bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociation of positively charged aliphatic epoxides. II. [C5H10O]+˙ epoxides and α,β unsaturated ethers
Authors: Bouchoux Guy , Djazi Feyçal , Hoppilliard Yannik , Jaudon Pascale , Nouts Nathalie
Published: May 2005

The unimolecular dissociations of C5 epoxides ions mono‐ or disubstituted at C1 give exclusive loss of CH3 and exclusive formation of methoxy vinyl carbenium ion, both in the source and in the 2nd field‐free region. In the case of the 1,2‐disubstituted ion in the 2nd field‐free region the loss of ethene is the only pathway, while a competition occurs for the trisubstituted ion leading to [C3H6O]+˙ and [C4H7O]+˙ ions, the structure of which are demonstrated. The first step of the different mechanisms is the cleavage of the heterocyclic CC bond.
An unexpected γ‐hydrogen rearrangement in the mass spectra of di‐ortho ‐substituted alkylbenzenes
Authors: Kingston Eric E. , Eichholzer John V. , Lyndon Paul , Macleod John K. , Summons Roger E.
Published: May 2005

In contradiction of long‐accepted mass spectrometric dogma, the site‐specific γ‐hydrogen rearrangement is observed in alkylbenzenes in which both ortho positions are blocked with methyl substituents. Mass spectrometric studies of a series of five trimethyl‐ and three tetramethylisopentylbenzenes have shown that this rearrangement is only suppressed to a significant degree in those compounds in which all three positions ortho and para to the isopentyl group are blocked. Deuterium labelling has confirmed the γ‐site‐specific origin of the migrating H atom while metastable studies have been used to investigate the mechanism of the rearrangement process.
Bifunctional even‐electron ions. IV. Fragmentation behaviour of aliphatic methoxonium ions containing an additional carbomethoxy group
Authors: Záhorszky U. I. , Schulze P.
Published: May 2005

As for the corresponding hydroxonium ions, the methoxonium ions \documentclass{article}\pagestyle{empty}\begin{document}${\rm R} \!-\! \mathop {\rm C}\limits^ + ({\rm OCH}_2)\! -\! ({\rm CH}_2)_n \! - \! {\rm COOCH}_3 $\end{document} (n = 0−5), b, show as the main reactions those triggered by functional group interaction, but the overall decomposition rate is not much influenced. Loss of CH3OH is the general primary fragmentation, originating preferentially from the COOCH3 group. The lowest homologue (b0) shows loss of C3H4O as the main primary reaction, while b1 shows loss of CH2CO besides CH3OH loss. The subsequent fragmentations exhibit strong chain‐length dependence. Methoxy anion migration is observed as a general reaction mode of fragment ions which still contain the COOCH3 group. The fragmentation behaviour of a and b and of the corresponding methoxy‐substituted bifunctional ions has been compared, and general conclusions have been drawn.
Studies in cluster ion formation. Part IV. Characterization of cluster ions formed during the fast atom bombardment of solutions of mixed tetraalkylammionium salts. A. Concentration effects and the influence of ionic size
Authors: Tolun Emirgül , Todd John F. J.
Published: May 2005

Cluster ion formation by fast atom bombardment mass spectrometry of 15 binary mixtures of tetraalkylammonium halide salts in liquid matrices has been studied. In some instances the replacement of even one of the cations in the pure cluster ion by a different cation to yield mixed cation cluster ions has a destabilizing effect on the clusters, and results in the disappearance of the ion intensity anomalies. The effect of the anion and cation sizes and also the matrix composition on the stability of mixed cluster ions is discussed.
Fragment–molecule adduct ion formation in positive methane chemical ionization mass spectrometry1
Authors: Maiyanoff Cynthia A. , Caldwell Gary W. , Chang S. Y.
Published: May 2005

