Metastable Ion Studies. V. The Identification of C2H4O+ Ion Structures from their Characteristic Kinetic Energy Releases

Metastable ion peaks for the fragmentation C 2 H 4 O + • → C 2 H 3 O + + H • have been studied in the first field-free region of a double focussing mass spectrometer under conditions of good energy resolution. Three isomeric C 2 H 4 O + • ions were generated[Formula: see text] (b) CH 3 CHO + , and (c) CH 2 =CHOH + • from ethylene oxide, acetaldehyde, and ethyl vinyl ether respectively, each fragment producing a different 1 m* peak having a characteristic shape and kinetic energy release. The above ions do not therefore interconvert prior to fragmentation and their characteristic 1 m* peaks permit their unequivocal identification, thus providing a powerful method for ion structure determination.In agreement with some recent collisional activation data it was found that the unbranched aldehydes, cyclic alcohols, and 2-haloethanols investigated generated (c) type C 2 H 4 O + • ions. These are also produced by glycidol and α-furfuryl alcohol. Some compounds generated composite 1 m* peaks, e.g. 1,3-dioxolane produces (a) and (c) ions, while compounds which produce prominent C 2 H 5 O + ions having the protonated acetaldehyde structure, generate m/e 44 ions of structures (b) and (c). In isopropanol these components were separated by a deuterium labelling experiment. Contrary to earlier proposals, pyruvic acid does not generate (b) type ions but produces predominantly ions of structure (c).