bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron impact mass spectrometry of some geminal bis‐sulphones
Authors: Benedetti Fabio , Nitti Patrizia , Pelli Beatrice , Traldi Pietro 
Published: May 2005

AbstractThe behaviour under electron impact of six 1,1‐bis(benzenesulphonyl)cyclioalkanes and of 1‐phenyl‐1‐(benzensesulphaonyl)cyclopropane has been studied in detail with the aid of exact mass measurements, linked scans for metastable ion analysis, collisional spectroscopy and kinetic energy release measurements. The molecular ions of these compounds undergo a sulphone‐sulphinate rearrangement with alkyl group migration on oxygen, in analogy with what is found for simple monosulphones and, in general, their fragmentation resembles that of mono‐sulphonyl compounds. Loss of SO2 from the molecular ion is observed for all substrates, but only in the case of 1, 1‐bis(benzenesulphonyl)cyclopropane is this followed by loss of the second SO2 unit; the first loss of SO2 is probably accompanied by rearrangement since the fragmentation pattern of [M − SO2]+˙ ions from this compound is different than that of the isobaric molecular ions of 1‐phenyl‐1‐(benzenesulphonyl)cyclopropane.
Low‐energy, low‐temperature mass spectra. 9—The linear undecanols
Authors: Brophy Joseph J. , Maccoll Allan 
Published: May 2005

AbstractThe 70 and 12 eV mass spectra of the six linear undecanols are reported. Apart from undecan‐1‐ol, whose spectrum is akin to that of undec‐1‐ene, the spectra are dominated by peaks corresponding to loss of water and α‐cleavage. The low voltage spectra are more readily interpreted.
The distonic ions HO+CHCH2C˙H2 and CH3C(O+H)CH2C˙H2
Authors: McAdoo David J. , Hudson Charles E. , Traeger John C. 
Published: May 2005

AbstractThe distonic ions HO+CHCH2C˙H2 (1) and CH3C(O+H)CH2C˙H2 (2) were directly generated, their decompositions characterized and their appearance energies determined by photoionization. Heats of formation derived from the appearance energies were 757 kJ mol−1 for 1 and 692 kJ mol−1 for 2. Deuterium labeling demonstrates that both ions decompose at low energies in the same ways as their isomers with the same skeletal structures, consistent with proposals that 1 and 2 are intermediates in the decompositions of those systems. Surprisingly, the values of the translational energy releases accompanying the formation of CH3CO+ and C2H5CO+ from 2 appear to be inversely proportional to the available excess energy. The 1,2‐H‐shift RC(O+H)CH2C˙H2 → RC(O+H)C˙HCH3 is compared to the corresponding, non‐occurring 1,2‐H‐shift in alkyl free radicals.
Enhanced selectivity in determining elemental composition: Concerted precise mass and isotope pattern moment analysis
Authors: Blom Karl F. 
Published: May 2005

AbstractA systematic procedure for establishing elemental composition from a concerted high‐resolution precise mass analysis of the monoisotopic molecular ion and a low‐resolution moment analysis of its isotope pattern is described. The combined method is more selective than a precise mass analysis alone. Factors affecting the enhancement in selectivity and some instrumental factors are discussed.
The preferred mode of cycloreversion of some 1,3,4‐substituted azetidin‐2‐ones upon electron impact
Authors: Auriel Michel , De Hoffmann Edmond , Scheers Philippe , Deffense Etienne 
Published: May 2005

AbstractThe mass spectra of some 1,3,4‐substituted azetidin‐2‐ones are measured. Fragmentation pathways are confirmed by use of both high‐resolution and mass‐analysed ion kinetic energy. They are consistent with the possible [2 + 2]‐ cycloadditions through which the azetidin‐2‐ones may be synthesized. More attention has to be paid to further fragmentations of the main fragments in assessing the preferred fragmentation mode. Influence of side‐chain substituents is discussed.
Mass spectrometry of 4N‐pyrimidinyl amino acids
Authors: Plaziak Adam S. , Celewicz Lech , Spychala Jaroslaw , Golankiewicz Krzysztof 
Published: May 2005

