Probing molecular structure and chemistry of reactive intermediates in the gas phase by using ion -molecule reactions in the FT -ICR mass spectrometer
Abstract
The first part of this thesis describes the elucidation of the gas-phase structure of five carbon monosaccharides. By using structure sensitive reagent ions, the dimethoxyphosphenium and 1,3-dioxalane-2-phosphenium ions, it was determined that five-carbon monosaccharides maintain their six-membered, crystalline structure in the gas phase. Computational examination of possible sugar conformers also revealed that the six-membered ring form is the most stable form for all five-carbon monosaccharides except D-lyxose, which prefers a five-membered ring. The second part of this thesis explores the reactivity of five charged phenyl radicals toward three alcohols and seven amino acids. First, the regioselectivity of four charged phenyl radicals in hydrogen atom abstraction reactions with ethanol, isopropanol, and t-butanol, was examined. It was determined that the H-atom abstraction reaction efficiency is predominantly controlled by the electron affinity of the reacting radical. It was also discovered that the regioselectivity is dependent on the electrophilicity of the radical, and less so on the hydrogen bond strength (i.e., BIDE of C-H bond), a result that was unexpected. Less electrophilic radicals were found to prefer hydroxyl hydrogens over carbon hydrogens, even though the O-H bond is significantly stronger than the C-H bond. Reactions with amino acids revealed several other reaction pathways besides H-atom abstraction, such as NH2 abstraction, SH abstraction and SCH3 abstraction. These reaction pathways seem to dominate the reactivity of most electrophilic radicals, whereas with least electrophilic radicals, these reaction pathways are undetectable. Some computational and experimental evidence suggests that these reactions may not be radical type reactions, but addition-elimination reactions.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry
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