bluuebunny/crossref_metadata_2025 huggingface dataset:
The nature and fragmentation pathways of the molecular ions of some arylureas, arylthioureas, acetanilides, thioacetanilides and related compounds
Authors: Baldwin Michael A. , Loudon Alexander G. , Maccoll Allan , Webb Kenneth S.
Published: May 2005

Evidence as to the nature of the molecular ions of the title compounds near the ionization thresholds and of their fragmentation processes is presented and discussed. The mode of formation of 5‐membered rings, involving the loss of an ortho substituent, is compared and contrasted with the formally similar process reported for the N‐dimethyl N'‐(o‐X‐phenyl) formamidines.
Bicyclic oxonium ions with an oxygen bridgehead
Authors: Van de Sanded C. C. , Vanhooren M. , Van Gaever F.
Published: May 2005

Electron impact induced fragmentation of 4‐(ω‐phenoxymethyl and ‐ethyl)tetrahydn pyranes results in abundant [M  93] + ions through loss of a phenoxy radical. These ions are all produced in high yields by isobutane chemical ionization through loss of phenol from the quai molecular ions. Labelling data (2H, 13C) provide evidence for the l‐oxoniabicyclo[2.2.1]heptane ai l‐oxoniabicyclo[2.2.2]octane structures of the electron impact produced decomposing (ion sour and first field free region) ions [M  93]L in the case of the methyl and ethyl compounds, respective.
Mass spectra of sulfur compounds: alkyl thiophenoxyacetates and thiophenoxythioacetates
Authors: Tomer Kenneth B. , Gleich Joan
Published: May 2005

The mass spectra of some alkyl thiophenoxyacetates and S‐alkyl thiophenoxythioacetates have been examined. Several rearrangement processes have been identified by high resolution mass measurement and isotopic labeling studies.
Interpretation Automatique des Spectres de Masse de Composes Organiques. Mise au Point
Authors: Bachiri Mohamed , Mouvier Gérard
Published: May 2005

Computerized methods for interpretation of mass spectra are increasing and many papers have now been published. Three different approaches can be used to identify an unknown compound. These methods are reviewed and discussed. First, the heuristic technique which tries to simulate the reasoning of the chemist and deduce the formulae. The only information needed are the mass spectra, the empirical formulae and the n.m.r. spectra. Some promising results have been obtained but the method has important restrictions. Another approach represents the mass spectra as points in a hyperspace. By developing decision surfaces it is possible to classify an unknown compound. This is called pattern recognition and the different empirical methods for recognizing patterns in mass spectral data are explained and reported. The last and simplest technique is to match an unknown spectrum against a library of standard references. When the unknown spectrum is in the library, this approach gives the best results.
The stereospecific loss of water from 1,4‐dihydroxy‐Δ6,7‐octalins under electron impact
Authors: Tureček F. , Vystrčil A. , Hanuš V.
Published: May 2005

The mass spectra of four of the six 1,4‐dihydroxy‐ Δ6,7‐octalins are reported. The spectra differ considerably, depending on the configuration of the hydroxyl groups. The relative amounts of 1‐3,1‐4, transannular 1‐3 and hydroxyl‐hydroxyl elimination of water from the molecular ions were determined by using specificaliy labelled compounds. Effects of configuration and conformation are discussed.
Metastable ions in chemical ionization
Authors: Cameron D. , Clark J. E. , Kruger T. L. , Cooks R. G.
Published: May 2005

The ion [C3H5]+ generated in a chemical ionization source by a variety of methods, including protonation and charge exchange, exhibits a metastable peak for H2 loss which is two orders of magnitude weaker than that formed in an electron impact source. The stable [C3H5]+ ions generated by electron impact and chemical ionization undergo collision‐induced dissociation to a comparable extent, both losing H2 by only one of the two competitive mechanisms observed for metastable ions. In contrast to the behavior of [C3H5]+, the molecular ions of p‐substituted nitrobenzene, generated by charge exchange at high source pressure, yield composite metastable peaks for NO loss which are very similar in shape and intensity to those generated by electron impact. The contrasting behavior of the metastable ions extracted from high pressure ion sources in the two systems may be due to differences in the efficiencies of quenching of the ionic states responsible for fragmentation as metastable ions. It is noteworthy that the NO loss reactions require considerably lower activation energies than does the H2 loss reaction.
Isomerization of hydrocarbon ions. VI—parameters determining the isomerization of aliphatic hydrocarbon ions
Authors: Leven Karsten , Heimbrecht Jörg
Published: May 2005

The radical or non‐radical character of aliphatic hydrocarbon ions determines the extent to which these ions equilibrate to a mixture of interconverting structures prior to decomposition. It is suggested that the radical (odd electron) ions have both lower thresholds for decomposition and higher barriers for isomerization that non‐radical (even electron) ions, thus explaining their reduced tendency for isomerization. Moreover, the molecular size seems to be a major influencing factor for the isomerization of unsaturated hydrocarbon molecular ions. With decreasing molecular size isomerization prior to decomposition becomes more pronounced. Collisional activation spectra of fragment ions (formed by loss of H2O from the corresponding alcohols) and of [C5H10]+and [C4H8]+molecular ions are reported in support of these conclusions.
Etude des fragmentations en spectrographie de masse de dithiolannes‐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 chaine éthylénique modifie les spectres par formation d'un ion benzothiopyrylium très stable.
Scanning of sector mass spectrometers to observe the fragmentations of metastable ions
Authors: Boyd R. K. , Beynon J. H.
Published: May 2005

Various methods of scanning the electric and the magnetic sectors of a double focusing mass spectrometer are critically discussed and assessed.
Ortho effects in organic molecules on electron impact. V—ortho effects of the nitro group in n‐substituted anilines
Authors: Ramana D. V. , Vairamani M.
Published: May 2005