AbstractThe electron impact mass spectra of N‐(1H‐2‐oxo‐4‐pyrimidinyl) amino acids are discussed. It was established that thermal elimination of water took place prior to mass fragmentation of all these compounds with the formation of bicyclic structures. The fragmentation of bicyclic ions led to 1H‐2‐oxo‐pyrimidinyl species.
Ortho effects in organic molecules on electron impact. Part 15. Oxygen transfers from the nitro group to both sulphur and olefinic double bonds in allyl o‐nitrophenyl sulphide
Authors: Ramana D. V. , Sundaram N. , George M. 
Published: May 2005

AbstractAn oxygen transfer from the nitro group to the CC group, followed by a simple cleavage, afford intense fragments corresponding to o‐nitrosothiophenol at m/z 139 and o‐nitrosothiophenoxy cation at m/z 138 during mass spectral fragmentations of allyl o‐nitrophenyl sulphide. Further, a concerted double oxygen transfer from the nitro group to the sulphur is proposed for the ejection of ṠO2H from the molecular ion of this compound, leading to the quinolinium cation at m/z 130. These processes are supported by the high‐resolution data, collision‐induced dissociation linked‐scan spectra and chemical evidence.
Negative ions generated by reactions with oxygen in the chemical ionization source. I. Characterization of gas‐phase and wall‐catalyzed reactions of fluorene, anthracene and fluoranthene
Authors: Stemmler Elizabeth A. , Buchanan Michelle V. 
Published: May 2005

AbstractThe methane negative ion chemical ionization (NICI) mass spectra of polycyclic aromatic hydrocarbons are usually dominated by molecular, M− ˙ or M  H− ions; however, ions resulting from additions to M have also been reported. Some of these ions have been observed at [M + 14]− ˙, [M + 15]−, [M + 30]− and [M + 32]−˙ and have been attributed to reactions with either oxygen‐containing impurities in the buffer gas or alkyl radical species generated by ionization of a hydrocarbon buffer gas. In this study, the NICI spectra of fluorene, anthracene and fluoranthene were studied in detail using quadrupole and Fourier transform mass spectrometers. Spectra were acquired when reactive species such as oxygen, water, nitrous oxide and carbon dioxide were added to the nitrogen buffer gas. Experiments with deuterated methane were also carried out. These studies indicated that buffer gas impurities affect the NICI spectra; however, gas‐phase ion‐molecule reactions were not responsible for all of the observed products. In addition to electron‐ and ion‐molecule reactions, ions were observed that resulted from wall‐catalyzed oxidation reactions followed by electron capture. These reactions were enhanced by the addition of oxygen and elevated ion source temperatures. Depending upon the parent PAH structure, oxidation products such as ketones, quinones and anhydrides were formed.
Acetic acid cluster ions for tuning and calibration in thermospray liquid chromotography/mass spectrometry
Authors: Heeremans C. E. M. , van Der Hoeven R. A. M. , Niessen W. M. A. , Tjaden U. R. , van Der Greef J. 
Published: May 2005

AbstractCombined liquid chromatography and mass spectrometry is frequently performed with the thermospray interface nowadays. With thermospray a special ion source has to be installed. Tuning and calibration of that special source is still a problem which has not been adequately solved, Reference compounds commonly used in conventional electron impact or chemical ionization mass spectrometry cannot be used in the thermospray source. Most of the solutions to this problem reported in the literature cause a rapid contamination of the ion source or may result in memory effects. In this paper the use of acetic acid ammonia cluster ions is proposed for tuning and calibration in thermospray. Abundant cluster ions can be observed over the mass range between m/z = 100 and 1000 when an eluent containing ammonium acetate and 0.5% acetic acid is used. Features of the mass spectra obtained in both filament‐off, filament‐on and discharge‐on modes will be discussed.
Fragmentation of the enolate ion of 2,3‐butanedione. Characterization of the acetyl anion by charge inversion mass spectrometry
Authors: Chowdhury Swapan , Harrison Alex. G. 
Published: May 2005

