bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural identification of fatty acid methyl esters by collision spectra of their [M  H]− species
Authors: Bambagiotti A. Massimo , Coran Silvia A. , Giannellini Valerio , Vincieri Franco F. , Daolio Sergio , Traldi Pietro 
Published: May 2005

AbstractNegative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass‐analysed ion kinetic energy spectra of [M  H]− species, obtained by OH− reaction with a selection of six C18 fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.
Intermolecular O‐methylation during EIMS of quaternary methoiodides of isoquinoline alkaloids
Authors: Huang Zhi‐Heng , Zhu Ji‐Ping , Zhou Yun‐Li 
Published: May 2005

AbstractQuaternary methoiodides of tetrahydroprotoberberine (THB) alkaloids (1‐8) tend to undergo preionization degradation in the mass spectrometer at elevated temperatures. Different reaction pathways have been found in relation to the structure of the substance studied. Permethylated alkaloids, e.g. tetrahydropalmatine‐CH3I (8), give predominantly the Hofmann degradation intermediates and the fragment ions derived therein, while the alkaloids with free phenolic group(groups), as exemplified by scoulerine‐CH3I (1), show a greater tendency to be methylated by an intermolecular CH3 transfer mechanism: magnified image The latter process has been systematically studied and the mechanism substantiated through comparison of the spectra of analogous series, B/E linked scan and CD3 labelling. Similar behaviour has been observed in bisbenzyltetrahydroisoquinoline alkaloids.
Loss of methyl from [H2CC(OH)CH3]+˙ ions prepared by electron impact ionization of unstable 2‐hydroxypropene
Authors: Tureček František , Hanuš Vladimír 
Published: May 2005

AbstractUnstable 2‐hydroxpropene was prepared by retro‐Diels‐Alder decomposition of 5‐exo‐methyl‐5‐norbornenol at 800°C/2 × 10−6 Torr. The ionization energy of 2‐hydroxypropene was measured as 8.67±0.05 eV. Formation of [C2H3O]+ and [CH3]+ ions originating from different parts of the parent ion was examined by means of 13C and deuterium labelling. Threshold‐energy [H2CC(OH)CH3]+˙ ions decompose to CH3CO++CH3˙ with appearance energy AE(CH3CO+) = 11.03 ± 0.03 eV. Higher energy ions also form CH2COH+ + CH3 with appearance energy AE(CH2COH+) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C2H3O]+ ions containing the original methyl group and [CH3]+ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate‐determining isomerization [H2CC(OH)CH3]+˙ →[CH3COCH3]+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.
Kinetic energy release in metastable ions from β‐keto esters
Authors: Moldovan Zaharie , Palibroada Nicolae , Mercea Victor , Mihǎilescu Gheorhe 
Published: May 2005

AbstractThe kinetic energy release, T, in metastable ion transitions accompanying the main fragmentation reaction by electron impact has been determined for methyl‐, ethyl‐ and propyl‐pivaloyl acetates. The measurements have been made using a MAT 311 mass spectrometer with inverse Nier–Johnson geometry, by high voltage and mass‐analysed ion kinetic energy methods. The peak width at 50% height has been used in the calculations. The T values and the shape of the metastable peaks are correlated to reaction types and to the alcohol radical.
Stereochemical effects in the electron impact mass spectra of cis–trans isomeric 1,2,3,5‐tetramethylcyclohexanes and some trimethylcyclohexanes
Authors: Herzschuh R. , Mann G. , Rennecke D. 
Published: May 2005

AbstractThe mass spectra of 10 isomeric trimethylcyclohexanes and six cis–trans isomeric 1,2,3,5‐tetramethylcyclohexanes are discussed. The thermochemically stable isomers show a higher abundance of the [MCH3]+ ions and a lower abundance of the [MC2H5]+ ions than the strained isomers. The log of the intensity ratio for loss of methyl and ethyl from the molecular ions correlates well with the strain energies and with the mean number of gauche arrangements of the stereoisomers.
Collisionally induced dissociative ionization of neutral products from ion fragmentations. 2—Collision gas effects and related phenomena
Authors: Clair Roberta , Holmes John L. , Mommers Alexander A. , Burgers Peter C. 
Published: May 2005