Some very interesting ortho effects are observed in the mass spectra of N‐benzyl‐o‐nitroaniline and N,N‐dibenzyl‐2,4‐dinitroaniline. Fragment ions arising from the transfer of oxygen from the nitro group to the benzylic carbon are seen in these spectra.
Stabile ‐Ionen in der Gasphase—eine CA‐Studie
Authors: Schwarz Helmut , Wesdemiotis Chrysostomos , Heimbach Heinz , Levsen Karsten
Published: May 2005

[C11H9]+‐Ionen aus sechs verschieden strukturierten Vorläufern werden mit Hilfe der Stoßaktivierungsspektren untersucht. Die Ergebnisse zeigen, daß die stabilen Ionen weitgehend als Benztropylium‐Ionen oder als eine Mischung rasch interkonvertierender Strukturen vorliegen.
The electron impact induced fragmentation of geminal dialkanoates
Authors: Ingram John G. K. , Barry Thomas C.
Published: May 2005

The mass spectra of representative 1,1‐dicarboxylates have been studied in order to identify fragmentation patterns typical of such compounds and thus to aid their characterization in complex mixtures. Two typical decomposition pathways were noted. One invoves the loss of a carboxylate group, and the other the ejction of an sliphatic sidechain. It is suggested that a similar gragmentation scheme is to be expected of the much more labile dialkanoates derived from ketones.
The electron impact induced fragmentation of aromatic aldoximes—III. On the loss of HCNO, OH⋅ and substituents and the role of substituent effects in the decomposition of cyclohexadiene type intermediate ions
Authors: Vijfhuizen Peter C. , Terlouw Johan K.
Published: May 2005

The mechanisms for loss of HCNO, OH˙ and the substituent X˙ from aromatic aldosimes were elucidated with the aid of deuterium labelling, metastable ion characteristics and substituent effects. It is proposed that the loss of HCNO occurs through a cyclohexadiene type intermediate ion generated via a 6‐membered ring hydroxyl hydrogen transer to the ortho position of the phenyl ring. This is followd by a second step which involves the trnsfer of a hydrogen atom from the ortho position to C‐1. It is inferred from the corelation with the mesomeric effect (σR+) of substituents that this step is rate determining. Loss of OH˙ and X˙ proceed via the same cyclohexadiene type intermediate ion but, depending upon the substituent, other pathways are also followed.
Stereochemistry and mechanism of electron impact induced elimination reactions in acenaphthenol and acetoxyacenaphthene
Authors: Manhart Daryl D. , Brown Peter , Hunter Duncan H.
Published: May 2005

The mechanisms for elimination of H2O from acenaphthenol and of AcOH from acetoxyacenaphthene under low energy conditions have been determined, using regiospecific and stereospecific deuterium labeling probes, and by measurement of ionization and appearance potentials for alternative pathways. Both concerted and stepwise processes must be invoked in order to explain the experimental data. Proximity effects appear to be the most important factors in determining mechanistic type.
Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds. XII‐pentafluorophenyl derivatives af phosphorus (V) halides
Authors: Jones Timothy R. B. , Miller Jack M. , Fild Manfred
Published: May 2005

The Mass spectral fragmentation processes for a number of alkyl and aryl subtituted phosphinyl and phosphonyllk halides and their thio analogs are discussed with respect to two intramolecular rearrangment processes. The first is aryl fluorine transfer to phosphorus and the second concerns a rearrangement depicted as follows, i.e. a reverse Arbuzov reaction RR′XPS→RXPSR′. Both pathways are supported by evidence obtained form metastable ions and mass analyzed ion kinentic energay spectra. The previously observed phenomenon of subtituent coupling is also describedc where ita occurs in the phosphinyl compounds. The mass spectra of a number of mixed fluoro‐pebtafkuorophenyl phosphorances are also discussed.
Structure and fragmentation mechanism of [C3H7S]+ ions
Authors: Broer W. J. , Weringa W. D.
Published: May 2005

From a comparison of the metastable ion bundance ratios for loss of C2H4 and H2S from [C3H7S]+ ions in a series of alkyl thio ethers and thiols it was concluded that in most compunds these ion s isomerize to a common structure prior to decomposition in the first field free region. The mechanism for C2H4 loss from the [C3H7S]+ ion gen erated from CH3SCH2CH3 was investigated in detail using 13C and 2H labelling. A rearrangement with formation of a cyclic intermediate prior to the decompistion reaction is proposed. The fragmentation is preceded by extensive hydrogen scrabling. The carbon atoms of the expelled C2H4 molecule are those of the CH2CH3 moiety.
Cyclization‐elimination reactions in the mass spectra of aminopyridine derivatives II‐aryl sulfonamides of 2‐aminopyridine and related compounds
Authors: Broxton Trevor J.
Published: May 2005

The mass spectra of aryl sulfonamides of some 2‐aminopyridines and 2‐aminopyrimidine show abundant peaks corresponding tothe loss of SO2 and HSO2 from the molecular ion. Evidence in favour of a cyclization‐elimination reaction involving bond formation between the pyridine ring nitrogen and the ortho position of the benzene ring is presented.
Effect of ortho substituents in the electron impact induced fragmentation of 2,2′‐disubstituted stilbenes
Authors: Mintas M. , Jakopčić K. , Klasinc L. , Güsten H.
Published: May 2005

The effect of ortho substituents NH2, OCH3, CH3, Cl and NO2 on the fragmentation of five symmetrically and five unsymmetrically 2,2′‐disubstituted stilbenes under electron impact was investigated. The fragmentation patterns deduced were supported by metastable transitions in the first and second field free regions and by exact mass measurements of prominent ions. In general, the fragmentation was found to be in accord with that of stilbene and the corresponding monosubstituted stilbenes. There are, however, some deviations from the general fragmentation scheme caused by direct through‐space interactions of the ortho, ortho′ substituents with concomitant loss of neutral fragments. It is supposed that the formation of 7‐membered cyclic or heterocyclic ions is the result of such through‐space reactions.
Durch Nachbargruppenbeteiligung induzierte (1,2)‐Chlorwasserstoff‐Eliminierung aus ionisiertem 2‐(β‐Chloräthyl)‐ benzoesäuremethylester
Authors: Borchers F. , Heimbach H. , Levsen K. , Morhenn H. , Schwarz H.
Published: May 2005

