bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds—VI. Perfluoroaromatic heterocyclic derivatives of sulfur, selenium and tellurium
Authors: Cohen S. C. , Massey A. G. , Lanthier G. F. , Miller J. M. 
Published: May 2005

AbstractThe mass spectra of the compounds C12F8M2 (M = S, Se), (I), C12F8M (M = S, Se, Te), (II) and C12F8SX2 (X = Br, I), (III), have been measured. Results indicate that sulfur‐carbon bonds are more stable under electron bombardment than either selenium‐carbon or tellurium‐carbon bonds. Numerous metastable‐supported transitions are evident, which are incorporated into comprehensive fragmentation schemes for these compounds. Many metastable transitions, not previously reported, were observed for the fluorocarbon fragments and a fragmentation scheme is reported.The bromine and iodine‐containing compounds behave remarkably like the heterocyclic systems, I and II, presumably due to initial loss of Br2 or I2 to form a ring system of type II.
The extent of electron‐impact‐induced ring contraction in the formation of [M − CH3] fragments from N‐acetylpiperidine
Authors: Richter W. J. , Liehr J. G. , Burlingame A. L. 
Published: May 2005

AbstractIn N‐acetylpiperidine, α‐carbon atoms (C‐2 or C‐6) of the ring have been recently identified as a source of loss of CH3 radicals from the molecular ion in addition to β‐carbon atoms (C‐3 or C‐5) and the acyl substituent (C‐8). Skeletal rearrangement by ring contraction to a five‐membered cyclic intermediate was invoked to be responsible for the expulsion of C‐2 or C‐6. Deuterium labelling suggested major and approximately equal contributions from the two losses of ring atoms as compared to an only minor contribution from loss of C‐8. 13C‐labelling of the latter now establishes the correctness of this inference, demonstrating that only 17% of the total loss of methyl arise from this position. Together with results of previous deuterium labelling this figure indicates that ring contraction contributes to the formation of [M − CH3] fragments to an extent of approximately 40%.
The mass spectra of some phenyl pyridyl ketones
Authors: Brown Ellis V. , Shambhu M. B. 
Published: May 2005

AbstractThe mass spectra of phenyl 2‐pyridyl, phenyl 3‐methoxy‐2‐pyridyl, phenyl 4‐methoxy‐2‐pyridyl, phenyl 5‐methoxy‐2‐pyridyl, phenyl 6‐methoxy‐2‐pyridyl ketones, phenyl 3‐pyridyl and phenyl 6‐methoxy‐3‐pyridyl ketones, and phenyl 4‐pyridyl ketone were studied. The major fragmentation pathway of all the ketones results in the formation of[C6H5CO]+ and [C5H4NCO]+ type ions. Another fragmentation path is the loss of carbon monoxide with formation of an [M  CO]+ ion after skeletal rearrangement.
Effets Isotopiques dans la Fragmentation par Impact Électronique de Méthanols Deutériés
Authors: Corval M. , Masclet P. 
Published: May 2005

AbstractLes spectres de masse des méthanols CH3OH, CH2DOH, CHD2OH, CD3OH, CH3OD et CD3OD ont été enregistrés pour des énergies nominales des électrons allant de 11 à 35 eV. Les courbes qui représentent la variation, en fonction de l'negie des électrons, des effets d'isotopie relatifs à la stabilité des ions moléculaires et aux probabilités de coupure des liaisons sont comparées à celles déerminées par un calcul a priori. En adoptant une fonction simple de distribution de l'énergie d'excitation et un nombre d'oscillateurs moitié du nombre thérique, l'accord obtenu est dans l'ensemble satisfaisant, sauf en ce qui concerne la stabilité des ions moléculaires, pour laquelle la forme des courbes pourrait s'interpréter par l'intervention d'un état électronique de l'ion moléculaire autre que l'éat fondamental.
Mass spectrometry of 2‐arylaziridin‐2‐ylphosphonates
Authors: Nishiwaki Tarozaemon 
Published: May 2005

