bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of charge‐exchange collision gas on ‘resolved’ E/2 mass spectra
Authors: Jonathan P. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractA survey of the mass spectroscopic technique producing resolved E/2 mass spectra is undertaken, primarily to determine its dependence on the charge‐exchange collision gas used. The applicability of the resultant spectra to ion structure studies is discussed. Instrumental effects, influencing the spectral pattern, are explained and will aid those utilizing this technique for ion structure determination.
Mass spectra of some 1‐substituted‐4‐acetoacetyl‐3‐methylpyrazol‐5‐ols
Authors: Singh S. P. , Vaid R. K. , Dinakar P. , Singh Lukhvinder 
Published: May 2005

AbstractThe fragmentation of 1‐phenyl‐, l‐(2′‐pyridyl)‐ and 1‐(4′‐methyl‐2′‐quinolyl)‐4‐acetoacetyI‐3‐methyIpyrazol‐5‐ols (compounds 1, 2 and 3, respectively) on electron impact has been studied and the major processes interpreted. The common feature in the mass spectra of these compounds is the loss of ketene, acetonyl radical, acetone and two molecules of ketene from the molecular ion. Whereas the ion generated after the last process, which corresponds to 1‐substituted‐3‐methyIpyrazol‐5‐ols, loses methyl cyanide in the case of 1, similar ions in the case of 2 and 3 lose Ċ2HO moiety, necessitating an intramolecular hydrogen transfer followed by ring fission and subsequent loss of methyl cyanide. All these and other related processes have been substantiated with the help of accurate mass measurements of the fragment ions and B/E linked‐scan spectra.
Electron ionization and chemical ionization fragmentation of o/p isomers of bisphenol‐A with tandem mass spectrometry
Authors: Peltonen Kimmo , Kostiainen Risto 
Published: May 2005

AbstractThe fragmentation of o/p isomers of bisphenol‐A was examined by using collisionally activated decomposition and the tanden mass spectrometric techniques. Also chemical ionization was performed using methane, isobutane and ammonia. The o/p position of the hydroxy groups in the bisphenol‐A molecule directed the fragmentation both in electron and chemical ionization.
Ion–molecule reactions of fragment ions derived from protonated allyl methyl ether
Authors: Maquestian André , Beugnies Didier , Flammang Robert , Houriet Raymond , Rolli Eric , Bouchoux Guy 
Published: May 2005

AbstractUnusual behaviour has been noted for allyl methyl ether (1) chemically ionized in a high‐pressure ion source. Tandem mass spectrometry indicates the formation of methylcyclopentadienyl and methoxy‐1‐propenylcarbenium ions (d, m/z 81 and e, m/z 85). The origin of these unexpected ions has been elucidated using conventional and Fourier transform ion cyclotron resonance experiments: primary fragment ions derived from protonated 1 (allyl ions a and methoxymethyl cations b) generate collision complexes with neutral 1, giving rise to the ions d and e, respectively, after methanol elimination.
Translational energy release and stereochemistry of steroids. IX‐The mechanism of the elimination of water from metastable ions in epimeric 3‐hydroxy steroids of the 5β‐series
Authors: Zaretskii Z. V. I. , Curtis J. M. , Brenton A. G. , Beynon J. H. , Djerassi Carl 
Published: May 2005

AbstractThe mechanism of water elimination from metastable molecular and [M − CH3˙]+ ions, as well as from ions deprived of ring D, in epimeric 3‐hydroxy steroids of the 5β‐series has been elucidated by deuterium labelling, by the measurements of the translational energy released during loss of water, and by collision‐induced decomposition mass‐analysed ion kinetic energy spectrometry. It was found that the dehydration of the metastable molecular ion in 3α‐hydroxy steroids of the 5β‐series occurs mostly regiospecifically as an elimination of the 3α‐hydroxyl together with the 9α‐hydrogen atom. The ring A in the molecular ion has to flip to the boat conformation to make this reaction possible. In the metastable molecular ion of 3β‐hydroxy steroids of the 5β‐series a different dehydration mechanism operates, with very little participation of the 9α‐hydrogen atom. The mechanisms of water loss from metastable [M − CH3˙]+ ions and from ions deprived of ring D differ from that of the molecular ion.
Pre‐ionization effects in the mass spectrometry of some azoxybenzenes
Authors: Waddell D. S. , Bunce N. J. , Boyd R. K. 
Published: May 2005