Durch die Untersuchung deuterierter Verbindungen und die Benutzung von Stoßaktivierungsspekten werden sowohl der Mechanismus der ungewöhnlich intensiven HC1‐Eliminierung aus 2‐(β‐Chloräthyl)benzoesäuremethylester als auch die Struktur des resultierenden Produkt‐Ions aufgeklärt. Es wird belegt, daß die stabilen magnified image‐Ionen (Lebensdauer τ ∼ 10−5s) als ionisierte 2‐Vinylbenzoesäuremethylester vorliegen, während die reaktiven Spezies (τ < 10−6s) wenigstens teilweise cyclisieren. Die HCL‐Abspaltung aus 2‐(β‐Chloräthyl)benzosäuremethylester stellt nur formal eine simple (1,2)‐Eliminierung dar. In Wirklichkeit handelt es sich um eine besondere Nachbargruppenbeteiligung der Esterfunktion.
Hydrogen migrations in mass spectrometry. IV—formation of [C6H7]+ in the chemical ionization mass spectra of alkylbenzenes
Authors: Leung Hei‐Wun , Harrison Alex. G.
Published: May 2005

Using specific deuterium labelling the mechanisms of the olefin elimination reactions leading to formation of [C6H7]+ in the H2 and CH4 chemical ionizatin mass spectra of ethylbenzene and n‐propylbenzene (and to [C2H5C6H6]+ in the CH4 chemical ionization mass spectra) have been investigated. The results show that the reaction does not occur by specific migration of H from the β position of the alkyl group to the benzene ring. For ethylbenzene 23–29% of the migrating H originates from the α‐position, while for n‐propylbenzene H migration from all propyl positions is observed in the approximate ratio, position 1:position 2:position 3=0.30:0.22:0.48. It is proposed that the results can be explained on the basis of competing H migration from each alkyl position involving cyclic transition states of different ring sizes, rather than by H randomization within the alkyl chain.
Collision induced dissociations of radical cations
Authors: Maquestiau André , Van Haverbeke Yves , Flammang Robert , De Meyer Claude , Das K. G. , Reddy G. Sudhara
Published: May 2005

The collision induced dissociation spectra of ions generated by ionization or fragmentation of various samples reveal at least five non‐decomposing structures. In contrast, the kinetic energy release measurements for the loss of carbon monoxide from the metastable ions are in agreement with the occurrence of a common reactive species. Isomerization into an ‘α,β‐unsaturated aldehyde‐like’ structure prior to fragmentation is proposed to accommodate these collision induced dissociation and mass analysed ion kinetic energy data. Some resuts suggest also that carbon monoxide loss from the phenol molecular ion may not occur via the cyclohexadienone tautomer.
Fragmentation sous l'Impact Electronique de Diamino‐4,5 Triazoles‐1,2,4 et d'Amino‐4 Mercapto‐5 Triazoles‐1,2,4
Authors: Aouial Mohamed , Bernardini Antoine , Viallefont Philippe
Published: May 2005

Les spectres de masse d'un certain nombre d'amino‐4 triazoles −1,2,4 porteurs d'un substituant amino, méthylamino, mercapto ou méthylmercapto en position 5 sont décrits et analysés. Cinq processus de fragmentation du cycle triazole, liés à la nature du groupement fonctionnel en position 5, sont mis en évidence; l'un d'eux, identifié dans tous less cas, résulte de la rupture des liaisons N‐2C‐2 et N‐4C‐5.D'autres dégradation sont également observées à partir du groupment amino en position 4.
Etude par Spectrométrie de Masse d'une Série de Phényl‐1 Naphtalènes Substitués et des Dihydro‐1,4 Naphtols‐1 Correspondants
Authors: Pfau Michel , Heindel Ned D. , Gülaçar Fazil O. , Buchs Armand
Published: May 2005

Une étude par spectrométrie de masse d'une série de phényl;‐1 naphtalenes substitués et des dihydro‐1,4napthols‐1 correspondants permet de proposer des modes de formation plausibles pour tous les ions importants. L'élimination de méthanol, qui aboutit à des ions majeurs, fait probablement intervenir le transfert d'un atome d'hydrogène par un état de transition à huit atomes.
Rearrangements in the electron impact induced fragmentations of sulfonyl chlorides
Authors: Davis Paul P. , Grossert J. Stuart , Langler Richard F. , Mantle William S.
Published: May 2005

The major fragmentation pattern obsrved in the mass spectra of simple alkane‐ and arylsulfonyl chlorides may be rationalized by loss of a chlorine atom from the molecular ion, followed by loss of SO2 with concomitant carbocation formation. The mass spectra of α‐mesyl sulfonyl chlorides and napthalenesulfonyl chlorides exhibit ions resulting from chlorine atom migration to the α‐carbon atom with concomitant loss of SO2. The mass spectra of α‐mesyl sulfonyl chlorides also show ions which involve chlorine atom migration to the β‐sulfonyl group.
Analogie Photochimique. II—Cyclisation des Aldéhydes δ,ε Insaturés sous Impact Electronique
Authors: Morizur Jean‐Pierre , Mercier Jacqueline , Furth Bernard , Kossanyi Jean
Published: May 2005

Les spectres de masse des aldéhydes δε‐insaturés gem‐diméthylés en 4 présentent un ion m/e 126 résultant de l'élimination d'une oléfine à partir de l'ion moléculaire. Cette élimination implique la cyclisation intermédiaire des aldéhydes insaturés en cyclohexanone, comportement analogue à celui observé en photochimie. Les abondances relatives des décompositions unimoléculaires d'ion m/e 126 (observées par balagyage combiné) confirment le mécanisme proposé.
Synthèse et Propriétés d'Alkylidénehydrazono‐2 Méthyl‐3 Dihydro‐2,3 Benzothiazoles
Authors: Richer Jean‐Claude , Beljean Martine , Pays Michel
Published: May 2005

