bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron‐impact‐induced hydrogen migration in organic molecules I–Substituent effects in the mass spectra of pivlanilides
Authors: Ramana D. V. , Vairamani M. , Kala S. 
Published: May 2005

AbstractSubstited pivalanilides give rise to fragments corresponding to anilies on electron‐impact, which is due to the migration of a hydrogen atom from the t‐butyl group to the nitrogen. The Hammett correlation indicates that the formation of this fragment is favoured by electron‐donating groups. The other interesting feature of these spectra is the migration of the aryl group to the t‐butyl carbon with the elimination of the neutral ketemine.
A detailed analysis of the complete hydrogen and carbon scrambling and fragmantation reactions of boron‐containing cationic species in the mass spectrometer
Authors: Pasto Daniel J. , Timony Peter E. 
Published: May 2005

AbstractA detailed analysis of the mass spectral behavior of trialkylboranes and deuterium and 13C labeled tri‐n‐butylborane, and comparison with the ion cyclotron resonance behavior, have revealed several unique features and herefore unrecognized rearrangement and fragmantation reactions:(1)the occurrence of intial fragmentation of the parent ion with apparently nearly exclusive loss of one complete alkyl radical; (2) the extensive formation of boron‐containing spiecies (>% of the total ion current)in the mass spectrometer relative to the virtual absence (<5%) of such spieces in the ion cyclotron resonance spectrum; (3) the dominant formation of boron‐containing species of the composition [CnH2n+2B]+ with [C2H6B]+ generally being the base peak; (4) the formation of appreciable quantities of alkane molecular ions (5 to 10% of the total ion current) up to [R2]+. (from R3B); (5) the characterization of a fragmentation reaction involving the loss of CH2; (6) the observation that very extensive hydrogen and carbon scrmbling occurs in the ions formed after the initial fragmentation of the parent ion. A mechanism which satisfactorily accounts for the fragmentation and rearrangement reactions is proposed which involves the reversible formation and rearrangement of protonated boracyclopropanes and cyclopropanes formed by cationic insertions in ß‐CH bonds.
A test of the concept of ‘charge localisation’ in methionine
Authors: Den Heuvel C. G. Van , Nibbering N. M. M. 
Published: May 2005

AbstractA previous re‐investigation of methionine has shown that the [C2H5S]+ ion is generated via rather complicated routes from the molecular ion. This has been interpreted as evidence against charge localisation in the fragmentation of the title compound. Deuterium labelling, high resolution mass measurements and metastable transitions have revealed, however, that the formation of the [C2H5S]+ ion is not in contradiction with the predicting capabilities of the concept of charge localisation.
Mass spectroscopy of hydroxamic acids: Fragmentation by the loss of the hydroxylamino oxygen
Authors: Akers Hugh A. , Atkin C. L. , Neilands J. B. 
Published: May 2005

AbstractThe mass spectra of three dihydroxamic acids have shown in each case prominent [M – 16]+· and [M – 32]+· ions. The spectrum of biosynthetically labeled rhodotorulic acid indicates that these ions arise from the sequential, specific loss of the hydroxylamino oxygens.
FRAGMENTIERUNGSDIAGRAMME ZUR AUFKLäARUNG DER ABBAUREAKTIONEN ORGANISCHER VERBINDUNGEN I–AROMATISCHE KOHLENWASSERSTOFFE
Authors: Schönfeld Wolfgang 
Published: May 2005

AbstractAm Beispiel einiger ausgewählter, aromaatisscher Kohlenwasserstoffverbindungen wird die Aussagekraaft der Fraagmentierungsdiaagraamme1,2 demonstriert. Der Haujptzerfallsweg bei allen juntersuchten Verbindungen–Benzol, Diphenyl, Naphthaalin, Anthraacen und Phenaanthrenist eine Kaskaade von Aacetylenaabspaltungen, die vom Molekül‐Ion bis zzum Endprodukt aus zwei Kohlenstoffatomen führt. Die wichtigsten Neutraalfraagmente sind Moleküle, deren freie Valenzen gegebenenfalls durch die Umlagerung von Wasserstoffatomen des entstehenden Ions abgesáttigt wurden. Aanthracen und Phenanthren sind aufgrund ihres Fragmentierungsverhaltens Klar unterscheidbar.
Comparative study of ion kinetic energy, chemical ionisation and field desorption spectra
Authors: Das K. G. , Kulkarni P. S. , Shinde M. B. 
Published: May 2005