AbstractThe ion retardation method (whereby an ion beam is prevented from entering a collision gas cell by means of a voltage applied thereto) for permitting the examination of the neutral products of unimolecular ion fragmentations has been extended to include observations of neutral products generated by collisions before the gas cell and their related phenomenology. Observations obtained using an ion beam deflection electrode, an alternative method of preventing the ion beam from entering the collision cell, are also reported. When low collision gas pressures are employed (<2×10−7 Torr He), this latter method provides collisionally induced dissociative ionization (CIDI) mass spectra of unimolecularly generated neutral fragmentation products, free of complications arising from events induced by collisions occurring outside the collision cell. The CIDI mass spectra of CH3˙, C2H4, CH3ĊO, CH3OH and C2H6 generated from positive ion precursors and CH3˙, CH3O˙ and C6H5NO2 generated by electron loss from negative ions are described.
Fragmentation and rearrangement reactions in certain 1,2,3‐triaryl‐2‐propen‐1‐ones following electron impact and chemical ionization
Authors: Madhusudanan K. P. , Mittal Shubhra , Durani S. , Kapil R. S. 
Published: May 2005

AbstractThe electron impact (EI) and chemical ionization (CI) mass spectra of certain 1,2,3‐triaryl‐2‐propen‐1‐ones (TAPs) have been studied in detail with the help of exact mass measurements, deuterium labelling and metastable data. TheE‐ andZ‐isomeric pairs do not show any difference in their behaviour under EI or CH4CI conditions. EI‐induced rearangement reactions in the TAPs include aryl migration to carbonium ion centres. A study of the metastable transitions reveals aryl group interchange in the molecular ions prior to fragmentation. Under EI conditions loss of arene involves either C(2) or C(3) aryl groups while under CI conditions the C(1) aryl is lost as a neutral arene molecule. Mechanisms for the different fragmentation modes are given.
Chemical ionization mass spectrometry using a glow discharge ion source combined with a nebulizer sampling system
Authors: Matsumoto Kozo , Kojima Hisanoa , Yasuda Kazuhiro , Tsuge Shin 
Published: May 2005

AbstractA glow discharge chemical ionization (CI) source equipped with a pneumatic nebulizer for sample introduction has been constructed. A comparative study of the discharge CI and conventional CI by electron impact from a hot filament is made for various polar compounds using oxygen‐containing reagents such as water and methanol. The potential utility of the discharge ion source to liquid chromatography/mass spectrometry is also discussed.
Stereospecific adduct ion formation in the chemical ionization mass spectra of E‐ and Z‐1,2,3‐triaryl‐2‐propen‐1‐ones
Authors: Madhusudanan K. P. , Mittal Shubhra , Durani Susheel , Kapil R. S. 
Published: May 2005

AbstractStereospecific adduct ion formation has been observed in the chemical ionization mass spectra (positive and negative) of certain E‐ and Z‐1,2,3‐triaryl‐2‐propen‐1‐ones. The Z isomers are found to give higher relative abundances of adduct ions than the E isomers. This has been interpreted in terms of the differences in the proton affinities of the isomers originating from their different degrees of enone resonance. Halide ion (CI− and Br−) attachment spectra of these compounds also show stereochemical differences in the relative abundances of [M]−˙ and [M+halide]− ions, though the effect is not as pronounced as in the case of the positive ion spectra.
1,2‐Carbon shifts in [C4H8O]+˙ and [C5H10O]+˙ ions
Authors: Hudson C. E. , McAdoo D. J. 
Published: May 2005