AbstractThe mass spectral fragmentations of 2‐arylaziridin‐2‐ylphosphonates having a carbonyl function at C(3) were studied. Cleavage of either a carbonyl group or PO(OR)2 from the molecular ion is the primary pathway.
Mass spectrometric characterization of pGlu‐peptides related to the thyrotropin releasing hormone
Authors: Bogentoft Conny , Chang Jaw‐Kang , Sievertsson Hans , Currie Bruce , Folkers Karl 
Published: May 2005

AbstractTwelve synthetic di‐ and tripeptides which are related to the thyrotropin releasing hormone (TRH) have been subjected to electron‐impact without conversion to more volatile derivatives as background for structural elucidation of unknown peptides isolated on a microgram basis.
The doubly‐charged ion mass spectra of hydrocarbons
Authors: Ast T. , Beynon J. H. , Cooks R. G. 
Published: May 2005

AbstractThe doubly‐charged ion mass spectra of some hydrocarbons, including a variety of structural types, have been obtained by a new technique in which doubly‐charged ions are charge exchanged with neutral molecules and so separated from singly‐charged ions. The spectra show strong similarities, independent of hydrocarbon structure; characteristic ions include [CmH2]++ (m = 2 to 5), [CnH6]++(n > 6), [C10H8]++, [C12H8]++, [C11H10]++, [C7H7]++·, [C9H7]++· and [C13H11]++·. The fragmentation pattern of 2‐phenylnaphthalene has been reconstructed, based on observed reactions of metastable doubly‐charged ions to give fragment doubly‐charged ions. In addition, we examined metastable ion fragmentations leading to two singly‐charged ions for some of the characteristic ions, using several compounds. The value of doubly‐charged ion mass spectra of hydrocarbons appears to lie in the information they provide on ion structures; this information was sufficient to permit the proposal of structures for the major ions encountered in this study.
Comparative studies of electron‐impact (EI) and field ionization (FI) mass spectra of pentaerythritol derivatives
Authors: Tou James C. 
Published: May 2005

AbstractThe EI Mass spectra of the polyfunctional pentaerythritol derivatives show that the molecular ions [M]+· exhibit extensive ion fragmentation. No Information about [M]+·. can be obtained. In Contrast to this, the FI Mass spectra of these compounds show intense [M]+· and/or [M + 1]+, and a characteristic ion at m/e 31, which is assumed to be the oxonium ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_2 = \mathop {\rm O}\limits^ + {\rm H} $\end{document}. Because of surface adsorption and field attraction, FI mass spectrometry presents a serious problem in quantitative analysis of a mixture containing compounds with quite different degrees of polarization.
Valence‐change in the mass spectra of metal complexes
Authors: Lacey M. J. , Shannon J. S. 
Published: May 2005

AbstractA review article is presented relating to the concept of valence‐change in the mass spectra of metal‐containing compounds. It is found that the modes of ion dissociation in these spectra are markedly dependent on the oxidation states normally assumed by the metal concerned and it is postulated that electron‐transfer may be possible between the complexed metal atom and its ligands in the ion, such that the odd‐ or even‐electron character of the ion is inter‐changeable. Ion reactions such as the consecutive loss of two radicals are normally of low probability in the mass spectra of organic compounds, but are often observed in the mass spectra of metal‐containing compounds and can be rationalized in terms of the valence‐change concept. Convincing evidence for valence‐change in some spectra is provided by the occurrence of reactions leading to the bare metal ion, or to the loss of neutral fragments containing the metal atom in a lower oxidation state than in the precursor molecule. Further applications of the concept may be found in the rationalization of the mass spectra of inorganic and organometallic compounds.
The mass spectra of the trimethylsilyl ethers of some hydroxylated di‐ and tetracarboxylic porphyrins
Authors: Chapman J. R. , Elder G. H. 
Published: May 2005

AbstractThe preparation and the mass spectra of the trimethylsilyl ethers of six hydroxyporphyrins are reported. In every case the side chain bearing the ether grouping is the most labile on electron‐impact and exhibits characteristic ‘benzylic’ cleavage. The presence of a metastable peak allows a definite identification of this cleavage to be made.
Electron‐impact induced fragmentation of dimethanonaphthalene‐type compounds
Authors: Malojčić R. , Stefanović D. 
Published: May 2005

