Low energy acetoin ions CH3C(O)C(H)(OH)CH3.+ decompose to CH3CO. and CH3CHOH+ via a remarkable “hidden rearrangement”

Tandem mass spectrometry based experiments on D and 18O labelled acetoin isotopomers show that the title reaction is not just a simple bond cleavage, but rather involves rearrangement via ion—dipole complexes; the intermediacy of a charge-transfer complex is proposed to account for the observed product ratios.