bluuebunny/crossref_metadata_2025_split huggingface dataset:
Substituent effects in mass spectrometry—III: Substituent effects in the dissociation of the molecular ions of para and meta substituted benzoic acids
Authors: Benoit F. 
Published: May 2005

AbstractThe effect of substituents on the electron‐impact‐induced fragmentation of the molecular ions of para and meta substituted benzoic acids has been examined. The substituent is observed to exert an effect on the ionisation potential of the molecular ion, on the appearance potentials of the primary daughter ions and on the amount of H/D scrambling in the molecular ion of the carboxyl‐d1 analogues prior to the loss of hydroxyl therefrom. The energy of activation for the loss of hydroxyl from the molecular ion is in general dependent upon the nature but not the position of the substituent, while the amount of H/D scrambling in the molecular ion of the carboxyl‐d1 derivative is dependent upon both the nature and the position of the substituent. No correlation of the relative ion abundances with σ+ constants was observed. The results are consistent with the molecular ions of each compound having a dissimilar energy distribution, which could arise either by different energy transfers from the electron beam to the molecule or by the participation of different isolated electronic excited states (or similar states but to varying extents) in the dissociation of the molecular ions.
Field ionization mass spectrometry—IV. Isotopically labeled heptanals
Authors: Brown Peter , Fenselau Catherine 
Published: May 2005

AbstractThe field ionization (FI) mass spectra of n‐heptanal and a series of deuterium labeled analogs have been studied, with the objectives of initiating systematic investigations of reaction mechanisms of FI produced ions and to permit comprison with those found for other ionization processes. It is now recognized that FI ions have: (a) lower average internal energies and (b) shorter residence times than similar ions generated by electron‐impact (EI), and the possibility exists of H/D‐randomization occuring in ions formed by desorption from the emitter, by unimolecular decomposition close to the emitter and by either ‘fast’ or ‘slow’ metastable decompositions.In this study only the peak shifts of normal ions could be utilized; accurate mass measurements of all major ions revealed elemental compositions similar to EI. A site‐specific McLafferty rearrangement gave the base peak at m/e 44 ([C2H4O]+.), although the apparently complementary ion at m/e 70 ([C5H10]+.) arose in a less specific process. Ions at m/e 43 ([C3H7]+) and 71 ([C5H11]+ 80%; [C4H7O]+ 20%) were apparantly generated without significant H/D‐scrambling. Of special interest was the observation of the rearrangement ion at m/e 86 ([C5H10O]+.) caused by loss of C‐2 and C‐3 as C2H4, as found for EI.It is concluded that at least in this system, decomposing molecular ions formed: (a) in the gas phase extremely close to the emitter and/or (b) on the emitter surface, have lifetimes sufficiently short to preclude complete H/D randomization. The results also provide evidence for common fragmentation mechanisms for heptanal molecular ions at both the low end and the high end of the energy distribution.
Mass spectrometry of heterocyclic compounds—III. Electron‐impact‐induced fragmentation of 1,2‐benzisothiazole and some 3‐substituted derivatives
Authors: Selva Antonio , Gaetani Enrico 
Published: May 2005

AbstractThe mass spectra of fifteen 1,2‐benzisothiazoles are reported; their fragmentation patterns have been investigated by labelling experiments, high resolution mass measurements and defocused metastable ion detection. The parent compound of the series, 1,2‐benzisothiazole, eliminates HCN after partial inter‐ring hydrogen scrambling. The extent of scrambling has been determined for normal daughter ions produced at different electron beam energies and also for metastable daughter ions, and is compared with the data reported for benzothiazole. Some 3‐substituted derivatives show unusual fragmentation patterns. The mechanisms of these processes are under further investigation.
Mass spectrometry in structural and stereochemical problems—CCXXII: Delineation of competing fragmentation pathways of complex molecules from a study of metastable ion transitions of deuterated derivatives
Authors: Smith D. H. , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractData on defocused metastable ions have been obtained for a series of structurally significant fragment ions in the mass spectra of the estrogenic steroid, estrone methyl ether and the alkaloid tropine. These data, in conjunction with measurements on defocused metastable ions in the mass spectra of isotopically labeled analogs and complete high resolution mass spectra provide important insights into the details of fragmentation processes, specifically: (a) an enumeration and determination of the frequent multiple origins of fragment ions in the mass spectra of such complex molecules, (b) specification of skeletal atoms lost and retained in concerted (one step) processes, and at each step of stepwise processes, leading to a particular fragment ion and (c) information on the relative contributions of concerted and stepwise processes resulting in the genesis of a given ion.
High resolution mass spectrometry in molecular structure studies—V: The fragmentation of amaryllis alkaloids in the crinine series
Authors: Longevialle P. , Smith D. H. , Burlingame A. L. , Fales H. M. , Highet R. J. 
Published: May 2005