AbstractThe mass spectrometry of azoxybenzene, and of several of its substituted variants, has been investigated under both electron ionization (EI) and chemical ionization (CI) conditions. The EI spectra largely confirm earlier mechanistic conclusions of Bowie et al. (J. Chem. Soc. B, 621 (1967)), but extend this work to consideration of the mechanism of formation of the [M − O]+˙ ion. This unexpected ion has been shown, using techniques of tandem mass spectrometry, to arise from pre‐ionization reduction to the corresponding azobenzene probably at the ion source surfaces. These pre‐ionization effects cause the observed spectra to vary markedly with the conditions, including partial pressure of the sample, within the EI source. Under CI conditions (both methane and isobutane reagent gases) the pre‐ionization reduction process is even more marked, and can involve reductive cleavage to the appropriate substituted anilines. Addition of water vapour favours the latter process over formation of [M − O + H]+. Analogous processes have been reported previously for nitroaromatics, suggesting that mass spectra of aromatic compounds substituted with oxygenated nitrogen atoms may all prove to be susceptible to similar effects.
Electron impact mass spectrometry of some naphthoxypolymethylenethiopyrimidines
Authors: Stobiecki Maciej 
Published: May 2005

AbstractThe electron impact induced fragmentation of a large number of 2‐ and 4‐S‐(2‐naphthoxy)‐polymethyienethiouracils is discussed in detail, with the aid of exact mass measurements and observation of metastable decompositions. The 2‐ and 4‐thiopyrimidine structures can be easily distinguished by their mass spectra.
A fuzzy classification for identification of double bond position in dodecadienic compounds based on mass spectral data
Authors: Gu Yuan 
Published: May 2005

AbstractA fuzzy classification and a computer pattern recognition program are presented for identifying double bond positional isomers of dodecadienic compounds by comprehensively analysing the mass spectra and calculating similarity coefficients of the compounds. Fifty‐four examples showed that this is an excellent classification method.
The [CH2 = CHOH/H2O]+˙ system: A theoretical study of distonic ions, hydrogen‐bridged ions and ion–dipole complexes
Authors: Postma R. , Van Helden S. P. , Van Lenthe J. H. , Ruttink P. J. A. , Terlouw J. K. , Holmes J. L. 
Published: May 2005

AbstractSeveral isomeric forms of the vinyl alcohol/water radical cation have been investigated by high‐level ab initio molecular orbital theory calculations, including electron correlation effects. Of the ions considered here, the anti form of the O ⃛H ⃛O bridged complex is calculated to be the lowest in energy, having a stabilization energy of 100 kJ mol−1 with respect to the dissociation products [CH2CHOH]+˙ and H2O. Although the isomeric ions may formally be represented as distonic ions, hydrogen‐bridged ions and ion–dipole complexes, the only significant barrier separating the isomers appears to be the anti↔syn isomerization barrier. However, in the O ⃛H ⃛O bridged complex this barrier is found to be considerably lowered relative to the anti↔syn isomerization barrier for the free vinyl alcohol radical cation.
Gas‐phase ion–molecule reactions of thioic and dithioic acid derivatives. Condensation reactions with alkenes and alkynes
Authors: Paradisi Cristina , Kenttämaa Hilkka , Le Quang T. , Caserio Marjorie C. 
Published: May 2005

AbstractA Fourier transform–ion cyclotron resonance study of thioacyl compounds as binary mixtures with unsaturated hydrocarbons has revealed that thioacetylium ions CH3CS+ generated by electron fragmentation fail to thioacyl‐ate even the most reactive aromatic hydrocarbons. Among the hydrocarbons studied, only 3‐hexyne and 2,4‐dimethyl‐2,5‐hexadiene were observed to react with CH3CS+. Apart from proton‐transfer reactions, the major ionic reaction of thioesters with arenes, alkynes and alkenes is condensation of the molecular ion of one component, usually the ester, with a neutral molecule of the other, resulting in the cleavage of the SCalkyl bond of the thioester. The nature of this reaction is discussed and a possible mechanism is suggested.
Awareness in mass speetrometry: An evaluation of services for retrieving and abstracting mass spectrometric literature
Authors: Lowes Stephen , Rose Malcolm E. 
Published: May 2005