The synthesis and the spectral properties of 2‐alkylidenehydrazono‐3‐methyl‐2,3‐dihydrobenzothiazoles are reported. In the mass spectra of each of these compounds, the main fragmentation implies the breaking of the N‐Nbond of the azine.
Collisional ionization of monocharged positive ions
Authors: Maquestiau André , Van Haverbeke Yves , Flammang Robert , De Meyer Claude , Menu Alain
Published: May 2005

Competitive fragementations of doubly charged ions formed by charge stripping have been observed for some hydrocarbon ions. The reproducibility of the abundance ratios indicates that they may be used to characterize the structural identity or non‐identity of non‐decomposing monocharged positive ions.
The mass spectrum of 1‐heptyl iodide
Authors: Stahl Daniel , Gäuumann Tino
Published: May 2005

The mass spectra of twelve 13C labeled compounds have been measured in order to investigate the fragmentation of the 1‐heptyl iodide molecular ion. A mechanism is proposed for each reaction leading to the ions containing the iodine atom. The loss of olefin from the heptyl ion derived from the 1‐heptyl iodide proceeds via extensive rearrangement of the linear ion. A non‐linear intermediate structure obtained via protonated substituted cyclopropane is suggested to explain the major fragmentation reactions of the heptyl ion.
Untersuchung von 2.4.6‐substituierten s‐Triazinen durch Gaschromatographie‐Massenspektrometrie
Authors: Zeman Alfred , Wörle Rudolf
Published: May 2005

Zahlreiche 2.4.6‐Trialkoxy‐s‐triazine wurden mittels Gaschromatographie‐Massenspektrometrie untersucht. Die Fragmentierung dieser Verbindungen bei Elektronenbeschuß wird diskutiert. Die Methode erlaubt, komplexe Triazingemische, die bei der Umsetzung von 2.4.6‐Trichlor‐s‐triazin mit Alkoholgemischen entstehen, schnell und sicher zu identifizieren.
Aliphatic chain–sugar interactions under electron impact. The loss of methanol from acylated methyl glycopyranosides
Authors: Puzo G. , Tichadou J. L. , Prome J. C.
Published: May 2005

Under electron impact, long chain acylated methyl glucopyranoside derivatives lose a methanol molecule from the molecular ion. The hydrogen atom which is transferred arises from the aliphatic chain. This reaction is important when the aliphatic chain contains four or more carbon atoms. The results may be explained by a two‐step hydrogen transfer: hydrogen transfer to the oxygen carbonyl of the ester group, and then to the methoxy glycosidic group prior to fragmentation.
The mass spectrometric fragmentation of some diastereoisomeric 4‐methyl‐1,3,2‐dioxaphosphorinanes
Authors: ZielińSka Barbara , Stec Wojciech J.
Published: May 2005

The mass spectra of nine diastereoisomeric pairs of 4‐methyl‐2‐X‐2‐Y‐1,3,2‐dioxaphosphorinanes have been examined. The differences between the intensities of particular ions in the mass spectra of geometrical isomers are reported and rationalized in terms of the conformations adopted by compounds.
Hydrogen rearrangement in molecular ions of alkyl benzenes: Appearance potentials and substituent effects on the formation of [C7H8]+ ions
Authors: Kuck Dietmar , Grützmacher Hans‐Fr.
Published: May 2005

The mechanism of the formation of [C7H8]+ ions by hydrogen rearrangement in the molecular ions of 1‐phenylpropane and 1,3‐diphenylpropane has been investigated by looking at the effects of CH3O and CF3 substituents in the meta and para positions on the relative abundances of the corresponding ions and on the appearance energies. The formation of [C7H8]+ ions from 1,3‐diphenylpropane is much enhanced at the expense of the formation of [C7H7]+ ions by benzylic cleavage, due to the localized activation of the migrating hydrogen atom by the γ phenyl group. A methoxy substituent in the 1,3‐diphenylpropane, exerts a site‐specific influence on the hydrogen rearrangement, which is much more distinct than in 1‐phenylpropane and related 1‐phenylalkanes, the rearrangement reaction being favoured by a meta methoxy group. The mass spectrum of 1‐(3‐methoxyphenyl)‐3‐(4‐trideuteromethoxyphenyl)‐propane shows that this effect is even stronger than the effect of para methoxy groups on the benzylic cleavage. From measurements of appearance potentials it is concluded that the substituent effect is not due to a stabilization of the [C7H7X]+ product ions. Whereas the [C7H7]+ ions are formed directly from molecular ions of 1‐phenylpropane and 1,3‐diphenylpropane, the [C7H8]+ ions arise by a two‐step mechanism in which the s̀ complex type ion intermediate can either return to the molecular ion or fragment to [C7H8]+ by allylic bond cleavage. Obviously the formation of this s̀ complex type ion, is influenced by electron donating substituents in specific positions at the phenyl group. This is borne out by a calculation of the ΔHf values of the various species by thermochemical data. Thus, the relative abundances of the fragment ions are determined by an isomerization equilibrium of the molecular ions, preceding the fragmentation reaction.
Excitation in ion–molecule collisions. A study of protonated aromatic molecules by ion kinetic energy spectrometry
Authors: Franchetti V. , Freiser B. S. , Cooks R. G.
Published: May 2005

Collision induced dissociation of protonated aromatic ions formed in a chemical ionization source has been studied using the technique of mass analyzed ion kinetic energy spectrometry. The observed fragmentations are concordant with those seen in the photodissociation spectra of the same ions with one significant exception. Loss of H is always a major collision induced dissociation process but is not observed in photodissociation spectra. This differences is not due to differences in the total amount of energy transferred in ionic excitation but to differences in the form in which the energy is supplied. Collision induced dissociation can lead to processes forbidden in photoexcitation, particularly those associated with electron unpairing in violation of the even→even+even rule for fragmentations.
Reference standards for negative ion mass spectrometry
Authors: Hirata Yukio , Matsumoto Kozo , Takeuchi Tsugio
Published: May 2005