AbstractHigh resolution mass spectral fragmentation patterns of Amaryllidaceae alkaloids in the crinine series have been investigated as well as those of certain isotopically labeled derivatives. Attention is directed to the particular importance of employing entire high resolution mass spectra in attempting the elucidation of structural correlations in compounds which display few significant relative intensity variations in a complex fragmentation pattern.
Mass spectra of polymeric thioformaldehydes (CH2S)3, (CH2S)4, (CH2S)5 and (CH2S)x
Authors: Peach Michael E. , Weissflog Eckhard , Pelz Norbert 
Published: May 2005

AbstractThe mass spectral fragmentations of various thioformaldehydes, 1,3,5‐trithiacyclohexane, 1,3,5,7‐tetrathiacyclooctane, 1,3,5,7,9‐pentathiacyclodecane and a polymeric form (CH2S)x have been examined. The principal features of the spectra are reported. The fragmentation occurred by fracture of the ring in the cyclic compounds with or without rearrangement.
The analysis of mixtures: IV
Authors: Halket J. McK. , Reed R. I. 
Published: May 2005

AbstractThe analysis of mixtures has been re‐examined and extended. The results have been applied to several mixtures, including steroids, distilled from a direct insertion probe with promising results. An experimental scheme is described to enable the determination of the number of components in a mixture by two distinct methods. This work forms an early stage in a general mixtures analysis system.
Mass spectra ofSceletiumalkaloids
Authors: Martin Ned H. , Rosenthal David , Jeffs P. W. 
Published: May 2005

AbstractThe mass spectra of several naturally occuringSceletiumalkaloids, as well as several synthetic variants, have been investigated. Techniques used include high resolution mass measurements, analysis of metastable transitions by the technique of ion defocusing and specific deuterium labeling in conjunction with low resolution mass spectrometry. Characteristic major fragmentation pathways have been determined for four basic structure types studied: thecis‐3a‐aryl‐octahydroindole ring system, exemplified by mesembrine; its 2,3‐pyrido analog,SceletiumA4; thesecoseries of pyridine bases, represented by tortuosamine; and thesecoanalog of the mesembrine‐type represented by tortuosamine; and thesecoanalog of the mesembrine‐type represented by dehydrojoubertiamine.
Mass spectra of acyl and α‐hydroxyalkyl derivatives of biferrocene
Authors: Hisatome Masao , Ichida Shigeto , Yamakawa Koji 
Published: May 2005

AbstractThe mass spectral fragmentation pathways of acyl and α‐hydroxyalkyl derivatives of biferrocene and related compounds are presented. A substituent effect for the cleavage of the cyclopentadienyl ring‐metal bonds has been found in the spectra of acyl derivatives. It has been shown that the fragmentation of α‐hydroxyalkyl derivatives proceeded via the ions corresponding to the [M]+⋅ ions of oxidation or hydrogenolysis products of the hydroxyl derivatives.
Metastable ion studies. IX—Thermochemistry and ion structures among fragmentating ions, an electron impact and field ionization investigation
Authors: Holmes John L. , Weese Gwynneth M. , Blair Alan S. , Terlouw John K. 
Published: May 2005

AbstractMetastable peak shapes, dimensions and relative abundances have been measured for the fragmentations ions were generated from but 1‐ene, cis‐and trans‐ but‐2‐ene, 2‐methylpropene, methylcyclopropane and cyclobutane. Forward and reverse activation energies for the above reactions have been estimated and daughter ion structures proposed. The pathway for the consecutive reaction which generates the metastable peak (m/e 56 → m/e 53) is proposed to be
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Observations on metastable peaks for fourteen assorted daughter ion fragmentations are also presented and the thermochemistry and daughter ion structures for some of the reactions are discussed. Metastable peaks for the fragmentation of ions generated by field ionization are also described.
Notiz zur protonenkatalysierten Gasphasencyclisierung von N‐Benzoyl‐α‐aminosäremethylestern
Authors: Höfle Gerhard , Höhne Gerhard , Respondek Johannes , Schwarz Helmut 
Published: May 2005

AbstractArt und Anzahl der Alkylsubstituenten am α‐C‐Atom der Titelverbindungen beeinflußen in entscheidender Weise die durch chemische Ionisation induzierte Methanol‐Eliminierung aus den [M + H]+‐Ionen. Die Cyclisierungstendenz entspricht sehr stark der von aktivierten Estern in kondensierter Phase.
The mass spectrum of 2,4‐dihydroxybenzophenone oxime
Authors: Kallury R. Krishna Mohan Rao , Rao E. V. Suguna Bhushana 
Published: May 2005