AbstractPresent results demonstrate that α,β‐shifts of the functional group carbon strongly dominate β,α‐methyl shifts in [C4H8O]+˙ and [C5H10O]+˙ ions, paralleling observations of others on methyl isobutyrate ions.
Multiple ionization, charge separation and charge stripping reactions involving polycyclic aromatic compounds
Authors: Kingston R. G. , Guilhaus M. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractThe 70 eV electron ionization mass spectra of polycyclic aromatic compounds are characterized by the presence of relatively stable multiply charged molecular ions [M]n+ (n=2–4). When generated from the compounds benzene, napthalene, anthracene, phenanthrene, 2,3‐benzanthracene, 1,2‐benzanthracene, chrysene, 9,10‐benzophenanthrene and pyrene, the relative abundances of the multiply charged ions increase dramatically with the number of rings. These compounds form multiply charged molecular ions (n=2, 3) which undergo unimolecular decompositions indicative of considerable ionic rearrangement. The main charge separation processes observed here [M]2+→m1++m2+, [M]3+˙→m3++m→+m42+) involve, in almost every case, one or more of the products [CH3]+, [C2H3]+˙ and [C3H3]+. This suggests the existence of preferred structures amongst the metastable parent ions. Information on the relative importance of the various fragmentation pathways is presented here along with translational energy release data. Some tentative structural information about the metastable ions has been inferred from the translational energy release on the assumption that the released energy is due primarily to coulombic repulsion within the transition state structure. For the triply charged ions these interpretations have necessitated the use of a coulombic repulsion model which takes account of an extra charge. Vertical ionization energies for the process [M]n++G→[M](n+1)+G+e− (charge stripping) have also been determined where possible for n=1 and 2 and the results from these experiments allow the derivation of simple empirical equations which relate successive ionization energies for the formation of [M]2+ and [M]3+˙ to the appearance energy of [M]+˙.
Hydrogen transfer in the retro‐Diels–Alder fragmentation of trans‐4‐amino‐, isopropyl‐amino‐, piperidino‐ and pyrrolidino‐2H‐1‐benzopyran‐3‐ols
Authors: Evans John M. , Gower John Leveson 
Published: May 2005

AbstractThe electron impact mass spectra of trans‐4‐amino‐, isopropylamino‐, pyrrolidino‐ and piperidino‐2H‐1‐benzopyran‐3‐ols show intense peaks corresponding to the retro‐Diels–Alder reaction. In addition significant ions due to hydrogen transfer to and from the retro‐Diels–Alder fragment ion are observed. The transfer of hydrogen to this retro‐Diels–Alder fragment ion is influenced by the nature and location of the aromatic substituents, and the amino group at C(4). The loss of hydrogen from the retro‐Diels–Alder ion is subject only to the nature of the amino group at C(4). Hydrogen transfer to the retro‐Diels–Alder ion is shown to arise from the gem‐dimethyl group at C(2), as it is attenuated by successive removal of the methyl groups.
Mass spectrometric studies on cyclo‐ and poly‐phosphazenes: 3—Polymerization of tris(o‐diphenylenedioxy)cyclotriphosphazene, [NP(O2C6H4)]3
Authors: Daolio Sergio , Traldi Pietro , Vecchi Enrico , Gleria Mario 
Published: May 2005

AbstractThe polymerization reaction of tris(o‐phenylenedioxy)cyclotriphosphazene, [NP(O2C6H4)]3, occurs in the ion chamber of a mass spectrometer under high‐sample vapour pressure conditions, leading to the formation of tetrameric, pentameric and hexameric species. There is evidence that, under electron impact conditions, the phosphonitrilic ring of [NP(O2C6H4)]3 breaks down, giving rise to a linear phosphazene radical cation, from which the polymerization reaction takes place by means of successive additions of neutral NP(O2C6H4) units. A comparison is made between this reaction and mass spectrometrically induced polymerizations of hexachloro‐ and hexa(phenoxy)‐cyclophosphazenes, previously reported.
Distinction between 17‐epimeric hydroxy steroids of the 3,17‐dioxygenated androstane series by chemical ionization
Authors: Prome Danielle , Prome Jean‐Claude , Stahl Daniel 
Published: May 2005

AbstractThe distinction between 17‐epimeric 3,17‐dioxygenated hydroxyandrostanes has been made by comparison of both their methane or ammonia positive and OH− negative chemical ionization (CI) mass spectra. In the methane or ammonia positive CI, the 17α‐configuration in the eight stereoisomeric 5ξ‐androstane‐3ξ,17ξ‐diols can be determined by the relative abundances of the ion [MH2 H2O]+. In the ammonia CI spectra, the ion [M+NH4H2O]+ possesses only a low abundance, but a comparison of the relative rates of the loss of water v. the loss of ammonia from [M.NH4]+ in the second field‐free region allows a clear distinction to be made between the 17α‐ and 17β‐series. In the OH− negative CI mass spectra, the 5ξ‐androstane‐3‐one‐17ξ‐ols produce an intense ion [MHH2O]− in the 17α‐series only.
Applications of charge stripping/charge exchange spectra of organic ions
Authors: Kingston E. E. , Beynon J. H. , Ast T. , Flammang R. , Maquestiau A. 
Published: May 2005

