Mass spectrometric studies of the oxocarbons CnOn (n=3-6)

The anion radicals CnOn-. (n = 3-6) can be generated by ionization of cyclic carbonyl compounds in the negative ion mode. The ions as well as the corresponding neutral counterparts are probed by means of different mass spectrometric techniques. The results suggest that oxocarbons, i.e. cyclic polyketones, are formed under conservation of the skeletons of the precursor molecules. At least for n = 3, however, the experimental findings indicate partial rearrangement of the expected cyclopropanetrione structure to an oxycarboxylate for the anion, i.e. O-.-C=C-CO2-. For n = 4 and 6 almost complete dissociation of the neutral polyones into carbon monoxide is found, whereas for n = 5 a distinct recovery signal indicates the generation of genuine cyclopentanepentaone.