AbstractThe mass spectra of endo,endo‐1,2,3,4,4a,5,8,8a‐octahydro‐1,4:5,8‐dimethanonaphthalen‐anti‐2‐01 (Ia) and its endo,exo‐2‐ol (IIa) and endo,exo‐10‐ol (IIIa) isomers have been examined. Fragmentation schemes have been constructed on the basis of metastable transition measurements, accurate mass determination and deuterium substitution. A presence of the double bond in the molecule and a favourable hydrogen atom orientation in the vicinity of the double bond play an important role in the ion degradation process.
Mass spectra of some azoles
Authors: Cotter J. L. 
Published: May 2005

AbstractThe principal electron‐impact fragmentation patterns of 3,4,5‐triphenyl‐1,2,4‐triazole, 2,5‐diphenyl‐1,3,4‐thiadiazole, their perfluorinated analogues and 2,5‐di(pentafluorophenyl)‐1,3,4‐oxadiazole have been established from metastable ion evidence and precise mass measurements. Although ions produced by expulsion of nitrogen from the molecular‐ions of these compounds are of low abundance, the simultaneous expulsion of nitrogen and a C7X5 radical (X = H or F) gives rise to abundant ions.
The mass spectra of five diacetyl[3]ferrocenophanes
Authors: Carroll Sammy R. , Pflug J. Lloyd , Winstead Jack A. 
Published: May 2005

AbstractA mass spectrometric study of five diacetyl[3]ferrocenophanes has been made. The molecular ion was the base peak in these five compounds. Fragment ions with relative intensities greater than 10 percent occurred only in those compounds having an acetyl group in the alpha position to the trimethylene bridge.
On the nature of the transition state leading to elimination of ketene from acetanilide
Authors: Hammerum Steen , Tomer Kenneth B. 
Published: May 2005

AbstractExamination of metastable peak abundance ratios for the elimination of HNC vs. DNC from the [M‐ketene]+· ion of various deuterium‐labeled acetanilides shows that the structure of this ion resembles aniline rather than cyclohexadieneimine. This is suggested to hold also for substituted acetanilides.
On the positional interchange of the phenyl‐ and hydroxyl groups in the [C9H11O]+‐ion, generated from 2‐methyl‐2‐phenylpropane‐1,3‐diol (C10H14O2) upon electron‐impact
Authors: Kerkhoff M. A. Th. , Nibbering N. M. M. 
Published: May 2005

AbstractIt is shown by deuterium‐labelling experiments, that a substantial part of the [M – CH2OH]+‐ions from 2‐methyl‐2‐phenyl‐propane‐1,3‐diol must have rearranged to carbonyl‐oxygen protonated phenylacetone by a positional interchange of the phenyl‐ and hydroxyl groups prior to decomposition.
Kinetic energy release in ionic fragmentations: Use as an ion structure probe
Authors: Jones E. G. , Bauman L. E. , Beynon J. H. , Cooks R. G. 
Published: May 2005

AbstractThe kinetic energy released in unimolecular reactions, as measured from the width of the corresponding metastable peak, shows only a small dependence on such parameters as source temperature, ion‐source residence time and ion acceleration voltage. Similarly, fragmenting ions generated from different members of an homologous series of molecular ions have been found to release the same kinetic energy and hence do not exhibit a degrees‐of‐freedom effect analogous to that for metastable abundances. In general, molecular ions formed by electron‐impact have been found to release slightly less kinetic energy on fragmentation than the corresponding ions formed via a fragmentation sequence. These observations suggest that kinetic energy release is a useful method of structural characterization of metastable ions; while increase in the average internal energies of the ions sample lead to larger energy releases, this effect is usually small. The use of a very narrow energy resolving (β) slit and a procedure in which the metastable peak width is extrapolated to zero slit width has been found to improve the accuracy of measurement of the kinetic energy release, particularly when the metastable and main beam peak widths are of comparable magnitude.
Spectres de masse des anomeres pyranniques et furanniques de la thymidine, de leurs acetates et des bromohydrines correspondantes
Authors: Ulrich J. , Cadet J. , Teoule R 
Published: May 2005

