bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of distal positional isomerism on peptide fragmentation. A comparison of dimethylaminobenzylidene and benzoyl derivatives
Authors: Haralambidou E. , Day R. A. 
Published: May 2005

AbstractThe electron‐impact‐induced fragmentation patterns of the positional isomers of N,N‐dimethylaminobenzaldehyde and their Schiff base derivatives of valylisoleucylalanine and leucyltryptophylleucine ethyl esters were determined. The electron‐impact‐induced fragmentation patterns of the positional isomers of N‐hydroxysuccinimido N′,N′‐dimethylaminobenzoate and of the corresponding N,N‐dimethylaminobenzoyl ethyl esters of the above peptides were compared. Significant differences among the isomers were noted between the Schiff base set and the substituted benzoyl set. The N‐blocking groups m‐ and p‐dimethylaminobenzylidene and m‐dimethylaminobenzoyl gave the most useful sets of sequence peaks of relatively uniform intensity with intense molecular ions. Positional isomerism was found to influence cleavage of both proximal and distal bonds.
A study of the fragmentation of cyclopentane‐1,3‐diols and of cyclopentane‐1,2,4‐triols
Authors: Singy Gérard A. , Buchs A. 
Published: May 2005

AbstractThe mass spectra of the two cyclopentane‐1,3‐diol and of the three cyclopentane‐1,2,4‐triol stereoisomers have been studied. Extensive deuterium labelling allows the detection of complex processes, especially for the elimination of water from the [M – H2OO]+· and [M]+· ions.
Fragmentation of 13C Labelled methylcyclohexanes under electron‐impact
Authors: Amir‐Ebrahimi Valia , Gault Franc̨ois G. 
Published: May 2005

AbstractThe methylcyclohexanes labelled with carbon‐13 in the five possible positions have been synthesised and their mass spectra recorded. By comparison of these spectra with those of the corresponding deuterated molecules, it was possible to accurately determine the nature and the contribution of the various fragmentation paths. More than ninety percent of the fragment ions formed from methylcyclohexane result from the rupture, at one stage or another, of one of the CC bonds attached to the tertiary carbon atoms. Besides the elemination of a polymethylene group from the ring, in either one or two steps, the two major fragmentation pathways involve the prior formation of a cyclohexyl or a cyclopentyl ion.
The high pressure nitric oxide mass spectra of aldehydes
Authors: Jardine Ian , Fenselau Catherine 
Published: May 2005

AbstractThe high pressure (0.5 Torr) nitric oxide mass spectra of some aldehydes, obtained using a 10% mixture of NO in N2, are reported. The 10% NO/N2 spectra of the monodeuterated analogs of some of them are compared to the electron‐impact and methane chemical ionization spectra, especially with reference to the process of hydride abstraction by nitrosonium ions.
Stossaktivierungsspektren von 2‐Alkoxybenzoesäuremethylestern
Authors: Levsen Karsten , Schwarz Helmut 
Published: May 2005

AbstractDie CA‐Spektren der [M – Alken]+·‐ und [M – Alkyl]+‐Ionen aus mehreren 2‐Alkoxybenzoesäremethylestern und zwei2H‐markierten 2‐Äthoxybenzoesäuremethylestern werden diskutiert. Es wird belegt, daß die nach 10−5s durch Stoßaktivierung zerfallenden [M – Alken]+·‐Ionen die Struktur eines ionisierten Salicylsäuremethylesters besitzen. Ferner wird nachgewiesen, daß auch nach 10−5skeineEquilibrierung zu einem strukturidentischen Ion eingetreten ist. Anhand der CA‐Spektren der markierten Derivate werden verschiedene Ionenstrukturen für die durch Stoßaktivierung erzeugten Tochter‐Ionen diskutiert.
Hydrogen shifts in the decomposition of branched chain alkane radical cations
Authors: Howe Ian 
Published: May 2005

