Gas-phase ion chemistry : 1. Electron impact generation of anions 2. Diol acidities 3. Isotope effects on electron transfer equilibria

Author

Catherine Ann Crowder

Date of Award

5-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemistry

Major Professor

John E. Bartmess

Committee Members

Schweitzer, Bartmess

Abstract

The use of ion cyclotron resonance mass spectrometry has permitted the investigation of several problems concerning gas-phase ion chemistry. The first is a way to generate a large selection of low energy anions by electron impact for use in studying gas-phase ion/molecule reactions. Dissociative attachment is a useful process for doing this, yet few cases are known in which anions can be produced from precursor molecules with large enough cross sections to make them feasible sources of ions in mass spectrometers. A design strategy for predicting the structure of a precursor molecule that could undergo dissociative attachment with a large cross section is elucidated. We propose the structure Ar-N=N-CR₂G, which can undergo dissociative attachment resulting in the formation of the R₂C=G^- carbanion. This precursor molecule is successful in giving the desired carbanions when the G group is either a nitro or perfluoroalkyl group. The gas-phase acidities of a series of diols are determined. By comparing the acidities of the diols with the acidities of comparable monoalcohols, it appears that the diols do form cyclic structures of varying degree by intramolecular hydrogen bonding. Isotope effects on the electron transfer equilibria of PhNO₂-h₅/PhNO₂-d₅ and Ph¹⁴NO₂/Ph¹⁵NO₂ have been investigated. The results for the PhNO₂-h₅/PhNO₂-d₅ system are in line with solution phase results which favor the formation of the light ion. The results for the Ph¹⁴NO₂/Ph¹⁵NO₂ system favor neither ion giving an equilibrium constant of essentially one, explaining solution-phase results that are solvent/counterion dependent. A correlation between bond shortening and lengthening upon anion formation and values for the gas-phase equilibrium constants is discussed.

Recommended Citation

Crowder, Catherine Ann, "Gas-phase ion chemistry : 1. Electron impact generation of anions 2. Diol acidities 3. Isotope effects on electron transfer equilibria. " Master's Thesis, University of Tennessee, 1989.
https://trace.tennessee.edu/utk_gradthes/12924