bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variation of relative ion abundances with accelerator potential in the mass spectrometer: The importance of source penetration
Authors: Howe Ian , Williams Dudley H. 
Published: May 2005

AbstractCalculations have been carried out, using the Quasi‐Equilibrium Theory of Mass Spectra to show that a decrease in penetration of the accelerating field intol the ion source of a mass spectrometer may significantly increase the number of primary daughter ions [A]+ produced from a molecular ion [M]+ in the source. The calculations show that this effect appears to be more important than the decay of [M]+ between source and collector in implementing an increase in [A]+/[M]+ at the collector with decreasing accelerator potential.
The mass spectra of small‐ring hetero‐cycles—II. Aziridinones (α‐lactams)
Authors: Baumgarten Henry E. , Parker Richard G. , Von Minden David L. 
Published: May 2005

AbstractThe mass spectra of six aziridinones (α‐lactams) are presented. The six aziridinones exhibit the same general fragmentation pattern, the primary processes being loss of the N‐t‐butyl group, loss of carbon monoxide and loss of t‐butyl isocyanate. Several additional rearrangement or fragmentation processes are observed with specific α‐lactams.
Ionization and dissociation of cyclic ethers and thioethers by electron‐impact. A comparison between 1,4 dioxane, 1,4 dithiane and 1,4 oxathiane
Authors: Condé‐Caprace G. , Collin J. E. 
Published: May 2005

AbstractThe various modes of fragmentation of 1,4 dithiane and 1,4 oxathiane under electron‐impact have been discussed using variation of their mass spectra with electrons energy, high resolution and AP of the main ions. It is shown that they are qualitatively very similar, but differ considerably from those of 1,4 dioxane.
Electron‐impact induced fragmentation of substituted pyrazolone azomethine dyes
Authors: Maier D. P. , Happ G. P. , Regan T. H. 
Published: May 2005

AbstractThe mass spectra of 18 substituted 1‐(p‐R2‐phyeyl)‐3‐R3‐4‐(p‐R1‐phenylimino)‐2‐pyrazolin‐5‐ones have been obtained. The major cleavages under electron bombardment take place in the pyrazoline nucleus, producing four major fragment ions whose abundance is related primarily to the electronic properties of R1. These ions appear to be produced from the molecular ion via an intermediate formed by the loss of CO. In most instances metastable ions are observed for the overall decomposition of the molecular ion to the four major fragment ions. A mechanism is proposed for these cleavages.
The mass spectra of substituted cyclobutanones
Authors: Weiss D. S. , Gagosian R. B. , Turro N. J. 
Published: May 2005

AbstractThe low resolution mass spectra of several di‐, tri‐and tetra‐methylated cyclobutanones were determined at high and low ionizing voltages. The spectra are discussed in terms of the competition between loss of CO or loss of a ketene from the molecular ion of the cyclobutanone. The mass spectral results are correlated with the known photochemical behavior of the cyclobutanones and possible mechanistic implications are discussed.
Mass spectra of chloro‐, aminochloro‐ and ethylaminochloro‐s‐triazines
Authors: Ross James A. , Tweedy B. G. 
Published: May 2005

AbstractThe mass spectra of cyanuric chloride and all of the possible amino‐and ethylaminochloro‐s‐triazines have been investigated. The simpler compounds provide evidence for the structures of low mass fragment ions found in the spectra of the more complex derivatives. Fragmentation patterns are presented which account for most of the major ions. These pathways involve either the initial loss of a chlorine atom (important for the simple aminochlorotriazines) or ring cleavage with expulsion of cyanogen chloride (important for cyanuric chloride). The ethyl derivatives undergo cleavage of the side chain prior to either ring cleavage or chlorine expulsion.
Carbon‐oxygen bond formation in electron‐impact ions of acetylenic sulfoxides and sulfones
Authors: Kinstle T. H. , Oliver W. R. , Ochrymowycz L. A. 
Published: May 2005

