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Products, rate constants and mechanisms of gas‐phase reactions of CX 3 + , CX 2 + , CX + (X = F and/or Cl) and Cl + with 1,1,1‐ and 1,1,2‐trichlorotrifluoroethane
Author(s) -
Marotta Ester,
Paradisi Cristina
Publication year - 2001
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.225
Subject(s) - chemistry , reactivity (psychology) , ion , chloride , chlorine , mass spectrometry , halide , divalent , reaction rate constant , chemical ionization , inorganic chemistry , medicinal chemistry , ionization , kinetics , organic chemistry , chromatography , physics , quantum mechanics , medicine , alternative medicine , pathology
The gas‐phase ion chemistry of 1,1,1‐ and 1,1,2‐trichlorotrifluoroethane was investigated with an ion trap mass spectrometer. Following electron ionization both compounds (M) fragment to [M − Cl] + , CX 3 + , CX 2 + , CX + (X = F and/or Cl) and Cl + . The reactivity of each of these fragments towards their neutral precursors was studied to obtain product and kinetic data. Whereas [M − Cl] + , CCl 3 + and CCl 2 F + cations are unreactive under the experimental conditions used, all other species react via halide abstraction to give [M − Cl] + and, to a far lesser extent, [M − F] + . In addition, CX 2 + ions form CClX 2 + in a process which formally amounts to chlorine atom abstraction, but more likely involves chloride ion abstraction followed by charge transfer. CX + ions also form minor amounts of CX 3 + product ions, possibly via chloride abstraction followed by or concerted with dihalocarbene elimination from the (incipient) [M − Cl] + ion. Trivalent carbenium ions are less reactive than divalent species, which in turn are less reactive than the monovalent ions (reaction efficiencies are given in parentheses): CF 3 + (0.70) < CF 2 + (0.78) < CF + (0.96). More interestingly, within each family of ions reactivity increases with the number of fluorine substituents (e.g. CF 2 + > CFCl + > CCl 2 + and CF + > CCl + ), i.e. reactivity increases with the ion thermochemical stability, as measured by available standard free enthalpies of formation. Evaluation of the energetics involved shows that reactions are largely driven by the stability of the neutrals more than of the ions. Finally, the products observed in the reaction of Cl + are attributed to ionization of the neutral via charge transfer and fragmentation. Copyright © 2001 John Wiley & Sons, Ltd.