The unimolecular metastable ion and collision-induced dissociation (CID) fragmentation reactions of protonated and methylated monoamides, monomethyl esters and methyl esters of the monoamides of maleic and fumaric acids were studied. In addition, some studies of the fragmentation of protonated and methylated maleic and fumaric acids were carried out. The ions derived from protonated maleic and fumaric acids show distinctly
mass spectra, that for the ion from the maleic acid being the same as that of [ MH Ô H 2 O ] ' protonated maleic anhydride ; the results show that the stereochemistry about the double bond is retained in the ions. Fragmentation of speciÐcally deuterium-labelled and protonated or deuterated maleic acids [ MH Ô H 2 O ] ' show that the added proton becomes scrambled with the carboxylic hydrogens prior to loss of The fragmen-H 2 O. tation of similarly labelled fumaric acids show that a 1,3-H' migration followed by elimination of is not the H 2 O only pathway to water elimination ; the results implicate proton migration from one carboxyl group to the other as well as some involvement of the C-bonded hydrogens in the water-loss reaction. A major fragmentation reaction of protonated maleamic acid forms this reaction is of only minor importance for protonated fumamic acid. NH 4 ' ; Other primary fragmentation reactions involve elimination of and from the protonated species. The NH 3 H 2 O protonated monomethyl esters fragment initially by loss of or loss of the former is more prominent H 2 O C H 3 OH ; for the maleate whereas the latter dominates for the fumarate. Protonation of methyl maleamate and methyl fumamate results in loss of or as primary fragmentation reactions ; these primary fragment ions NH 3 CH 3 OH undergo less facile further fragmentation for the maleamate than for the fumamate. The adducts of the CH 3 ' monoamides fragment by loss of and the CID spectra of the adducts are distinctly di †erent NH 3 , H 2 O CH 3 OH ; from those of the protonated methyl esters of the monoamides, indicating predominant addition of the methyl to the amide oxygen. The adduct of monomethyl maleate fragments primarily by loss of methanol, the two CH 3 ' methyl groups having become equivalent prior to fragmentation. A minor fragmentation route involves loss of dimethyl ether, a reaction not observed for protonated dimethyl maleate. Elimination of dimethyl ether is a major fragmentation channel for the adduct of monomethyl fumarate. Since this reaction channel is not observed CH 3 ' for protonated dimethyl fumarate, the results indicate predominant addition to the carbomethoxy group of CH 3 ' the monoester.