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

The anion radicals CnOn-. (n = 3-6) can be generated by ionization of cycli c carbonyl compounds in the negative ion mode. The ions as well as the corr esponding neutral counterparts are probed by means of different mass spectr ometric techniques. The results suggest that oxocarbons, i.e. cyclic polyke tones, are formed under conservation of the skeletons of the precursor mole cules. At least for n = 3, however, the experimental findings indicate part ial rearrangement of the expected cyclopropanetrione structure to an oxycar boxylate 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 c yclopentanepentaone. (Int J Mass Spectrom 188 (1999) 17-25) (C) 1999 Elsevi er Science B.V.