AbstractA comparison of the fragmentation processes operating in the first field free region was made with the fragmentation in the ion source under electron ionisation, chemical ionisation and field desorption conditions for some selected compounds which undergo retro‐DielsI‐Alder fragmentation in the ion source under electron ionisationconditions. The fragmentation processes which com‐ete with retro‐Diels‐Alder fragmentation under chemical ionisation and field desorption conditions are discussed. The complementary nature of these techniques are illustrated.
Use of ion‐molecule reaction equilibria to identify structural isomers
Authors: McIver Robert T. 
Published: May 2005

AbstractA new approach is described for identifying structural isomers which cannot be distin‐guished on the basis of their electron‐impact mass spectra. Using a pulsed ion cyclotron resonance mass spectrometer, equilibrium constsnts are measured for ion‐molecule reactions involving various C8H10 isomers and C7H8O isomers. The equilibrium constants are shown to be highly sensitive to the structural features of the various isomers.
FRAGMENTIERUNGSDIA GRAMME ZUR AUFKLÄRUNG DER ABBAUREAKTIONEN ORGANISCHER VERBINDUNGEN II–PPOLYMETHYL‐ UND CHILORBENZOLE
Authors: Schönfeld Wolfgang 
Published: May 2005

AbstractVollständige Zerfallsschemata werden zur Untersuchung der Fragmentierungs‐eigenschaften von Polymethyl‐ und Chlorbenzolen herangezogen. Der Verstärkte + M‐Effekt der Methylgruppe am ionisierten, aromatischen‐Ionen stark methylierter Verbindungen wechselt im Verlauf ihres Abbaus wiederholt zwischen dem Sechs‐ und Siebenringskelett. Mit dem ver‐stärkten + M‐Effekt kann auch der Abbau von Chlorbenzolen erklärt werden. Im Chlortropylium‐Ion ist die CCI‐Bindung in nachweisbarem Maße gefestigt.
Pyrrolo [1,2‐a] [1,3,5] triazine‐2,4(1H, 3H)‐diones. III—Fragementation under electron‐impact
Authors: Traynor J. R. 
Published: May 2005

AbstractThe mass spectra of eight pyrrolo[1,2‐a][1,3,5]triazie‐2,4(1H, 3H)‐diones have been examined. An unusual feature in the fragmentation of those compounds having a 7‐alkoxycarbonyl function, namely loss of the whole ester grouping with concomitant hydrogen rearrangement, is discussed.
Ion structure determination through collisions of ions of high kinetic energy
Authors: Cooks R. G. , Beynon J. H. , Litton J. F. 
Published: May 2005

AbstractThrough studies on [C6H6]+ and [C6H5]+ it is shown that charge stripping provides information on ion structure which is complementary to that given by collision‐induced dissociation. Stripping involves a more uniform sampling over the range of ion internal energies than does collision‐induced dissociation which preferentially samples higher energy ions.
Mass spectrometry of heterocyclic compounds VIII–electron‐impact‐induced fragmentation of 1,2‐diphenyl‐pyrazolidine‐3,5‐dione and some 4‐substituted derivatives
Authors: Selva Antonio , Citterio Attilio , Merlini Lucio 
Published: May 2005

AbstractThe mass spectra of 1,2‐diphenyl‐pyrazolidine‐3,5‐dione and twenty‐one 4‐substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4‐position of the heterocycle and/or from the ß‐position of the 4‐substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4‐d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4‐unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4‐derivatives by the loss of 4‐substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron‐impact and/or thermal decompostion of some complex compounds containing more than one 1,2‐diphenyl‐pyrazolidine‐3,5‐dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4‐substituent groups can be excluded.
Collision‐induced dissociation of the lower alcohols. A thermochemical study
Authors: Cooks R. G. , Hendricks L. , Beynon J. H. 
Published: May 2005

