AbstractThe loss of CH3˙ from the molecular ions of cyclohexene oxide and 5,6‐dihydro‐4‐methyl‐2H‐pyran has been investigated. On the basis of metastable peak shape analysis, collision‐induced dissociation/mass‐analysed ion kinetic energy spectra and thermochemical data it is concluded that the same [C5H7O]+ ion is formed in both cases.