Gas-phase ion -molecule reaction studies of π-type radicals and biradicals: Description and characterization of a novel tandem flowing afterglow - guided ion beam apparatus
Abstract
The gas-phase ion-molecule reactions of π-type radicals and biradicals were investigated by using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. Reaction exothermicities, thermodynamic quantities, and singlet-triplet gaps were estimated by density functional theory and ab initio calculations. The first study examined the rate of hydrogen atom abstraction by different types of pyridinium monoradicals from several neutral reagents. The rate of hydrogen atom abstraction was rationalized through the use of an ionic curve-crossing model. Second, the reactivity of four delocalized π-type biradicals, the 2,6-dimethylenepyridinium ion, N-(3-methylenephenyl)-3-methylenepyridinium ion, the N-phenyl-3,5-dimethylenepyridinium ion and the N-(3,5-dimethylphenyl)pyridinium ion were investigated. The predicted closed-shell singlet biradical (2,6-dimethylenepyridinium ion) was found to react by both radical and electrophilic pathways with the reagents studied. The other biradicals exhibited exclusive radical type reactivity, i.e., H-atom abstraction, consistent with a triplet electronic ground state. The third reaction study involved the characterization a distonic nitrene ion, N-phenyl-3-nitrenopyridinium ion, that was produced in the gas phase from an azide precursor. The reactions of the distonic nitrene ion revealed that a mixture of isomers were generated upon nitrogen extrusion from the N-phenyl-3-azidopyridinum ion. The ring-expanded and ring-contracted isomers displayed electrophilic and acidic reactivity, respectively. The triplet nitrene, which exhibited radical type reactivity, was found to be the most dominant of the three isomeric ions observed. Finally, the description and characterization of a new tandem flowing afterglow - guided ion beam instrument are presented in the last chapter. The instrument will be used to obtain thermochemical values, such as bond dissociation energies and gas-phase basicities, for distonic ions of the types described in the previous chapters.
Degree
Ph.D.
Advisors
Kenttamaa, Purdue University.
Subject Area
Analytical chemistry|Physical chemistry|Organic chemistry|Chemistry
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