Fragment–molecule (F+M) adduct ions of a variety of heterocyclic systems have been observed in positive methane chemical ionization spectra at relatively low sample concentrations, i.e. in the microgram range. The relative abundance of these adduct ions increases with sample concentration. Possible mechanisms of formation of F+M are discussed. Formation of such ions should be recognized as an artifact, otherwise such F+M adduct ions in chemical and electron ionization may be mistaken for impurities present in a sample.
Tandem mass spectrometry for identifying fatty acid derivatives that undergo charge‐remote fragmentations
Authors: Deterding Leesa J. , Gross Michael L.
Published: May 2005

A variety of fatty acid functional derivatives were desorbed by fast atom bombardment and collisionally activated. Derivatives having a high proton affinity such as fatty amides, pyrrolidides and picolinyl esters fragment to give decompositions that originate remote from the charge site. In contrast, derivatives having a low proton affinity such as fatty acids and fatty esters fragment to give charge‐initiated decompositions. Therefore, the choice of the fatty acid functional derivative is important in effecting charge‐remote decompositions of the [M + H]+ ions. The collisional activation spectra of the [M + H]+ ions of fatty alcohols and fatty amines were also compared. Based on this comparison, the internal energy required in order for charge‐remote fragmentations to occur is estimated to be between 1.4 and 2.9 eV. This work is a guide in designing functional derivatives of fatty acids that undergo charge‐remote reactions.
Comparison of low‐energy CAD spectra of sulphonium, ammonium and phosphonium cations, propene elimination from allyl‐substituted oniums
Authors: Mestdagh Hélène , Morin Nicole , Rolando Christian
Published: May 2005

The low‐energy collision‐activated dissociation of symmetrical n‐butyl‐substituted and of allyl‐substituted onium cations has been recorded using fast atom bombardment ionization and a tandem mass spectrometry quadrupole mass spectrometer. Structure of the fragments and decomposition pathways have been ascertained using a multi‐quadrupole MS/MS/MS triple analyser instrument. Whereas most sulphonium cations exhibit only heterolytic cleavages, fragmentation of ammonium and phosphonium is mainly homolytic. Allylic sulphonium, and to a lesser extent allylic ammonium, easily undergo propene elimination. This reaction, which does not occur in 1‐propenyl oniums, might involve a McLafferty type rearrangement.
Mass spectra of dihydroxy stereoisomers of 3‐methoxy‐1,3,5(10)‐estratrienes
Authors: Schade Wolfgang , Schubert Gerd , Schönecker Bruno
Published: May 2005

Electron impact mass spectral data for each of the four isomeric 16,17‐, 15,17‐ and 14,17‐diols of 3‐methoxy‐1,3,5(10)‐estratriene and the 15,17‐diols of 3‐methoxy‐14β‐1,3,5(10)‐estratriene are reported. The mass spectra of the diols show very similar fragmentation patterns except for differences in the relative abundances of particular ions. The different [M − H2O]+˙/[M] +˙ and [M − 2H2O] +˙ [M] +˙ ratios can be used for distinguishing between the four isomeric 3‐methoxy‐1,3,5(10)‐estratriene‐14,17‐diols as well as between the four isomeric 3‐methoxy‐14β‐1,3,5(10)‐estratriene‐15,17‐diols. No significant differences could be detected in the spectra of the epimeric 16,17‐and 15,17‐diols of 3‐methoxy‐1,3,5(10)‐estratriene.
Structural determination of modified fatty acids by collisional activation of cationized molecules
Authors: Adams Jeanette , Gross Michael L.
Published: May 2005

The nature and location of a variety of modifications of fatty acids are determined by collisional activation (CA) of [M + 2Li − H]+ ions. The sample molecules are cationized in situ on the probe tip, desorbed by fast atom bombardment and, upon CA, undergo charge‐remote decompositions. This approach is a direct, totally instrumental method for structure elucidation. Advantages of CA of [M + 2Li − H]+ ions are that fatty acids with substituents in close proximity to the carboxylate terminus and modified short‐chain acids are readily determined: decompositions of carboxylate anions of these fatty acids result in collision‐activated dissociation (CAD) spectra that give incomplete structural information. However, the CAD spectra of some [M − H]− ions, such as those from epoxy acids, are simpler to interpret than those of the [M + 2Li − H]+ ions. Thus, CA of fatty acid [M + 2Li − H]+ ions is a complementary approach to CA of [M − H]− ions for determining the fatty acid structures investigated here. The use of this approach for analyzing complex mixtures of modified fatty acids is also evaluated.
Unimolecular and collision‐induced fragmentation of protonated nitroarenes
Authors: Crombie Richard A. , Harrison Alex G.
Published: May 2005