AbstractHeat of formation data are consistent with formation of the t‐butyl ion when C3H7 is eliminated from the molecular ion of 2‐methylhexane. The 1–2 hydrogen shift that must accompany this reaction is confirmed via a deuterium isotope effect upon the low energy metastable decomposition.
Fragmentations de quelques derives thiophosphores sous l'impact electronique. I—migration de groupes phenyles et methyles dans les derives du diphenylthiophosphorane
Authors: Cauquis G. , Divisia B. , Ulrich J. 
Published: May 2005

AbstractLa localisation de la charge d'ionisation dans les diphénylthiophosphoranes substituspar des groupes phényle, méthyle, benzyle, méthylthiométhyle, phénacyle, amino et N‐benzylidèneé amino a permis d'élucider leurs réctions de fragmentation sous l'impact électronique. La composition atomique des divers fragments été déterminée par la mesure précise de leur masse. Ces mécanismes de fragmentation sont confirmés par la présence de nombreux pics d'ions métastables. Les principales fragmentations des composés par la présence de nombreux pics d'ions métastables. Les principales fragmentations des composés phénacyl et aminodiphénylthiophosphoranes s'expliquent par la migration importante de groupes phényles et méthyle du phosphore vers le soufre. Dans les composés benzyl, méthylthiométhyl et N‐benzylidéneamino, l'élimination d'espéces neutres très stables (respectivement le radical benzyle, le thioformaldéhyde et le benzonitrile) favorise d'autres mécanismes de fragmentation.
Die Massenspektren substituierter Succinimide
Authors: Schoch S. , Blos I. , Rüdiger W. 
Published: May 2005

AbstractDie Massenspektren von Succinimid, vier monosubstituierten und zehn disubstituierten, gesättigten Succinimiden, sowie von sechs ungesättigten (Äthyliden‐substituierten) abgeleitet, die die Identifizierung unbekannter substituierter Succinimide erlauben, welche beim Abbau natürlicher Pyrrol‐Pigmente erhalten werden.
Analyse par Spectrometrie de Masse de Derives Fluores en Serie Pyrimidine et Pyrazine
Authors: Hitzke J. , Guion J. 
Published: May 2005

AbstractLes dérivés flourés des trichloro‐, dichloropyrimidines et dichloropyrazines ont été synthétisés et analysés par r.m.n. 1H et 19F, associée à la chromatographie couplée avec la spectrométrie de masse. Le comportement de ces composés l'impact électronique est présenté et discurté dans ce travail. Les différences observées pour les spectres masses d'isomérs de position nous permettent de confirmer les grandes voies de dégradation proposées.
Massenspektrometrische Analyse von 2‐Alkoxy‐und 2‐Alkylmerkapto‐(1,3,2)Diox‐, Oxathi‐und Dithi‐Arsolanen
Authors: Adler Oswald , Kober Friedhelm 
Published: May 2005

AbstractDie Massenspektren der Arsolane (CH2)2XY AsZR (X, Y und Z= O oder S) bei elektronenstoß‐ und Chemischer Ionisation werden verglichen und die Haupt‐Fragmentierungsreaktionen angegeben. Elektronenstoss‐Ionisation‐ und Chemische‐Ionisation‐Spektren zeigen eine Dimeerisierung der Arsolane.
Negative ions in organic mass spectrometry. II—Negative ion mass spectra of simple thio and dithio esters.
Authors: Rullkötter Jürgen , Budzikiewicz Herbert 
Published: May 2005

AbstractThe 70 eV negative ion mass spectra of some simple aromatic and aliphatic thio and dithio esters are discussed. A characteristic fragmentation process, a rearrangement analogous to the nitro‐nitrite conversion of aromatic nitro compounds, is observed for aromatic thio esters.
Fragmentation Sous Impact Electronique de la Pyrrolidine et D'Isoindolines N‐Nitrosees et N‐Aminees
Authors: Denhez Jean Pierre , Ricard Michègle , Dizabo Pierre , Rogic Dunja 
Published: May 2005