AbstractMigration of the ethynyl group, from sulfur to oxygen in acetylenic sulfoxides and sulfones leads to several documented examples of carbon‐oxygen bond forming rearrangement reactions.
Zum Mechanismus Massenspektrometrischer Fragmentierungsreaktionen—V: Substituenteneffekte auf Intramolekulare Substitutionen des Phenylrestes in den Massenspektren von N,N‐Dimethyl‐N′‐Phenylformamidinen
Authors: Grützmacher Hans‐Friedrich , Kuschel Heinz 
Published: May 2005

AbstractDas Massenspektrum des N,N‐Dimethyl‐N′‐phenylformamidins(I) besitzt einen großen Peak von [M  H]⊕‐Ionen. Durch Deuterierung wird gezeigt, daß bei dieser Reaktion ebenso wie bei der entsprechenden Fragmentierung von Thioformanilid (V) eines der beiden ortho‐städigen H‐Atome des Phenylkerns abgespalten wird und Benzimidazolium‐Ionen (a) entstehen.Der Einfluß von Substituenten am Phenylkern auf die Intensität und das AP dieser Ionen und auf das IP der Molekü‐Ionen wird gemessen. Aufgrund dieser Ergebnisse wird ein Mechanismus für die Cyclilsierungsreaktion vorgeschlagen.
Kinetic studies in mass spectrometry—IV. The [M — Cl] reaction in substituted chlorobenzenes and the question of molecular ion isomerization.
Authors: Brown Peter 
Published: May 2005

AbstractThe [M]+˙ → [M  Cl]+ reaction in a series of m‐ and p‐X substituted chlorobenzenes has been studied, utilizing a simple kinetic approach, comparison of metastable ion relative abundances, and by measurement of ionization and appearance potentials. All evidence obtained is consistent with rearrangement prior to cleavage in the molecular ions, in which substituent position becomes effectively randomized. These findings are related to known hydrogen randomization reactions occurring in either the molecular ion or [M  Cl] ion of chlorobenzenes. Mechanisms involving carbon scrambling via such species as ionized benzvalenes or prismanes, or ring‐opening to isomeric acyclic molecular ions in which hydrogen randomization might occur can be entertained, but mechanisms involving simple hydrogen shifts in the intact benzene ring appear less likely.
The decomposition of a triply‐charged metastable positive ion of biphenyl
Authors: Beynon J. H. , Caprioli R. M. , Baitinger W. E. , Amy J. W. 
Published: May 2005

AbstractThe transition, [C12H10]+3→[C11H7]+2 + [CH3]+, has been detected both in the ion kinetic energy spectrum and in the mass spectrum of biphenyl. The width of a resulting ‘metastable peak’ has been measured by setting the magnetic field to accept [C11H7]+2 ions and scanning the high voltage at fixed electric sector voltage. The kinetic energy released in the decomposition, calculated from the peak width, amounted to 4.5 eV. With the assumption that this energy release is due entirely to charge separation, the charge distribution in [C12H10]+3 is discussed. The derivation of the equations used to calculate the energy released is given in the Appendix.
The McLafferty rearrangement in aliphatic aldehydes and ketones—a previously unconsidered mechanistic pathway
Authors: Gerrard A. F. , Hale R. L. , Liedtke R. , Faul William H. , Brown Charles Allan 
Published: May 2005

AbstractThe possibility of a mass spectrometric counterpart to the cyclobutanol formation which is encountered in the photolysis of carbonyl compounds has been investigated by preparing 5,5,5‐[2H3]‐2‐methylpentanal (II) and 6,6,6‐[2H3]‐3‐methylhexan‐2‐one (III) and examining their mass spectra at high and low voltage.
The mass spectra of some naphthoquinones. Lapachol, isolapachol and related compounds
Authors: Elwood Thomas A. , Dudley Kenneth H. , Tesarek Joan M. , Rogerson Peter F. , Bursey Maurice M. 
Published: May 2005

AbstractSeveral alkylhydroxynaphthoquinones and chemically related cyclic compounds were subjected to mass spectrometric investigation. Fragmentation pathways were elucidated by use of metastable ions, relative intensities of normal ions and accurate mass measurement. In these series, differences in the spectra of 1,2‐ and 1,4‐naphthoquinones are slight. Evidence for ring expansion in ions from furans is suggested.
Fragmentation of arylated medium‐ring compounds. The question of rearrangement of molecular‐ion precursors to [C4Ar4]+˙
Authors: Hoffman Michael K. , Elwood Thomas A. , Rogerson Peter F. , Tesarek Joan M. , Bursey Maurice M. , Rosenthal David 
Published: May 2005

