The Collisionally Induced Dissociation of Allyl and 2-Propenyl Cations

Article abstract of DOI:10.1002/oms.1210181219

Pure (1+) and CH3C(1+)=CH2 ions are generated only in metastable fragmentations of ^1+., X=Cl, Br, I, and ^1+., X=Br, I, respectively.For ion source generated (1+) ions there is some structural interconversion.The structure characteristic feature of their collisional activation mass spectra is the ratio m/z 27 (¹⁺):m/z 26 (^1+.).For CH3C(1+)=CH2 the ratio is only weakly dependent upon the translational energy of the ion.For (1+), the ratio rises sharply as translational energy is reduced, from 0.9 at 8 kV to c. 3 at 1 kV. (1+) ions generated by charge reversal of (1-) show higher ratios, resulting from their lower average internal energy content.It must therefore be emphasized that (1+) ion structure assignments should only be made using reference data which apply to specific experimental conditions. (1+) daughter ion structures for a number of well-known fragmentations have been established.The heat of formation of the 2-propenyl cation was measured to be 969+/-5 kJ mol^-1.Labelling experiments show that at low internal energies, allyl cations do not undergo atom randomization in c. 1-2 μs; high internal energy ions of longer lifetime (c. 8 μs) show complete atom randomization.H¹⁺ atom loss from <13CH3CH=CH2>^+. has been shown to generate <13CH2CHCH2>(1+) and 13CH2=C(1+)-CH3 without any skeletal rearrangement.