AbstractThe unimolecular and collision‐induced fragmentation reactions of the enolate ion of 2,3‐butanedione, [CH3COCOCH2]−, have been studied, Unimolecular fragmentation on the metastable ion time‐scale forms [HCCO]−, [C2H3O]−, [C3H5O]− and [CH3CO2]−. Charge inversion mass spectrometry shows that the [C2H3O]− ion is the acetyl anion while the [C3H5O]− product is the acetone enolate ion; formation of the latter product involves a large release of kinetic energy (T 1/2 = 0.99 eV). The fragmentation reactions occurring following collisional activation have been determined for 8 keV collisions and over the range 1.5–30 eV center‐of‐mass collision energy. Formation of [HCCO]− and [CH3CO]− are of the most important reactions following collisional activation and it is concluded that the two reactions have similar critical reaction energies even though formation of [HCCO]− is favored thermochemically.
Electron impact mass spectral study of thiodiglycollic acid and its ester and amide derivatives: Mechanism of loss of H2O from thiodiglycollic acid
Authors: Srinivas R. , Kumar Anil , Viswanadha Rao G. K. 
Published: May 2005

AbstractThe mechanism of H2O loss from the molecular ion of thiodiglycollic acid is elucidated with the aid of collision‐induced dissociation and deuteration experiments. These studies show that the predominant pathway for the H2O loss involves the carboxy‐ and γ‐methylene interaction. The fragmentation behaviour of ester and amide derivatives of thiodiglycollic acid deduced by linked‐scan and high‐resolution techniques is described.
The mass spectra of some vicinally substituted nitropyridines
Authors: Rasala Danuta , Gawinecki Ryszard 
Published: May 2005

AbstractThe fragmentation behaviour of 22 vicinally substituted nitropyridines has been studied under electron impact conditions. The decomposition patterns were found to be strongly affected by interaction of the substituent with the nitro group and the ring nitrogen. AH fragmentation sequences depend to a great extent on the position of the substituent in the ring.
The electron impact‐induced cyclization of o‐carboxy‐ and o‐carboxamidocyclopropylbenzenes
Authors: Lebedev Albert T. , Alekseeva Tatyana N. , Kutateladze Tatyana G. , Mochalov Sergey S. , Shabarov Yury S. , Petrosyan Valery S. 
Published: May 2005

AbstractThe isomerization of M+ ˙ of o‐carboxy‐ and o‐carboxamidocyclopropylbenzenes into five‐ and six‐membered heterocycles due to the ortho effect has been demonstrated by means of electron impact mass spectra, high‐resolution mass spectrometry data and metastable ion spectra. The criteria for the quantitative estimation of the degree of cyclopropane cyclization into these isomeric cycles were formulated. The nature and quantity of heterocyclic ions proved to be in good accord with the results for cyclization of the same cyclopropanes in the strong acid solutions.
Functional group interaction in the fragmentation of protonated 2,7‐octanedione
Authors: Mueller Dieter R. , Domon Bruno , Blum Wolfgang , Richter Wilhelm J. , Reiner Hartmut , Keller Rolf , Fischer Peter 
Published: May 2005