The unimolecular fragmentation reactions of 28 protonated nitroarenes, occurring on the metastable ion time‐scale, are reported. In addition, the collision‐induced fragmentation of the same species have been studied at 10 eV and at 50 eV collision energy. When an OH, COOH or NH2 substituent is ortho to the nitro function, the dominant fragmentation involves loss of H2O, for both unimolecular and collision‐induced reactions. When there is an electron‐releasing substituent ortho or para to the litro group, loss of OH is the dominant fragmentation reaction both on the metastable ion time‐scale and for ions activated by collision. When the electron‐releasing substituent is meta to the nitro group, loss of NO2 is the dominant low‐energy unimolecular fragmentation reaction while loss of HNO2 is the most important fragmentation for ions activated by 50 eV collisions. Elimination of NO from [MH]+ occurs to a significant extent in the unimolecular fragmentation of protonated nitrobenzene and those protenated nitrobenzenes containing electron‐ attracting substituents. In the collision‐induced dissociation of these species loss of HNO2 occurs at the expense of loss of NO. The results are consistent with protonation predominantly at the nitro group. The results are discussed in terms of the use of neutral loss scans in tandem mass spectrometry to monitor complex mixtures for nitroarenes.
The effect of vibrational energy content on the neutralization–reionization mass spectra of [H2]+˙ ions
Authors: Bordas‐Nagy Joszef , Holmes John L.
Published: May 2005

Neutralization‐reionization experiments were performed on beams of [H2]+˙ ions of different, known vibrational energy content using a variety of neutralization target gases (Xe, H2, Ne) and reionization gases (He, O2). The recovery of [H2]+˙ ions was found to be only weakly dependent on the vibrational energy of the original [H2]+˙ ions. The ion kinetic energy spectra of H+ fragments from the neutralization‐reionization experiments were independent of the collision gas; the processes by which they were generated were identified.
The unimolecular chemistry of [1,2‐propanediol]+˙: a rationale in terms of hydrogen‐bridged radical cations
Authors: Van Baar Ben L. M. , Burgers Peter C. , Holmes John L. , Terlouw Johan K.
Published: May 2005

By combining results from a variety of mass spectrometric techniques (metastatle ion, collisional activation, collision‐induced dissociative ionization, neutralization–reionization spectrometry and appearance energy measurements) and the classical method of isotopic labelling, a unified mechanism is proposed for the complex unimolecular chemistry of ionized 1,2‐propanediol. The key intermediates involved are the stable hydrogen‐bridged radical cations [CH2C(H)H…︁O…︁O(H)CH3]+˙, which were generated independently from [4‐methoxy, 1‐butanol]+˙ (loss of C2H4) and [1‐methoxyglycerol]+˙ (loss of CH2O), [CH3CO…︁H…︁O(H)CH3]+˙ and the related ion‐dipole complex [CH2C(OH)CH3/H2O]+˙. The latter species serves as the precursor for the loss of CH3˙ and in this reaction the same non‐ergodic behaviour is observed as in the loss of CH3˙ from the ionized enol of acetone.
Low–energy, low‐temperature mass spectra. 8—The McLafferty rearrangement
Authors: Maccoll Allan
Published: May 2005

