bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Mass 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

Die 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

Acetylacetone (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

Mit 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

The 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

Die 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

L'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

Mass 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

A 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

Examination 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

The 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

L'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.
The analysis of mixtures II–Pattern separation III–Pattern separnration
Authors: McK. Halket J. , Reed R. I.
Published: May 2005

The work previously described has been extended and amplified. Product moment correlation coefficients are shown to be useful in separation of component spectra. The 'ab initio' analysis of a four component mixture is described.
The fragmentation of cavinine–a new amaryllis alkaloid in the crinine series
Authors: Samuel E. H. C.
Published: May 2005

The fragmentation of cavinine, a new amaryllis alkaloid in the crinine series, is discussed.
SPECTROMETRIE DE MASSE DES AMINO‐4 STEROIDES
Authors: Marazano Christian , Longevialle Pierre
Published: May 2005

La 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

Programs 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

Die 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

The 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

Die 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

High 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

In 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

The 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

Primary 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

The 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

The 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

Possible 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

The 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

The 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.
Fragmentation de derives phenyles de l'isobenzofuranne et de l'isoindole
Authors: Denhez Jean‐Pierre , Ricard Michèle , Corval Madeleine
Published: May 2005

L'influence de la nature de L'hétéeroatome sur les processus de fragmentation de deux couples d'hétéerocycles est discutée.
Mass spectrometry of 3‐substituted 4‐hydroxyisoquinolines and their derivatives
Authors: Terent'ev P. B. , Lomakina N. P. , Kost A. N.
Published: May 2005

Under 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.
Metastable transitions in n‐butane and n‐butane‐d7
Authors: Smith Richard D. , Futrell Jean H.
Published: May 2005

Metastable ions have been investigated for n‐butane d7 molecular ions using a tandem mass spectrometer which samples unimolecular decay processes occuring during the time interval of c.2 μs to 4 ms after ion formation. Some 37% of ions formed by 70 eV electron impact decay on this time scale. The competing unimolecular processes observed, in order of relative importance, are methance, methyl radical and hydrogen atom elimination. The slow metastables sample the threshold energy regime of unimolecular reactions responsible for forming the ordinary mass spectrum of butance and very large isotope effect are noted for the deuterated molecule.
On the determination of desorption temperatures in field desorption mass spectrometry
Authors: Winkler H. U. , Linden B.
Published: May 2005

The field desorption temperatures of some compounds are determined by indirect heating of the emitters. The temperatures thus obtained are lower, compared with those determined by other authors. The reasons for this deviation are discussed.
Electron impact studies on oximes: Mass spectra of the condensation products of aniline, phenol and thiophenol with benzhydroximoyl chloride
Authors: Hemalatha D. , Kallury R. Krishna Mohan Rao
Published: May 2005

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

The relative rates of competing metastable decompositions of fourteen isomeric C7H14 monoolefins were measured and compared. In every case except one the most important metastable reaction was loss of either CH3 or C2H4, but the rates of these and the other reactions observed varied over a wide range. It was concluded that the molecular ions of these compounds probably do not isomerize to a common structure prior to metastable decay. It was found that a terminal double bond strongly enhances metastable loss of C2H4 and that the additional presence of a 2‐methyl substituent favours this reaction still more. Several possible mechanisms for this transition are discussed, but none was found to explain the observed results satisfactorily.
Correction of metastable peak shapes to allkow for instrumental broadening and the translational energy spread of the parent ion
Authors: Baldwin Michael A. , Derrick Peter J. , Morgan Roger P.
Published: May 2005

Graphs are presented which can be used to correct metastable peak widths for both instrumental broadening and translational energy spread of the parent ion.
Basic mass spectrometric investigations of amino acid‐fluorescamine derivatives
Authors: Shieh Jeng‐Jong , Leung Katherine , Desiderio Dominic M.
Published: May 2005

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Electron capture processes in a series of copper (II) β‐diketonate complexes of formula Cu[R1COCHCOR2]2 (where R1 is an alkyl, perfluoroalkyl or aryl group and R2 either an alkyl or aryl group) have been examined. Molecular anions, ligand ions and some novel rearrangement ions have been observed with these compounds. Relative intensities of fragment ions were dependent on the substituents R1, R2 as well as the electron energy and compound pressure in the ion source. By operating the mass spectrometer at compound pressures of c. 4×10−6 Torr and higher, reproducible negative ion mass spectra (free from any significant ion‐molecule contributions) have been obtained for all compounds of the series.
Collisional activation spectra of quarternary ammonium cations produced by field desorption
Authors: Gierlich H. H. , Röllgen F. W. , Borchers F. , Levsen K.
Published: May 2005