AbstractThe commercially available methods for keeping mass spectrometrists aware of a vast literature are assessed. CA Selects: Mass Speetrometry was found convenient for browsing of current literature but disappointing in its coverage. The lack of an index makes it impracticable for retrospective searching. On the other hand, the Mass Speetrometry Bulletin contains over three times more references, is sectionalized for casual browsing, and its individual issue and annual indices make it very suitable for current and retrospective searching of specific topics. Chemical Abstracts itself contains many more mass spectrometric references than its CA Selects: Mass Speetrometry derivative but that information is difficult to extract comprehensively using the volume indices provided. Both Mass Speetrometry Bulletin and Chemical Abstracts can be accessed by on‐line systems. Use of computer searches proved to be excellent for current awareness and retrospective searching of selected topics within mass spectrometry. The mass spectrometrist can readily generate a tailor‐made set of terms to extract just the information of personal interest from Mass Speetrometry Bulletin and/or Chemical Abstracts. A detailed search requires use of both databases. On‐line searching provided faster and more comprehensive extraction of information than manual searching. On‐line systems would, however, be too expensive for browsing in general mass Speetrometry. Some problems and improvements in the various services are described and the role of some publications reviewing mass Speetrometry is briefly discussed.
Triazolopyridine, a new derivative for the structural determination of fatty acids by gas chromatography/mass spectrometry
Authors: Vetter Walter , Meister Walter , Oesterhelt Gottfried 
Published: May 2005

AbstractTriazolopyridine is proposed as a new derivative for the location of branches and double bonds in fatty acids. It is compared with previously used derivatives and found to be clearly superior to the pyrrolidide and slightly superior to the β‐picolinyl ester with regard to the structure‐specific fragmentation pattern. It is prepared by reacting the activated acid with 2‐hydrazinopyridine followed by cyclization.
Electron impact mass spectra of isobenzofurans, isonaphthofurans and some of their Diels–Alder adducts
Authors: Dibble Peter W. , Rodrigo Russell 
Published: May 2005

AbstractThe mass spectra of a wide variety of substituted isobenzofurans (IBF) have been studied by the direct examination of stable IBFs and IBF ions formed in the retro‐Diels–Alder cleavage of oxabicyclo adducts. In general, the fragmentation patterns observed are very dependent upon the nature and position of substitution. The dimethyl acetylenedkarboxylate adducts also show additional interesting and novel fragmentation pathways that are not IBF related.
A mass spectrometric study of halogenated beryllium μ4‐oxohexa‐μ‐acetates
Authors: Sipachev Viktor A. , Nekrasov Yurii S. 
Published: May 2005

AbstractThe electron impact mass spectra of Be4O(CHal3CO2)6 (Hal = F, Cl) are reported. The compounds give two series of fragment ions, [Be4OLx]+ and [Be4OL+]+, where L is an intact ligand or its fragmentation product. The major ligand dissociation path is the elimination of CHal2CO2 with halogen transfer to the metal. Other processes of importance are the loss of acid anhydride fragments, CF2 with fluorine shift to the carboxyl group carbon atom, and halogens. Trinuclear ions also undergo decarboxylation, e.g. to give [Be2O(CHal3CO2)2(CHal3)]+. Both spectra contain comparatively intense peaks of double‐charged ions. The fragmentation patterns are rationalized by stereochemical considerations.
A mass spectral study of the acid‐catalysed oxygen exchange in laevulinic acid
Authors: Srzić D. , Horvat J. , Šunjić V. , Kralj B. 
Published: May 2005

AbstractThe sequence, i.e. site selectivity of the acid‐catalysed 16O/18O exchange in laevulinic acid (1) is studied by mass spectrometry, ion kinetic energy spectroscopy and accurate mass measurements on 1 and its 13C(1)‐labelled congener. In the fragmentation pathways all ions of interest in the spectrum of 1 originate from the molecular ion, which may exist in six tautomeric or isomeric forms (1a–1d). The mechanism of gas‐phase cyclization of 1a is rationalized in terms of three different pathways. Formation of the most prominent fragment ions and the sequence of 16O/18O exchange at the carbonyl and carboxy group are discussed. The results indicate the ions of m/z 56, m/z 61 and m/z 98 to be the only three which have incorporated oxygen atoms originating from the carboxy group in 1 and could thus be used in further elucidadon of the rearrangement mechanism of 5‐hydroxymethylfuran (2) or 5‐hydroxymethylfuran‐2‐carbaldehyde (3) into laevulinic acid (1).
The effects of emitter heating on field ionization mass spectra of nitrogen‐containing organic molecules
Authors: Nelson P. R. , Abbey L. E. , Moran T. F. 
Published: May 2005

AbstractField ionization mass spectra of nitrogen‐containing organic compounds were examined as a function of carbon dendrite emitter heating current. The intensities of singly charged molecular, quasimolecular and dimer ions decreased with increasing emitter heating current; whereas, the opposite trend was observed for singly charged fragment ions. The abundance of doubly charged ions originating from aromatic compounds increased with heating current.
Comparison of [C6H6]2+ ion structures: Application of electron capture induced decomposition to the study of isomers
Authors: Vékey Kàroly , Gareth Brenton A. , Beynon John H. 
Published: May 2005

