Showing papers by "Asher Mandelbaum published in 1987"
13 citations
TL;DR: In this article, low energy collision induced dissociation (CID) spectra indicate that m/z 173 [MI]+ ion formed by the loss of a halogen atom from diethyl chloro- and bromo-succinate under electron impact are mixtures of O-protonated species formed by hydrogen migration.
Abstract: Low energy collision induced dissociation (CID) spectra indicate that m/z 173 ions formed by the loss of a halogen atom from diethyl chloro- and bromo-succinate under electron impact are mixtures of O-protonated diethyl maleate (>90%) and fumarate (<10 %). Hydrogen migration precedes the C-halogen bond cleavage in these cases. The low energy CID spectrum of the m/z 173 [MI]+ ion obtained from diethyl iodosuccinate shows that only a small fraction of the [MI]+ ions are the O-protonated species formed by hydrogen migration. The results of this study demonstrate the potential of low energy CID in the determination of structure (including configuration) of gas phase ions.
8 citations
TL;DR: In this article, the fragmentation of the dimethyl and diethyl esters of maleic and fumaric acids have been studied as a function of the internal energy of the molecular ions using charge exchange techniques and metastable ion studies in combination with isotopic labelling.
Abstract: The fragmentation of the dimethyl and diethyl esters of maleic and fumaric acids have been studied as a function of the internal energy of the molecular ions using charge exchange techniques and metastable ion studies in combination with isotopic labelling. The dimethyl ester molecular ions show distinctive behaviours at both low and high internal energies, indicating that interconversion of the molecular ions does not occur. The fumarate molecular ion fragments by elimination of CH2O and (CO2 + CH3) in the metastable ion time-frame, while the maleate ester fragments primarily by loss of CH3O. At higher internal energies both molecular ions fragment primarily by loss of CH3O but the fragment ion from the maleate ester shows a greater stability, presumably because it assumes the cyclic cationated maleic anhydride structure. The diethyl maleate and diethyl fumarate molecular ions show identical metastable ion characteristics; in addition the [COS]+· charge exchange mass spectra are very similar. These results indicate that low-energy molecular ions interconvert. At higher internal energies interconversion does not occur, and, although both moiecular ions fragment by loss of C2H5O, the resultsint fragment ions show different stabilities and fragmentation reactions.
8 citations
TL;DR: The low energy CID mass spectra of m/z 173, C8H13O4+, obtained from the diethyl ester of cis,syn,cis-l,2,3,3a,4,5,5a,6,7,8,8a,9,10,10a-dodecahydrophenanthrene-9, 10-dicarboxylic acid indicate that the formation of this ion from both precursors takes place by migration of a hydrogen atom from an allylic �
Abstract: Low energy CID mass spectra of m/z 173, C8H13O4+, obtained from the diethyl ester of cis,syn,cis-l,2,3,3a,4,5,5a,6,7,8-decahydroindacene-4,5-dicarboxylic acid and cis,syn,cis-l,2,3,4,5,6,7,8,8a,9,10,10a-dodecahydrophenanthrene-9,10-dicarboxylic acid indicate they have the structure of protonated diethyl maleate. This finding together with previous deuterium labelling results suggest that the formation of this ion from both precursors takes place by migration of a hydrogen atom from an allylic δ-position followed by the concerted cleavage of two allylic CC bonds in analogy to the ground state retro-Diels–Alder fragmentation.
6 citations