AbstractCollision‐induced dissociation of the molecular ions and of some of the fragment ions foremed on ionization of methanol, ethanol and n‐propnol have been studied at high energy resolution in a mass spectrometer. The translational energy lost upon collision and the kinetic energy releasedupon fragmentation of the collisionally excited species have been measured by the methods of ion kinetic energy spectromety. The results of the translational energy loss measurements compare well with excitation energies predicted for each reaction form breakdown curves showing the relative abundances of the ionsas a fuction of internal energy. This correspondence is evidebce that the ionic reactions following electron‐impact excitation and those following collisional excitation with neutral molecules at relative traslational energies in the range of several kilovolts are at least qualitatively independent of the method of excitation. The occurrence of the corresponding spontaneous fragmentations in the alcohols has also been studied and the kinetic energy releases accompanying these reactions have been determined. In a few cases, metastable peaks were observed which did not increase in intensity when collision gas added and this phenomenon is associated with particular features of the reaction thermochemistry. Reactions which generally occur to very small extents in mass spectromety, such as methylene elimination, have been observed in highly excited ions. The methods developed in this study allow the decription of the thermochemistry of the reaction of highly excited ions, indlcuding the experimental determination of the partitioning of the nonfixed energy of the activated complex. This procedure complemets and extends energy partitioning studies made on metastable ions in which the partitioning of the reverse activation energy is the more readily accessible.
Transposition des Cycles Satures en Spectrometrie de Masse IV—Dioxolanes Derives de Cetones a Cycle Moyen et Grand
Authors: Audier Henri‐Edouard , Fetizon Marcel , Tabet Jeain‐Claude 
Published: May 2005

AbstractLe mécanisme de frangementation des éthylètals des cyclanones à cycle moyen ou grande a été réétudié. La fragmentation peut ětre entièrement expliquée à l'aide d'un nouveau réarrangement qui implique une contraction de cycle et des migrations d'hydrogène qui ont été vérifiées sur des composés deutériés.
On field desorption mass spectrometry of salts
Authors: Schulten H.‐R. , Röllgen F. W. 
Published: May 2005

AbstractThe types of ion occurring in the field desorption mass spectra of inorganic and organic salts are discussed. In contrast to general experience with field desorption mass spectrometry molecular ions are either absent or of low intensity. The energetically and kindetically favoured process of cluster formation, however, generates ions from which the molecular structure can be easily derved. Some specific aspects for the analyses of salts by field desrption mass spectrometry are outlined.
Combined deuterium labeling and appearance potential measurements to uncover competing reaction mechanisms in the electron‐impact‐induced loss of water from cyclohexanol
Authors: Green Mark M. , Bafus Don , Franklin J. L. 
Published: May 2005

AbstractThe appearance potentials for loss of H2O and DOH from the constitutional isomers 3,5‐dideuterocyclohexanol and 4,4‐ dideuterocyclohexannol show, in agreement with proposals based on stereoselectivites, that 1,3 loss of water is energetically more costly than 1,4 loss of water.
Beurteilungskriterien für Klassifikatoren zur automatischen Spektreninterpretation (pattern recognition)
Authors: Rotter H. , Varmuza K. 
Published: May 2005

AbstractIn den Letzten Jahren wurden zahlreiche Verfahren der Zeichenerkennung für die automatische Interpretation von chemisch‐physikalischen Daten erprobt. Gute Erfolge wurden insbesondere mit Klassiufikatoren für niedrig aufgelöste Massenspektren erzielt. Die Angaben über die Güte der Spektrenklassifikatoren (‘Prozenstsatz richtig klassifizierter Spektren’) waren jedoch oft mathematisch unzureichend definiert. In dieser Arbeit werden mit Hilfe grundlegender Prinzipien der Wahrscheinlichkeitsrechnung und der Informationstheorie objektive Beurteuilungskriterien für binäre Klassifikatoren abgeleitet. Ein Klassifikator ist eine Rechenvorschrift, um aus einem Merkmalsvektor (Massenspektrum) und den a priori‐Wahrscheinlichkeiten der Klassenzugehörigkeiten (chemischen Strukturen) für diesen Merkmalsvektor die a posteriori‐Wahrscheinlichkeiten zu berechnen. Für den Vergleich der Güte von Klassifikatoren sind die Klassifizierungsfähigkeiten für die einzelnen Klassen oder der Informationsgewinn geeignet. Die angegebenen Formeln werden durch Beispiele aus der Massenspektrometrie erläutert.
Electron‐impact‐induced fragmentation of some isomeric cyclopropyl picolyl and pyridyl ketones
Authors: Glenn David F. , Edwards William B. 
Published: May 2005

AbstractThe electron‐impact‐induced fragmentation of three cyclopropyl picolyl ketones and three cyclopropyl pyridyl ketones has been studied with the aid of deuterium labeling, high resolution mass measurements and metastable mode operation.
Ionisation and appearance potentials of alkylketones
Authors: Mouvier G. , Hernández R. 
Published: May 2005

