The formation of the styryl ion in the mass spectra of cinnamyl compounds

The formation of the styryl ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm PhCH = }\mathop {\rm C}\limits^{\rm + } {\rm H} $\end{document} in the mass spectra of some cinnamic compounds is shown to occur via the intermediate formation of the cinnamoyl ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Ph} - {\rm CH} = {\rm CH} - {\rm C} \equiv \mathop {\rm O}\limits^{\rm + } $\end{document} rather than by direct cleavage of the bond α to the double bond.