Collisional activation spectra of quarternary ammonium cations produced by field desorption are reported. The principal fragmentation pathways of these ions are discussed. Furthermore, it is demonstrated that collisional activation in conjunction with field desorption is useful for the elucidation of the structure of complex organic cations.
Massenspektrometrische Untersuchung organischer Stickstoffverbindungen. XXVII—Intramolekulare Redoxreaktionn bei ionisierten ortho‐substituierten Nitroaromaten
Authors: Schwarz Helmut , Sezi Recai , Levsen Karsten , Heimbach Heinz , Borchers Friedrich
Published: May 2005

Mit Hilfe der Stoßaktivierungsspektroskopie wird belegt, daß die stabilen magnified image‐Ionen aus o‐Nitrobenzaldehyddimethylacetal als ionisierte o‐Nitrosobenzoesäuremethyleser vorliegen. Ferner wird—im teilweisen Gegensatz zu den Resultaten älterer Arbeiten—belegt, daß die durch elektronenstoßin duzierte H2O‐Eliminierung aus o‐Nitrobenzylalkohol, HCN‐Abspaltung aus o‐Nitrobenzylcyanid order HNO‐Verlust aus o‐Nitrobenzaldoxim erzeugten magnified image‐Ionen praktisch vollständig die Struktur von 2.1‐Benzisoxazolin‐3‐on besitzen. Ionisierter o‐Nitrosobenzaldehyd lagert sich vor dem stoßinduzierten Zerfall vollständig in 2.1‐Benzisoxazolin‐3‐on um, während 2‐Benzoxazolinon und 3‐Hydroxy‐1.2‐benzisoxazol innerhald von 10−5s weitgehend strukturstabil sind.
Stereochemistries of electron impact induced hydrogen abstraction reactions proceeding through 6‐membered transition states
Authors: Eadon George
Published: May 2005

The stereochemistries of nine electron‐impact induced eliminations proceeding from derivatives of thecis‐4‐t‐butyl system have been determined. The predominantciselimination observed in every case is consistent with the substantial integrity of the cyclohexyl ring prior to fragmentation, and with a cyclic transition state for hydrogen abstraction. The stereochemistries of electron impact induced eliminations from 11 derivatives of thetrans‐4‐t‐butylcyclohexyl system exhibit a dichotomy. The predominatntransstereochemistry observed in six electron impact induced eliminations, and the nonstereospecific electron impact induced dehydration oftrans‐4′‐t‐butylcyclohexyl‐ethanol are consistent with nonconcerted elimination from a chair‐like cyclohexyl ring. Conversely, the McLafferty rearrangement oftrans‐4′‐t‐butyl‐cyclohexyl‐2‐propanone proceeds nonstereospecifically.trans‐4‐t‐Butylcyclohexyl acetaldehyde, 2‐methyl‐3‐(trans‐4′‐t‐butylcyclohexyl)‐1‐propane andtrans‐4‐t‐butylcyclohexyl‐S‐methyl xanthate exhibit predominantcisMcLafferty rearrangement stereochemistry. This result may be due to fragmentation through boat‐like conformers in these compounds.
Ionisation et Fragmentation en Spectrométrie de Masse. VI—Energie d'Activation de la Fragmentation Principale des Monohalogénobenzènes
Authors: Bouchoux Guy
Published: May 2005

L'énergie d'activation de la fragmentation principale des monohalogénobenzènes [C6H5X⋅]+ → [C6H5]+ + X⋅ (X = Cl, Br, I) est calculée par diverses méthodes. L'analyse des ions métastables indique l'absence d'une énergie de recombinaison des fragments appréciable. Ces résultats sont comparés aux données expérimentales.
Der Zerfall von Substituierten p‐ Toluesäuren—eine neuartige Skelettumlagerung
Authors: Budzikiewicz H. , Scheipers R. , Rullkötter J.
Published: May 2005

p‐Carboxy‐ und p‐Carbomethoxybenzylionen zerfallen unter CO‐Eliminierung zu p‐Hydroxy‐ bzw. p‐Methoxybenzylionen.