AbstractThe fragmentation of 2,7‐octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH4)), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H2O and C2H4O from the [M + H]+ ion competes with sequential loss of H2O and C6H10, and that both processes occur via the same [MH ‐ H2O]+ intermediate. This intermediate is likely to be formed via intramolecular gas‐phase aldol condensation and subsequent dehydration. The resulting C(1) protonated 1‐acetyl‐2‐methylcyclopentene structure readily accounts for the observed further decomposition to CH3CO+ and 1‐methylcyclopentene (C6H10) or, alternatively, to [C6H9]+ (e. g. 1‐methylcyclopentenylium) ions and acetaldehyde (C2H4O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low‐energy collision‐induced dissociation (CID) of the [MH ‐ H2O]+ ion. The common intermediate shows a CID behaviour indistinguishable by these techniques from that of reference ions, which are produced by gas‐phase protonation of the authentic cyclic aldol or by gas‐phase addition of an acetyl cation to 1‐methylcyclopentene in a CI (CH3COOCH3) experiment.
Gas‐phase ion‐molecule bimolecular and clustering reactions in dilute solutions of acetonitrile in xenon, krypton, argon, neon and helium
Authors: Lilies Andreas J. 
Published: May 2005

AbstractGas‐phase bimolecular and clustering reactions of acetonitrile in Xe, Kr, Ar, Ne and He were studied at high chemical ionization pressures in the new coaxial ion source at Auburn. With electron energies near the ionization threshold, the mass spectra are exceedingly simple and are comprised of [CH4CH]+ and clusters of [CH4CN]+ with various ligands such as H2O and CH3CN. At higher electron energies many other peaks appear. The intensities of the new peaks depend upon the ionization potential of the charge transfer gas, the ionizing electron energy and the ion source conditions, and are due to reactions of fragment ions. Residence time distributions at electron energies above the ionization threshold (∼ 30 eV) demonstrate that two molecular structures are present in the ion beam at m/z 42, one presumably is protonated acetonitrile ([CH3CNH]+) while the evidence indicates that the second species does not contain acidic hydrogens. With ionizing electron energies near threshold (∼ 10. 5 eV) only one structure is observed. Studies with electron energies near the ionization threshold under high‐pressure chemical ionization conditions result in greatly simplified mass spectra and are possible only because of the coaxial geometry of the ion source.
Fragmentation of certain substituted azadispiro(5.1.5.2)pentadec‐9‐ene and azadispiro(4.1.4.2)tridec‐8‐ene derivatives under electron ionization
Authors: Madhusudanan K. P. , Bhat Neelima , Bhaduri A. P. , Vairamani M. 
Published: May 2005

AbstractA study of the electron ionization mass spectra of certain azadispiro(5.1.5.2)pentadec‐9‐ene‐7,15‐diones and azadispiro(4.1.4.2)tridec‐8‐ene‐6,13‐diones and their derivatives has revealed that these molecules undergo fragmentation primarily by two routes, viz. loss of CO and elimination of the substituent on the pyrrolidine nitrogen. Under positive ionization conditions loss of CO is the predominant process in the diones as it releases the ring strain, while in the 6‐ or 7‐ols loss of the substituent on nitrogen is the favoured pathway. The further decomposition pathways of these primary fragments [M  CO]+˙ and [M  OR3]+ have been delineated with the help of high‐resolution mass measurements, D2O exchange and metastable spectra, These compounds give very simple negative ion spectra showing only [M  OR3]− and [NCO]− ions except the N‐hydroxy compounds which show [M  H]− ions as well.
Fast atom bombardment mass spectrometry of carbobenzyloxy‐protected amino acids and peptides
Authors: Danieli Bruno , Rubino Federico Maria , Cremonesi Alfredo 
Published: May 2005

AbstractThe positive fast atom bombardment (FAB) mass spectra of 15 N‐carbobenzyloxy derivatives of α‐amino acids are presented together with those of some synthetic peptides containing other widely employed protecting groups. The data obtained allow a fragmentation pattern to be established for the N‐carbobenzyloxy moiety and to obtain detailed structural information on the main fragment ions. A study of the ion current ratio vs. time pattern shows that important fragments derive from the parent protonated molecule through FAB‐induced condensed‐phase reactions.
Electron impact mass spectrometry of some 2,11‐diaza[3.3]cyclophane derivatives
Authors: Pappalardo Sebastiano 
Published: May 2005

