Routes of formation and decomposition of the m/z 59 ions with elemental composition C3H7O generated upon electron impact ionization of methyl propanoate

It is shown that the peaks at m/z 31, 29 and 15 in the mass-analyzed ion kinetic energy spectrum of the m/z 59 ions generated from methyl propanoate upon electron impact ionization originate from decompositions of m/z 59, i.e. C 2 H 3 O 2 + ions having the O=C=O + CH 3 structure, and of m/z 59, i.e. C 3 H 7 O + ions having the CH 3 CH=O+CH 3 structure. The latter ions contribute <1% to the total abundance of the m/z 59 ions in the standard mass spectrum. However, these m/z 59 C 3 H 7 O + ions are responsible for the relatively significant amounts of the m/z 31 and 29 ions generated in the microsecond time frame. Based upon deuterium labelling and supported by calculations at the ROHF/6-31G * level of theory, the m/z 59 C 3 H 7 O + ions are suggested to be formed via a complex skeletal rearrangement of the molecular ions of methyl propanoate and subsequent loss of a formyl radical.