6212-69-7Relevant articles and documents
Karabatsos et al.
, p. 37 (1962)
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Fraenkel,G.,Henrichs,M.,Hewitt,J.M.
, p. 3345 (1980)
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Isomerization and Fragmentation of Aliphatic Thioether Radical Cations in the Gas Phase: Ion-Neutral Complexes in the Reactions of Metastable Ethyl Propyl Thioether Ions
Zappey, Herman W.,Ingemann, Steen,Nibbering, Nico M. M.
, p. 1887 - 1892 (2007/10/02)
The dominant unimolecular reactions of the molecular ion of ethyl propyl thioether are (i) loss of a methyl radical from the ethyl or the propyl group, (ii) loss of an ethyl radical from the propyl group and (iii) elimination of a propene molecule and an allyl radical by transfer of one or two hydrogen atoms, respectively, from the propyl group to the sulphur atom.The loss of a methyl radical on the μs timescale involves only the propyl entity and is preceded by an isomerization of this group to an isopropyl group.Partial loss of the positional identity of thehydrogen atoms of the propyl group occurs during the reactions of the metastable ions, but incorporation of hydrogen or carbon atoms from the ethyl group into the formed neutral species does not occur.The reactions of the metastable ions are discussed in terms of cleavage of the C-S bond assisted by a 1,2-hydride shift in the incipient carbenium ion leading to an ion-neutral complex of a thioethoxy radical and a secondary propyl carbenium ion.The ion-neutral complex can recombine to form the molecular ion of ethyl isopropyl thioether prior to methyl radical loss, or react by proton transfer to give a complex of CH3CH2SH+. and CH2=CH-CH3, which may dissociate or undergo hydrogen atom transfer followed by elimination of an allyl radical.The partial loss of positional identity of the hydrogen atoms during the decomposition of the metastable ions is mainly a result of reversible proton transfer between the constituents, which competes favourably with 1,2-hydride shifts within the carbenium ion entity of the complex.
Isomerization of Alkane Molecular Ions
Holmes, John L.,Burgers, Peter C.,Mollah, M. Yousuf A.,Wolkoff, Peder
, p. 2879 - 2884 (2007/10/02)
The appearance energies of daughter ions for the major low-energy fragmentations, namely, losses of C2H6, CH4, and CH3*, of pentane and methylbutane radical cations have been measured.These reactions for ions of low internal energy content (rate constants in the range 1E5 - 1E7 s-1) have been studied by observations of metastable peak shapes.The behaviors of a variety of 13C- and 2H-labeled compounds were also examined.Hydrogen atoms do not extensively lose their positional identity in any of these fragmentations.For methylbutane, loss of C2H6 and CH3* yielded ionized propene and 2-butyl cations, respectively, at their calculated thermochemical thresholds.Loss of CH4 proceeded at an energy greater than that calculated for the production of ionized but-2-ene, methylpropene, but-1-ene, or methylcyclopropane.The labeling experiments permitted the separation of the complex Gaussian-type metastable peak for CH4 loss into high and low kinetic energy release components, each appropriately relating to the generation of different daughter ions via competing mechanistic pathways.Large isotope effects were observed, similar in magnitude to those observed for the loss of methane from the methylpropane radical cation.Ethane elimination is preceded partially (ca. 20-25percent) by a 1-2 methyl shift and a concominant 2-1 H shift; isotope effects associated with this reaction are discussed. for pentane, losses of CH3* and CH4 take place at the same energy, corresponding to the calculated threshold for production of the secondary cations; 13C labeling experiments showed that the penultimate C atoms are not lost but that C-3 is lost (46percent) in these reactions, with an ease similar to terminal C atom losses (54percent).As with methylbutane, 2H labeling permitted the separation of the metastable peak for methane loss into components having different kinetic energy releases and attributable to the production of different (+*) daughter ions.Although C2H6 loss was observed to take place at energies down to the calculated thermochemical threshold for generation of ionized propene, the appearance energy of the metastable peak was the same as that for CH3* and CH4 losses.Labeling experiments showed that the central C atom is not lost in this reaction.Detailed analysis of the observations leads to the conclusion that the CH3*, CH4, and C2H6 eliminations from pentane radical cations are preceded by an isomerization to energy-rich ionized methylbutane.