The negative ion mass spectra of phosphonitrile chlorides (PNCl2)n (n≥3) are studied. Since this series of compounds give very intense negative [M]− and [MCl]− ions, they can be used as good reference standards for negative ion mass spectrometry.
Isomerisation du Thiazole et de l'Isothiazole avant Fragmentation
Authors: Salmona Gérard , Vincent Emile‐Jean
Published: May 2005

Les ions moléculaires du thiazole et de l'isothiazole s'isomérisent en une structure commune prépondérante avant de se fragmenter. Ceci est mis en évidence par l'analyse de l'intensité des ions métastables et des libérations d'énergie cinétique.
Etude par Spectrométrie de Masse de la Fragmentation d'une Série de Diols Aliphatiques
Authors: Blanc Pierre‐Alain , Gülaçar Fazil O. , Buchs Armand
Published: May 2005

La fragmentation d'une série de diols aliphatiques de formule générale HO(CH2)nOH avec n = 2‐11 a été étudiée à l'aide de molécules marquées avec du deutérium. Les marquages du n‐butanediol‐1,4 et du n‐hexanediol‐1,6 ont notamment permis de mettre en évidence des réactions d'échange intramoléculaire d'hydrogène; ces échanges deviennent plus importants avec l'allongement de la chaîne.
Chemical ionization mass spectra of some 2‐norbornyl derivatives
Authors: Jelus Barbara L. , Dalrymple David L. , Michnowicz John , Munson Burnaby
Published: May 2005

Chemical ionization mass spectra of exo‐ and endo‐2‐norbornanols and their phenylurethane derivatives have been obtained with several reactant ions. Small differences are noted in the abundances of norbornyl and [M+H]+ ions for the phenylurethane derivatives: more norbornyl ions with the exo compounds. Relative rate constants for decomposition of [M+H]+ ions, kexo/kendo ≅ 1‐2. No evidence was found for s̀‐participation in the decomposition of these ions. The i‐C4H10 chemical ionization spectrum of endo‐2‐norbornanol contains a much greater abundance of [M‐H]+ ions than the i‐C4H10 chemical ionization spectrum of exo‐2‐norbornanol. This difference presumably results from steric hindrance toward attack of the endo hydrogen.
Stereochemisch kontrollierte Cope‐analoge Zerfallsprozesse von Sulfinylverbindungen im Massenspektrometer
Authors: Lüdersdorf Reinhard , Praefcke Klaus , Schwarz Helmut
Published: May 2005

Das Ausmaß der Eliminierung von HX (X = SOCH3, SCH3) aus [MSTol]+‐bzw. [MHHSTol]+‐Ionen (Tol = CH3C6H4), die sowohl durch Elektronenstoßionisation als auch durch chemische Ionisation aus 2‐sulfinylsubstituierten Cyclopentanthiocarbonsäure‐S‐arylestern erzeugt werden, wird in entscheidender Weise durch die Stereochemie der vicinalen Substituenten bestimmt.
Field ionization mass spectrometry of higher n‐alkenes
Authors: Rang S. A. , Müürisepp A.‐M. A. , Liitmaa M. M. , Eisen O. G.
Published: May 2005

In a strong electric field the molecular ions of n‐alkenes ≤C‐12 decompose via cleavage of the CC bond β to the double bond to form the characteristic alkenyl ions that may be used for the identification of positional isomers. For 3‐alkenes (>C‐10), 4‐, 5‐ and 6‐alkenes the formation of the ions with m/e 54 via double β‐cleavage is typical. The field ionization mass spectra of the cis and trans isomers are indistinguishable.
Three‐dimensional representation of metastable peaks at high mass resolution
Authors: Lacey Michael J. , Macdonald Colin G.
Published: May 2005

Isobaric daughter ions formed from a common metastable ion have been analysed at high mass resolution. A three‐dimensional representation is used to summarize the data for competitive CO and C2H4 losses and competitive CHO˙ and C2H5˙ losses from metastable molecular ions of cyclohexanone.
Intensitätsverhalten von Molekülanionen organischer Substanzen unter verschiedenen Versuchsbedingungen
Authors: Albers Georg , Knof Hans
Published: May 2005

Quantitative Messungen negativer Ionen werden von einigen ausgewählten organischen Verbindungen mit einem umgebauten kommerziellen Massenspektrometer bei 10−4 Torr Quellendruck durchgeführt. Aus der gemessenen Druckabhängigkeit der Molekülionenintensität von Einzelverbindungen und von binären Mischungen kann auf zwei verschiedene Quellen langsamer Sekundärelektronen geschlossen werden. Die Ionenintensität hängt bei niedrigen Gesamtdrücken in der Ionenquelle linear von der Probenmenge in einem doppeltlogarithmischen Maßstab ab, und die langsamen Elektronen werden hauptsächlich durch Wandeffekt erzeugt, während bei hohen Drücken Plasmaeffekte mit einer nichtlinearen Druckabhängigkeit auftreten.
Studies directed toward synthesis of quassinoids. VI—mass spectral fragmentation of D‐ring seco esters and δ‐lactone derivatives of cholic acid
Authors: Dias Jerry Ray , Ramachandra R. , Nassim Bahman
Published: May 2005

Analogy and deuterium labeling demonstrate that considerable remote group interaction occurs between functional groups at positions 7 and 16 in 16, 17‐secosteroids. It is proposed that ion‐dipole interact̂ions separations of distances of 10 to 2 Å will involve energies of 1–30 kcal mol−1 and can play a significant role in fragmentation processes. Successive loss of one, two and three HOAc molecules from a milecular or daughter ion increase progressively in relative intensity; irregularity in this pattern indicates the operation of special factors or multiple genesis of daughter ions having the same m/e. Evidence is presented which suggests that facile ketene ejection from the acetate functional group only occurs from a radical ion and must be preceded by transfer of a hydrogen radical from the acetate group to the site of charge localization.
Mécanismes de fragmentation en spectrométrie de masse par ionisation chimique. III—ions formés par cyclisation
Authors: Audier H. E. , Milliet A. , Perret C. , Tabet J. C. , Varenne P.
Published: May 2005