The McLafferty rearrangement giving rise to the McLafferty ion, the complementary ion and a protonated molecule is discussed in the cases of the alkenes, alkanals, alkanones, alkanoic acids and alkanoic esters, in terms of the low‐energy, low‐temperature mass spectra. Based on the behaviour of the alkanals, which show a series of peaks corresponding to [M − CnH2n]+˙, it is suggested that these also involve McLafferty rearrangements from rearranged distonic ions. The same processes are held to be responsible for similar series of peaks in the case of the alkenes and that of the amines. Where possible the energetics of the processes concerned are discussed. The low‐energy mass spectra of the linear alkenes propene to octene and those of the octenes are reported.
Tandem mass spectrometry of peptides. Relationship between translational energy loss and fragment ion mass
Authors: Sheil Margaret M. , Derrick Peter J.
Published: May 2005

Incident ion energy E1 and collision gas pressure have been adjusted so as to obtain a satisfactory tandem mass spectrum of the m/z 1882 ion formed from valme‐gramicidin A (relative molecular mass 1881). Translational energy losses ΔE have been determined (at Ei = 14.8 keV) from the precise positions of a large number of fragment ion peaks in the spectrum. The variation in ΔE for different fragment ions is great and the magnitudes of ΔE are large (being commonly of the order of 102 eV). It is shown how very large energy losses ΔE can arise, if the parent ion decomposes to a small fragment ion which itself collides and decomposes further. Implications of the dependence of ΔE upon fragment ion mass for the scan laws of four‐sector instruments are discussed briefly.
Reduction processes in the fast atom bombardment mass spectrometry of sulfonyl esters of diazonaphthalenones
Authors: Kyranos James N. , Du Sorbier Bertrand M. , Wronka John , Vouros Paul , Kirby Daniel P.
Published: May 2005

Orthoquinone diazides, which are widely used in microlithography, have attracted considerable attention, especially in terms of their application in the production of high‐contrast resists. Previous electron impact mass spectrometric results have confirmed that the primary fragmentation process of these compounds is the elimination of N2 to form an indenoketene ion. This is analogous to the photodecomposition pathway which makes them effective in the lithographic process. Those results also revealed the occurrence of an alternative process, which involves a two‐hydrogen reduction of the intermediate species formed prior to conversion to the ketene. The present study investigates the behaviour of the orthoquinone diazides when there is an abundance of protons available to form the reduction product. Several different types of diazonaphthalenone sulfonyl esters, ranging in complexity from the monosubstituted phenol esters to disubstituted dihydroxybenzophenones, were examined using fast atom bombardment mass spectrometry. Although reduction was the primary process in the hydrogen‐rich matrices, the extent of reduction was characteristic of the particular isomer as well as the matrix used.
Translational energy release and stereochemistry of steroids. VIII‐The mechanism of the elimination of water from metastable ions in epimeric 3‐hydroxy steroids of the 5α‐series
Authors: Zaretskii Z. V. I. , Curtis J. M. , Brenton A. G. , Beynon J. H. , Djerassi Carl
Published: May 2005

The mechanism of water elimination from metastable molecular, [M − CH3˙]+ and [M − ring D]+˙ ions of epimeric 3‐hydroxy steroids of the 5α‐series has been elucidated. Deuterium labelling, the measurement of the translational energy released during the loss of water, and collision‐induced decomposition mass‐analysed kinetic energy spectrometry were the techniques used. It was found that the mechanisms of water loss from metastable M+˙ and [M − ring D]+˙ ions is different from that from [M − CH3˙]+ ions.
Translational energy release and stereochemistry of steroids. XI—Determination of the configuration of α,β‐unsaturated 3‐keto steroid alcohols with the hydroxyl group in rings C and D
Authors: Zaretskii Z. V. I. , Curtis J. M. , Brenton A. G. , Beynon J. H.
Published: May 2005

The elimination of water from metastable molecular ions of epimeric hydroxy steroids of the Δ4‐3‐keto series containing a hydroxyl group in the conformationally rigid rings C and D has been studied. The measurement of translational energy released during the loss of water and collision‐induced decomposition (CID) mass‐analysed ion kinetic energy (MIKE) spectrometry were the techniques used. It was found that it is possible to determine the configuration of the hydroxy steroids of this series on the basis of the CID MIKE spectra of [M − H2O]+˙ ions formed by dehydration of metastable molecular ions in the first field‐free region of a reversed geometry double‐focusing mass spectrometer.
Electron impact mass spectrometry of some geminal bis‐sulphones
Authors: Benedetti Fabio , Nitti Patrizia , Pelli Beatrice , Traldi Pietro
Published: May 2005

