In the cell of a Fourier transform ion cyclotron resonance mass spectromete
r, the reactions of C3H6O+. (m/z 58) isomer ions CH3OCHCH2+. (1) and (CH2CH
2OCH2+)-C-. (2) with selected neutral molecules serve to distinguish clearl
y between these structures. It is shown that, contrary to earlier assumptio
ns, the m/z 58 ions formed by fragmentation of 1,4-dioxane(+.) do not corre
spond to a single structure. The main component corresponds to structure 2,
but structure 1 is also present to the extent of about 7%, The mechanism o
f fragmentation is discussed.