bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometry of heterocyclic compounds. V—Substituent effects on the fragmentation pathways of 3,5‐diphenyl‐1,2,4‐oxadiazole derivatives
Authors: Selva A. , Zerilli L. F. , Cavalleri B. , Gallo G. G. 
Published: May 2005

AbstractThe 70 eV mass spectra of a number of derivatives of 3,5‐diphenul‐1,2,4‐oxadiazole substituted either in the 5‐phenyl (fifteen) or in the 3‐phenyl (four) position, have been studied using exact mass measurements and metastable determinations by the defocusing technique. The substituent effects on the heterocyclic cleavage are not very important for electron‐withdrawing and weak electron‐donating groups. The main cleavage is the formal retro 1,3‐dipolar cycloaddition with the positive charge retained by the C7H5NO (orYC7H4NO in the case of the 3‐substituted derivatives) fragment specifically containing the 3‐phenyl, as oreviously observed for 3,5‐diphenyl‐1,2,4‐oxadiazole using labelling experiments. Two other minor primary processes leading to benzoyl and nitrile ions, both containing the 5‐phenyl, become important in the case of the electron‐donating substituted compounds. Correlation of the abundance of these fragmednts and of the molecular ions with σ+ (para) Brown constants is discussed. Proximity effets are shown by some ortho derivatives.
Energetische Betrachtungen zur Intramolekularen Solvatisierung von Ionen bei der Elektronenstoss‐Induzierten Fragmentierung von α,ω‐Bis‐(Trimethylsilyl)‐Äthern
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand 
Published: May 2005

AbstractEs wird mit Hilfe von AP‐Messungen gezeigt, daß die stabilen [M – CH3]+‐Ionen aus α,ω‐Bis‐(Trimethylsily)‐äthern des Typs TMSO(CH2)nOTMS (n = 2 bis 7) keine cyclische Struktur besitzen.
Application of the indo molecular orbital method to ortho effects in mass spectra. Cleavage of cis‐β‐methoxystyrene
Authors: Kao Jar‐Lin , Parker Carol E. , Bursey Maurice M. 
Published: May 2005

AbstractThe principal fragmentation of the cis‐β‐methoxystyrene molecular ion is loss of the methyl group. Although this compound has a π system similar to that of phenyl acetate, the substituent effect of a strongly electronegative ortho substituent is insignificant for this fragmentation; but for the same substitution in phenyl acetate, it had been shown to be important. The INDO method was used to show that bond orders confirm the lack of the substituent effect in the cis‐β‐methoxystyrene system.
Electron‐impact mass spectrometry of Nuphar alkaloids
Authors: LaLonde Robert T. , Wong Chun F. , Woolever John T. , Auer Egmont , Das Kala C. , Tsai Amy I‐M. 
Published: May 2005

AbstractPrincipal peaks in the mass spectra of deoxynupharidine are accounted for on the basis of high resolution mass spectrometry and peak shifts in the mass spectra of deoxynupharidine‐4‐d1 and deoxynupharidine‐6β, 7β‐d2. Cleavage of the quinolizidine ring system of deoxynupharidine occurs predominantly in ring A, giving m/e 136, 107, 98, 94 and 81. The origins of the family of ions [M — alkyl]+ and m/e 178 are considered. A comparative survey is made of the occurrence of these ions, and others, in the mass spectra of piperidine, quinolizidine and thiospirane types of Nuphar alkaloids. Attention is directed toions useful in distinguishing structural types.
Electron‐impact and thermal degradation of Rhodamine F5G chloride and related compounds
Authors: Davie Elizabeth , Morris John H. , Smith W. Ewen 
Published: May 2005

AbstractThe mass spectra and thermal decomposition of Rhodamine F5G hydrochloride have been studied in detail. Fragmentation schemes are presented which show that fragmentation in the mass spectrometer involves principally the substituents on the 9‐phenylxanthhydrol nucleus. Mass spectral studies of the related compounds Rhodamine B500 hydrochloride, Rhodamine F5G hydroxide and Rhodamine F5G dihydrogen phosphate are also reported. The thermal decomposition of Rhodamine F5G hydrochloride leads to initial loss of ethyl chloride and formation of the zwitterion which rearranges at higher temperature to a lactone. The further pyrolysis has also been studied.
Photoionisation mass spectra of volatile derivatives of short peptides and appearance potentials of their characteristic ions
Authors: Orlov V. M. , Varshavsky Ya. M. , Miroshnikov A. I. 
Published: May 2005