AbstractLes spectres de masse des dérivés N‐aminés de la pyrrolidine, de l'isoindoline et de la diphényl isoindoline ont été étudiés. L'utilisation d'une résolution moyenne et du marquage au deutérium a permis de mécanismes de fragmentation.
Massenspektrometrische Untersuchungen an 1.1‐Difluorcyclopropanen
Authors: Kamel M. , Kimpenhaus  , Riepe W. 
Published: May 2005

AbstractDie Massenspektren von verschiedenen substituierten 1.1‐Difluorcyclopropanen wurden aufgenommen und ihr Fragmentierungsverhalten untersucht. die Tendenzen in den Bildungswahrscheinlichkeiten der Bruchstükionen bei verschiedenen Difluorcyclopropanen lassen sich qualitativ mit bekanten empirischen Substituenteneffekten erklären.
Mass spectrometry of pyrrolo [2, 3‐ b] pyrazines and pyrazino [2, 3‐ b]indole
Authors: Clark B. A. J. , Parrick J. 
Published: May 2005

AbstractThe first mass spectra of pyrrolo [2, 3‐b] pyrazine and some of its derivatives and of pyrazino [2, 3‐b] indole are reported and compared with those of related compounds. Differences between the spectra of some aryl substituted derivatives are described and discussed.
Mass spectra of substances ionized by fission fragment induced desorption
Authors: Becker Otmar , Fürstenau Norbert , Knippelberg Werner , Krueger Franz R. 
Published: May 2005

AbstractThe mass spectra of substances of physiological and pharmaceutical interest such as steroids, alkaloids, sugars, glycosides and similar, obtained by fission fragment induced desorption as first applied by Macfarlane are presented. The behaviour of organic and inorganic salts is also discussed, including that of mixtures of salts and organic substances. Comparison is made with field desorption data, where available, and electron impact data for those substances of sufficient volatility.
Etude par Spectrométrie de Masse de Silanes et de Stannanes Aromatiques
Authors: Lageot C. , Guillemonat A. 
Published: May 2005

AbstractLes spectres de masse de six composés du type Et3SiC6H4  ZRxR3−x (Z = Si et Sn, R = Et, R′ = Cl) ont été interprétés. Les résultats ne peuvent être expliqués que par une réorganisation du cycle benzénique sous une forme linéaire.
Hétérocycles des Eléments du Groupe IV. VII—Spectrométrie de Masse de Silacyclopentènes
Authors: Lageot C. , Guillemonat A. 
Published: May 2005

AbstractLes spectres de masse de nouveaux silacyclopenténes ont été étudiés. Les méchanismes intervenant sont proches de ceux de la série des germacyclopenténes. Ils conduisent principalement à une rétention de la charge sur l'hétéroatome, à une migration d'hydrogéne, à la formation d'ions du type ‘silylénïd’ et à l'expulsin d'un substituant fixé sur l'hétéroatome.
The Use of two scanning modes for the analysis of metastable peaks
Authors: Lacey Michael J. , MacDonald Colin G. 
Published: May 2005

AbstractTwo scanning modes can be used sequentially to determine the relative abundances of a series of daughter ions formed from the same parent ion in the field free region preceding the first sector of a double focusing mass spectrometer. Hydrogen exchange reactions in the molecular ions of benzoic acid and anisole have been analysed by these procedures, and a study of diphenylmethane demonstrates that the usual procedure of single scans gives rise to peaks that might be interpreted erroneously.
Mass spectral hydrogen rearrangements of 1,1′‐bicycloalkyldiols under electron impact
Authors: Deutsch Joseph , Chriki Miriam 
Published: May 2005