AbstractRearrangement of the molecular ions of tetracyclone, tetraphenylquinone, tetraphenylthiophene dioxide and pentaphenylcyclopentadienol prior to decomposition, rather than formation of a symmetrical [C4Ar4]+˙ ion, is considered as an alternative method for the production of [C2Ar2]+˙. The p‐fluoro substituent is used to elicit information about the positional origins of the [C2Ar2]+˙ fragments. Operation of a double focusing mass spectrometer in the defocused mode reveals that the integrity of the molecular ion in different systems is affected to varying degrees, ranging from total lack of rearrangement to virtually complete scrambling.
The mass spectra of thiochromanone and related compounds
Authors: Harrison A. G. , Thomas M. T. , Still I. W. J. 
Published: May 2005

AbstractThe mass spectra of thiochromanone (I), isothiochromanone (II)‐2‐, 3‐ and 8‐methylthiochromanone and the sulfoxides and sulfones derived from these cyclic sulfides have been determined and the major fragmentation routes established. For the iso series loss of SO or SO2 competes effectively with the retro‐Diels‐Alder reaction; however, for the thiochromanone derivatives the retro‐Diels‐Alder reaction is the major fragmentation route. There is no evidence for rearrangement of the sulfoxides or sulfones to sulfenates or sulfinates, respectively, prior to fragmentation.
Mass spectrometry of hop compounds—II: Mass spectra of related oxygen heterocyclic compounds
Authors: Shaw S. J. , Shannon P. V. R. 
Published: May 2005

AbstractMass spectra have been determined of a number of phloroglucinol derivatives and closely‐related compounds encountered in chemical studies of hop components. Initial fission involving acyl, alkyl or alkenyl side‐chains gives predominantly even‐electron ions which then fragment their oxygen heterocyclic rings by elimination of neutral molecules, whilst gem‐dialkenyl centres show preference for loss of an alkenyl group. The fragment ions induced by electron‐impact may be correlated to a useful extent with molecular structure.
Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen–II: Methoxygruppenwanderungen und Ringfragmentierungen in den Massenspektren der Methylather cyclischer Polyalkohole
Authors: Winkler Johann , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractZusammenfassung‐Die Massenspektren der Methyläther von Cyclopentan‐, cyclohexan, und Cycloheptandiolen besitzen einen deutlichen Peak m/e 75 von Ionen dr Struktur ⊕CH OCH3)2, die durch 1,3‐, 1,4‐ oder 1,5‐Wanderung einer Methoxygruppen entstehen. Die Bildung dieser Ionen ist nicht abhängig von der Stereochemie des Ausgangsmoleküs, vermutlich erfolgt die Methoxygruppenwanderung in einem durch α‐spaltung entstandenen offenkettigen Radikal‐Ion: magnified imageBei Cycloalkanen mit drei und mehr Methoxygruppen geben die Umlagerungsionen m/e 75 durchweg einen der gröten Peaks der Massenspektren.Die von einem carbinol‐C‐Atom ausgehenden Bindungen sind geschwächt. Die Anwesenheit mehrerer Carbibnol‐C‐Atome in den Molekül‐Ionen cyclischer Polymethoxyverbindungen begünstigt daher Fragmentierungen. die von den Zerfallsreaktionen einfachr Cyclanolderivate abweichen und charakteristisch für die Stellung der Methoxygruppen sind.
The mass spectra of 5,10‐dihydro‐5‐10‐o‐benzenophenarsazine (azarsatriptycene) and its oxide
Authors: Earley R. A. , Gallagher M. J. 
Published: May 2005

AbstractThe fragmentation of azarsatriptycene and its oxide proceed with initial rearrangement of the molecular ion to give polycyclic systems: it is suggested that similar rearrangements may account for the behaviour of triptycene itself in the mass spectrometer.
Mass spectra of 5,10‐dihydrophenarsazines, 5,10‐dihydrophenarsazine and phenophosphazine oxides, and related heterocycles
Authors: Earley R. A. , Gallagher M. J. 
Published: May 2005