AbstractStructures of [C6H6]2+ ions formed by electron impact from benzene, 2,4‐hexadiyne and 1,5‐hexadiyne have been investigated by the recently developed electron capture induced decomposition method, by charge‐separation reactions and by ion abundances in electron impact mass spectra. Significant differences were found among the isomers indicating the structural integrity of these [C6H6]2+ ions. The observed differences indicate that the most likely atomic configuration of [C6H6]2+ ions produced from benzene and 2,4‐hexadiyne is the same as in the corresponding neutral species. A new method is suggested by which the structure (atomic configuration) of doubly charged ions may be determined.
Ortho effects in organic molecules on electron impact. Part 16. Novel oxygen transfers from the nitro group to acetylenic carbons in 2‐nitrodiphenylacetylenes
Authors: Ramana D. V. , Krishna N. V. S. Rama 
Published: May 2005

AbstractOxygen transfers to both acetylene carbons are noticed in parallel fragmentation pathways during the electron impact induced decompositions of 2‐nitrodiphenylacetylene. The oxygen transfer to β‐acetylenic carbon leads to the most abundant ion corresponding to benzoyl cation while transfer to the α‐acetylenic carbon affords less intense fragments corresponding to [MOH]+, [MCO]+ ˙ and [MCO2]+ ˙. The proposed fragmentation pathways and ion structures are supported by high‐resolution data, linked‐scan spectra and chemical substitution.
Electron impact fragmentation of some cyclohexyl thiophosphororganic amides
Authors: Moldovan Zaharie , Palibroda Nicolae , Culea Monica , FeneşAn Ioan , Hantz Andrei 
Published: May 2005

AbstractThis paper presents the mass spectra, fragmentation pathways and structures of ions obtained by electron impact from methyl cyclohexyl phosphinomorpholinylamidothioate (1), cyclohexyl phosphonomorpholinylamidochloridothioate (2), cyclohexyl morpholinylamidophosphonothioic acid (3) and O‐methyl cyclohexyl phosphonomorpholinylamidothioate (4). The fragmentation pathways and ion structures were established by exact mass determinations on compound 1 and by metastable transitions of all the compounds.
Secondary processes in mass spectrometry of alkylmercury halides
Authors: Zagorevskii D. V. , Mikeladze M. Sh. , Nekrasov Yu. S. , Lependina O. L. 
Published: May 2005

AbstractThe sensitivity of the mass spectrometer towards RHgX alkylmercury halides in the electron impact technique was found to decrease in the order X = Cl > Br > I. The intense peaks corresponding to the more heavy halides registered in the mass spectra of RHgX were shown to arise owing to the secondary processes of halogen exchange occurring in the mass spectrometer. The non‐volatile bromine and iodine compounds adsorbed in some form on metallic surfaces of the ionization chamber (so‐called ‘memory effect’) could be the source of heavy halogens. These reactions are hampered in chemical ionization mass spectrometry under the sufficiently high pressure of the reagent gas (NH3).
Calibration in positive and negative ion fast atom bombardment using salt mixtures
Authors: Vékey Károly 
Published: May 2005

AbstractTwo salt mixtures are described far mass calibration in fast atom bombardment: CsI and NaI for positive ion mode, and CsI and CsF for negative ion mode. The mixtures give many more peaks than CsI and therefore better mass accuracy can be obtained both in scanning and in peak‐matching mode. Their use is especially advantageous for computerized data acquisition. The mass range of 23–3500 for positive ion mode, and 19–3000 for negative ion mode, has been tested and gave good results.
Hydrogen rearrangements in alkyl‐, styryl‐ and alkyl propenyl sulfoxides
Authors: Liu Lilian Kao , Su C. Y. , Li Wen‐Shan 
Published: May 2005