Abstract1,1′‐Bicycloalkyl‐2,2′‐diols (mixtures of stereoisomers) and 1,1′‐diols on electron impact give rise to strong peaks equivalent to [M‐1]+ions, corresponding to cycloalkenone fragments and obviously involving hydrogen atom migrations. Deuterium labelling and substitution techniques reveal the operation of different rearrangement mechanisms for the two series of isomeric compounds. Thus, in the 1,1′‐bicycloalkyl‐2,2′‐diols a ring hydrogen atom is involved in the rearrangement, whereas in the 1,1′‐bicycloalkyl‐1,1′‐diols (pinacols) the hydroxylic hydrogen atoms migrate.
An investigation of the mechanism of single and double hydrogen atom transfer reactions in alkyl benzoates by the ortho effect
Authors: Tajima Susumu , Azami Tadashige , Shizuka Haruo , Tsuchiya Toshikazu 
Published: May 2005

AbstractSingle and double hydrogen atom transfers in reactions (1) and (2) in the mass spectra of ethyl benzoate, isopropyl benzoate, and isobutyl benzoate have been investigated with reference to the ortho effect: (1) [C6H5CO2R]+⋅ → [C6H5CO2H]+⋅ (m/z 122) + (R‐H); (2) [C6H5CO2R]+⋅ → [C6H5CO2H2]+ (m/z 123) + · (R‐2H). It is demonstrated that the intermediate ion [C6H5CO2H2]+ has the protonated benzoic acid structure with the hydrogen atom on the carbonyl group.
Electron impact induced fragmentation of steroidal diketones with ‘abnormal’ stereochemistry
Authors: Patterson Donald G. , Lavanchy André , Djerassi Carl 
Published: May 2005

AbstractThe mass spectral fragmentations of steroidal diketones with ‘unnatural’ sterechemistry at positions 8, 9 and 14 have been examined by the use of high resolution, metastable defocusing and isotopic labeling techniques. In addition, the elucidation of fragmentation pathways was greatly facilitated by the use of the INTSUM computer program. In contrast to 14α‐11‐ones, where the McLafferty rearrangement is of minor importance in directing the fragmentation, it is suggested that the ketones in the present study, by virtue of their ring C flexibility, readily undergo the McLafferty rearrangement. If correct, this would represent a further example of available ground state conformations controlling fragmentation after electron impact.
Mass spectrometric fragmentation of the oxetanes of 3,5‐dimethylisoxazole, 2,4‐dimethylthiazole and 1‐acetylimidazole
Authors: Nakano Tatsuhiko , Mart Alfonsoín 
Published: May 2005

AbstractThe mass spectra of the oxetanes of 3,5‐dimethylisoxazole, 2,4‐dimethylthiazole and 1‐acetylimidazole have been studied with the aid of high resolution mass spectrometry. The spectra exhibit characteristic fragmentation patterns which are common to all these oxetanes and are classified as five processes.
Carbene elimination from ionized methanoannulenes
Authors: Wesdemiotis Ch. , Schwarz H. , Budzikiewicz H. , Vogel E. 
Published: May 2005

AbstractEvidence is produced to demonstrate that loss of CH2 from methanoannulenes is a multistep process initiated by a rearrangement yielding (at least in the case of 1,6‐methano[10]annulene) the isomeric benzocycloheptenes. Loss of CF2, however, apparently is a cheletropic reaction accompanied by rearomatization, thus giving rise to the formation of the molecular ion of naphthalene in the case of 11,11‐difluoro‐1,6‐methano[10]annulene. These findings present further evidence for the parallel behaviour of the bridged annulenes regarding thermal transformations and fragmentation of the molecular ions.
Doubly charged ion mass spectra. 2—aromatic hydrocarbons
Authors: Mathur B. P. , Burgess E. M. , Bostwick D. E. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra for 15 aromatic hydrocarbons have been obtained using a Nier‐Johnson geometry, Hitachi RMU‐7L mass spectrometer operating at 1.6 kV accelerating voltage. The doubly charged ion spectra have features that are characteristic of the individual compounds. Unsaturated aromatic molecules show intense molecular ions in contrast to saturated, substituted or heteroatom compounds which undergo extensive fragmentation. Ionization energies for forming doubly charged molecular ions and appearance energies for the prominent doubly charged fragment ions have been measured. Calculations of the SCF energies and structures of various doubly charged ions have been carried out. Measured and calculated ionization/appearance energies are in reasonable accord and lend support to the suggested ion structures.
Mass spectrometry of halo‐pyrazolium salts
Authors: Larsen Elfinn , Egsgaard Helge , Pande Umesh C. , Begtrup Mikael 
Published: May 2005