AbstractThe electron‐impact‐induced fragmentation of eight 5,10‐dihydrophenarsazines and three 5,10‐dihydrophenarsazine oxides proceeds by loss of the exocyclic arsenic substituents to give the stable ion (II) as the base peak followed by loss of arsenic to give a carbazole species (III). The fragmentation pattern is independent of substituents at either hetero‐atom in the cases examined. Dihydrophenophosphazine oxides behave similarly but give as the base peak an ion in which the phosphoryl grouping is retained.10,11‐Dihydro‐5‐phenyl‐5H‐dibenzo[b, f][1,4]azarsepine and 2,3‐dihydro‐1,2‐diphenyl‐1H‐benz [c]azarsole fragment by different pathways. It is suggested that the ability of arsenic and phosphorus to sustain a positive charge by dπ‐pπ bonding is the dominating factor in these fragmentations.
Mass spectral studies on tanshinones
Authors: Hayashi T. , Inouye Y. , Ohashi M. , Kakisawa H. , Tatematsu A. , Kinoshita T. 
Published: May 2005

AbstractThe mass spectra of three groups of tanshinones have been examined and a number of characteristic features noted which might be helpful in the micro‐identification of the natural products. The fragmentation patterns are similar to each other except for the relative intensity within the same group of tanshinones and are accounted for in terms of the general fragmentations of furans and quinones. Characteristic ions at m/e 178, 165 and 152 found in all kinds of tanshinones may be considered to be of highly aromatized hydrocarbon fragments and are of good for the structure elucidation of these compounds.
Mechanism of the expulsion of oh from the [M  C2H4]+˙ ion from ethyl benzoate
Authors: Shapiro Robert H. , Tomer Kenneth B. , Caprioli Richard M. , Beynon John H. 
Published: May 2005

AbstractIon kinetic energy spectra of the esters C6H5C18OOC2D5 and C6H5COOC2D5 show that the ion formed by loss of C2D4 from the molecular ion has the deuterium atom attached to the carbonyl oxygen atom. Transfer of this deuterium to the other oxygen can only take place via exchange reactions involving the ortho‐hydrogen atoms and requires at least two complete rotations of the side‐chain.
The expulsion of OH˙ from the [M  C2H4]+˙ ion from ethyl benzoate: Ring‐deuterated compounds
Authors: Shapiro R. H. , Tomer K. , Beynon J. H. , Caprioli R. M. 
Published: May 2005

AbstractMass spectra and ion kinetic energy (IKE) spectra of o‐, m‐ and p‐d1 ethyl benzoates have given further information on the loss of OH˙ and OD˙ from the [M  C2H4]+˙ ions. The ‘metastable peaks’ in the mass spectra give information on fragmentations in the field‐free region following the electric sector; the IKE spectra give information on fragmentations in the field‐free region preceding this sector. Transfer of hydrogen and deuterium from the ortho‐positions on the ring to the carboxyl group can occur, but scrambling of ring hydrogens does not take place. A sample of o‐d1 benzoic acid was also examined and confirmed that similar transfer reactions occur in this compound too.
Electron‐impact promoted fragmentation of alkyl‐N‐(1‐phenylethyl)‐carbamates of primary, secondary and tertiary alcohols
Authors: Pereira W. E. , Halpern B. , Solomon M. D. , Duffield A. M. 
Published: May 2005

AbstractThe mass spectra of twenty N‐alkyl‐(1‐phenylethyl)‐carbamates derived from primary, secondary and tertiary alcohols have been investigated using deuterium labeling and high resolution mass spectrometry. These derivatives are suitable for the determination of the isotopic purity of primary and secondary, but not of tertiary alcohols. Several of the primary and secondary alcohol derivatives yield an ion formally equivalent to the product ion of a McLafferty rearrangement. Deuterium labeling established, however, that the usual site specificity associated with the McLafferty rearrangement process was lacking in these carbamate derivatives. In addition a double hydrogen rearrangement process was observed in the mass spectra of several of the carbamates derived from tertiary alcohols.
Studies on the mass spectra of 6‐methylthiopurine and its C‐and N‐methyl derivatives
Authors: Deutsch Joseph , Neiman Zohar , Bergmann Felix 
Published: May 2005