Abstract2,4‐Dihydroxybenzophenone Oxime is found to undergo loss of OH·, H2O, NHOH·; and PhCNO when subjected to electron impact, revealing novel hydrogen and skeletal migrations. The fragmentation mechanisms are found to differ considerably from those of benzophenone oxime and we confirmed these cleavages by exact mass measurements and deuterium labelling.
Mass spectra of heterocyclic compounds. IV–2,4,5‐Trioxoimidazolidines
Authors: Corral Renée A. , Orazi Orfeo O. , Zinczuk Juan 
Published: May 2005

AbstractGeneral fragmentations induced by electron impact of twenty‐one examples of 2,4,5‐trioxoimidazolidines are rationalized with the aid of metastable transitions, high resolution measurements and deuterium and 18O labelling. The results can be used for the recognition of different types of derivatives.
Analogies Photochimiques. III—Diméthyl‐4,4 allyl‐2 Cyclohexanone. Elimination Inattendue de C2H4O et Perte de 15 Unités de Masse
Authors: Morizur Jean‐Pierre , Mercier Jacquelline , Niazi Riad 
Published: May 2005

AbstractLe spectre de masse de la diméthyl‐4,4 allyl‐2 cyclohexanone, présente un ion m/z 122 correspondant à l'élimination D'une molécule D'acétaldéhyde à partir de l'ion moléculaire. Le marquage isotopique montre que quatre atomes D'hydrogène sont tranférés lors de cette élimination. L'ion moléculaire de la diméthyl‐4,4 allyl‐2 cyclohexanone perd également 15 unités de masse à partir du substituant allyle. Les mécanismes sont discutés en analogie avec le comportment photochimique.
Mass spectral identification of isomeric fluoronitroanilines
Authors: Fu Emil W. , Rosenberg Ira E. 
Published: May 2005

AbstractThe electron impact and methane chemical ionization mass spectra of 2‐fluoro‐5‐nitroaniline and 4‐fluoro‐3‐nitroaniline have been investigated. Similar fragment ions were observed for both compounds under electron impact conditions, but the difference in the relative ion intensities of two key fragment ions allowed the positive identification of these two isomers. The difference can be attributed to an ortho effect involving fluorine and the amino substituent. A fragmentation pathway consistent with this observation is suggested.
Electron impact fragmentations of 1‐ and 3‐aryl‐3‐buten‐1‐ols
Authors: Smith Grant Gill , Voorhees Kent J. 
Published: May 2005

AbstractThe electron impact fragmentation of 1‐ and 3‐aryl‐3‐buten‐1‐ols show several distinguishing fragmentations. α‐Cleavage predominates in the fragmentation of the 1‐aryl‐3‐buten‐1‐ols to such an extent that molecular ions of only low intensity are observed. The ion resulting from α‐cleavage fragments readily with the loss of the ring substituent to the phenyl ion. An intense molecular ion is observed in the 3‐aryl series and a loss of 70 u is a major fragmentation in this series. Based on deuterium labeling studies, this unique fragmentation was explained by a hydroxylic hydrogen migration to the ring accompanied by the loss of allene and formaldehyde. Other major fragmentations observed in the 3‐aryl series are: a McLafferty‐type rearrangement (loss of formaldehyde), loss of 33 u (water + methyl radical), and the loss of 43 u (C2H3O and C3H7). The proposed mechanisms have been substantiated by deuterium labeling and high resolution mass spectrometry. Substituent effects play a major role in the 3‐aryl series, but are insignificant in the 1‐aryl series.
Structure and fragmentation of [C3H7O]+ ions formed by chemical ionization
Authors: Harrison Alex. G. , Gäumann Tino , Stahl Daniel 
Published: May 2005

AbstractThe unimolecular metastable and collision‐induced fragmentation reactions of [C3H7O]+ ions produced by gas‐phase protonation of acetone, propanal, propylene oxide, oxetan and allyl alcohol have been studied. The CID studies show that protonation of acetone and allyl alcohol yield different stable ions with distinct structures while protonation of propanal or propylene oxide yield [C3H7O]+ ions of the same structure. Protonated oxetan rearranges less readily to give the same structure(s) as protonated propanal and propylene oxide. The [C3H7O]+ ions fragmenting as metastable ions after formation by CI have a higher internal energy than the same ions fragmenting after formation by EI. Deuteronation of the C3H6O isomers using CD4 reagent gas shows that loss of C2H3D proceeds by a different mechanism than loss of C2H4. The results are discussed in terms of potential energy profile for the [C3H7O]+˙ system proposed earlier.
Metastable and collision induced fragmentation of some small cluster ions: Ar2+ Ar3+, ArN2+ and N4+
Authors: Illies Andreas J. , Bowers Michael T. 
Published: May 2005