AbstractThe McLafferty‐type rearrangements, which are the most facile fragmentation for the styryl‐ and the alkyl propenyl sulfoxides, have been proven to involve at least a β‐hydrogen by deuterium labelling studies. γ‐Hydrogen also rearranges, yet a cyclopropane instead of an alkene is eliminated. Furthermore, alkyl propenyl sulfoxides undergo hydrogen migration only to the surfinyl oxygen.
Structures and stabilities of [C3H2]+ ˙ and [C3H2]2+ ions
Authors: Wong Ming Wah , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital theory using basis sets up to 6‐311G* *, with electron correlation incorporated via configuration interaction calculations with single and double substitutions, has been used to study the structures and energies of the C3H2 monocation and dication. In agreement with recent experimental observations, we find evidence for stable cyclic and linear isomers of [C3H2]+ ˙. The cyclic structure (, a) represents the global minimum on the [C3H2]+ ˙ potential energy surface. The linear isomer (, b) lies somewhat higher in energy, 53 kJ mol−1 above a. The calculated heat of formation for [HCCCH]+ ˙ (1369 kJ mol−1) is in good agreement with a recent experimental value (1377 kJ mol−1). For the [C3H2]2+ dication, the lowest energy isomer corresponds to the linear [HCCCH]2+ singlet (h). Other singlet and triplet isomers are found not to be competitive in energy. The [HCCCH]2+ dication (h) is calculated to be thermodynamically stable with respect to deprotonation and with respect to CC cleavage into CCH+ + CH+. The predicted stability is consistent with the frequent observation of [C3H2]2+ in mass spectrometric experiments. Comparison of our calculated ionization energies for the process [C3H2]+ ˙ → [C3H2]2+ with the Qmin values derived from charge‐stripping experiments suggests that the ionization is accompanied by a significant change in structure.
Scatter profiling: A potentially useful technique for isomeric ion distinction and stability determination
Authors: Ballantine J. A. , Reid C. J. 
Published: May 2005

AbstractA method to determine the extent of angular scattering of fragment‐ion products of keV‐collision‐activated decomposition (CAD) reactions and, in particular, the collisional scatter incurred by the parent ions prior to their dissociation, is outlined. Since the half‐widths of the collisional scatter profiles correlate approximately with the mean reaction endothermicities for some ‘test’ reactions, the method may, in principle, be used to estimate the stabilities of isomeric ion structures relative to a common fragmentation threshold level. For single‐proton‐loss CAD reactions of some [H3, C, X]+ ions (X = F, Cl, OH) with either [H3CX]+ or ylidion, [H2CXH]+ structure, collisional scatter is found in each case to be greater for the isomeric ion with the more stable structure. The estimated magnitudes of the mean energy depositions occurring in the keV‐collision‐activation processes are generally much larger than the calculated minimum energy requirements, suggesting that survivable [M  H]+ products can be formed with up to several eV of internal energy.
The cycloaddition of the 1,3‐butadiene radical cation with acrolein and methyl vinyl ketone
Authors: Castle Lyle W. , Gross M. L. 
Published: May 2005

AbstractThe 1,3‐butadiene radical cation reacts with acrolein and methyl vinyl ketone to produce ‘stable’ adducts. The nature of the reaction and the structures of the adducts were investigated by collisional activation decomposition (CAD) combined with tandem mass spectrometry (MS/MS), and also by Fourier transform mass spectrometry. The CAD spectra of gas‐phase adducts were compared with those of suitable model compounds. On that basis, it was determined that the 1,3‐butadiene radical cation undergoes a cycloaddition with these α,β‐unsaturated carbonyl compounds. The butadiene radical cation serves as the ‘ene’, and the acrolein and methyl vinyl ketone react as dienes, forming cycloadducts having 2‐ethenyl‐2,3‐dihydropyran radical cation structures.
Formation of [C18H36]+ ˙ and [C7H7O2]+ in the mass spectrum of n‐octadecyl benzoate
Authors: Meyerson Seymour 
Published: May 2005

AbstractA series of deuterium‐labeled n‐octadecyl benzoates serves to extend the literature using lower homologues for study of the mass‐spectral reactions characteristic of alkyl esters. The benzoic acid radical cation (a) arises largely via hydrogen migration from C(2), as expected for the conventional mechanism passing through a six‐membered quasicyclic intermediate; the presence of contributions from other processes is simply noted in passing. The octadecene radical cation (b) and protonated benzoic acid (c) arise by paths seemingly closely related to each other but differing from the path dominant for a. The data are rationalized in terms of a reaction sequence passing through two ion‐neutral complex intermediates. The first, (d), consists of octadecyl carbenium ion and benzoyloxy radical; the second, (e), consists of octadecene radical cation and benzoic acid. The ionized partner in d appears to undergo none to several hydride migrations, but most prominently one; that in e may dissociate promptly to yield b or may persist, undergoing multiple hydride migrations to effect essentially complete scrambling of hydrogens, before dissociating to yield c. The argument for this mechanistic sequence to form b and c rests basically on its ability to account plausibly for the experimental data, and literature precedents cited for specific aspects of it furnish additional support. The low critical energies and small kinetic energy releases observed in this work are in accord with the characteristics listed by McAdoo for decompositions mediated by ion‐neutral complexes, and the selection of an octadecyl, as opposed to a smaller alkyl, ester predisposes the molecule to favor such low‐energy processes.