AbstractThe ionisation potentials of a series of alkylketones have been measured by the electron‐impact technique using the second derivative method. The ionisation efficiency curves were obtained with a conventional mass spectrometer and the data treated by means of a minicomputer. These results are compared with those given by photoelectron spectroscopy, which has enabled us to test our mass spectrometric method and to distinguish between the adiabatic and the vertical ionisation potentials. It has been observed that the electron‐impact technique can lead to the adiabatic ionisation potential in favourable cases.We have determined the appearance potentials of fragmentations [A]+ = [RCO]+ and [B]+ = [CH3CO]+, arising from the rupture of bonds in the α position with respect to CO, for a large series of methylalkylketones. The standard heats of formation of these ions have been calculated. The excess energy of the fragmentation reaction, corresponding to the kinetic shift, is found to be small or negligible for the decomposition giving ion [A]+, requiring a smaller activation energy and high in the case of ions [B]+. This kinetic shift becomes larger for an increase in the activation energy and the vibrational degrees of freedom of the molecular ion, as postulated by the quasi‐equilibrium theory. An important fraction of the kinetic shift is due to the ‘competitive shift,’ i.e. the excess energy that must be supplied to the molecular ion for it to yield [B]+ ions in sufficient amounts to be detected by the mass spectrometer. This is confirmed by the claculation of the fragmentation rate constants for the 2‐butanone molecular ion.
Massenspektroskopische Fragmentierungsreaktionen. X—Zum Mechanismus der Methyl‐ und Äthylabspaltung bei benzanellierten 6‐ und 7‐gliedrigen heterocyclen
Authors: Budzikiewicz H. , Lenz U. 
Published: May 2005

AbstractEs wird gezeigt, daß Methyl‐ und Äthyleliminierung aus 6‐ und 7‐gliedrigen benzanellierten Heterocyclen in der Regel nach verschiedenen konkurierenden Mechanismen erfolgt, wobei deren Art und relative Bedeutung vom Heteroatom abhängen.
The reactive states of ions: Dimethyl‐hexadienes and tetramethylcyclobutenes
Authors: Rennekamp Michael E. , Hoffman Michael K. 
Published: May 2005

AbstractThe principal decomposition routes of molecular ions of cis, cis‐3,4‐dimethyl‐2‐4‐hexadiene, cis, trans‐3,4‐dimethyl‐2,4‐hexadiene, cis‐1,2,3,4‐tetramethylcyclobutene and trans‐1,2,3,4‐tetramethylcyclobutene were studied using ion kinetic energy spectroscopy. Evidence indecates that loss of radicals from [M]+· appears to proceed via an electronically excited state, while loss of a neutral molecule appears to involve complete equilibration of structure within the system, or may involve both ground state and excited state pathways.
The reactive states of ions: Octatrienes and dimethyl substituted cyclohexadienes
Authors: Rennekamp M. E. , Hoffman M. K. 
Published: May 2005

AbstractThe principal decomposition routes of molecular ions of cis, cis, cis‐2,4,6‐octatriene, cis, cis, trans‐2,4,6‐octatriene, trans, cis, trans‐2,4,6‐octatriene, trans‐5,6‐dimethyl‐1,3‐cyclohexadiene and cis‐5,6‐dimethyl‐1,3‐cyclohexadiene were studied using ion kinetic spectroscopy. The loss of radicals from [M]+· appears to proceed via a ground state, while loss of a neutral molecule appears to involve either complete equilibration of structure within the system or both ground state and excited state pathways.
Über die elektronenstossinduzierte phenyl‐Umlagerung bei 4‐Phenyl‐chinuclidinen
Authors: Achenbach H. , Wörth J. , Schneider W. , Bochow H. 
Published: May 2005

AbstractDie Massenspektren von 4‐Phenyl‐chinuclidinen sind gekennzeichnet durch den bevorzugten Verlust von C7H7 aus dem Molekülion. Dieser unerwartete Fragmentierungsprozeß ist nur im Zuge einer Phenyl‐Umlagerung verständlich.
Silylumlagerungen in den Massenspektren stereoisomerer 5‐Methylcyclohexan‐1,3‐diol‐TMS‐äther
Authors: Winkler F. J. , Robertson A. V. 
Published: May 2005

AbstractDie Bildung der Silylumlagerungsionen [ROSi(CH3)2]+ aus [M–CH3]+‐Ionen der epimeren 5‐ Methylcylohexan‐cis‐1,3‐diol‐TMS‐äther ist unabhängig von der 5‐ Me‐Konfiguration im Gegensatz zu den stereochmischen Effekten der 5‐Me‐Gruppe bei den Eliminierungen aus [M]+· verwandtr Derivate.
Elektronenstossinduzierte 1.1‐Eliminierung aus Phenylhydroxylamin‐derivaten
Authors: Schwarz Helmut , Zon Gerald , Tsui Fai‐Po 
Published: May 2005