AbstractL'étude du spectre de masse des anomères pyranniques et furanniques de la thymidine, de leurs acétates et des bromohyrines correspondantes apporte des informations, intéressantes pour l'analyse de al configuration anomérique de ce type de composés, décisives pour la dimension de l'hétérocycle oxygéné.La stabilité des ions molécularies va de pair avec la stabilité chimique de ces molécules: les ions moléculaires des formes β sont plus ceux des formes α. L'instabilité des ions moléculaires des bromohydrines est telle qu'ils ne sont détectables que pour la forme β furannique.L'elimination du radical CH2OH ou CH2OAc est caractéristique de la forme furannique. L'élimination de CH2O dans la forme β furannique est due à la proximité stérique de la base et de l'hydroxyle en 5′ du sucre. Les ions de rearrangement [BH  CHCH2]+ et dérivés proviennent d'und rupture du sucre favorisée dans la forme furannique.Après cassure de la liaison glycosidique, les ions [B + H]+˙ et [B + 2H]+ formés sur la base, et [S]+ sont sensibles à la stéréochimie de la molécule. L'´elimination d'une molécule d'eau (ou d'acide ac´etique) est mormalement plus facile dans un cycle à 6 chaînons (pyrannique).L'élimination simultance de 2 molécules d'eau ou d'acide acétique, prépondérante dans la forme furannique, nous a conduit à conduit à admettre und rupture du cycle pour former un ion à sttructure aliphatique conjuguée; la forme pyrannique donne un ion cyclique aromatique, en 2 étapes.
Mass spectrometry of onium compounds—XVII: Anilinium carboxylates. orthoeffect in anthranilic acid derivatives
Authors: Hvistendahl Georg , Undheim Kjell 
Published: May 2005

AbstractThe N,N,N‐trimethylanilinium carboxylates are transmethylated to the isomeric esters before evaporation in the mass spectrometer. Pyroltic reactions and electron‐impact fragmentations are elucidated by means of deuterio analogues. The orthoisomer behaves anomalously in that initial expulsion of a methyl radical is important. Deuteration has shown this reaction to take place along two distinct routes, either from the nitrogen or from the ester.
Mass spectrometry of onium compounds‐XVIII: Evaporation of N‐arylpyridinium‐3‐oxides
Authors: Undheim Kjell , Hansen Per Egil 
Published: May 2005

AbstractComparision of the fragmentation patterns and ionisation potentials for 3‐hydroxy‐2‐phenylpyridine and N‐arylpyridinium‐3‐oxides shows that the latter are evaporated as mesoins. The 2,4‐dinitrophenyl derivative constitutes an exception in that transarylation to the corresponding ether takes place before evaporation.
Metastable ion studies of various C3H6 radical cations
Authors: Gross Michael L. , Lin Ping‐Huang 
Published: May 2005

AbstractMetastable abundance ratios have been measured involving four decomposition reactions of C3H6 radical cations formed from a variety of precursors. The ratios are quite similar in accord with extensive isomerization to a propene structure prior to fragmentation. Small, yet constant differences are observed for those C3H6 ions which have been shown to be formed as cyclic ions by ion cyclotron resonance studies. The differences are interpreted to reflect internal energy variations, which result because the initially formed ions have two different structures. The abundance ratios are shown to depend on ionizing energy, repeller voltage and accelerating voltage, but are independent of the degrees‐of‐freedom in the precursor as well as the number of steps necessary to produce the [C3H6]+· Despite small variations in metastable ratios, the classification of various [C3H6]+· ions can be achieved under a variety of conditions which affect the internal energy of the decomposing ions.
Schiff base derivatives of peptide esters: Relative abundance of N‐terminal, C‐terminal and ‘internal’ fragments as a function of the blocking group
Authors: Patil Gunvant V. , Hamilton Robert E. , Day Richard A. 
Published: May 2005