AbstractMass spectra of the volatile derivatives of short peptides were studied by the photoionisation method with the use of monochromatic photons. The dependence of the intensity of the main peaks on the photon energy was analysed from 7·5 to 13·0 eV. The data obtain reveal the influence of the chemical structure of amino acid residues on the relative probability of the decomposition of peptide molecular ions at the CHCO and CONH bonds, resulting in the formation of positively charged aldimine and amino acid N‐terminal fragments, respectively. These data may be used as a basis for the application of the photoionisation technique to mass spectrometric sequential studies in peptides.In peptides containing residues of aliphatic amino acid the decomposition results mainly in the formation of aldimine ions, the stability of which increase with the increase of the alkyl chain size. In peptides containing residues of aromatic amino acids the decomposition is usually observed leading to formation of the amino acid ions.Ionisation potentials, as well as photoionisation efficiency curves and appearance potentials were determined for characteristic ions. Comparison was made of the values of the appearance potentials of different fragments formed upon decomposition of molecular ions. It has been shown that for peptides containing aliphatic amino acid moieties the appearance potentials of aldimine fragments are always lower than those inherent to peptides containing aromatic amino acid residues. The larger the size of an aliphatic chain, the lower is the energy of formation of these fragments. For all the compounds studied, including the peptides containing aromatic amino acid residues, the appearance potentials of the aldimine ions did not exceed those of the amino acid ions. These data indicate that, contrary to the experiments with electron‐impact with energy of about 70 eV, upon ionisation with photons with energy from 7·5 to 13·0 eV, the aldimine fragments appear directly due to primary decomposition of molecular ions, independent of the formation of the amino acid fragments. The photoionisation efficiency curves for peptides containing different types of amino acid residues facilitate the choice of an optimal photon energy providing unequivocal information on the amino acid sequence in the peptide under study.
Massenspektrometrische Untersuchung von Amiden. IX—Nachbargruppenwechselwirkung Statt Ringkontraktion bei der Fragmentierung von Carbonsäurepiperididen
Authors: Schwarz Helmut , Bohlmann Ferdinand , Petersen Rolf‐Dieter 
Published: May 2005

AbstractDie für N‐Acetylpiperidine typischen Ringkontraktionen spielen bei der Fragmentierung von Piperididen höherer, gesättigter Carbonsäuren nur eine untergeordnete Rolle. Sowohl durch die Untersuchung 2H‐markierter Piperidide als auch durch die Messung von Auftrittspotentialen wird eine Nachbargruppenwechselwirkung der Amidfunktion bei der Abspaltung von von CH3˙ und C2H5˙ wahrscheinlich gemacht.
Chelation as a process following chemisorption upon emitters for field desorption and field ionization mass spectrometry
Authors: Hass J. Ronald , Sammons Martin C. , Bursey Maurice M. , Kukuch Bruce J. , Buck Richard P. 
Published: May 2005

AbstractAcetylacetone (Hacac) admitted as a gas to an ion source containing CoCl2 adsorbed on a field ionization/field desorption emitter produces the ion [Co(acac)Cl]+. Similar ions arising from interaction of adsorbed salt and a ligand admitted as a gas were found for CoCl2 and trifluoroacetyl acetone, and for FeCl2 and acetylacetone. The chelation process represents a new kind of reaction of chemisorbed species in field ionization mass spectrometry.
Massenspektrometrische Untersuchungen an Benzophenon und Substituierten Benzophenonen. II—Berechnung von Ionenhäufigkeiten
Authors: Heller R. , Krenmayr P. , Varmuza K. 
Published: May 2005

