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

Abstract

Metastable ion peaks for the fragmentation C2H4O+ • → C2H3O+ + H• have been studied in the first field-free region of a double focussing mass spectrometer under conditions of good energy resolution. Three isomeric C2H4O+ • ions were generated[Formula: see text] (b) CH3CHO+, and (c) CH2=CHOH+ • from ethylene oxide, acetaldehyde, and ethyl vinyl ether respectively, each fragment producing a different 1m* peak having a characteristic shape and kinetic energy release. The above ions do not therefore interconvert prior to fragmentation and their characteristic 1m* 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 C2H4O+ • ions. These are also produced by glycidol and α-furfuryl alcohol. Some compounds generated composite 1m* peaks, e.g. 1,3-dioxolane produces (a) and (c) ions, while compounds which produce prominent C2H5O+ 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).