O^−• chemical ionization of carbonyl compounds

Abstract

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.

Didehydro radical anions from ketones via O− chemical ionization

“…Marshall et al [25] allowed O •− to react with C 4 C 7 carbonyl compounds, in a hybrid BEqQ instrument, and reported the deprotonated ketone ([M-H] − ) to be the base peak, along with lesser amounts of [M-2H] •− and other ions, in their spectra. These qualitative reports demonstrate that radical anions can be synthesized through O •− chemistry.…”

O− and OH− chemical ionization of some fatty acid methyl esters and triacylglycerols

“…High-purity (99% by gas chromatography and thin-layer chromatography) fatty acid methyl esters and triacylglycerols were purchased from Sigma Chemical Co. (St. Louis, MO) and were used as received. Tables I and 2 6125 (10) 153 (12) 181 (14) 209 (20) 237 (20) 265 22263 (82) 263 (9) 263 (9) 261 (45) 259 {I 00) 259 (15) 291 (20) 291 (14) 291 (13) 291 (14) 289 (1(0) 287 (1(0) 287 (20) 287 (34) 115 (13) 143 (13) 171 (13) 199 (11) 227 (12) 255 (10) 283 (9) 281 (14) 281 (91 281 (8) 279 (8) 277 7277 (7) 309 (10) 309 (7) 309 (7) 309 7307 (8) 305 (6) 305 5 a nucleophile than OH-. One also should note that in the 0-' CI mass spectra the ratio increases substantially for unsaturated FAMES (to a value in the range 1.4-5.1).…”

“…Again, deuterium labeling would be useful, but is difficult. It is interesting to note that no [M -2H]-' ions are observed in the reaction of 0-' with the esters, although this is a significant reaction channel with many ketones [13].…”

“…In a continuation of our studies [12,13,18,20] of 0-' CI of organic molecules, we report here the 0-' CI mass spectra of a selection of fatty acid methyl esters (FAMES) and triacylglycerols. Because of the importance of fatty acids and their derivatives, such as lipids, in biological systems [Z'l], there have been many studies of the electron ionization (En and positive ion CI mass spectra of these classes of compounds [22][23][24][25][26][27], although suprisingly few studies in the negative ion field.…”

“…The oxide radical anion, 0-', is unusual among negative ion CI reagent ions in that not only is it a strong Br~nsted base, but also it is a radical. As a result, it reacts with many organic substrates, not only by proton abstraction, but also by H atom abstraction, by Hi' abstraction, and by H atom and alkyl radical displacement [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This variety of pathways creates the possibility that 0-' CI can provide more structural information than other negative ion reagents, and this has been demonstrated in a number of studies [8][9][10][11][12][13].…”