AbstractMit Hilfe der einfachsten Gleichung der Quasi‐Gleichgewichts‐Theorie wurden die Klastogramme von Benzophenon und neun substituierten Benzophenonen im Bereich von 12 bis 24 eV berechnet. Es wurden Konkurrierende Reaktionen und Folgereaktionen berücksichtigt. Die Energieverteilungsfunktion von Yeo und William wurde auf Grund der Ergebnisse, die für Benzophenon erhalten wurden, modifiziert. Berechnete und gemessene Klastogramme stimmen gut überein. Die Berechnungen bestätigen die aus anderen Arbeiten gewonnene Vermutung, daß Benzoylund Aminobenzoyl‐Ionen aus Aminobenzophenonen an der Bildungsschwelle mit einer beträchtlichen Überschußenergie behaftet sind.
Redistribution reactions in the ion source of a mass spectrometer of complexes of titanium (iv), tin (iv) and germanium (iv) with 8‐quinolinolato and halo or ethoxy ligands
Authors: Barrett C. G. R. , Charalambous J. , Copperthwaite R. G. , Frazer M. J. 
Published: May 2005

AbstractThe relative intensities of peaks in the mass spectra of the compounds MX4−noxn (oxH = 8‐quinolinol; n = 2; M = Ti; X = F, Cl, Br or OEt; M = Sn; X = F, Cl, Br or I; M = Ge; X = Cl or Br; n = 1; M = Ti; X = OEt) depend on the insertion temperature and the residence time of the sample in the mass spectrometer. In most cases ions which cannot arise by fragmentation of the respective molecular ions are observed. These ions arise from the ionisation and fragmentation of species which are due to redistribution reactions in the mass spectrometer. The fragmentation pattern of the compounds MX2ox2 (X = halogen), mainly involving loss of ligand radicals, is related to the common oxidation states of the metals and reflects the metal‐halogen bond strength. The molecular ions of the compounds Ti(OEt)4−noxn (n = 0, 1 or 2) fragment by loss of intact ligand radicals.
Stereochemische effekte bei der elektronenstoßindu‐zierten fragmentierung von threo‐ und erythro‐1.2‐diphenyl‐1.2‐bis‐(trimethylsiloxy)‐äthan
Authors: Bohlmann Ferdinand , Friedrich Tiqvah , Köppel Claus , Schwarz Helmut 
Published: May 2005

AbstractDie Bildung der Ionen m/e 147 [C5H15OSi2]+ aus den Titelverbindungen wird in entscheidender Weise durch die Geometrie des Übergangszustandes der Reaktion [M  Ch3+] → m/e 147 beeinflußt.
Transposition des cycles satures en spectrometrie de masse II–Ethylene acetals derives de cyclopentanones et de cyclohexanones
Authors: Audier Henri Edouard , Fetizon Marcel , Tabet Jean‐Claude 
Published: May 2005

AbstractL'étude détaillée des spectres de masse des éthyléne acétals dérivés de cyclopentanones et de cyclohexanones apporte de nouveaux arguments en faveur d'une transposition de l'ion moléculaire. Un modèle simplifié permettant l'étude quantitiative de ce réarrangement est proposé. L'influence de divers facteurs structuraux sur ce réarrangement est discutée.
ZUM MECHANISMUS MASSENSPEKTROMETRISCHER FRAGMENTIERUNGSREAKTIONEN BEI A/B‐CIS‐ VERKNüPFTEN 3α‐HYDROXYSTEROIDEN MIT UND OHNE 11‐KETOGRUPPE
Authors: Ende M. , Spiteller G. 
Published: May 2005

AbstractMass spectra of steroids containing a carbonyl group in position 11 and a 3α‐hydroxy group in a cis connected A/B ring system are characterised by very strong [M – 72]+· key ions and may therefore be clearly differentiated from the spectra of their isomers. The mechanism of this fragmentation reaction was investigated by deuterium labelling and the DADI technique. The 3α‐hydroxy group is eliminated together with the 9α‐H atom. Next a hydrogen atom is transferred from the A ring to the B/C/D ring system. This causes the cleavage of the C‐3C‐4 bond and expulsion of C atoms 1 to 4 as butadiene. In 3α‐hydroxy‐5α‐androstanes possessing no 11‐keto group an analogous [M – 18]+. fragment is fromed, followed by the elimination of ethylene originating mostly from C‐1 and C‐2.
The ramberg‐bäcklund process in the fragmentation of two benzylic β‐disulfones
Authors: Hardstaff W. R. , Langler R. F. 
Published: May 2005