The 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

The 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

The 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

A 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

The 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

The 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

An 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

The 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

Combined 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

The 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

The 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

The 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

The 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

The 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

Gas‐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

A 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

The 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

The 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

Mechanisms 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

Moving 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

The 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

The 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

The 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

Three 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.
A photoionization study of [C4H7]+ ions in the gas phase
Authors: Traeger John C.
Published: May 2005

The ionization and [C4H7]+ appearance energies for a series of C4H7CI and C4H7Br isomers have been measured by dissociative photoionization mass spectrometry. Cationic heats of formation, based on the stationary electron convention, are derived. No threshold ion is observed with a heat of formation corresponding to the trans‐1‐methylallyl cation, although there is evidence for formation of the less stable cis isomer. A 298 K heat of formation of 871 kJ mol−1 is obtained for the cyclopropylcarbinyl cation, with the cyclobutyl cation having a higher value of 886 kJ mol−1. At the HF/6‐31G** level, ab initio molecular orbital calculations show the 2‐butenyl, isobutenyl and homoallyl cations to be stable forms of [C4H7]+, being less stable than the trans‐1‐methylallyl cation by 101 kJ mol−1, 159 kJ mol−1 and 164 kJ mol−1, respectively. However, threshold formation is not observed for any of these ions, the fragmentation of appropriate precursor molecules producing [C4H7]+ ions with lower energy structures.
New explorations of in situ reactions of boron‐containing compounds during fast atom bombardment mass spectrometry
Authors: Rose Malcolm E. , Webster Matthew J.
Published: May 2005

Various reactions, intentional or unwanted, between several types of boron‐containing compound and multifunctional nucleophilic substrates occurring on the probe tip can be examined in situ by negative‐ion fast atom bombardment mass spectrometry (FABMS). Unwanted reactions of spiroborates with common liquid matrices can be avoided by using tetraethylene glycol diethyl ether as solvent for FABMS. Even so, the components of mixtures of spiroborates undergo ligand exchange with each other. Different orientations of hydroxy groups in isomeric diols, hydroxyacids and dicarboxylic acids can be differentiated by reaction on the probe tip with trialkyl borates, producing negatively charged spiroborates, or preferably with dibenzeneborinic acid ethanolamine complex. Successful reaction in the latter case can be assessed by observing the eliminated ethanolamine by positive‐ion FABMS and formation of the corresponding negatively charged borate in the negative‐ion mode. Potential applications of this methodology are discussed.
Mass spectrometric fragmentation patterns of isomeric 5‐methyl‐3‐alkyl‐2‐alkenylpyrazines
Authors: Brophy Joseph J. , Sun Chang‐Ming , Tecle Berhane , Toia Robert F.
Published: May 2005

The detailed mass spectral fragmentation pathways of a series of both naturally occurring and synthetic 5‐methyl‐3‐alkyl‐2‐aIkenylpyrazines have been elucidated with the aid of deuterium labels placed specifically in the alkenyl side‐chain. The influence on the fragmentation pattern of the stereochemistry of the alkenyl group as well as the relative placement of the groups on the pyrazine nucleus have also been evaluated. This provides information of some diagnostic value in the assignment of structures by mass spectrometry to new compounds within this class.
Skeletal rearrangement for water loss from molecular protonated ions of t‐butoxycyclohexane
Authors: Diakiw Vladimir , Gordon Patrick M. , Kingston Eric E. , Shannon James S. , Lacey Michael J.
Published: May 2005