AbstractThe application of a new technique which involves the combination of charge stripping and charge exchange processes has been investigated. Ions are charge‐stripped in the second field‐free region of a triple‐sector mass spectrometer (BEE geometry), and then subjected to a charge exchange reaction in the third field‐free region. The resulting charge stripping/charge exchange (CS/CE) spectrum is free from interference, which is otherwise common in charge stripping spectra. Comparisons between charge stripping and CS/CE spectra are made in cases where both kinds of spectra are obtainable. In order to assess the applicability of this new technique to studies of isomeric ion structures, species for which charge stripping spectra have previously been unobtainable have been chosen. CS/CE spectra of [C6H6]+˙, [C6H5]+, [C8H10]+˙ and [C7H7O]+ ions from a variety of precursors are recorded: in most cases, sufficient differences are observed to permit distinction between isomeric structures (or mixtures of structures). Previous studies which have shown that stable doubly charged molecular ions of ethane cannot be formed by the charge stripping technique are confirmed from its CS/CE spectrum.
Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study
Authors: Bouchoux Guy , Hoppilliard Yannik , Flament Jean‐Pierre 
Published: May 2005

AbstractThe relative energies of 11 [C3H3O]+ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3‐21G and 4‐31G* basis set and configuration interaction). The four most stable structures are: a ([CH2CHCO]+), b
equation image
c ([CHCCHOH]+) and d ([CH2CCOH]+); their relative energies at the CI/4‐31G*//3‐21G level are 0, 117, 171 and 218 kJ mol−1, respectively. The isomerizations c→[CHCHCHO]+→[CH2CCHO]+→ a and dissociations into [C2H3]++CO and [HCO]++C2H2 are explored. The calculated potential energy profile reveals that the energy‐determining step is the 1,3‐H migration c→[CHCHCHO]+. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.
A structural investigation of [C6H6]2+ and [C6H6]+˙ ions involved in charge exchange reactions
Authors: Guilhaus M. , Kingston R. G. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractMass‐analysed ion kinetic energy spectra for collisional activation (CA) of [C6H6]+˙ formed via electron capture by [C6H6]2+ ions in collision with neutral benzene molecules have been compared for the C6H6 isomers benzene, 1,5‐hexadiyne and 2,4‐hexadiyne. Comparisons of fragment abundance and total CA fragment yields were also made for [C6H6]+˙ ions generated by electron ionization (EI). CA conditions of ion velocity and collision gas pressure were identical in these comparisons. In general the fragment abundance patterns for the ions formed by charge exchange were very similar to those for singly charged benzene ions generated by EI. However, significant variations in CA fragment yield (the ratio of the total CA fragment ion abundance to the abundance of the incident unfragmented ions) were observed. It is not clear from the results whether these variations reflect structurally different ions or ions of different internal energies. The CA spectra of [C6H6]+˙ ions derived from charge exchange reactions between the benzene dication and the target gases He, Ne, Ar, Kr and Xe have also been recorded and, once again, very similar fragment abundance patterns were observed along with large variations in total CA fragment yields. Charge exchange efficiency measurements are reported for reactions between the benzene dication and the targets He, Ne, Ar, Kr, Xe and C6H6 (benzene) and also for the doubly charged ions derived from the linear C6H6 isomers. In the latter case Xe and benzene targets were used. The energetics and efficiency measurements for the former reactions suggest that for targets such as He and Ne the processes probably involve excited states of the doubly charged ions. The efficiencies measured for the latter reactions were distinctly different for the three C6H6 isomers and may indicate a strong dependence of charge exchange cross‐section on doubly charged ion structure.
Laser‐ion beam photodissociation studies of C4H4 radical cations
Authors: Krailler R. E. , Russell D. H. 
Published: May 2005

AbstractThe laser‐ion beam photodissociation for [C4H4]+˙ ions produced from a variety of precursors has been studied. Based on the data it is apparent that two structurally distinct forms of the [C4H4]+˙ ion are produced by fragmentation of larger systems. The relative population of the various structural forms is very dependent on the internal energy of the fragmenting ion, with 1‐buten‐3‐yne [C4H4]+˙ ions being favored at low internal energies. As the internal energy of the reactant ion is increased, the relative population of butatriene [C4H4]+˙ ions increases. The laser‐ion beam photodissociation technique is able to selectively sample these two structural forms.
Stable [C2H7O2]+ isomers: Experimental and theoretical evidence for the existence of protonated peroxides and proton‐bound dimers in the gas phase
Authors: van Driel Jan H. , Heerma Wigger , Terlouw Johan K. , Halim Herman , Schwarz Helmut 
Published: May 2005

