On the loss of ethylene from [C3H7O]+ ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {{\rm CHOH}}\limits^{\rm + } $\end{document}

The results of some ³C and ²H labelling experiments plus some measurements of reaction thermochemistry and translational energy releases, permit a significant simplification of the mechanistic pathways by which C₃H₇O]⁺ ions of structure fragment by loss of C₂H₄. The relationships between these ions and some of their isomeric forms are explored and clarified.