bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metastable transitions in n‐butane and n‐butane‐d7
Authors: Smith Richard D. , Futrell Jean H. 
Published: May 2005

AbstractMetastable ions have been investigated for n‐butane d7 molecular ions using a tandem mass spectrometer which samples unimolecular decay processes occuring during the time interval of c.2 μs to 4 ms after ion formation. Some 37% of ions formed by 70 eV electron impact decay on this time scale. The competing unimolecular processes observed, in order of relative importance, are methance, methyl radical and hydrogen atom elimination. The slow metastables sample the threshold energy regime of unimolecular reactions responsible for forming the ordinary mass spectrum of butance and very large isotope effect are noted for the deuterated molecule.
Electron impact studies on oximes: Mass spectra of the condensation products of aniline, phenol and thiophenol with benzhydroximoyl chloride
Authors: Hemalatha D. , Kallury R. Krishna Mohan Rao 
Published: May 2005

AbstractThe condensation products derived from aniline, phenol and thiophenol by treatment with benzhydroximoyl chloride, exhibited a stepwise (in the first two cases) or concerted (in the third case) loss of OH. and C6H5N from the corresponding skeletally rearranged molecular ions, affording [C6H5CX]+ ions (where X = NH or o or S) when subjected to electron impact. The process has been substantiated by deuterium labelling and exact mass measurements. The base peaks in all the spectra were due to the aniline, phenol and thiphenol radical ions as the case may be, obtained by a shift prior to fragmentation of the oxime hydrogen to the heteroatom contained in these ions.
Competing metastable decompositions of [C7H14]+· ions
Authors: Falick Arnold M. , Tecon Pierre , Gäumann Tino 
Published: May 2005

AbstractThe relative rates of competing metastable decompositions of fourteen isomeric C7H14 monoolefins were measured and compared. In every case except one the most important metastable reaction was loss of either CH3 or C2H4, but the rates of these and the other reactions observed varied over a wide range. It was concluded that the molecular ions of these compounds probably do not isomerize to a common structure prior to metastable decay. It was found that a terminal double bond strongly enhances metastable loss of C2H4 and that the additional presence of a 2‐methyl substituent favours this reaction still more. Several possible mechanisms for this transition are discussed, but none was found to explain the observed results satisfactorily.
Basic mass spectrometric investigations of amino acid‐fluorescamine derivatives
Authors: Shieh Jeng‐Jong , Leung Katherine , Desiderio Dominic M. 
Published: May 2005

AbstractMass spectra of fluorescamine derivatives of seventeen of the naturally occuring amino acids have been studied using electron ionization mass spectrometry. Seven fragmentation processes of fluorophors are proposed and elucidated by accurate mass measurements, stable isotope incorpor‐ation and low resolution spectra. Two major pathways contributed most of the predominant peaks in the mass spectra. All fragmentations involve specific rearrangements of the spiro ring, while some lose the amino acid sidechain. Identification of the amino acid is unequivocally established in the low resolution spectra. Loss of one oxygen atom from the dehydrated fluorophors was found for all compounds studied. The site of this loss was determined by incorporation of 18O into the carbonyl groups of fluorescamine.
The mass spectra of cyclopropabenzenes
Authors: Singy Géarard A. , Pfyffer Jean , Müller Paul , Buchs Armand 
Published: May 2005

AbstractCyclopropabenzene, 1,1‐difluorocyclopropabenzene and their 2,5‐diphenyl analogues were studied by mass spectrometry. With the help of deuterium labelling, complete hydrogen scrambling was shown to occur before the loss of a hydrogen atom from the molecular ions.
Elimination reactions of ions in the gas phase. IV—Comparative investigation of water elimination in odd and even electron hydroxyl cations of 6‐undecanol
Authors: Kuster Th. , Seibl J. 
Published: May 2005