AbstractThe results of a study on collision induced dissociation and a search for metastable reactions of four gas phase ion‐molecule clusters, Ar2+, Ar3+, ArN2+ and N4+, are presented. The ionic clusters were formed in a high pressure mass spectrometer ion source which was cooled to enhance the association products. Subsequent fragmentations were studied using mass analyzed ion kinetic energy spectrometry. Decomposition pathways consistent with experimental collision induced dissociation peak shapes and ab initio potential diagrams are presented for the fragmentation of Ar2+ and N4+. Mechanisms for the collision induced dissociation of Ar3+ and ArN2+ are suggested. No metastable reactions for any of the cluster ions were observed. This result is in conflict with the results of Märk et al. using electron impact ionization of neutral van der Waals' clusters formed in a supersonic nozzle beam.
Scanning a triple quadrupole mass spectrometer for doubly charged ions
Authors: Kenttämaa H. I. , Wood K. V. , Busch K. L. , Cooks R. G. 
Published: May 2005

AbstractCharge exchange reactions within a triple quadrupole mass spectrometer characterize doubly charged ions formed in the ion source. Two methods have been developed for identifying the singly charged ions formed from doubly charged ions by charge exchange in the collision quadrupole. The first is based on the characteristically high kinetic energy‐to‐charge ratios of the products of charge exchange; this property can be used to separate these ions from all other singly charged ions. This retarding potential method is analogous to procedures for recording doubly charged ion mass spectra using sector instruments. The second method is based on the fact that, although mass remains constant in the charge exchange reaction, the change in mass‐to‐charge ratio can be followed. A charge exchange linked scan, predicated on changes in charge rather than mass, but otherwise analogous to neutral loss/gain scans, is described. Information on the structure of doubly charged ions can be obtained by recording the fragmentation products of dissociative charge exchange. The utility of the charge exchange linked scan for the selective identification of polynuclear aromatic compounds in a complex mixture is described. The methods given can be generalized to cover other charge permutation reactions.
Peptide sequencing by metastable mapping
Authors: Farncombe Martin J. , Jennings Keith R. , Mason Rod S. , Schlunegger Urs P. 
Published: May 2005

AbstractThe amino acid sequence of three simple peptides has been determined by the technique of metastable mapping. The products of decompositions in the first field free region of a forward geometry double focussing mass spectrometer are studied by decreasing the electric sector field between scans of the magnetic field.
Studies in chemical ionization mass spectrometry 10—CI(CH3NH2) spectra of olefins
Authors: Budzikiewicz H. , Laufenberg G. , Brauner A. 
Published: May 2005

AbstractBoth alkenes and cyloalkenes react with [CH3NH2]+˙. The possibilities and limitations of CI(CH3NH2) for the identification of structural isomers and for the determination of double bond positions are discussed. The quasi‐molecular ions [M+CH3NH2]+˙ are shown to fragment in a manner observed for amines under MIKE conditions rather than at 70 eVelectron impact, which suggests that one is dealing with long‐lived low‐energy species.
Characterization of and energy deposition in [C2H4O2]+˙ ions using energy‐resolved mass spectrometry
Authors: Jiang Y.‐X. , Wood K. V. , Cooks R. G. 
Published: May 2005

AbstractEnergy‐resolved mass spectrometry (ERMS) has been used to distinguish [C2H4O2]+˙ ions generated from seven precursor molecules. The low collision energy ERMS data confirm conclusions reached from previous high‐energy experiments; all seven ions have different structures or mixtures of structures. Structural distinctions are at least as easy to make using the two‐dimensional ERMS data as through collisional activation at high energy. The average internal energy deposited in low‐energy collisions (30 eV) is shown to be similar to the internal energy deposited at 8 keV in these systems.
Interference peaks in collisional activation mass spectra: The loss of CH3˙ from [C13H9] ions
Authors: Holzmann Gerhard , Terlouw Johan K. , Hop Cornelis E. C. A. , Burgers Peter C. 
Published: May 2005