AbstractThe most significant mass spectral features of thirteen title compounds are discussed with the aid of high‐resolution mass measurements and metastable peak analysis. The decomposition patterns of the compounds investigated are strongly affected by N‐substitution and by methyl substituents ortho to the bridging chains (ortho effects). A unique feature connected with symmetrical macrocycles, bearing at least two ortho methyl substituents on each phenyl ring, is the presence in their spectra of diagnostically important peaks, corresponding to [M  RNH2]+˙ and [M  2RNH2]+˙ (R = Ts, H, CH3). These daughter ions are proposed to be associated with the formation of cage compounds (multibridged cyclophanes), generated by an intramolecular [4 + 4] cycloaddition reaction of unstable linear bis‐(o‐xylylene) precursors.
Fast atom bombardment (FAB) mass spectrometry of piperidine N‐oxide derivatives and free radical quenching under FAB conditions
Authors: Yan Lin , Fang Yiwei , Fang Min , Zhu Lizhi , Shen Dekang , Liang Xiyun 
Published: May 2005

AbstractMechanisms are proposed for the formation of M+, [M + 2H]+ and [M + 3H]+ ions in the fast atom bombardment (FAB) mass spectra of 4‐(2,2,6,6‐tetramethyl‐1‐oxyl)‐piperidol and its carboxylates. Free radical quenching induced by the fast atom beam has been observed. The effects of temperature on the radical quenching and of acid on the FAB mass spectra are discussed. The experiment showed that the volatile liquid samples with vapour pressures higher than that for glycerol produced M+ even‐electron molecular ions, and the FAB mass spectra were similar to the corresponding electron ionization mass spectra. For the solid samples, it was found that the free radicals were quenched during the FAB process so that the mononitroxide and dinitroxide compounds produced [M + 2H]+ and [M + 3H]+ ions, respectively. Further experiments showed that the intensities and stabilities of [M + 2H]+ and [M + 3H]+ ions could be improved by addition of acids.
Analysis of the degradation products of diproteverine by moving belt LC/MS
Authors: Redrup Michael J. , Risbridger Gerald D. , Skett Peter W. 
Published: May 2005

AbstractMoving belt LC/MS has been used to identify the degradation products of the slow calcium membrane channel inhibitor, Diproteverine, after storage at elevated temperature and humidity. The major products observed result from oxidation. Two of these products, both ketones, yield [M  14 + H]+ ions by chemical ionization. These unusual ions also occur for some simple aromatic ketones used as model compounds and are shown to arise by reduction of the carbonyl group to a methylene by the reagent gas.
The haloacetyl ions; a thermochemical study
Authors: Holmes John L. , Dakubu M. 
Published: May 2005

AbstractThe haloacetyl ions [XCH2CO+], X = Cl, Br, I, have been produced by the dissociative ionization of selected precursor molecules and identified via their fragmentation characteristics. Their heats of formation, Δ, were 708 ± 8, 750 ± 25 and 784 ± 10 kJ mol−1, respectively, all appreciably above ΔH for [CH3CO+], 653 kJ mol−1. The effect of halogen substitution α to carbonyl is discussed for neutral molecules and their molecular ions.
Fast atom bombardment mass spectrometry of neutral methanide and ionic carbene platinum(II) derivatives
Authors: Cetini Giuseppe , Operti Lorenza , Vaglio Gian Angelo , Bandini Anna Laura , Banditelli Guido , Minghetti Giovanni 
Published: May 2005

