Phenol and live acydic isollleric compounds have been investigated using electron impact and 6eld ionization tedmiqms, mass panlysed ion kinetic energy spectrometry and dlision induced dissociation mass analysed ion kinetic energy speehometry. The ldnetic energy release data corresponding to the elimination of earbon monoxide from the molecular ions sbow that at least two stmetmes of the reactant ion are involved. The electron impact and h i d ionization coilision induced dissociation mass analysed ion kinetic energy spectra indicate that d e r eleetron impact conditions, the phenol ion partially isomerizes to another ion stroctnre. An isomerization of about 40% to the stroctme of cfs-2-hexen-4-p-l-ai is in good accordance with the spectral data.