AbstractElectron‐impact (EI) mass spectrometry of peptide derivatives is usually interpreted in terms of fragmentation where the charge resides on the N‐terminal fragments and to a lesser degree on the less common, charged C‐terminal fragments. Substituted and unsubstituted benzylidene, cinnamylidene, α‐ and β‐naphthylidene derivatives of a reference tripeptide, valileala, gave both N‐ and C‐terminal fragments as well as molecular ions. The order of increasing ion current (normalized) in C‐terminal fragments was: acetylacetonyl, 4‐dimethylaminonaphthylidene, p‐dimethyl‐aminobenzylidene, 3‐pyridylmethylidene, p‐diethylaminocinnamylidene, benzylidene, 2‐hydroxy‐naphthylidene, 4‐pyridylmethylidene, p‐nitrobenzylidene, p‐methoxybenzylidene, p‐cyanobenzylidene, cinnamylidene, p‐dimethylaminocinnamylidene, β‐indolylmethylidene, β‐naphthylidene, 2‐pyridylmethylidene and α‐naphthylidene. The order for this value among the N‐terminal fragments is significantly different, however (Day, Falter, Lehman and Hamilton, J. Org. Chem. in press). In addition to N‐ and C‐terminal fragments, many spectra contain internal fragments, arising from loss of fragments from both ends, which provide sequence information. These fragments are found in the mass spectra of Schiff bases formed from various aromatic aldehydes with peptide esters. The interpretation of the latter pattern is facilitate in some cases by deuterium labeling at the α‐carbon of the N‐terminal amino acid residue of peptides. Such a pattern provides sequence information supplemental to that available involving N‐ and C‐terminal fragmentations. In derivatives of hexaglycine, tetraphenylalanine and tryptophylmethionylaspartyl (β‐OEt) phenylalanine amide, for example, substantial sequence information was contained in the internal fragments; in some cases the sequence could be deduced only if the internal fragments were utilized. The 4‐dimethylamino‐naphthylidene derivatives have proven to be the most useful to date in terms of volatility, tendency to maximize cleavage into N‐terminal fragments, intensity of molecular ions and generation of useful mass spectra of certain peptide esters refractory to mass spectrometry in the form of any other derivative investigated.
Die Massenspektren der Nikotin‐N‐Oxide und der mit Ihnen Verwandten Tetrahydrooxazine
Authors: Schüller D. , Harke H.‐P. 
Published: May 2005

AbstractDie massenspektren der drei Nikotin‐N‐oxide werden zusammen mit den Spektren von Tetrahydrooxazinen diskutiert. Die Verbindungen mit N‐Oxide‐Ffunktion im 5‐gliedrigen Ring lagern sich vor der Fragmentierung durch Elektronenstoß z.T. thermisch um.
Massenspeaktrometrische Untersuchungen zur Ketenabspaltung aus Zimtalkohol
Authors: Schwarz Helmut , Köppel Claus , Bohlmann Ferdinand 
Published: May 2005

AbstractDie Ketenabspaltung aus dem Molekül‐Ion des Zimtalkohols kann nicht beschrieben werden durch den Mechanismus, der beim isomeren Dihydrozimtaldehyd die Bildung von C2H2O zeigt. Auch die elektronenstossinduzierte Isomerisierung von Allylakoholen zu Ketonen liefert keine plausiblen Erklärungen f¨︁r die experimentell bestimmte 2H‐Anteile im Ion [C7H8]+˙. Es wird gezeigt, dass bevorzugt, aber nicht ausschliesslich, die Wasserstoffe der Seitenkettten‐C‐Atome (1) und (2) an der Bildung des Neutralteiles teilnehmen.
Mass spectrometry of tropylium halides
Authors: Hvistendahl Georg , Undheim Kjell , Gyöösi Peter 
Published: May 2005

