Interpretation of gas phase dissociation processes in mass spectrometry using ab initio and density functional calculations

The research reported in this dissertation focuses on applications of ab initio electronic structure calculations and density functional theory (DFT) to understand and interpret the dissociation reactions of gaseous ions. Techniques of tandem mass spectrometry were used to generate and select specific gaseous ions based on a mass-to-charge ratio. Collision-induced dissociation (CID) of the selected ions lead to novel, interesting product ions. Calculations of ground state and transition state structures and their energies were used to explain and predict reaction pathways.;Our research group discovered a mild, low energy, bench-top process to produce gaseous alkalides using a mass spectrometer. Our method could facilitate novel applications of gaseous metal anions as selective reagents for gas phase ion-molecule and ion-ion reactions. Ab initio and density functional calculations were used to explain the dissociation mechanism for this unusual process. The formation of alkalides occurs via production of a metal-carbon dioxide anion intermediate with a bidentate three-center two-electron bond to the metal. The metal atom acquires a partial negative charge in the intermediate structure.;Tetrahydropyranyl ethers are important alcohol protecting groups that are used in chemical synthesis. The gas phase chemistry of protonated tetrahydropyranyl ethers was investigated using isotopic labeling studies and ab initio calculations together to explain the gas-phase chemistry of these derivatives.;The gaseous 2,3,4-trimethoxyphenyl anion undergoes a novel "ring-walking" dissociation mechanism in which the charge site of the carbanion migrates around the phenyl ring. Density functional calculations were here used to identify the rate-determining step of the dissociation process involved and to predict the kinetic isotope effect (KIE) associated with deuterium labeling of the precursor ion.;The dissociation processes of isomeric protonated 2-, 3-, and 4-haloanilines show an example of an ortho effect for the fluorinated, chlorinated, and brominated cases. Anions of alkali metal sulfobenzoate salts undergo dissociation processes that proceed with an unusual reduction of the metal cation and loss of a neutral metal atom.