La fragmentation en spectrométrie de masse par ionisation chimique de composés bifonctionnels peut conduire à la formation d'ions cycliques.
Fragmentation sous l'impact electronique d'imidazo[1,5‐b]triazepinones‐1,2,4 et d'imidazo[4,5‐b]pyridinones
Authors: Bernardini Antoine , Viallefont Philippe , Zniber Rachid
Published: May 2005

Les spectres de masse des deux séries d'imidazo[1,5‐b]triazépinones‐1,2,4 et d'imidazo[4,5‐b]pyridinones, obtenues par condensation de diamino‐1,5 imidazoles avec un dérivé β‐dicarbonylé, sont décrits et analysés. Les principales fragmentations sont données et leur utilité à la détermination de structures des composés isomères est montrée.
Energetics of the loss of H2 from [C3H7]+
Authors: Mead Phillip T. , Traeger John C. , Christie John R. , Derrick Peter. J.
Published: May 2005

The internal energies of [C3H7]+ ions contributing to the metastable peak [C3H7]+ → [C3H5]+ + H2 are higher (by perhaps > 100 kJ mol−1) than those of the ion contributing to the threshold current in appearance energy measurements on [C3H5]+. The measured appearance energy may lead to an underestimation of the activation energy, i.e. negative ‘kinetic shift’, due to quantum, mechanical tunnelling. The distribution of energy released in the decomposition can be explained on the basis that much of the reverse activation energy and a statistical proportion of the excess energy is released as translation.
Mass spectra of bile acid methyl ester acetate derivatives
Authors: Dias Jerry Ray , Nassim Bahman
Published: May 2005

Deuterium labeling in the acetate derivatives of cholic acid demonstrates that electron impact induced consecutive loss of HOAc from the molecular ion occurs in the following order of decreasing preference: 12α‐OAc > 7α‐OAc > 3α‐OAc. Numerous examples are presented showing that consecutive loss of HOAc from a common ion generally increases progressively with relative intensity. In the acetate pregnan‐20‐one derivatives of cholic acid, loss of 43 mass units from the molecular ion comes from the 12α‐OAc and not the 17β‐acetyl sidechain. Ketene is ejected from an acetoxy group located in an α position to a carbonyl on which an ion‐radical charge is localized.
Field desorption mass spectrometry of 1‐methylpyridinium salts
Authors: Larsen Elfinn , Egsgaard Helge , Holmen Hans
Published: May 2005

Quaternary pyridinium salts were investigated by field desorption, field ionization and electron impact mass spectrometry. Thermal decomposition of the salts under field desorption conditions was found to give very abundant volatile products, identified as the dihydro analogues and the ‘methides’ of the cations. The formation of the volatile compounds, especially those with molecular weights corresponding to those of the (cation −1), (cation +1) and (cation +13) was studied in detail by deuterium and 13C labelling experiments.
Studies of cyclic acetals. XXIII—low resolution, electron impact mass spectra of some 6,8‐dioxa‐3‐thiabicyclo[3.2.1]octanes and related 2‐acetoxy, 3‐oxo and 3,3‐dioxo derivatives
Authors: Calinaud Pierre , Gelas Jacques , Horton Derek , Wander Joseph D.
Published: May 2005

Low resolution, electron impact mass spectra of 6,8‐dioxa‐3‐thiabicyclo[3.2.1]octane and eight C‐methyl or ‐phenyl derivatives are, in the main, similar to those of the corresponding 3,6,8‐trioxa homologs. Oxygenation on C‐2 or on the sulfur atom decreases the number of prominent fragments in the scheme of decomposition and apparently affords greater opportunity for formation of small, stable, acylium ions, but the added oxygen atoms generally do not direct major new modes of fragmentation.
Labelling studies of hydrogen rearrangements in the chemical ionization mass spectra of cyclohexanone and its derivatives
Authors: Diakiw Vladimir , Goldsack Robert J. , Shannon James S. , Lacey Michael J.
Published: May 2005

Deuterium labelling studies indicate that loss of water from the protonated molecular ion of cyclohexanone involves competitive site‐specific eliminations. Loss of alcohol from the protonated molecular ions of 4‐alkoxycyclohexanones involves competition between a direct cleavage, a 1,3‐hydrogen rearrangement and consecutive losses of alkene and water.
Ion–molecule reactions of methoxymethyl cations with some organic substrates studied by ion cyclotron resonance spectrometry
Authors: van Doorn R. , Nibbering N. M. M.
Published: May 2005

The reactions of methoxymethyl cations generated from dimethyl ether with propene, butene‐2, vinyl methyl ether, acetaldehyde and acetone have been studied. The collision complexes, generated with the olefines, may eliminate an olefine, a methanol and a formaldehyde molecule as shown by double resonance experiments. From deuterium labelling it is found, that in the cases of propene and butene‐2 the elimination of an olefine is accompanied by an extensive H/D interchange in the collision complexes, which has been shown not to occur in the long‐lived reactant methoxymethyl cations if the internal energy of the methoxymethyl cations is less than 2.3 eV. The H/D interchange in these collision complexes is reduced in the elimination of methanol and is almost completely suppressed in the elimination of formaldehyde. In reactions with vinyl methyl ether, however, the eliminations of methanol and formaldehyde from the corresponding collision complexes appear to proceed with extensive H/D interchange. These observations point to acyclic collision complexes rather than 4‐membered ring complexes. The collision complexes generated with acetaldehyde and acetone decompose by elimination of formaldehyde only. Deuterium labelling has shown that the formaldehyde molecule contains the original methylene group of the reactant methoxymethyl cations. In addition, 18O labelling in acetone has shown that the original oxygen atom of the methoxymethyl cations is retained completely in the eliminated formaldehyde. These observations exclude any formation of 4‐membered ring collision complexes and can only be explained by acyclic complexes. Possible mechanisms of all reactions mentioned are discussed in the light of these results.
Identification of amino acid thiohydantoin derivatives by chemical ionization mass spectrometry
Authors: Okada Kozo , Sakuno Akemi
Published: May 2005

