Isomerization of hydrocarbon ions. VI—parameters determining the isomerization of aliphatic hydrocarbon ions

The radical or non-radical character of aliphatic hydrocarbon ions determines the extent to which these ions equilibrate to a mixture of interconverting structures prior to decomposition. It is suggested that the radical (odd electron) ions have both lower thresholds for decomposition and higher barriers for isomerization that non-radical (even electron) ions, thus explaining their reduced tendency for isomerization. Moreover, the molecular size seems to be a major influencing factor for the isomerization of unsaturated hydrocarbon molecular ions. With decreasing molecular size isomerization prior to decomposition becomes more pronounced. Collisional activation spectra of fragment ions (formed by loss of H₂O from the corresponding alcohols) and of C₅H₁₀]⁺ and C₄H₈]⁺ molecular ions are reported in support of these conclusions.