共查询到20条相似文献,搜索用时 15 毫秒
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Ernst Pittenauer Günter Allmaier Erich R. Schmid Wolfgang Stanek Gottfried Heinisch 《Journal of mass spectrometry : JMS》1991,26(6):595-600
The mass spectrometric fragmentation behaviour of pyridazine and four monosubstituted derivatives containing a pbenylalkyl side-chain (3- and 4-benizylpyridazine, 3- and 4-(2-pbenylethyl)pyridazine) was investigated. In the electron impact ionization mess spectra of the 3-substituted compounds abundant [M – H]+ peaks are observed. This allows a clear distinction between 3- and 4-substituted pyridazines, as the spectra of the latter isomers show only very weak [M – H]+ signals. The stability of [M – H]+ ions derived from 3-alkylpyridazines (deduced from only the very low abundance of further fragment ions) gives strong evidence for a cyclic structure of these ions. One fragmentation pathway typical of the parent pyridazine, the [M - N2] fragmentation, was not detectable with any of the phenylalkylpyridazines investigated. Instead, loss of HCN, H3CN+ and N2H+ was observed. An interesting fragmentation, observed with 3-(2-phenylethyl)pyridazine, is the loss of +CH3 from the molecular ion and also from the [M – H]+ ion. 相似文献
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Tian Q Li D Barbacci D Schwartz SJ Patil BS 《Rapid communications in mass spectrometry : RCM》2003,17(22):2517-2522
Electron ionization (EI) mass spectrometry was used to differentiate four structurally closely related citrus limonoid aglycones, including limonin, nomilin, obacunone, and deacetylnomilin. The limonoids were isolated and purified from citrus seeds. Structures of major fragment ions were elucidated by high-resolution mass spectrometry (HRMS) and fragmentation pathways were proposed. The fragmentation patterns observed in the EI spectra can be used as important references for the positive characterization of limonoid aglycones. 相似文献
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Begala M Forni A Delogu G Podda G Prati F Torre G Tubaro M 《Rapid communications in mass spectrometry : RCM》2004,18(1):59-66
A series of cis- and trans-isomeric aziridines has been studied under electron impact (EI) and electrospray ionization (ESI) conditions. The fragmentation patterns of the examined compounds have been elucidated by means of sequential product ion fragmentation experiments (MS(n)) performed using an ion trap mass spectrometer. Particular attention has been paid to isomer characterization in these precursors of azetidinones, that in turn are precursors of new beta-lactam antibiotics. 相似文献
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Pentti Oksman Géza Stájer Kalevi Pihlaja Mati Karelson 《Journal of the American Society for Mass Spectrometry》1994,5(2):113-119
Electron impact ionization mass spectrometry indicates that the behavior of W-unsubstituted pyrirnidin-4-ones with CH2-R type substitution at C-2 differs from homologs that are N-substituted and/or 2-aryl- or 2-methyl-substituted. A dominant intramolecular cycliza-tion was found to occur between 3ZV (in agreement with the predominance of the 3NH tautomers) and the ortho positions of the aryl moiety in compounds with a CH2-aryl substitution at C-2. Theoretical calculations with an AMI SCFR method on 2-, 6-, and 2, 6-disubstituted pyrimidin-4-ones support the mass spectrometric observations. 相似文献
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A study of the fragmentation of l-methyl-3-(2-benzothiazolylhydrazono)-2-indolinones on electron impact reveals that the major processes involve N? N bond fission and the competing loss of CO from the molecular ion. 相似文献
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Electron ionization mass spectrometric study of 1,4-dihydro-4-substituted 2,6-dimethyl-3,5-bis(alkoxycarbonyl)pyridines 总被引:1,自引:0,他引:1
Salehi H Li Q Yin H Ding Y Guo Q 《Rapid communications in mass spectrometry : RCM》2004,18(24):3093-3098
Using the accurate masses obtained from a time-of-flight instrument and the tandem mass spectrometric (MS/MS) data from an ion trap instrument, electron ionization mass spectra of a series of 1,4-dihydro-4-substituted 2,6-dimethyl-3,5-bis(alkoxycarbonyl)pyridines are reported and rationalized. Two sets of fragmentation pathways are proposed. One involves the formation of fragment ions containing the 1,4-dihydropyridine structure, and the other of ions containing a pyridine ring. 相似文献