AbstractDie Reaktivität der Titelverbindungen unter Elktronenstoß ist vergleichbar mit dem thermischen Verhalten. Bei geeigneter Substitution findet eine ungewöhnliche 1.1‐Eliminierung statt, die die Charakteristik einer linear cheletropen Reaktion besitzt.
The concept and rôle of charge localization in mass spectrometry
Authors: Williams D. H. , Beynon J. H. 
Published: May 2005

AbstractThe concepts of charge localization and of radical localization are considered both with regard to their validity and to their usefulness in explaining and predicting the unimolecular fragmentation pathways for positively charged ions formed from organic compounds. It is concluded that there is experimental support for these concepts.
The mass spectra and ionization potentials of the neutral fragments produced during the electron bombardment of aromatic compounds
Authors: Reeher John R. , Flesch Gerald D. , Svec Harry J. 
Published: May 2005

AbstractA mass spectrometer equipped with a dual ionization chamber ion source has been used to characterize directly the neutral species produced in the dissociative ionization of gases by electron impact. Neutral fragment mass spectra have been obtained for the electron ionization and fragmentation of benzene, toluene, o‐xylene, m‐xylene, p‐xylene, mesitylene and isotopically labeled toluene. The neutral fragment mass spectra correlate well with the structures of the molecules. The abundant species in the neutral fragment mass spectra also correlate reasonably well with the abundant complementary positive ions of the normal mass spectra. Ionization potentials have been determined for the abundant neutral species produced. Where comparisons with values reported elsewhere are possible, the agreement is usually within ±0.2 eV or less.
The mechanism of CO loss in the electron impact‐induced fragmentation of benzoin and its methyl ether
Authors: Klasinc L. , Stefanović D. , Adam S. , Güsten H. 
Published: May 2005

AbstractThe electron impact‐induced fragmentation of benzoin methyl ether gives rise to the formation of an m/e 91 fragment ion which is not present in the mass spectrum of benzoin. Deuterium and 13C labelling, as well as low energy experiments, revealed that this ion is formed from [M – benzoyl]+ by transfer of both the ether methyl group and the hydrogen atom from the α‐position to the adjacent phenyl ring followed by loss of CO and hydrogen.
Energetic consideration applied to the mass spectra of some aromatic compounds
Authors: Williams Dubley H. , Bowen Richard D. 
Published: May 2005

AbstractIt is shown that the ‘metastable’ mass spectra of a series of monosubstituted benzenes are consistent with reaction over the lowest available energy surfaces. The non‐occurrence of some qualitatively possible decomposition pathways may therefore be used to place lower limits on the heats of formation of gaseous cations. Conversely, where characterized reactions are preempted by new reactions upon introduction of additional substituents, upper limits may be placed upon the heats of formation of the ionic products of the new reactions. The concepts are employed to deduce that C3H6 elimination from n‐butylbenzence subsequent to ionization leads to ionized toluene rather than ionized methyleneclohexadience.
Field desorption mass spectra of involatile sulphonic acids, sulphonates and dyestuff materials
Authors: Mathias Alan , Williams Albert E. , Games David E. , Jackson Anthony H. 
Published: May 2005

AbstractAbstract‐Useful field desorption mass spectra can be obtained from involatile sulphonic acids and sulphonates, even when large dyestuff molecules are involved. Unusual cluster ions are commonly found, which can be singly or doubly charged. Most ions can be assigned, however, and the great potential of field desorption mass spectrometry in the identification of these involatile species is clearly established.
Mass spectral fragmentation of functionalized lanostanes‐I
Authors: Dias Jerry Ray 
Published: May 2005

AbstractMass spectra of various functionalized lanostanes and their deuterated analogs are compared. It is proposed that the transfer of a hydrogen from the 18‐methyl group to the 11‐oxo group via a McLafferty rearrangement is made geometrically possible by prior ionization of the 13,14 bond which allows an optimum interatomic distance between the oxygen and hydrogen to be acquired; the 8,9 double bond is a requisite for electronic induction of this specific process. Transfer of the hydrogen from the 7β‐hydroxy group to position 14 is implicated in the mass spectrum of 3β‐acetoxy‐7β‐hydroxy‐5α‐lanostan‐11‐one.