The chemical ionization mass spectra of 16 amino acid thiohydantoins were examined using isobutane or ammonia as reagent gases. Except for a few cases, including some aromatic amino acids, the chemical ionization spectra were much simpler than the corresponding electron impact spectra. Therefore, the major component in the amino acid thiohydantoin mixture was easily detected by chemical ionization mass spectrometry. The combination of the chemical ionization method and thiohydantoin formation was applied successfully to the sequence analysis of model peptides.
The formation of [CH5O]+ and ions from the molecular ions of isobutyl alcohol
Authors: Tajima Susuma , van der Greef Jan , Nibbering Nico M. M.
Published: May 2005

On the basis of field ionization kinetic and deuterium labelling experiments, it is shown that the molecular ions of isobutyl alcohol generate [CH5O]+ ions at 10−11 s via a 1,4‐shift of a hydrogen atom from one of the methyl groups to the oxygen atom, followed by a 1,2‐elimination of protonated methanol with a hydrogen atom of the other methyl group. At times > 10−11 s two distinct interchange processes between hydrogen atoms appear to compete with this reaction, as shown from field ionization kinetic experiments and metastable decompositions. Ion cyclotron resonance experiments on the long‐lived [CH5O]+ ions further demonstrate that they are protonated methanol ions. Arguments are put forward that the ions, generated by a specific 1,3‐elimination of a molecule of water from metastable decomposing molecular ions, have an isobutene structure.
Mass spectroscopy of natural products. II—allogibberic acid—A model for the skeletal fragmentation of the molecular ions of GA3 type gibberellins
Authors: Voigt D. , Adam G. , Schmidt J. , Franke P.
Published: May 2005

The positive ion mass spectrum of allogibberic acid was examined and fragmentation routes involving the carbon skeleton are proposed on the basis of mass measurements and metastable ion observations. The results are compared with the mass spectra of 3‐hydroxy‐epiallogibberic acid, as well as gibberellin A3 (GA3), 3‐epi‐GA3, 3‐dehydro‐GA3 and iso‐GA3, the latter compounds all being capable of undergoing aromatization of ring A giving a key ion corresponding to the molecular ions of the allogibberic acid and 3‐hydroxy‐epiallogibberic acid models, respectively. All the gibberellin derivatives investigated show the same fragmentation of the skeleton. Thus, the behaviour under electron impact of the GA3 type gibberellins follows a general pattern.
Chemical ionization spectra of trimethylsilylated amino acids and oligopeptides
Authors: Budzikiewicz H. , Meissner G.
Published: May 2005

The isobutane chemical ionization mass spectra of trimethylsilylated amino acids and oligopeptides are discussed.
Ionization and appearance potentials in organic chemistry. II—Appearance potentials and enthalpy differences for the stereoisomers of methylbicyclo[4.4.0]decanes
Authors: Zaikin V. G. , Musaev I. A. , Kurashova E. Kh.
Published: May 2005

The ionization potentials for the stereoisomers of trans‐fused 2‐ and 3‐methylbicyclo[4.4.0]decanes and the appearance potentials for the ions at m/e 137 [M–CH3]+, 109, 96, 95 and 82 were measured by the electron impact method. The ionization potentials and appearance potentials of the [M–CH3]+ ions appeared to be equal for each of the epimers. Appearance potentials of the other ions were always lower for the less stable epimer. No quantitative correlation was observed between the difference in the appearance potentials for any ions and the differences in enthalpies of the ground states.
The Structures of the [2M–1]+ ions formed from benzene in a high pressure mass spectrometer source
Authors: Harris J. A. , Morgan R. P. , Beynon J. H.
Published: May 2005

The ionic species [C12H11]+ has been formed by ion‐molecule reactions in benzene at high pressure (˜0.5 Torr). This ion has been shown to be stable for at least 10−5 s and its structure has been inferred by a study of its unimolecular and collision induced fragmentations in both the first and second field free regions of the ZAB‐2F mass spectrometer.
Structure and fragmentations of [C3H7S]+ ions
Authors: Broer W. J. , Weringa W. D.
Published: May 2005

The principal fragmentation reactions of metastable [C3H7S]+ ions are loss of H2S and C2H4. These reactions and the preceding isomerizations of [C3H7S]+ ions with six different initial structures were studied by means of labelling with 13C or D. From the results it is concluded that the loss of H2S and C2H4 both occur at least mainly from ions with the structure [CH3CH2CHSH]+ or from ions with the same carbon sulfur skeleton, with the exception of the ions with the initial structure [CH3CH2SCH2]+, which partly lose C2H4 without a preceding isomerization. For all ions, more than one reaction route leads to [CH3CH2CHSH]+. It is concluded that the loss of H2S is at least mainly a 1,3‐elimination from the [CH3CH2CHSH]+ ions. Both decomposition reactions are preceded by extensive but incomplete hydrogen exchange.
Origin of the [C4H9O]+ ions in the mass spectrum of n‐butyl ethyl ether
Authors: Hudson Charles E. , McAdoo David J.
Published: May 2005

The mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C4H9O]+ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α‐ and β‐hydrogens and a γ‐hydrogen from the butyl group. The minor route involves the loss of ethylene from the [MH]+ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α‐ and β‐methylenes and a γ‐hydrogen, while the methyl is the δ‐methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec‐butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n‐ and sec‐butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n‐pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3‐pentyl and 2‐pentyl ether ions. Di n‐butyl and n‐butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.
Profil de Pics Métastables (Pertes de NO·) en Série Nitroindazolique
Authors: Maquestiau A. , Van Haverbeke Y. , Vanovervelt N. , Flammang R. , Elguero J.
Published: May 2005

