GENERATION, REACTION, AND FRAGMENTATION OF GAS-PHASE ANIONS USING FOURIER TRANSFORM MASS SPECTROMETRY
Abstract
Collision-induced dissociation (CID) was used in conjunction with ion-molecule reactions to investigate the fragmentation and reaction behavior of gas-phase anions by Fourier transform mass spectrometry (FTMS). Besides using CID to obtain ion structural information, the technique was also used to generate and study unique anions that have no other known method of formation. Collision-induced dissociation of a series of ester enolates was investigated. Two primary modes of fragmentation were observed that lead to CID products characteristic of the acyl and alkoxyl moieties of the ester enolates. The primary mode of fragmentation appears to be sensitive function of the structures and the proton affinities of the two possible product ions. Secondary dissociations of the primary product alkoxide ions were observed to generate enolate ions or other stabilized anions. CID was also used to synthesize interesting and unusual gas-phase anions. Dimethylsilanone enolate was generated by CID of trimethylsiloxide anion, (CH(,3))(,3)SiO('-). Reactions of this ion with selected neutral substrates demonstrated a markedly different chemistry relative to the analogous carbon enolate anion. The proton affinity of dimethylsilanone enolate was bracketed to be 366 (+OR-) 3 kcal/mol by reactions with a series of reference acids. Silanone hydrate anion, (CH(,3))(,2)Si(O)OH ('-), was formed by reaction of the enolate anion with alcohols bearing betahydrogens. (MS)('n) experiments were carried out to substantiate the structures of the product ions formed. CID was used to synthesize tautomeric propenyl anions, cyclopropyl anion, and related homologs. These anions were conveniently prepared by CID of carboxylate anions via loss of carbon dioxide. The vinylic anions and cyclopropyl anion, studied in the gas phase for the first time, produced distinctly different products in reactions with N(,2)O and CS(,2). Other vinyl anions were investigated to aid in the mechanistic interpretation and understanding of the reactivity differences.
Degree
Ph.D.
Subject Area
Analytical chemistry
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