AbstractEleven halogen substituted 1‐methyl‐2‐phenylpyrazolium bromides or chlorides were investigated by field desorption, field ionization, and electron impact mass spectrometry. Dealkylation was found to be the predominant thermal decomposition. An exchange between covalent and ionic halogen prior to dealkylation was observed and is discussed in detail.
Ammonia chemical ionization mass spectra of esters and amides of oxyacids of phosphorus
Authors: Cload P. A. , Hutchinson D. W. 
Published: May 2005

AbstractChemical ionization mass spectrometry using ammonia as the reagent gas has been carried out with esters and amides of a variety of oxyacids of phosphorus (phosphates, phosphonates, phosphites and phosphoramidates). In all cases, the protonated molecular ion is a major species in the spectrum and the percentage of the total ion current carried by these protonated molecular ions is always considerably greater than that carried by the molecular ions in the corresponding electron impact mass spectra. In the chemical ionization mass spectra only limited fragmentation of the protonated molecular ion occurs from which useful information on the structure of phosphorus derivatives may be inferred.
The mass spectra of some benzyl esters and thioethers
Authors: Corina D. L. , Wright J. N. , Ballard K. E. 
Published: May 2005

AbstractThe electron impact mass spectra of a large number of benzyl esters of carboxylic acids are reported. The fragmentation behaviour is discussed and the esters are divided into groups according to structure and fragmentation. For most esters benzylic cleavage with H transfer competes with simple cleavage.
Electron impact mass spectrometry of some macrocyclic tetraesters
Authors: Traldi Pietro , Vettori Umberto , Podda Gianni , Maccioni Antonio , Corda Luciana 
Published: May 2005

AbstractThe electron impact mass spectrometric behaviour of five recently synthesized macrocyclic tetraesters is described and discussed in detail with the aid of exact mass measurements, linked scans and collisional activation experiments. The unusual primary loss of a dehydrogenated catecholic radical leads to a very stable cation which is the precursor of the most of the fragmentation products.
On the electron impact induced hydroxyl loss from o‐nitrostyrene
Authors: Depke Gisbert , Klose Walter , Schwarz Helmut , Blum Wolfgang , Richter Wilhelm J. 
Published: May 2005

AbstractUnimolecular hydroxyl (OD˙) loss from regio‐ and stereo‐specifically labelled o‐nitrostyrenes 1a, 1c and 1d results in the formation of an ion which upon collisional activation gives identical mass spectra. Suggestions are made which aim at explaining: (i) the loss of stereochemical integrity of the diastereotopic methylene hydrogens in the course of hydroxyl elimination; and (ii) to account for the collision induced losses of CO and HNC from the [M—hydroxyl]+ ion.
Low energy, low temperature mass spectra: I—selected derivatives of n‐octane
Authors: Bowen Richard D. , Maccoll Allan 
Published: May 2005

AbstractThe low voltage, low temperature mass spectra of a series of octane derivatives n‐C8H17X with X=CH3, OH, OCH3, NH2, NHCH3, N(CH3)2, CO2H, CO2CH3, CO2C2H5, CHO and COCH3 are reported and discussed, using arguments involving thermochemistry where appropriate. The structures of these compounds can be uniquely assigned on the basis of such mass spectra.
Photodissociation of alkane ions in the source of a mass spectrometer: A potential analytical technique
Authors: Kim M. S. , Morgan T. G. , Kingston E. E. , Harris F. M. 
Published: May 2005