Abstract6‐Methylthiopurines which bear a 9‐NH‐ or a 9‐NCH3‐group (class A) form an [M—1]‐ion with much higher abundance than do the 1‐, 3‐, or 7‐methyl derivatives (class B). The higher stability of the [M—1]‐ion in class A may be explained by ring closure to N‐7.Methyl radicals are cleaved from N‐, but not from S‐ or C‐methyl groups, with the exception of the 7‐methyl derivative, in which the S‐CH3‐group can also split off a methyl radical. The methylthio group may lose all of the following fragments: S, SH, SCH, SCH2 and SCH3. In the remaining purine skeleton, in general first the pyrimidine and subsequently the imidazole ring breaks down with elimination of HCN.
Spectres de masse de phosphonates diméthyliques dérivés du norbornane, du norbornéne et du nortricyclane
Authors: Callot Henry J. , Benezra Claude 
Published: May 2005

AbstractLes spectres de rnasse de phosphonates diméthyliques (I à X) dérivés du norbornane, du norbornène et du nortricyclane ont été étudiés. La fragmentation des isoméres endo et exo est trés comparable (seules les intensités des pics varient légèrement) sauf pour les dérivés saturés I et II où l'orientation du groupe P(O)(OCH3)2 inhence les coupures. Les spectres des dérivés du norbornène III et IV et du composé nortricyclique isomère IX sont très différents. La fragmentation des phosphonates I à X est dominée par la localisation de la charge sur le fragment phosphoré.
Elektronenstoß‐induzierte Fragmentierung von 1,2,3,‐Thiadiazolen
Authors: Zeller K.‐P. , Meier H. , Müller Eu. 
Published: May 2005

AbstractDie Massenspektren einiger alkyl‐, aryl‐, acyl‐ und aroylsubstituierter 1,2,3‐Thiadiazole und des Benzothiadiazols werden mitgeteilt und interpretiert. Nach der Abspattung von N2 aus dem Molekiilion erleidet das [M—N2]+.‐ion eine Art WolRsche Umlagerung zu einem Thioketen‐Ionen‐Radikal. Ais Beweis wird die Bildung von Fragmentionen angefiihrt, die eine solche Umlagerung voraussetzen. Außerdem wird die Eliminierung von S bzw. ·SH aus dem nicht ungelagerten [M—N2]+.‐Ion diskutiert.
Mass spectrometry in structural and stereochemical problems—CXCIX Contrasting fragmentations of singly‐ and doubly‐chargedo‐,m‐ andp‐hydroxyalkylphenones and their trimethylsilyl ethers
Authors: Smith Grant Gill , Djerassi Carl 
Published: May 2005

AbstractHigh resolution mass spectrometry, metastable defocusing and deuterium labeling of trimethylsilyl (TMS) ethers have been used to study the electron‐impact induced fragmentations ofo‐,m‐andp‐hydroxyalkylphenones and their TMS ether derivatives. These derivatives have proven useful in contrasting the fragmentation patterns of singly‐ and doubly‐charged ions because of the competing fragmentations: α‐cleavage and a McLafferty rearrangement from the ketone moiety and methyl cleavage from the TMS group. A proximity effect was responsible for a markedly increased methyl radical loss from theo‐TMS ether. This fragmentation was minor with them‐andp‐isomers. Significantly intense doubly‐charged ions were formed from ketonic cleavage and by the loss of a TMS methyl radical. The sequence of fragmentation depended on the size of the alkyl group attached to the ketone carbonyl. There was no evidence found for a McLafferty rearrangement occurring from the doubly‐charged molecular ion of the TMS ethers of the hydroxyalkylphenones but the rearrangement occurred from the doubly‐charge molecular ion ofbis‐3‐(1‐oxopentyl)‐4‐hydroxy‐phenyl‐methane and, of course, from the singly charged [M]+.Thebis‐p‐hydroxyphenylmethane derivatives were studied in an effort to increase the intensity of the doubly‐charged ions as it was expected that the charges would be separated by a longer distance.
The mass spectra of benzamide and thiobenzamide
Authors: Holmes J. L. , Benoit F. 
Published: May 2005