AbstractEvidence is presented for the gas phase generation of at least eight stable isomeric [C2H7O2]+ ions. These include energy‐rich protonated peroxides (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_2 {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (e), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm (H)OH} $\end{document} (f) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm O}\mathop {\rm O}\limits^{\rm + } {\rm (H)CH}_{\rm 3} {\rm (g)),} $\end{document} (g)), proton‐bound dimers (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm 3} \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} (h) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH2 = O} \cdot \cdot \cdot \mathop {\rm H}\limits^{\rm + } \cdot \cdot \cdot {\rm HOCH}_{\rm 3} $\end{document} (i)) and hydroxy‐protonated species (ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} {\rm (OH)CH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} (a), $\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH(OH)}\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (b) and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm OCH}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2} $\end{document} (c)). The important points of the present study are (i) that these ions are prevented by high barriers from facile interconversion and (ii) that both electron‐impact‐ and proton‐induced gas phase decompositions seem to proceed via multistep reactions, some of which eventually result in the formation of proton‐bound dimers.
Gas phase reactions of chloride ion with aryl‐substituted nitrocyclohexenes
Authors: Das K. G. , Reddy A. Mahender , Mallaiah M. , Madhusudanan K. P. 
Published: May 2005

AbstractChloride ion chemical ionization studies of some aryl‐substituted nitrocyclohexenes have demonstrated that benzylic anion formation is favoured in the gas phase. Anchimeric assistance by neighbouring phenyl groups and the effect of olefinic functions have a significant influence on the stability of the carbanions.
Fragmentation of 1,4,5,8‐tetraazaphenanthrenes upon electron impact: A new example of structural integrity of gas phase heteroaromatic cations
Authors: Nasielski‐Hinkens Raymonde , Kaisin Michel , Flammang Robert , Maquestiau André 
Published: May 2005

Abstract1,4,5,8‐Tetraazaphenanthrene and some derivatives have been studied by mass and ion kinetic energy spectrometries. Deuterium labelling experiments show an unexpected structural integrity of the gas phase molecular ions which eliminate H(D)CN, even near threshold energies (field‐free region reactions). The loss of N(1(8)) predominates largely over the loss of N(4(5)); the consecutive losses of H(D)CN are also highly specific. A similar specificty is observed for the chlorinated and methylated isomers. The atoms of the homocycle are not involved in the first steps of the fragmentation as indicated by the behaviour of 9‐chloro‐and 9‐methyl‐tetraazaphenanthrenes.
Thermospray mass spectrometry of diazonium and di‐, tri‐ and tetra‐quaternary onium salts
Authors: Schmelzeisen‐Redeker G. , Röllgen F. W. , Wirtz H. , Vögtle F. 
Published: May 2005

AbstractVarious diazonium, multiply charged ammonium and pyridinium salts and one diphosphonium salt have been analysed by thermospray (TSP) mass spectrometry. The intact cation forms the base peak in all spectra. Typically only a few, yet structurally significant, ions are observed. For diazonium salts the level of fragmentation can be controlled by the temperature of the TSP interface while the fragmentation of the quaternary salts is found to be rather insensitive to interface temperatures.
Electron impact and chemical ionization mass spectra of some tetra‐acetylated anomeric glycosides
Authors: Kulkarni P. S. , Kulkarni S. Y. , Pansare V. S. 
Published: May 2005

AbstractElectron impact and chemical ionization (CH4, iso‐C4H10 and NH3) mass spectra of some tetra‐acetylated anomeric glycosides have been examined with a view to the characterization of anomeric pairs. Minor differences observed in the relative intensities of common ions in the anomeric pairs in the electron impact mass spectra are found to be enhanced in the methane and isobutane chemical ionization mass spectra. In the absence of thermal decomposition, the β‐anomers show greater ion abundances of common glycosyl ions than the α‐anomers. Ammonia chemical ionization mass spectra show complementary behaviour indicating strong adduct ions and practically no fragmentation.
Fragmentation of the chain in the mass spectra of the pyrrolidides of alkylcyclohexanecarboxylic acids
Authors: Vetter W. , Meister W. 
Published: May 2005

AbstractThe electron impact mass spectra of the pyrrolidides of both the cis‐ and trans‐octylcyclohexanecarboxylic acids show the structure of the aliphatic chain, despite the steric hindrance of a direct H transfer from the chain to the functional group.