AbstractAlkane ions generated by 70 eV electron ionization are irradiated in the source of a reversed geometry, double focusing mass spectrometer by 2.41 eV (514.5 nm) photons from an argon ion laser. The ions in the chamber are extracted, accelerated to 6 keV and spectra obtained by scanning the field of the magnet. The laser light is mechanically chopped and changes in the peak heights of the mass spectra resulting from photodissociation of ions in the ion chamber are recorded using a phase‐sensitive detector to give what are referred to as photoinduced spectra. The peaks for the molecular ions of alkanes are large relative to other peaks in the photoinduced spectra, a situation which contrasts with that for the mass spectra. The relative photodissociation cross‐sections of several alkanes, C6C10, C12 and C16, have been measured and those of linear and branched [C10H22]+˙ ions are compared. Some of the characteristic features of the photoinduced spectra make the identification of the sample simpler than from mass spectra. The method is applied to the analysis of some alkane mixtures and its potential in analytical work discussed.
Kinetic energy release during CO loss by rearrangement of α‐benzoylcarbenium ions
Authors: Grützmacher Hans‐Friedrich , Dommröse Anne‐Marie 
Published: May 2005

AbstractPrimary α‐benzoylcarbenium ions (a) and tertiary α‐benzoyldimethylcarbenium ions (b) are obtained by chemical ionization of ω‐hydroxyacetophenone and its dimethyl derivative, respectively. Both α‐acylcarbenium ions decompose by a rearrangement reaction and subsequent loss of a CO molecule. The kinetic energy released during this process by metastable ions a and b has been determined under different experimental conditions. The kinetic energy released during the CO elimination from the tertiary α‐benzoyldimethylcarbenium ions b is independent of the experimental conditions and gives rise to dish‐topped peaks with T50=440±20 meV in the MIKE spectra of b. In contrast to this the kinetic energy releases and the peak‐shapes in the MIKE spectra of the primary α‐benzoylcarbenium ion a varies with the experimental conditions. The mechanism of this rearrangement reaction is discussed, and it is shown by a MNDO calculation of the heats of formation of the relevant ions that the different characteristics of the kinetic energy release during the fragmentation of primary and tertiary carbenium ions can be attributed to different types of reaction energy profiles.
Sequence analysis for an unknown peptide by molecular secondary ion mass spectrometry
Authors: Seki Setsuko , Kambara Hideki , Naoki Hideo 
Published: May 2005

AbstractPositive and negative molecular secondary ion as well as metastable ion mass spectra for various peptides are investigated to clarify their fragmentation regularity. The fragmentation regularity is derived by considering all the possible bond cleavages at the peptide bond or at the adjacent bonds. It is demonstrated that the amino acid sequence for an unknown peptide can be determined by interpreting the positive and negative secondary ion and metastable ion mass spectra using this fragmentation regularity.
Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2‐pentanone molecular ion
Authors: Laderoute Keith R. , Zwinselman Jan J. , Harrison Alex. G. 
Published: May 2005

AbstractThe [C4H70]+ ions [CH2CHC(OH)CH3]+ (1), [CH3CHCHC(OH)H]+ (2), [CH2C(CH3)C(OH)H]+ (3), [Ch3CH2CH2CO]+ (4) and [(CH3)2CHCO]+ (5) have been characterized by their collision‐induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2‐pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C5H10O]+˙ system.
A mass spectrometric study of the adducts of acetylacetone and cyanogen (Traube's isomers)
Authors: Basato M. , Corain B. , Veronese A. C. , Daolio S. , Pelli B. , Traldi P. 
Published: May 2005

AbstractThe mass spectrometric behaviour of the title compounds has been studied in detail with the aid of deuterium labelling, exact mass measurements, linked scans and collisionally activated decomposition experiments. An interesting conversion reaction of the cyanoenaminedione isomer into the corresponding furane derivative, which appears complete in the second field free region, has been thoroughly investigated.