AbstractA new fragmentation process is reported for two benzylic ß‐disulfones. The proposed fragmentation Scheme is analogous to the Ramberg‐Bäcklund rearrangement of α‐halosulfones in aqueous base.
Electron‐impact‐induced rearrangements in the mass spectra of phosphinyl stabilized triphenylphosphonium ylides
Authors: Tökés Lászlo , Jones Gordon H. 
Published: May 2005

AbstractExamination of the mass spectra of some methyl and phenyl phosphonate stabilized triphenylphosphonium ylides revealed that these compounds are quite stable to electron‐impact and provided valuable structural information. They exhibit strong molecular and [M ‐ H]+ ions, and fragment ions which are characteristic for the phosphonium or the phosphonate portion of the molecules. Numerous rearrangement ions were detected, however, the most prominent of which involves the migration of a phosphonate phenyl to the ylide carbon, leading to the base peak (m/e 352) in the spectrum of diphenyl triphenylphosphoranylidenemethylphosphonate. The mechanism of these fragmentations has been studied with the aid of high resolution analysis and deuterium labeled analogs whose preparation is reported.
Substituent effect and rearrangements in the electron‐impact spectra of long chain esters of m‐and p‐methoxybenzoic acid
Authors: Winnik Mitchell A. , Kwong P. Y. Y. 
Published: May 2005

AbstractThe mass spectra of eighteen n‐alkyl estars of p‐methoxybenzoic acid are examined. Few differences exist in the spectra of the corresponding para and meta isomers. We describe a new rearrangement, loss of OH from the molecular ion, whichis observed only in the para substituted isomkers. Oxygen‐18 labeling indicates that the oxygen lost in the [MOH]+ ion derives from the carbonyl. No indication is found of hydrogen abstration from the chain by the methoxy group competing withthe benzoate ester rearrangement. We find a substituent effect on that rearrangement, with electron‐donating groups decreasing the values of [ArCO2H2]+/[ArCO2H]+· ion ratios. this ratio decreases as the ester chain length increases.
Transposition de Cycles Satures en Spectrometrie de Masse III—Etude des Spectres en Basse Tension des Cyclanones
Authors: Audier H. E. , Fetizon M. , Tabet J. C. 
Published: May 2005

AbstractL'étude de la fragmentation des cyclanones (cycloheptaanone, cyclooctanone, quelques dérivés méthylé et deutérié) a été reprise. Tous les pics observés sont interprétables sur la base d'un réarrangement de l'ion moléculaire. Ce réarrangement est particuliérement important à basse tension.
SPECTROMETRIE DE MASSE DES AMINO‐4 STEROIDES
Authors: Marazano Christian , Longevialle Pierre 
Published: May 2005

AbstractLa fragmentation des amino‐4 stéroïdes en spectrométrie de masse est étudiée, et des interprétations proposées pour les principales fragmentations. La libération d'un radical primaire lors de la formation des principaux ions explique la relative lenteur de ces réaction attestée par l'existence d'importantes réactions d'éactions d'échangeH‐D dans le cas du dérivé deutérié en 3 et 5.
A program for generating empirical spectrum classification schemes
Authors: Gray N. A. B. 
Published: May 2005

AbstractPrograms are described which derive a set of compound classification tests from data specifying a required classification hierarchy and example low resolution mass spectra. The generated tests are expressed in terms of conventional operations such as searching for a molecular ion and checking for fragment ions. These tests can be used in a laboratory computer to give real‐time classification of spectra collected by gas chromatography mass spectrometry.
MASSENSPEKTROMETRISCHE UNTERSUCHUNG ORGANISCHER STICKSTOFFVERBINDUNGEN XVIINeue aspekte zum mechanisums der methyleliminierung aus ungesättigten carbonsäureamiden
Authors: Richter Bernd , Schwarz Helmut 
Published: May 2005

