Structure and Reactivity of Hydrocarbon Ions

  • P. Ausloos
  • S. G. Lias


In kinetic studies of free-radical reactions, which are largely based on information obtained from end-product analysis, the structures of the free radicals formed in a given system are generally well established, and the rate constants measured for elementary reactions can be unambiguously ascribed to a well-characterized reactant radical. In contrast, kinetic studies of the reactions of hydrocarbon ions have generally been carried out in the mass spectrometer, where the structure of a reactant ion cannot be determined directly. Although numerous attempts have been made to derive information about ionic structures by correlating mass spectrometric information such as appearance potentials or measured reaction rates with the properties of ions of known structure (techniques which will be described in detail below), there are few cases where the structures of reactant hydrocarbon ions have been unambiguously established in the mass spectrometer. The problem is complicated by the well-known tendency of ions to isomerize. Thus, the propyl ions formed in the fragmentation of n-butane parent ions cannot be assumed to have the n-propyl structure, but may have several structures; in contrast, the propyl radicals formed in the pyrolytic fragmentation of n-butane are known to have the n-propyl structure. Furthermore, the relative abundances of the various isomers will depend on the energy deposited in the ions. This means that the composition of the isomeric reactant ions will vary with temperature and with pressure (since the extent of collisional deactivation of the excited precursors of certain isomer ions will vary with pressure) and with the ionizing energy.


Kcal Mole Neutral Product Reactant Pair Appearance Potential Collisional Deactivation 
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Copyright information

© Plenum Press, New York 1972

Authors and Affiliations

  • P. Ausloos
    • 1
  • S. G. Lias
    • 1
  1. 1.Physical Chemistry Division, Radiation Chemistry SectionNational Bureau of StandardsUSA

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