L-Ala6)-cyclo-(1ã-4å), was successfully synthesized, but was also too insoluble for characterization or testing in an ion selective electrode (ISE) sensor format. Compound 6d, cyclo(L-Glu1�D-Leu2�Aib3�L-Lys4�D-Leu5�D-Ala6)-cyclo-(1ã-4å), was successfully synthesized and characterized. When 6d was incorporated into an ISE sensor and tested as an ammonium ionophore, results indicated that the bicyclic peptide lacked solubility in the ISE membrane. A 13C-NMR study has been initiated in order to evaluate selectivity of 6d for ammonium over potassium and sodium cations in solution. Preliminary results with the potassium ionophore valinomycin as a control have been completed.