AbstractDie Methyl‐Eliminierng aus α,β‐ungesättigten Carbonsäureamiden wurde erneut untersucht. Durch die Untersuchung 2H‐markieter Modellverbindungen wird gezeigt, daß der Verlauf dieser Reaktion viel komplexer ist als ursprünglich angenommen wurde.
Electron‐impact fragmentation of penta‐fluorophenyldimethylsilyl ethers of some sterols of biological importance
Authors: Poole C. F. , Morgan E. D. 
Published: May 2005

AbstractThe mass spectral properties under medium and high resolution of a new protecting group for sterols is described and its ability to direct fragmentation is compared with established derivatives. The mass spectra obtained are characterised by strong molecular ions which fragment to produce a more even ion distribution than the familiar TMS ethers. This results in enhanced abundance of hydrocarbon fragments, with molecular structural details given greater prominence than is found with other derivatives.
MASSENSPEKTROMETRISCHE UNTERSUCHUNG VON 2‐ARYL‐1.2.3‐THIADIAZINEN. EIN STRUKTURBEWEIS
Authors: Entenmann G. 
Published: May 2005

AbstractDie Massenspektren von 2‐Aryl‐1.2.3‐thiadiazinen und ihren Salzen sind nur in einigen Beispielen (2‐Phenyl‐1.2.3‐thiadiazine) frei von Zersetzungsprodukten. Diese Spektren erlauben eine Entscheidung zwischen der 1.2.3‐Thiadiazinstruktur und der N‐Aminoisothiazol‐struktur: Die Verbindungen liegen als 1.2.3‐Thiadiazine vor.
High resolution mass spectrometric study of organosilicon compounds. Siloxazolidones: Cyclized amino acid‐silane derivatives
Authors: Ho Benedict Y. K. , Spialter Leonard , Smithson Lee D. 
Published: May 2005

AbstractHigh resolution mass spectra have been obtained for a series of methyl, ethyl and phenyl substituted siloxazolidones (cyclic compounds derived from the condensation of organosilane derivatives with amino acids). The effects on the mass spectra of these compounds upon substitution at the saturated ring carbon and at the silicon atom, the migratory nature of the phenyl group on nitrogen, and theextent of biphenyl radical ion formation in the skeletal rearrangement processes have been examined.
Molecular weight determination by cationisation
Authors: Röllgen F. W. , Schulten H.‐R. 
Published: May 2005

AbstractIn General cationised molecules are more stable than redical molecular ions or protonated molecules. The fragmentation of the polar molecules resulting from a cationsation by for instance alkali ions, has a higher activation energy than splitting off fuctional groups after a protonation. Cationisation is therefore an intersting tool for the determination of molecular weights. Three different methods for achiving a cationisation are described and discussed: (1) field‐indiced cationisation at low anode temperatures using a heterogenous reaction of the molecules in the gas phase with molecules of a salt in the adsorption layer on the field anode; (2) a largely thermally induced catisation at high emitter temperatures and low electric fields; (3) a cationisation, causing less thermal excitation to the molecules, using the field desorption technique.
The structure of the [C2H5O]+ ion in the mass spectrum of diethyl ether
Authors: Phillips G. R. , Russell M. E. , Solka B. H. 
Published: May 2005

AbstractThe structure of the [C2H5O]+ ion in the spectrum of diethyl ether was examined by use of deuterated ether, CH3CD2OCH2CH3. The results show that, at all electron energies from threshold to 70 eV, the predominant ion is a rearrangement ion, probably protonated acetaldehyde, with very little of the [C2H5O]+ being formed by direct carbon‐oxygen bond cleavage. Appearance potential measurements made on the m/e 45, m/e 46 and m/e 47 ions in the deuterated ether show that the threshold structure of the rearrangement ion is protonated acetaldehyde.
The electron‐impact‐induced fragmentation of aromatic aldoximes: I
Authors: Vijfhuizen P. C. , Heerma W. , Dijkstra G. 
Published: May 2005