AbstractReactivity differences between odd ([M]+) and even electron ions (α‐cleavage product) were studied by comparing water elimination mechanisms in 6‐undecanol. The compounds specifically labelled with deuterium in positions 6, 5 + 7, 4 + 8 and 3 + 9 were made, and a detailed investigation of tghe metastable ion transitions carried out. A highly specific 1,4 elimination of water without preceding intramolecular hydrogen exchange occurs from [M]+, but equal amounts of 1,3 and 1,4 elimination of water preceded by specific hydrogen exchange between ‐OH and the hydrocarbon chain occurs from the α‐cleavage ion [M – C5H11]+. To make such distinctions a thorough examination of metastable ions is essential.
Determination of the site of protonation of substituted benzenes in water chemical ionization mass spectrometry
Authors: Martinsen D. P. , Buttrill S. E. 
Published: May 2005

AbstractThe site of protonation of a substituted benzene may be determined using chemical onization mass spectrometry with D2O as a reagent gas. The observation of extensive exchange of the ring hydrogens for deuteriums is linked to protonation on the benzene ring. The lack of this exchange coupled with the formation of cluster ions (the association of the protonated species with one or more D2O molecules) is evidence of protonation on the substituent rather than the ring. Aniline, benzaldehyde and nitrobenzene are observed to protonate at the substituent while toluene, bromobenzene, biphenyl and iodobenzene protonate on the ring. The dimethylbenzenes protonate on the ring while the diaminobenzenes protonate at one of the substituents. The dihydroxybenzenes, as well as a number of other compounds in which an oxygen is attached directly to the ring, protonate predominantly at the substituent although a small amount of exchange of one ring hydrogen is observed.
1,3‐Dipolar character of 6‐membered aromatic rings. XXIV—mass spectrometry of 1‐aryl‐3‐oxidopyridinium
Authors: Dennis Nicholas , Ibrahim Badreldin , Katritzky Alan R. 
Published: May 2005

AbstractEvaporation of 1‐aryl‐3‐oxidopyridiniums is sometimes accompanied by rearrangement to 3‐aryloxypyridine, but not to valence bond tautomers of the starting products. The fragmentation patterns are elucidated by metastable peaks and precise mass measurements and discussed.
The use of ion‐molecule reactions in the mass spectrometric location of double bonds
Authors: Ferrer‐Correia A. J. V. , Jennings K. R. , Sharma D. K. Sen 
Published: May 2005

AbstractA method for the location of the positions of carbon‐carbon double bonds using high pressure mass spectrometry is proposed. A known olefinic molecular ion reacts with a second, unknown olefin to form a four‐centre complex, which fragments with retention of the structural identity of methylene and substituted methylene groups to eliminate a new olefin molecule and to form an unsaturated ion from which the position of the double bond in the unknown olefin can be inferred. Vinyl methyl ether proved to be a convenient reagent gas and its molecular ion undergoes the required reaction with several classes of olefinic compound. Conjugated dienes and unsaturated compounds containing electronegative groups do not undergo this reaction.
Fragmentation des δ‐Dicetones, Analogies Avec le Comportement Photochimique
Authors: Morizur Jean‐Pierre , Casals Pierre‐Francois , Ferard Jacqueline , Ropert ReéGine , Keravec Maurice 
Published: May 2005

AbstractLa fragmentation de trente ‐dicétones est reportée. Les principles voies de dèradations ont été rationalisées Les mécanismes proposés s'appuiten sur des composés marqués sélectivement au deutérium, des ions métastables et des mesures exactes de mkassse. A côté des coupures et rérrange ments classiquees l'accent est mis sur l'elimination de molécules neutres: perte d'eau suivie ou précédée de cells d'éthyléne ou d'éthyléne substitué qui ferait intervenir un ion cyclobutanol intermédiaire. Ce rérrangement est á rapprocher du comportement photochimique de ces composés pour lesquels la réction de Yang est observée.
Hydrogen scrambling in the long‐lived protonated benzene ion generated from benzyl amine in the i.c.r. spectrometer
Authors: Bruins Andries P. , Nibbering Nico M. M. 
Published: May 2005