AbstractThe fast atom bombardment mass spectra of a series of neutral methanide and ionic carbene platinum(II) complexes of formula dPePtL2 and [dPePt(LH)2](BF4)2 (dPe = (C6H5)2PCH2CH2P(C6H5)2; L = C(OCH3)‐NCH3, C(OCH3)  NC6H11, C(OCH3)  NC6H4p CH3), respectively are reported. Glycerol, 3‐mercapto‐1,2‐propanediol, bis (2‐hydroxyethyl)sulphide, 3‐nitrobenzyl alcohol, and 2,4‐di‐tert‐pentylphenol have been used as matrices. Neutral and ionic derivatives containing the same ligand behave similarly and give the same quasi‐molecular [dPePtL(L + H)]+ ion by different primary processes. Stepwise breakdown of the ligands L with retention or further loss of atoms or molecules of hydrogen is observed for all these complexes, followed by ejection of radicals from the dPe ligand. Elimination of CH3OH from [dPePtL(L + H)]+ also occurs. The highest ionic yields of both neutral methanide and ionic carbene complexes are observed in 3‐mercapto‐1,2‐propanediol, in bis(2‐hydroxyethyl)sulphide, and in 3‐nitrobenzyl alcohol with respect to glycerol. The [dPePt(LH)2]2+ doubly charged ions are present in the spectra obtained with 3‐nitrobenzyl alcohol and are rather strong when L is C(OCH3)  NCH3 and C(OCH3)  NC6H4p CH3. Substitution of ligands L with a molecule or with a fragment of a sulphur containing matrix takes place very seldom with this series of complexes.
Unimolecular reactions of [C5H10O]+ ˙ radical cations derived from4‐penten‐1‐ol
Authors: Bowen Richard D. , Harrison Alex G. 
Published: May 2005

AbstractThe reactions of metastable [C5H10O]+ ˙ radical cations produced by ionization of 4‐penten‐1‐ol are reported and discussed. These [C5H10O]+ ˙ species undergo mainly ethyl radical loss, with smaller contributions of methyl radical and water expulsion. 2H‐Labelling studies reveal different specificities of hydrogen selection in these three fragmentations. The behaviour of these [C5H10O]+ ˙ ions is compared to those reported previously for isomeric radical cations containing linear alkenyl chains and a terminal hydroxyl group.
On the generation and characterization of the spiro[2,5]octadienyl anion in the gas phase
Authors: Maas Wilfrid P. M. , Van Veelen Peter A. , Nibbering Nico M. M. 
Published: May 2005

AbstractThree routes have been explored in both a high‐pressure chemical ionization (CI) source and a low‐pressure Fourier transform ion cyclotron resonance (FT‐ICR) cell to generate the spiro[2,5]octadienyl anion in the gas phase: (i) proton abstraction from spiro[2,5]octa‐4,6‐diene; (ii) expulsion of trimethysilyl fluoride by phenyl ring participation following fluoride anion attack upon the silicon centre of 2‐phenylethyl trimethylsilane; and (iii) collisionally induced dissociation (CID) of the carboxylate anion of 3‐phenylpropanoic acid via carbon dioxide loss. From comparison of the CID spectra of various reference [C8H9]− ions with those of the [C8H9]− ions which could be generated via the routes (i) and (iii) in the CI source it can be concluded that only the third route yields a [C8H9]−ion whose CID spectrum is not inconsistent with the one expected for the spiro[2,5]octadienyl anion. In the FT‐ICR cell [C8H9]− ions are generated along all three routes; their structures have been identified by specific ion‐molecule reactions and appear to be different. Route (i) yields an α‐methyl benzyl anion, probably due to isomerization within the ion‐molecule complex formed. An ortho‐ethylphenyl anion is formed along route (ii), presumably due to an intramolecular ortho proton abstraction in the generated trimethylsilyl fluoride solvated 2‐phenylethyl primary carbanion. The [C8H9]− ion formed along route (iii) shows reactions similar to those of the 1,1‐dimethylcyclohexadienyl anion which is structurally related to the spiro[2,5]octadienyl anion. Furthermore, the [C8H9]− ion generated via route (iii) reacts with hexafluorobenzene under expulsion of only one hydrogen fluoride molecule which contains exclusively one of the original phenyl ring hydrogen atoms. On the basis of all these observations it is therefore quite likely that the spiro[2,5]octadienyl anion is formed by collisionally induced decarboxylation of the 3‐phenylpropanoic acid carboxylate anion and can be a long‐lived and stable species in the gas phase.