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The mass spectra of a series of substituted 3-methyl-4-benzylideneamine-5-styrylisoxazoles are reported and discussed. The spectra of these isoxazoles show a characteristic fragmentation pattern different from the 5-styryl-4-nitroisoxazoles. Perhaps this is due to the presence of the Schiff base at position 4. 相似文献
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The positive ion mass spectra of several chromium(III) β-diketonates with aliphatic α-substituents have been investigated. Metastable peaks in the spectra confirm that ions containing substituents with γ-H atoms undergo propene loss. This implies a McLafferty rearrangement of an open-chain ligand structure. Ethyl radicals are lost from n-butyl substituents; methyl groups are cleaved from the molecular ions of complexes formed from methyl-substituted ligands. The main fragment is, as expected, [ML2]+; however, its further fragmentation is different from that of [ML3]+. Electron donating substituents stabilize doubly charged molecular ions. 相似文献
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Ellen Inutan Sarah Trimpin 《Journal of the American Society for Mass Spectrometry》2010,21(7):1260-1264
A simple device is described for desolvation of highly charged matrix/analyte clusters produced by laser ablation leading
to multiply charged ions that are analyzed by ion mobility spectrometry-mass spectrometry. Thus, for example, highly charged
ions of ubiquitin and lysozyme are cleanly separated in the gas phase according to size and mass (shape and molecular weight)
as well as charge using Tri-Wave ion mobility technology coupled to mass spectrometry. This contribution confirms the mechanistic
argument that desolvation is necessary to produce multiply charged matrix-assisted laser desorption/ionization (MALDI) ions
and points to how these ions can be routinely formed on any atmospheric pressure mass spectrometer. 相似文献
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Leopoldo Ceraulo Paolo De Maria Antonella Fontana Sara Frascari Domenico Spinelli 《Journal of heterocyclic chemistry》1992,29(6):1657-1662
The study of the electron ionization mass spectra of 5-nitro-3-thiophenecarboxanilides 1-24 has shown peculiar effects induced by the 5-nitro group on the fragmentation of molecular ions M and the thenoyl cation a (Scheme 1). A comparison of the abundances of the important fragment ions for 5-nitro-3-thiophene-carboxanilides with those of the corresponding 3-thiophenecarboxanilides shows that the extent of C-N amide bond cleavage decreases in the former series as a consequence of the increased bond strength. The produced ion a does not eliminate carbon monoxide as 2- and 3-thenoyl cations usually do. Again this behaviour depends on the electronic effects of the nitro group which strongly destabilizes the 5-nitro-3-thienyl cation and consequently strengthens the carbon-3 carbonyl carbon bond. Recalling the behavior of the previously studied 2- and 3-thiophenecarboxanilides most of the 2′-substituted 5-nitro-3-thiophenecarboxanilides give loss of the ‘ortho’ substituent of the phenyl ring furnishing the cyclic ion g(Scheme 2). In the instance of 2′-alkyl substituted derivatives the formation of abundant ions h' by loss of 5-nitrothenoyl radical from M (Scheme 3) was observed, thus confirming the occurrence of a cryptic ‘ortho’ effect. The results are also discussed in relation to those obtained on some related benzoylanilides. 相似文献
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A compound associated with oxidized flavor in red wines was recently-identified as 3-methyl-2,4-nonanedione (MND). In order to quantify it, positive chemical ionization (PCI) in an ion trap was studied using conventional liquid reagents such as methanol, acetonitrile, and acetone, as well as non-conventional liquid reagents such as ethyl acetate, diethyl ether, pentane, isohexane, and heptane. Under laboratory conditions, very different response factors were obtained with MND depending on the gas. We also compared the detection limit of conventional CI with hybrid chemical ionization (HCI). Finally, this compound was quantified in red wines by liquid/liquid extraction without any derivatization steps, followed by GC/MS-CI analysis, using methanol as the reagent gas. Coelutions of compounds with the same m/z were checked using methanol-d(4). The method we developed was linear in the 10-300 ng/L range of MND concentrations, with satisfactory repeatability. The detection limit was 4.3 ng/L, over 3 times lower than the olfactory perception threshold of this compound (16 ng/L). The suitability of this method for assaying this diketone in red wine was demonstrated by the analyzing many wines from different vintages. 相似文献