bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane with aliphatic alcohols
Authors: Orlando Ron , Strobel Fred , Ridge D. P. , Munson Burnaby 
Published: May 2005

AbstractMixtures of tetramethylsilane and helium have been found to form [M + 73]+ adducts, hydrated trimethylsilyl ions and alkyl ions with aliphatic alcohols. The adduct ions were found to be formed by displacement of water from the hydrated trimethylsilyl ion. Ratios of the abundances of the adduct ions to the hydrated trimethylsilyl ion can be used to differentiate among primary, secondary and tertiary alcohols. Sensitivities for a number of alcohols with the tetramethylsilane/helium chemical ionization reagent system are approximately equal.
A metastable ion study of the electron impact fragmentation of some substituted 2,6‐pyrido‐containing crown ethers
Authors: Chen S. N. , Wang M. L. , Chen S. C. , Jing Z. Z. , Baldwin M. A. , Wu C. T. , Wang X. J. 
Published: May 2005

AbstractExtensive networks of metastable ions link the major peaks in the electron impact mass spectra of two crown ethers containing 2,6‐pyrido units. High‐resolution mass measurements and the metastable peaks allow the elucidation of the fragmentation pathways. The spectra are influenced more by the presence of aromatic substituents than by the 2,6‐pyrido units.
Competing polar cycloreversion reactions under electron impact ionization in 3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides
Authors: Kulkarni P. S. , Sahasrabudhe S. D. , Tilak B. D. 
Published: May 2005

AbstractThe mass spectral fragmentation modes of a variety of substituted 3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides have been investigated. The ionic cycloreversions occur by two competing stepwise heterolytic cleavages, α and β to the phosphorus atom, producing heterodiene and heteropolarophile iminophosphorane ions. Substituents strongly influence the competitive fragmentation modes. Formation of heterodiene ion by retro‐Diels–Alder decomposition is preceded by hidden 1,3‐hydrogen shift and is the predominant proces in the metastable time region. Further fragmentation of the heterodiene ion occurs by electrophilic substitution‐elimination of the hydrogen atom.
Ring contractions of dihydro‐ and tetrahydro‐1,5‐benzodiazepines in electron ionization mass spectrometry
Authors: Chai Wen‐Gang , Wang Guang‐Hui , Jin Sheng , Lin Zu‐Ming , Liu Ping 
Published: May 2005

AbstractElectron ionization mass spectra of a series of 2,4‐disubstituted dihydro‐ and tetrahydro‐1,5‐benzodiazepines are discussed. The fragmentation of these compounds is dominated by ring contractions of diazepine, which give both five‐ and six‐membered rings, benzimidazoles and quinoxalines. Tetrahydro compounds showed a tendency to eliminate one nitrogen from the ring system and give quinoline rings through NH2 and NH4 eliminations. The electron ionization spectra of cis and trans isomers of tetrahydro compounds are identical.
An attempt to distinguish between the components of a mixture of isomeric fragment ions
Authors: Bujtás György , Hollósi Miklós , Majer Zsuzsa 
Published: May 2005

AbstractThe [C7H10NO3]+ ion in the normal mass spectrum of 2‐ethoxycarbonyl‐5‐oxo‐2‐pyrrolidinepropanoic acid was shown to correspond to a mixture of two isomeric structures. By decreasing the ionizing electron energy, the one containing a CH2CH2COOH group becomes dominant. The proportion of the concentrations of the two isomeric ions was calculated by comparing their daughter ion spectra (obtained by linked scan at constant B/E) with the analogous spectra of a derivative partially labelled by deuterium at the carboxyl and amide groups.
Charge inversion and neutralization–reionization mass spectra of some alkoxide ions
Authors: Mercer Roger S. , Harrison Alex G. 
Published: May 2005

AbstractThe charge inversion mass spectra of C1 to C3 alkoxide ions have been obtained using He, N2 and O2 as collision gases. The three collision gases show similar efficiencies for collisional charge inversion and produce similar mass spectra, although fewer high‐energy oxenium ions are formed when O2 and N2 are used as collision gases. Using two collision cells and an intermediate deflector electrode the alkoxide ions have been neutralized in the first collision cell and the fast neutrals ionized in the second cell. The neutralization–reionization mass spectra obtained are similar to the direct charge‐inversion mass spectra indicating that mainly alkoxyl radicals are produced, although, depending on the neutralization collision gas and the alkoxide ion studied, other neutrals are formed in small yields. Deuterium isotopic labelling has been used to show that the main fragmentation reactions of the unstable oxenium ions formed involve 1,1‐elimination of H2 or an alkane.
Mass spectral study of bicyclic peroxides. 1. Dioxabicyclo[n.2.2]alkanes and the corresponding dioxabicyclo[n.2.2]alkenes
Authors: Mruzek Margaret N. , Bloodworth A. J. , Eggelte Henny J. 
Published: May 2005

AbstractA series of dioxabicyclo[n.2.2]alkanes (n = 1,2,3 and 4) and dioxabicyclo[n.2.2]alkenes were studied under electron impact ionization. The fragmentation pathways were elucidated with the aid of accurate mass measurements, metastable scan techniojei and deuterium labelling. The preferential fragmentation of molecular ions in dioxabicyclo[n.2.2]alkanes corresponds to the loss of hydroperoxyl radical ·OOH. Hydrogens that are participating in this elimination come primarily from the syn position on the two‐membered carbon bridge. The dioxabicyclo[n.2.2]alkenes undergo the retro‐Diels–Alder process, which produces dioxygen and 1,3‐cycloalkadiene. In both saturated and unsatutated peroxides subsequent fragmentation of the hydrocarbon ring depends upon the value of n.
Gas‐phase protonation and methyl cation transfer from methyl halide ions
Authors: Houriet R. , Rolli E. , Flammang R. , Maquestiau A. , Bouchoux G. 
Published: May 2005

AbstractThe ion‐molecule reactions between [CH3X]+˙ [CH3XH] +, [CH3XCH3]+ ions (X = F, Cl, Br, I) and a number of nucleophiles have been studied by ion cyclotron resonance techniques. Protonation of the nucleophiles is observed to occur from both the molecular ions [CH3]X+˙ and protonated species [CH3XH]+ whereas dimethylhalonium ions [CH3XCH3]+ react principally by methyl cation transfer. A notable exception occurs in methyl iodide where the molecular ions [CH3I]+˙ act both as proton and methyl cation donors, whereas dimethyliodonium ions are found unreactive. The results are discussed with reference to the use of alkyl halides as reagent gases in chemical ionization experiments.
Endothermic proton transfer reactions from three [C6H6]+˙ isomers
Authors: Kinter Michael T. , Bursey Maurice M. 
Published: May 2005

AbstractA triple quadrupole mass spectrometer was used to establish the proton affinities of phenyl, CH3CCCCCH3 and HCCCH2CCCH radicals as 870±29, 824±25, and 757±21 kJmol−1, respectively, from the kinetic energy of benzene, 2,4‐hexadiyne, and 1.5‐hexadiyne molecular ions at which the onset of proton transfer to less basic species occurs in the second rod assembly. These values were confirmed by other triple quadrupole experiments involving bracketing of exothermic proton transfers.
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

AbstractThe 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

AbstractIn 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

AbstractAs 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

AbstractCluster 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

AbstractFragment–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

AbstractA 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

AbstractThe 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

AbstractElectron 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

AbstractThe 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

AbstractThe 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

AbstractNeutralization‐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

AbstractBy 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

AbstractThe 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

AbstractIncident 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

AbstractOrthoquinone 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

AbstractThe 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

AbstractThe 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.