AbstractIt is shown by reactions with various bases in an i.c.r. cell that an almost complete H‐D randomization takes place in the gaseous and long‐lived [C6H2D5]+ ion, generated from C6D5CD2NH2 by electron impact, but not in its precursor ions. This follows from the ratio of [H]+ vs [D]+ transfer to bases, obtained from double resonance signals. The ratio appears to be reliable only if the protonated (deuterated) base is stable and does not undergo unimolecular decompositions.
Studies of cyclic acetals. XXII—limitations on the use of alkyl substituents as pseudoisotopic labels: The electron impact mass spectra of alkylated derivatives of 3,7,9‐ and 4,7,9‐trioxabicyclo[4·2·1]nonanes
Authors: Calinaud Pierre , Gelas Jacques , Horton Derek , Wanders Joseph D. 
Published: May 2005

AbstractLow resolution, electron impact mass spectra are tabulated for eleven methylated derivatives of 3,7,9‐trioxabicyclo[4·2·1]nonane, 4,7,9‐trioxabicyclo[4·2·1]nonane and nine methylated derivatives, and 6‐ethyl‐3,7,9‐trioxabicyclo[4·2·1]nonane. In general, a substantial proportion of the fragmentation subsequent to electron impact can be rationalized according to a few, simple decomposition pathways that are inferred from analysis of mass number shifts caused by changes in substitution; however, major alterations in fragmentation are apparent in a few of these examples, which signals that, for several of the 4,7,9‐trioxabicyclo[4·2·1]nonanes, the substituent acts not as an inert label but as a fragmentation‐directing group.
On the mechanism for loss of CO from aromatic oximes. Evidence for a nucleophilic attack from fluorine labelling
Authors: Vijfhuizen Peter C. , Van Der Schee Henk , Terlouw Johan K. 
Published: May 2005

AbstractThe mehanisms for loss of CO from benzaldoxime and acetophenone oxime have been investigated with the aid of both fluorine and deuterium labelling as well as field free region metastable peak shapes. Kinetic evergy release data and the metastable ion abundance raion test were used to obtain information about the product ions. It is proposed that loss of CO from both are generated via the nucleophilic attack of the oxygen lone pair eletrons at the ortho position of the phenyl ring as the first step in the reaction sequence.
An unusual electron impact induced fragmentation of methylbenzofurazans
Authors: Razmara Fereidoun , Waight E. S. 
Published: May 2005

AbstractThe electron impact mass spectra of 4‐and 5‐methylbenzofurazans exhibit an ion corresponding to the loss of CHO from the molecular ion. Loss of NO from the molecular ion is quite unimportant, in contrast to the behaviour of benzofurazan and some other substituted benzofurazans, in which loss of NO is the dominant process.
Über quantitative Beziehungen zwischen Fragmenten und ihren relativen Intensitäten im Massenspektrometer. II—Untersuchungen Über die Beeinflussung Relativer Ionenintensitäten Durch Experimentelle Faktoren und Ihre Bedeutung für den bei Tertiären Alkoholen AUfgefundenen [Ionenmasseneffekt]
Authors: Záhorszky U. I. 
Published: May 2005

AbstractDie Abhängigkeit der Intensitätsverhälthisse aus konkurrierende α‐spaltungen von experimentellen Einflüssen, wie Electronennergie, Quellentemperatur, SEV‐ und Fokussierungsbedingungen wird untesucht. Ein Massendiskriminierungseffekt der Ionenoptik wird gefunden. Es wird gezeigt, daß der an tertiären aliphatischen Alkoholen gefundene [Ionenmasseneffekt] echt ist. Er tritt nach den bisherigen kenntnissen deutlich bei solchen aliphatischen Verbindungen auf, die unter Elektronenstoß keinen Moleküpeak zeigen und sehr stabile Ionen aus der α‐spaltung bilden. Zu seiner Erklärung werden zwei alternative Vorschläge angeboten.
Über quantitative Beziehungen Zwischen Fragmenten und Ihren Relativen Intensitäten im Massenspektrometer. III—Messung der Intensitätsverhältnisse aus der α‐SWpaltung von Tertiären Alkjoholen und Äthern bei Niedriger Elektronenenergie
Authors: Záhorszky U. I. 
Published: May 2005

