Gas-phase ion chemistry of fluoromethanes by ion cyclotron resonance spectroscopy. New techniques for the determination of carbonium ion stabilities. [Substituent effects]
The gas-phase ion chemistry of the fluoromethanes CH/sub 4-n/F/sub n/(n = 1-4) has been investigated using the techniques of ion cyclotron resonance spectroscopy. The kinetics of reactions involving parent and fragment ions have been determined over a range of pressure and electron energies using trapped ion techniques complemented by the more usual method of examining the variation of ion abundance with pressure. Fluoride-transfer reactions between substituted carbonium ions are a dominant feature of the observed ion chemistry. A detailed examination of these processes provides information relating to carbonium ion stabilities. Several criteria, including hydride affinities of carbonium ions (R/sup +/-H/sup -/ heterolytic bond dissociation energies) and adiabatic ionization potentials of the corresponding free radicals, indicate the order of decreasing stability of fluoromethyl cations to be CHF/sub 2//sup +/ is greater than CH/sub 2/F/sup +/ is greater than CF/sub 3//sup +/ is greater than CH/sub 3//sup +/. A second important feature of the observed ion chemistry concerns halonium ion formation. While (CH/sub 3/)/sub 2/F/sup +/, (CH/sub 2/F)/sub 2/F/sup +/, and (CHF/sub 2/)/sub 2/F/sup +/ are readily formed in nucleophilic displacement reactions involving the protonated parent and corresponding neutral of CH/sub 3/F, CH/sub 2/F/sub 2/, and CHF/sub 3/, respectively, the species (CF/sub 3/)/sub 2/F/sup +/ is not observed. The binding energies of fluoromethyl cations to fluoromethanes decrease with increasing fluorine substitution in the neutral. The basicities (proton affinities) of the fluoromethanes also decrease with increasing fluorine substitution.
- Research Organization:
- California Inst. of Tech., Pasadena
- OSTI ID:
- 7224696
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 96:5; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400104* -- Spectral Procedures-- (-1987)
400301 -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
BINDING ENERGY
CHEMICAL REACTION KINETICS
ELECTRONEGATIVITY
ENERGY
FLUORINATED ALIPHATIC HYDROCARBONS
GAS ANALYSIS
HALOGENATED ALIPHATIC HYDROCARBONS
ION CYCLOTRON RESONANCE SPECTROSCOPY
ION SPECTROSCOPY
KINETICS
ORGANIC COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
REACTION KINETICS
SPECTROSCOPY
STABILITY
THERMOCHEMICAL PROCESSES
TRAPPING