Isotopic labelling and chemical substitution support the proposition that the skeletal rearrangement for water loss from molecular protonated ions of t‐butoxycyclohexane involves competition between three reaction pathways. The principal reaction pathway (83%) involves migration of the t‐butyl group to the 2‐(6‐) position of the cyclohexyl ring with reciprocal hydrogen transfer. A second reaction pathway (12%) involves ring contraction followed by reciprocal exchange of the t‐butyl group with the 2‐(5‐) hydrogen atom of the nascent cyclopentyl ring. The third reaction pathway (5%) involves rearrangement of a proton‐bound complex to permit ipso attack by isobutene. Stereospecific substitutions indicate that the principal reaction pathway is susceptible to 1,3‐diaxial interactions.
Negative‐ion‐negative‐ion neutralization‐reionization (−NR−)
Authors: McMahon Adam W. , Chowdhury Swapan K. , Harrison Ale X. G.
Published: May 2005

There are four neutralization‐reionization processes which can be studied. In the first two, gaseous cations are collisionally reduced and the resulting fast neutrals are either oxidized by collisional electron removal (NR) or reduced further by collisional electron attachment (NR−). In the third and fourth processes, gaseous anions are collisionally oxidized and the resulting fast neutrals are either oxidized further by collisional electron removal (−NR) or reduced by collisional electron attachment (−NR−). These four processes are illustrated briefly using the interrelated species [SF5]+ and [SF5]−. Negative‐ion‐negative‐ion neutralization‐reionization (−NR−) processes are illustrated for [CH3O]−, [C2H5O]−, [CO3]− and [HCO3]− and compared with −NR processes. In addition, collisional electron attachment ionization of fast neutrals formed in unimolecular fragmentation of cations is illustrated. The −NR− studies of [CO3]− and [HCO3]− show that both CO3 and HCO3 are stable neutral species with lifetimes greater than 0.7 μs.
Neutralization‐reionization study of C6H6O isomers
Authors: Turecek Frantisek , Drinkwater Donald E. , Maquestiau Andre , McLafferty Fred W.
Published: May 2005

Neutralization‐reionization (+NR+) mass spectrometry is employed to examine the behavior of C6H6O isomers in the gas phase. Phenol and cyclohexa‐2,4‐dienone are found not to interconvert following neutralization with mercury of their corresponding cation radicals at 9.9 keV kinetic energy. A very low extent of isomerization is observed following collisional activation of fast C6H6O neutrals with helium. The +NR+ and collisionally activated dissociation spectra, the latter obtained at unit mass resolution, are used to identify these [C6H6O]+ ˙ isomers. Hexa‐1,3,5‐trienal is found to cyclize spontaneously to cyclohexa‐2,4‐dienone during attempted pyrolytic preparation. The thermochemistry of these C6H6O molecules and cation radicals is discussed on the basis of experimental data and MNDO calculations.
Kinetics of acrylamide/glutathione binding by fast atom bombardment and thermospray mass spectrometry
Authors: Harrison M. E. , Baldwin M. A.
Published: May 2005

The kinetics of the binding of the neurotoxin acrylamide to the cysteine residue of glutathione has been studied. At 37 °C and pH 7.3 the second order rate constant has been determined to be 0.72 ± 0.06 mol−1 dm3 min−1 by thermospray mass spectrometry. The critical energy at pH 11.5 measured over the temperature range 10–37°C by fast atom bombardment mass spectrometry was measured as 24.6 kJ mol−1.
Laser Desorption electron impact mass spectrometry: Studies of ion radical fragmentation mechanisms and hydrogen/deuterium rearrangement in time‐resolved experiments
Authors: Fenselau Catherine , Emary W. Bart , Cotter Robert J.
Published: May 2005

Laser desorption of neutral molecules followed by electron impact ionization is shown to produce gaseous ion radicals that undergo fragmentation analogous to that observed with electron impact and field ionization. Spectra were measured of heptanal and four deuterium‐labeled analogs regenerated from bisulfite derivatives, and compared with electron impact, chemical ionization and field ionization spectra published previously. Lifetimes of desorbed neutral molecules and of ions were found to influence the fragmentation process as reflected in isotope patterns. This is explained on the basis of internal energies.