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I. Studies of Collision Broadening of Ion Cyclotron Resonance Lineshapes. II. Studies of the Gas Phase Ion Chemistry of Fluoroethanes


Ridge, Douglas Poll (1973) I. Studies of Collision Broadening of Ion Cyclotron Resonance Lineshapes. II. Studies of the Gas Phase Ion Chemistry of Fluoroethanes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FMJE-KV22.


In Section I theoretical calculations of gas phase ion mobilities are reviewed. The results of measurements of ion cyclotron resonance linewidths of ions in methane and ions in hydrogen are presented. The relationship between ion mobilities, collision frequencies and ion cyclotron resonance linewidths is reviewed. The results of the linewidth measurements are compared with DC mobility measurements and theoretical calculations of the mobility. The results of previous ion cyclotron resonance linewidth measurements are in serious disagreement with DC mobility measurements. The results of the present study, however, agree well with recent mobility measurements. Except for H+ and H3+; in hydrogen the results of the linewidth measurements are consistent with the theory of Mason and Schamp which is based on a three term 12-6.-4 ion molecule interaction potential. It is concluded that weak chemical bonding occurs between hydrocarbon ions and methane and that the anisotropy of the H2 molecule plays a significant role in determining the cyclotron resonance linewidths of ions in hydrogen. The parameters which determine the 12-6-4 potentials which best characterize the interaction between the ion-neutral pairs studied are estimated. It is concluded that the interaction of H+ and H3+ with H2 are too energetic to be adequately represented by a 12-6-4 potential. Measurements of the linewidths of Na+ ions in the C3H6O isomers are found to increase linearly with dipole moment in quantitative agreement with a simple model. The implications of this result are discussed.

In Section II a series of fluoride transfer reactions between fluoroalkyl cations and fluoroalkanes in the gas phase are described. In one case (CH3CHF+ + CH3CF3 → CH3CF+2 + CH3CHF+2) equilibrium is observed so that a free energy change can be assigned from the final ratio of the ionic products. From this result and from observations of competitive fluoride transfer reactions in mixtures of fluoroalkanes a sequence of fluoride affinities of fluoroalkyl cations is deduced (the fluoride affinity of R+ is -ΔH for the reaction R+ + F- → RF). Including the results of previous studies the sequence in order of decreasing fluoride affinities is C2F+5 > CF+3 > CH+3 > CH2F+ > CHF+2 > CHF2CHF+ > CH2FCHF+ > CH3CF+2 > CH3CHF+ > C2H+5. The effects of fluorine substituents on ethyl cation stability are discussed. A simple electrostatic model is proposed to account for the destabilization of fluoroethyl cations by β fluorine substituents.

The base induced elimination of HX from alkyl halides (RX) in the gas phase is proposed and its observation reported. The reaction CH3O- + C2H5F → CH3OHF- + C2H4 is shown by isotopic labelling and kinetic studies to be a based induced 1,2 elimination. Analogous reactions are observed between CH3O- and CH3CHF2, CH3CF3, CH2FCHF2, and CHF2CHF2. It also appears that F- reacts with fluoroethanes in an analogous way. Other substrates from which bases appear to eliminate HX are β-chloroethanol, ethylene bromohydrin and CH3CC13. Proton transfer between fluoroethanes and CH3O- is also observed. The fluoroethyl anions formed transfer F- to the parent fluoroethanes. The thermochemical consequences of the observed reactions with regard to the binding in species of the type XHY- and with regard to the electron affinities of the fluoroethyl anions are discussed.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Beauchamp, Jesse L.
Thesis Committee:
  • Unknown, Unknown
Defense Date:18 September 1972
Additional Information:Thesis title listed in 1973 Commencement Program is: Thesis: I. Studies of Collision Broadening of Ion Cyclotron Resonance Spectra. II. Studies of the Gas Phase Ion Chemistry of Fluoroethanes.
Record Number:CaltechTHESIS:07232018-123515101
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11132
Deposited On:23 Jul 2018 20:56
Last Modified:21 Dec 2019 03:06

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