Les libérations d'énergie cinétique associées aux fragmentations (pertes de NO·) des ions moléculaires de nitroindazoles ont été mesurées. Les résultats montrent que le profil des pics métastables correspondants permettent de différencier les cinq isomères.
The mechanism for elimination of acetic acid from 1‐acetoxy‐ and 2‐acetoxytetralin
Authors: Wojinski Stanley F. , Gross Michael L.
Published: May 2005

By employing deuterium substitution and metastable ion defocusing methods, it has been determined that 1‐acetoxytetralin undergoes a highly regiospecific (>98%) 1,4‐elimenation of acetic acid. The mechanism closely parallels that for loss of water from 1‐tetralol in terms of specificity. However, unlike the water loss, which shows a significant kinetic isotope effect (KH/KD = 2.0) and a large release of translational energy (270 meV), the expulsion of acetic acid occurs without an isotope effect and with release of only 10 meV of kinetic energy. Competitive with acetic acid loss is the elimination of ketene which has been shown to occur by a 4‐centered transition state. The 2‐acetoxytetralin exhibits the more traditional 1,2‐elimination of acetic acid which contrasts with a 1,3‐elemination of water for the corresponding alcohol.
The isobutane chemical ionization mass spectra of 2‐methyl substituted 1,3‐cycloalkanediol diacetates and dimethyl ethers
Authors: Dhaenens L. , Van De Sande C. C. , Vangaever F.
Published: May 2005

The isobutane chemical ionization mass spectra of 2‐methyl‐1,3‐cyclopentane and 1,3‐cyclohexanediol diacetates and dimethyl ethers reveal that the proton bridge in the protonated cis diol derivatives is sensitive to conformational and steric effects. The latter dominate in the case of the methyl ethers on account of the smaller ring created by the proton bridge in the ethers in comparison with the diacetates. Finally, the spectra of the trideuterocetates and trideuteromethyl ethers reveal the occurrence of protolysis in the ionizing plasma.
Massenspektrometrische Untersuchungen an Organophosphorverbindungen. II—Elektronenstoßinduzierte Fragmentierungen von Tetraorganodiphosphandisulfiden
Authors: Keck Helmut , Kuchen Wilhelm
Published: May 2005

Das massenspektrometrische Fragmentierungsverhalten sowie einige Umlagerungsprozesse in den durch Elektronenstoß induzierten 70 eV Massenspektren von Tetraorganodiphosphandisulfiden R2P(S)‐P(S)R2 (R  CH3, C2H5, n‐C3H7, n‐C4H9, C3H5, C6H5) und CH3RP(S)–P(S)CH3R (R  C2H5, n‐C3H7, n‐C4H9, C6H5, C6H5, C6H5,CH2) werden aufgeführt und diskutiert. Fragmentierungsschemata, die in übereinstimmug mit der Messung metastabiler übergänge nach der Methode DADI und Defokussing stehen, werden angegeben. Die Elementarzusammensetzung der meisten Ionen wurde durch Massenfeinbestimmung ermittelt. Im Gegensatz zu Organophosphansulfiden R3P(S) wird hier praktisch keine Schwefelabspaltung beobachtet. Erster Fragmentierungsschritt bei diesen Verbindungen ist die Spaltung einer P–C‐Bindung unter Abspaltung von R⋅. Folgeschritt ist dann die Eliminierung von RPS unter Bildung von [R2PS]+, aus dem in fast allen Spektren der Basispeak resultiert. Die phenylsubstituierten Verbindungen ergeben Spektren, in denen mit hoher Intensität [(C6H5)3P]+. bzw. [(C6H5)2CH3P]+. auftreten, die aus [M]+. durch Wanderung von C6H5 entstanden sind. Es wird angenommen, daß sich das Molekülion vor seiner Fragmentierung in einen P–S‐Vierring umlagert.
Electron impact mass spectra of 2‐[acyl(alkyl)amino]oxazoles
Authors: Mallen D. N. B. , Cort L. A. , Cockerill A. F.
Published: May 2005

The mass spectral behaviour of 2‐methyl‐N‐butyl‐N‐(4‐methyloxazol‐2‐yl)propanamide is characterized by cleavage of the acylamino substituents and the elimination of a hydroxyl radical. An understanding of this elimination has been obtained from the analysis of further 2‐[acyl(alkyl)amino]oxazoles and the use of deuterium labelled compounds.
Field desorption of non‐electrolytes using simply activated wire emitters
Authors: Giessmann U. , Heinen H. J. , Röllgen F. W.
Published: May 2005

The high field strengths obtained with activated emitters are necessary to accomplish field desorption of non‐electrolytes, i.e. samples containing neither salts nor acids. A simple procedure to produce activated emitters in a few seconds for this mode of field desorption is described. The method was applied to W and Pt wires, as well as carbon fibres.
Formation and stability of gaseous tolyl ions
Authors: McLafferty Fred W. , Bockhoff Frank M.
Published: May 2005

Collisional activation mass spectra confirm that tolyl ions can be produced from a variety of CH3C6H4Y compounds. High purity o‐, m‐ and p‐tolyl ions are prepared by chemical ionization of the corresponding fluorides (Y=F) as proposed by Harrison. In electron ionization of CH3C6H4Y formation of the more stable tropylium and benzyl ionic isomers usually accompanies that of the o‐, m‐ and p‐tolyl ions. Isomerization of low energy [CH3C6H4Y]+⋅ to [Y–methylenecyclohexadiene]+⋅ is proposed to account for most [benzyl]+ formation, while the tropylium ion appears to arise from the isomerization of tolyl ions formed with higher internal energies, [o‐, m‐, p‐tolyl]+→ [benzyl]+→ [tropylium]+, consistent with Dewar's predictions from MINDO/3 calculations.