AbstractThe mass spectra of benzamide, thiobenzamide and their N‐d2 analogues have been studied In addition to fragmenting by simple bond cleavages the molecular ions dissociate partly from their imide forms. Equilibration or ‘scrambling’ of ortho ring hydrogen atoms with amide hydrogen did not occur in benzamide but such exchange must take place in the thiocompound whose fragmentation behaviour is very complex. Neither labelled compound produced the label‐retaining benzoyl (thiobenzoyl) cation which has been the subject of much interest in the mass spectrum of O‐d1 benzoic acid.
Mass spectrometry in structural and stereochemical problems—CCIV. Spectra of hydantoins II. Electron impact induced fragmentation of some substituted hydantoins
Authors: Corral Reneé A. , Orazi Orfeo O. , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractThe mass spectral decomposition modes of hydantoin and derivatives containing alkyl and phenyl substituents have been investigated using isotopic labeling techniques. The loss of carbon monoxide from the molecular ions of these compounds was shown to preferentially involve the C‐4 carbonyl group. Other fragmentation processes characteristic of the hydantoin ring system and the effect on this of alkyl and phenyl substitution are described.
The mass spectra of some s‐triazolo[4,3‐a]pyrazines
Authors: Potts K. T. , Brugel E. 
Published: May 2005

Abstracts‐Triazolo[4,3‐a]pyrazine underwent decomposition by loss of nitrogen from its molecular ion whereas in the 3‐alkyl derivatives the corresponding alkyl cyanide was eliminated from the 5‐membered ring. The introduction of a carbonyl or thiocarbonyl group into the 3‐position resulted in predominant loss of the triazole ring in the fragmentation process; however, with a 3‐amino substituent, the first fragment eliminated from the molecular ion was cyanamide. Methyl substitution in the 6‐membered ring resulted in the formation of ring expanded ions. On phenyl substitution, however, an interesting 1,2‐phenyl migration was observed. The mass spectra of several analogous s‐triazolo[1,5‐a]pyrazines are also described.
Carbon monoxide expulsion on electron‐impact: Hybrid fragmentation of α‐keto hemithioketals
Authors: Fenselau Catherine , Chandler H. A. , Pyles M. , Sander D. L. , Robinson C. H. 
Published: May 2005

AbstractThe fragmentation pattern and mass spectrum of 1‐(ethylene‐1′‐oxy‐2′‐thio)‐cyclohexan‐2‐one differ markedly from those of the related mono‐functional cyclohexane derivatives, cyclohexanone and (ethylene‐1′‐oxy‐2′‐thio)‐cyclohexane. This investigation delineates facile expulsion of carbon monoxide as the major hybrid fragmentation. The possibility of ring recyclization accompanying the expulsion is discussed.
Electron‐impact studies—LX Negative‐ion mass spectrometry of functional groups skeletal‐rearrangements in aryl nitro compounds
Authors: Bowie J. H. 
Published: May 2005

AbstractThe molecular anions of nitrobenzenes containing an electron‐withdrawing substituent eliminate NO· via a skeletal rearrangement process in the order ortho > para > meta. An ortho substituted nitrobenzene may eliminate a neutral molecule after the loss of NO· Hydrogen‐rearrange‐ment processes, hydrogen‐scrambling processes, and unusual concerted eliminations are noted in certain spectra. Isomeric nitrobenzenes are generally more readily differentiated by negative‐ion than positive‐ion mass spectrometry.
Ortho effect: The fragmentation of isopropyl 2‐hydroxychlorocarbanilates
Authors: Still Gerald G. 
Published: May 2005

AbstractThe mass spectra of isopropyl 2‐hydroxychlorocarbanilate indicate a preferential ortho intramolecular rearrangement which yields a chloro 2‐benzoxazolinone intermediate ion. A com‐parison of the fragmentation of ortho, meta and para hydroxy analogs of isopropyl 3‐chlorohydroxy‐carbanilate indicates the existence of an ‘ortho effect’ during the fragmentation of isopropyl‐chloro 2‐hydroxycarbanilates.