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I. Gas phase anion reactions: Transesterification, Claisen-Schmidt, and water elimination from fatty acid carboxylates. II. Fragmentation pathways of benzofuroxan and benzofurazan derivatives
Abstract
The major subject of this dissertation involves three gas-phase anion reactions: transesterification, Claisen-Schmidt, and water elimination from fatty-acid carboxylates. Tandem-sector and Fourier Transform mass spectrometers are employed for these investigations. Fatty acid carboxylates, desorbed into the gas phase by fast atom bombardment, undergo both metastable-ion and collisionally activated dissociation to eliminate water via an ion-neutral complex involving hydroxide ion and neutral ketene (Chapter 1). The gas-phase, base-catalyzed transesterification of acetate esters is described in Chapter 2. Evidence is presented from kinetics, equilibrium constants, and thermochemically derived data that transesterification proceeds in the gas phase by the attack of the acetate enolate anion on alcohol. The formation of the larger alkyl acetate enolates is favored, which is in contrast to liquid-phase chemistry. The effect of substituents was investigated for the gas-phase, base-catalyzed Claisen-Schmidt reaction of the acetone enolate anion and various para-substituted benzaldehydes (Chapter 3). The Hammett constants for the substituents correlate the extent of stabilization of the negative charge in the formation of covalently bound adducts that eliminate water. The second main part of this dissertation deals with the fragmentation pathways of benzofuroxan and benzofurazan derivatives. The loss of oxygen is investigated to discern whether it is a thermal degradation process or primarily an ionic process. In another study, the mechanism for the formation of fragment ions that can be used to distinguish between angular and linear isomers is elucidated.
Subject Area
Analytical chemistry
Recommended Citation
Haas, George William, "I. Gas phase anion reactions: Transesterification, Claisen-Schmidt, and water elimination from fatty acid carboxylates. II. Fragmentation pathways of benzofuroxan and benzofurazan derivatives" (1994). ETD collection for University of Nebraska-Lincoln. AAI9510971.
https://digitalcommons.unl.edu/dissertations/AAI9510971