AbstractVon 30 tertiären aliphatischen Alkoholen und 24 Äthern teriärer Alkohole wurden die Ionenintensitätsverhältnisse aus konkurrierenden α‐Spaltungen bei 13 eV gemesen. Die Intensitätsverhältnissen der Ionen [M  Alky1]+ und [M  Alkyl2]+ bei Alkyl stimmen mit den reziproken Massenverhältnissen der zugrundeliegenden Ionen gut überein (Ionenmasseneffekt). Die Intensitätsverhältnisse von [M  Alkyl]+ und [M  Methyl]+ sind immer zu hoch, doch lassen sich aus ihnen indirekt Intensitätsverhältnissen von [M  Akyl2]+ bestimmen, die ebenfalls gut mit den Werten anch dem Ionenmasseneffekt übereinstimmen. Durch die indirekte Bestimmungsmethode wird gezeigt, daß auch bei den 2,2‐Dialkyl‐1,3 dioxolanen (Äthylenketale) der ionenmasseneffekt eine dominierende Rolle spielt.
Zur Elektronenstoß‐Induzierten Methylabspaltung aus Homoadamantan
Authors: Zeller Klaus‐Peter , Berger Stefan 
Published: May 2005

AbstractDurch 13C‐Markierung der Position 4 des Homoadamantans wird gezeigt,daß bei derelektronenstoß‐induzierten CH3‐Abspaltung aus dem Molekül‐Ion jedes Kohlenstoff‐Atomder CH2‐CH2‐Brücke zu 25% beteiligt ist.
CA‐Untersuchungen zu wahren und vermeintlichen Cyclisierungsreaktionen von Ionen in der Gasphase—Eine Nachlese zu anomalenortho‐Effekten
Authors: Schwarz H. , Sezi R. , Rapp U. , Kaufmann H. , Meier S. 
Published: May 2005

AbstractMit Hilfe der Stoßaktivierungsmassenspektrometrie werden durch die Verwendung geeigneter Referenz‐Ionen sowohl die Zerfallsmechanismenortho‐substituierter Benzolderivate als auch die Strukturen der resultierenden Produkt‐Ionen aufgeklärt.
The mass spectral fragmentation of 1,4‐butanediol
Authors: Horváth Gyula , Kuszmann János 
Published: May 2005

AbstractThe behaviour of 1,4‐butanediol under electron impact at 70 and 12.5 eV has been studied with the aid of high resolution mass spectra. Based on metastable ion decompositions and deuterium labelling, mechanisms are proposed for the formation of the abundant ions of this compound.
On the loss of CH from o‐methylbenzaldoxime. Evidence for an ortho assisted oxime→nitrone isomerization
Authors: Vijfhuizen Peter C. , Terlouw Johan K. 
Published: May 2005

AbstractIsomerization of oxime molecular ions into nitrone molecular ions upon electron impact does not generally occur, but it was established with the aid of deuterium labelling that it is essential for loss of CH from o‐methylbenzaldoxime.
Peptides containing aminophosphonic acids. IV—mass spectra of the peptides containing aminomethylphosphonic acid
Authors: Yamauchui Kiyoshi , Mistsuda Yasuhiro , Kinoshita Masayoshi 
Published: May 2005

AbstractThe fragmentation behavious under electron of di‐ and tri‐peptide analogues containing amino acid (aa) and aminomethylphosphonic acid (ap) groups are described. Successive fragmentations of the molecular ions provided a convenient method for the sequence determination of peptides containing aa and ap units.
Etude des fragmentations en spectrographie de masse de dithiannes‐1,3 substitués en 2 par des groupements insaturés
Authors: Dedieu Michel , Pascal Yves‐Louis , Dizabo Pierre , Basselier Jean‐Jacques 
Published: May 2005