AbstractIt was concluded from earlier metastable ion and collisional activation experiments that [C13H9]+ ions generated by dissociative ionization of stilbenes and diphenylmethane consist of a mixture of isomeric structures. It is shown in this paper that the methyl loss upon which this conclusion rests originates to a large extent from metastable molecular ions decomposing in the magnetic sector field (interference signal). Our results do not show, nor do they require, that more than one isomeric [C13H9]+ species is present. The importance of recognizing such interference signals is stressed.
Chemical ionization mass spectrometry with amines as reactant gases. I—amine chemical ionization mass spectrometry of flavonoid aglycones
Authors: Bankova V. S. , Mollova N. N. , Popov S. S. 
Published: May 2005

AbstractChemical ionization mass spectrometry of 34 flavones, isoflavones, flavanones, chalcones and aurones with aliphatic amines and ammonia as reactant gases have been investigated. Some unusual ions have been obtained and are discussed. This method can be used to determine the type of flavonoid and the location of some functional groups in the molecule.
Translational energy release and stereochemistry of steroids. VII—the loss of angular methyl groups after the dehydration of molecular ions of cholesterol and related C(5)‐unsaturated 3β‐hydroxy steroids
Authors: Zaretskii Z. V. I. , Kustanovich Z. , Kingston E. E. , Beynon J. H. , Djerassi Carl , Tökes L. 
Published: May 2005

AbstractThe translational energy, T, released during the loss of the angular 18‐ and 19‐methyl groups both from metastable molecular ions and metastable [M  H2O]+ and [M  2H2O]+ ions, in C(5)‐unsaturated mono‐and di‐hydroxy steroids, as well as in their 19‐nor and deuterated analogues bearing the label in the 19‐methyl group, has been measured. It was found that, while the T values for the 19‐CH3 loss, following the dehydration of the molecular ions, are increased substantially when compared to those for the same loss from the molecular ions, the T values for the 18‐CH3 loss are increased much more moderately. Nevertheless, the amounts of translational energy released in the [M  H2O]+˙  18‐CH3˙ and [M  2 H2O]+˙  18‐CH3˙ transitions are still higher than those found for the respective 19‐methyl loss, in accordance with the general rule established recently.
Sensitivity of charge transfer reactions to hydrocarbon ion structures
Authors: Shields G. C. , Wennberg L. , Wilcox J. B. , Moran T. F. 
Published: May 2005

AbstractCharge transfer reactivities of hydrocarbon ions have been measured with time‐of‐flight techniques, and results correlated with theoretical structures computed by self‐consistent field molecular orbital methods. Recombination energies, ion structures, heats of formation, reaction energetics and relative charge transfer cross‐sections are presented for molecular and fragment ions produced by electron bombardment ionization of CH4, C2H4, C2H6, C3H8 and C4H10 molecules. Even‐electron bridged cations have low ion recombination energies and relatively low charge transfer cross‐sections as compared with odd‐electron hydrocarbon cations.
Ion‐molecule reactions observed for nitroaromatic compounds in negative ion fast atom bombardment mass spectrometry
Authors: Balasanmugam Kesagapillai , Miller Jack M. , Smith Richard W. 
Published: May 2005

AbstractAnalyses of a series of nitroaromatic compounds using fast atom bombardment (FAB) mass spectrometry are discussed. An interesting ion‐molecule reaction leading to [M + O − H]− ions is observed in the negative ion FAB spectra. Evidence from linked‐scan and collision‐induced dissociation spectra proved that [M + O − H]− ions are produced by the following reaction: M + NO2− → [M + NO2]− → [M + O − H]−. These experiments also showed that M−˙ ions are produced in part by the exchange of an electron between M and NO2− species. All samples showed M−˙, [M − H]− or both ions in their negative ion FAB spectra. Not all analytes studied showed either [M + H]+ and/or M+˙ in the positive ion FAB spectra. No M+˙ ions were observed for ions having ionization energies above ∼9 eV.
Mass spectrometry of bis‐quinolizidine alkaloids: 13‐keto and hydroxy substituted derivatives of sparteine and lupanine
Authors: Wyrzykiewicz E. , Wysocka W. , Wiewiórowski M. 
Published: May 2005

AbstractThe mass spectral fragmeutations of 13‐ketosparteine, 13‐hydroxysparteine, 13‐epihydroxysparteine, 13‐ketolupanine, 13‐keto‐α‐isolupanine, 13‐hydroxylupanine, 13‐hydroxy‐α‐isolupanine, 13‐epihydroxylupanine and 13‐epihydroxy‐α‐isolupanine are reinvestigated and discussed. Fragmentation pathways, elucidation of which was assisted by accurate mass measuiements and metastable transitions, are proposed. The fragmentation assignments are not consistent with those previously reported in the literature. Many fragment species of the same m/z (low‐resolution spectra) are composed of two fragment ions of different elemental compositions (high‐resolution spectra). The obtained data create a safe basis for distinguishing structural and stereoisomers.