O(-•) chemical ionization of carbonyl compounds.

The negative ion chemical ionization mass spectra of twentyeight C4 to C7 carbonyl compounds were recorded using the oxide radical anion O(-•) as reagent ion. As noted earlier, the reactions occurring include H(+) abstraction, H 2 (+•) abstraction, H- atom displacement, and alkyl radical displacement. In addition, the [M-2H](-) ions fragment further by alkyl radical elimination. The relative importance of these reactions depends strongly on molecular structure, with the result that isomer distinction frequently is possible. Where this is not possible, as for isomeric aldehydes, the collisional charge inversion mass spectra of common product ions provides isomer distinction. The H 2 (+•) abstraction reaction is shown to involve abstraction not only of two hydrogens from the same α-carbon but also, in part, abstraction of one hydrogen from each α-carbon.