AbstractLes spectres de masse des produits étudiés montrent un ion moléculaire toujours abondant. Certaines fragmentations mettent en jeu la perte du groupement éthylénique; d'autre correspondent à des coupures du cycle dithiannique, suivies éventuellement de recyclisations impliquant la chaine éthylénique et les possibilités de résonance qu'elle permet. La présence d'un noyau phényle dans la chaîne éthylénique modifie les spectres par formation d'un ion benzothiopyrylium très stable.
Mechanistic aspects of cyclization‐elimination reactions: 2′‐azabenzanilides
Authors: Broxton T. J. , Pang Y. T. , Smith J. F. , McLafferty F. W. 
Published: May 2005

AbstractProminent peaks in the mass spectra of 2′‐azabenzanilides appear to involve molecular ion cyclization followed by the loss of CO and then H. Effects of structure on the abundance of these and [MCHO]+ ions indicate that the ring nitrogen provides a radical‐like reactive site for cyclization, and that stabilization in the product ions of the unpaired electron as well as of the ionic site is important for the reaction.
Four‐centre skeletal rearrangements in the mass spectra of thioanilides
Authors: Broxton Trevor J. , Rowe Jeffrey E. 
Published: May 2005

AbstractAbundant peaks in the mass spectra of thioanilides involve loss of a substituted thiophenoxy radical by a process involving aryl migration from nitrogen to sulfur (a four‐centre skeletal rearrangement). The effects of substituents on this process have been studied. Substituents in the amide ring, in the acid part of the molecule and on the nitrogen atom were studied. Four‐centre aryl migrations seem to be favoured if the aryl group migrates from one atom to either a more polarizable or a more electronegative atom, and in the case of thioanilides this migration is more important in tertiary compounds than in secondary compounds.
Chemical ionization mass spectrometry of bifunctional cyclopentanes and cyclohexanes. A correlation between stereochemistry and chemical ionization spectra
Authors: Van Gaever F. , Monstrey J. , Van de Sande C. C. 
Published: May 2005

AbstractA correlation has been fround between the stereochemistry of 3‐methoxyeyclopentyl and 3‐methoxyccyelohexyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MHCH3OH]+ ions are more abundant for the trans isomers. A similar situation occurs in the iow temperature methane chemical ionization spectra of the coresponding trimethylsilylethers.
Réarrangements cycliques de N‐alkylbromo‐1,2,4‐triazoles sous l'impact electronique
Authors: Maquestiau André , Van Haverbeke Yves , Flammang Robert , Mispreuve Henri 
Published: May 2005

AbstractQuelques réactions de réarrangement faisant intervenir la chaîne latérale de N‐propylbromotriazoles sont étudiées par les techniques ‘MIKE’ et ‘CID.’ La perte d'un radical allyle produit une structure bromotriazole protontée par double transfert d'hydroghe vers le noyau hétérocyclique. L'élimination d'ithylbéne donne naissance à des structures isoméres des ions moléculaires des méthylbromotriazoles. Enfin, les résultats montrent qu'il n'y a pas de réaction d'extension cyclique au niveau des ions [MC2H5]+ de ces composés.
The mass spectra of intramolecularly hydrogen bonded 2(1H)‐quinoxalinone and 2H‐1,4‐benzoxazin‐2‐one
Authors: Inagaki Takeshi , Iwanami Yasuo 
Published: May 2005

AbstractThe mass spectra of those 3‐phenacyl derivatives of 2(1H)‐quinoxalinone and 2H‐1,4‐benzoxazin‐2‐one with an intramolecular hydrogen bonding showd that: (1) the primary elimination of the shole sidchain is reduced as compared with an unchelated derivative; (2) the importan t fragmentation routes in the quinoxalinone series are ring cleavage with loss of CO followed by recyclization and expulsion of a hydrogen atom, and this can also occur in the reverse order; (3) this reverse process is virtually absent in the benzoxazinone series. Finally, the doubly charged molecular ions appear to undergo an analogous decomposition giving fairly intense [M‐CO]2+ or [M‐(CO+H or CI]2+ ions.
The mass spectra of dimethoxytoluenes
Authors: Florêncio Helena , Heerma Wigger , Dijkstra Geo 
Published: May 2005