AbstractPrimary fragmentations of benzaldoxime include loss of H·, OH·, HCN, CO and HCNO and this paper discusses the first three losses. The previously reported losses of H2O and O were proven to be thermal in origin. Information about the investigated fragmentations was obtained from the deuterated analogues and their metastable characteristics. The OH· elimination is complex. The loss of HCN exhibits a metastable with a composite structure. This fragmentation may occur both via a 4‐centred and 5‐centred mechanism. A fluorine atom at the ortho position of the phenyl ring favours the 5‐centred mechanism.
The mass spectrometric behaviour of dimethylcyclosiloxanes
Authors: Pickering G. R. , Olliff C. J. , Rutt K. J. 
Published: May 2005

AbstractThe fragmentations of [(CH3)2SiO]n, (Dn), where n = 4, 5, 6, 7, 8, 9, 10, 12 and 15 are reported. The behaviour of these compounds under electron‐impact is governed by the size of the siloxane ring. Rings smaller than D6 have base peaks corresponding to [M – 15]+ ions; larger rings all show base peaks of m/e 73 [Si(CH3)3]+. A transannular mechanism previously applied only to D5 and D6 is extended and modified to account for the behaviour of larger rings. A ring con‐traction mechanism is proposed which leads to the formation of smaller rings and doubly charged ions. A new transannular mechanism is proposed to account for the production of [M – 177]+ and [M – 193]+ ions.
Mass spectrometry of heterocyclic compounds. X—The unusual cleavage of the alkyl–oxygen bond of 3‐carboxyesters of 2‐phenyl‐4‐pyridones
Authors: Selva A. , Gennaro A. , Caramella P. 
Published: May 2005

AbstractThe dominant and unusual electron impact‐induced losses of CH3⋅ and C2H5⋅ from molecular ions of 3‐carbomethoxy and 3‐carbethoxy derivatives of 2‐phenyl‐4‐pyridones are explained by invoking the participation of the phenyl group.
Mechanism of nitric oxide loss in 3,6‐diphenyl and 3,5,6‐triphenyl‐4‐nitro cyclohexenes under electron ionization
Authors: Das K. G. , Madhusudanan K. P. 
Published: May 2005

AbstractPossible mechanisms have been proposed for the loss of nitric oxide from the molecular ions of 3,6‐diphenyl‐ and 3,5,6‐triphenyl‐4‐nitro cyclohexenes. Elimination of nitric oxide in 3,6‐diphenyl nitro cyclohexenes involves oxygen migration to one of the double bond carbon atoms. In the 3,5,6‐triphenyl analogues, it involves a 3‐membered cyclic transition state.
Electron impact mass spectrometry of nuphar alkaloids. II—Thiohemiaminals
Authors: Lalonde Robert T. , Wong Chunfook , Tsai Amy I‐M. 
Published: May 2005

AbstractThe appearance of m/e 228 and 176 ions, useful in ascertaining the presence of the hemiaminal hydroxyl, are discussed for six thiaspirane‐type hemiaminals isolated from Nuphar luteum and three epimeric pairs of α‐thiohemiaminals derived from (–)‐deoxynupharidine. Other groups of ions useful in ascertaining stereochemical differences of the sulfur moiety in α‐thiohemiaminals are discussed for the same compounds. One such group of ions is comprised of 248, 246 and 231; a second is 192 and 191.
The mass spectra of 2‐ and 4‐monohydroxy‐ and 2, 4‐dihydroxy‐1, X‐naphthyridines
Authors: Czuba W. , Woźniak M. , Kowalska T. , Grzegożek M. 
Published: May 2005

AbstractThe mass spectra of 2‐and 4‐monohydroxy‐and 2, 4‐dihydroxy‐1, 5‐, ‐1, 6‐, ‐1, 7‐and 1, 8‐naphthyridines are reported. Fragmentation mechanisms are proposed and discussed.
Mass spectrometry of 3‐substituted 4‐hydroxyisoquinolines and their derivatives
Authors: Terent'ev P. B. , Lomakina N. P. , Kost A. N. 
Published: May 2005

AbstractUnder electron impact, 3‐aryl‐4‐hydroxyisoquinolines form [M – H]+, [M – CO]+ and [M – H – CO]+ ions with a subsequent elimination of HCN or CH3CN. A cyclic structure for the [M – H]+ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH3⋅, as well as H⋅; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]+, [M – OH]+ and [M – CH5⋅]+ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.