AbstractThe base peak and highest mass number in the spectra of tropylium iodide and bromide corresponds to the mass of the cation. Both appearance potential (AP) measurements and the fragmentation pattern strongly indicate that the gaseous species present is the tropylium radical. Rediction to the corresponding volatile free radical thus takes place prior to evaporation.
Single and double hydrogen rearrangements in the mass spectra of O‐ethyl, S‐alkyl methanephosphonothioates
Authors: Tashma Zeev , Katzhenler Jeoshua , Deutsch Joseph 
Published: May 2005

AbstractWhereas the oxygen analogues of the title series gives rise to double hydrogen rearrangement on electron‐impact, alkylthiophosphonates show in addition a McLafferty rearrangement. The quantitative relationship between these two rearrangements in the thio series is dependent upon the chain length and branching on the alkyl group attached to sulphur. Comparison of the mass spectra of these compounds indicates that in the pathway of the double hydrogen rearrangement the hydrogen transferred to the sulphur atom originates primarily from the carbon δ to sulphur.
Permethylation of barbiturates. Separation and characterization of the reaction products by gas chromatography‐mass spectrometry
Authors: Thompson R. M. , Desiderio D. M. 
Published: May 2005

AbstractA Series of barbiturates (I) has been permethylated with the methylsulfinylmethide carbanion and methyl iodide and the products (II to IV) separated, quantified and characterized by g.c.‐m.s. The ratios and fragmentation patterns of II to IV are highly dependent upon the nature of the R‐groups. All fragment ions have been confirmed by accurate mass measurements or perdeuteriomethylation.
Fragmentation behaviour and ring expansion of 1‐methylimidazole and 1‐methylpyrazole upon electron‐impact
Authors: van Thuijl J. , Klebe K. J. , van Houte J. J. 
Published: May 2005

AbstractThe relative losses of unlabelled vs. labelled HCN from the [M]+˙ and [M – 1]+ ions of a number of specifically labelled 1‐methylimidazoles (I) and 1‐methylpyrazoles (II) have been determined. Hydrogen randomisation in the molecular ions prior to fragmentation is insignificant. Expulsion of HCN follows two distinct pathways: elimination involving positions 2 and 3 (predominant in I) and elimination involving the methyl group and the nitrogen atom at position 1 (predominant in II). The molecular ions eject H˙ from the methyl groups to a high degree of specificity. In both cases some contribution by position 5 is observed. The resultant [M – 1]+ ions exhibit extensive, but incomplete hydrogen randomisation. Loss of HCN from these ions is consistent with intermediacy of ring‐expanded ions, but notably in II a proportion of the HCN is generated from the group. A mechanism for this observation is presented.
Echtzeit‐Datenerfassungssystem mit minimaler hardware für den Einsatz in der Routine‐Massenspektrometrie im organischen Laboratorium
Authors: Schwarzenbach R. , Clerc J. T. 
Published: May 2005

AbstractZusammenfassung‐Ein Echtzeit‐Datenerfassungssystem für den Einsatz bei der Routineanwendung der niedring auflösenden Massenspektrometrie im organischen Laboratiorium wird beschrieben. Das Datensystem ist für die Lösung jener Probleme optimiert, die in der Routine am häufigsten auftreten. Die Verwendung aufwendiger Programme erlaubt die Realisierung eines vielseitigen, benützerfreundichen Systems mit minimaler Hardware‐Konfiguration. Datenfluss und logische Struktur der Programme werden eingehend beschrieben.
Skelettumlagerungen unter Elektronenbeschuß–VII: Alkyl‐N‐Phenylcarbamate
Authors: Wünsche C. 
Published: May 2005

AbstractDie Massenspektren einfacher Alkyl‐N‐Phenylcarbamate werden beschrieben, Die bekannte Skelettumlagerung, die beim Aethyl‐N‐phenylcarbamat zu einem [C6H5NHCH2]+‐Ion2 führt, wird auch bei den Methyl‐, Propyl‐ und Butylhomologen beobachtet. Anhand deuterium‐ und 13C‐markierter Verbindungen wird gezeigt, daß der von Lewis 1964 formulierte Umlagerungs‐ mechanismus die tatsächlichen Verhältnisse nicht richtig wiederzugeben vermag.