AbstractThe primary fragmentation reactions in the dimethoxytoluenes have been studied and compared with those in dimethoxybenzenes and monomethoxytoluenes. Labelled analogues and metastable ion characteristics were used to elucidate the reaction mechanisms. The formation of stable quinoid‐type ions directs many fragmentation pathways. Analytically useful spectral characteristics are indicated.
Charge location and fragmentation under electron impact. IV—the behaviour under electron impact of some N‐methyl, N′‐R‐1,2,4‐phosphadiazetidine‐3‐ones and related compounds
Authors: Baldwin M. A. , Loudon A. G. , Dunmur R. E. , Schmutzler R. , Gregor I. K. 
Published: May 2005

AbstractThe ionization potentials of a series of N‐methyl,N′‐R‐1,2,4‐phosphadiazetidine‐3‐ones and related compounds have been determined. The nature of the highest occupied orbital of the molecules and the use of empirical rules to rationalize the variations in the ionization potentials are discussed. The changes in the fragmentation patterns are related to the different low ionization potential site(s) in each molecule. The occurrence of various rearrangement ions are discussed on a similar basis.
The nature of the [C2H6N]+ and [CH4N]+ ions formed by electron impact on methylated formamides, acetamides, ureas, thioureas and hexamethylphosphoramide
Authors: Loudon A. G. , Webb K. S. 
Published: May 2005

AbstractBy means of appearance potential measurements and metastable analysis, it is shown that the [C2H6N]+ and [CH4N]+ ions formed from methylated formamides, acetamides, ureas and thioureas rearrange upon formation to structures similar to the [MH]+ ions from mono‐ and dimethylamine.
Ionization and dissociation of C6F6 isomers under electron impact
Authors: Praet M‐Th. , Hubin‐Franskin M‐J. , Delwiche J. P. , Schoos R. 
Published: May 2005

AbstractThe mass spectra of hexafluorobenzene, hexafluorobicyclo[2.2.0]hexa‐2,5‐diene (perfluoro‐Dewar benzene) and 1,1,1,6,6,6‐hexafluorohexa‐2,4‐diyne, and the fragmentation mechanisms of their parent ions are reported. The behaviour of the two cyclic isomers under electron impact is very similar; the linear one behaves quite differently. The ionization potentials of the molecules and the appearance potentials of the fragment ions (both normal and metastable) have been measured. The heats of formation of [C6F5]+ and [C5F3]+ are calculated. A value for the heat of formation of 1,1,1,6,6,6‐hexafluorohexa‐2,4‐diyne is proposed.
The substituent effect in the fragmentation of phenylcyclohexanols
Authors: De Angelis F. , Forcellese M. L. , Gambacorta A. , Nicoletti R. 
Published: May 2005

AbstractAll the main fragmentation pathways undergone by trans‐4‐ and trans‐2‐p‐substituted phenylcyclohexanols have been studied, and the ionic abundances have been correlated with the σ constants. This analysis shows that electron withdrawing substituents, increasing the fraction of molecular ions having sufficient energy to decompose, favour all fragmentations. However, along with this ‘non‐specific’ substituent effect, there is a ‘specific’ effect, in the opposite sense, increasing the formation of the [M—59]+ and [M—85]+ ions with increasing electron releasing power of the substituents. The loss of water, although it is almost exclusively a 1,4 elimination in the case of trans phenyl cyclohexanols, is not specifically influenced by the substituents.
Studies in negative ion mass spectrometry. VII—Negative ion mass spectra of copper (II) β‐diketonate complexes
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K. 
Published: May 2005

AbstractElectron capture processes in a series of copper (II) β‐diketonate complexes of formula Cu[R1COCHCOR2]2 (where R1 is an alkyl, perfluoroalkyl or aryl group and R2 either an alkyl or aryl group) have been examined. Molecular anions, ligand ions and some novel rearrangement ions have been observed with these compounds. Relative intensities of fragment ions were dependent on the substituents R1, R2 as well as the electron energy and compound pressure in the ion source. By operating the mass spectrometer at compound pressures of c. 4×10−6 Torr and higher, reproducible negative ion mass spectra (free from any significant ion‐molecule contributions) have been obtained for all compounds of the series.