bluuebunny/crossref_metadata_2025_split huggingface dataset:
Natural isotopes as a tool in the elucidation of elemental composition and fragmentation pathways by tandem mass spectrometry
Authors: de Hoffman Edmond , Auriel Michel 
Published: May 2005

AbstractComparison of daughter spectra obtained by tandem quadrupole mass Spectrometry from ions selected from an isotopic cluster of the same elemental composition can be efficiently used to find out the elemental composition of a fragment. This even applies with ions of high mass and with low abundance isotopes such as 18O. By this method, loss of CO and HCO˙ from the phenol molecular ion is confirmed and the absence of CO loss from the p‐tert‐butyl‐pbenol molecular ion is made obvious. Limitations of the method are discussed in the case of a bicyclic imidazolidinone.
Bifunctional even‐electron ions. V. Fragmentation behaviour of aliphatic hydroxonium ions containing an additional cyano group
Authors: Záhorszky U. I. , Schulze P. 
Published: May 2005

AbstractThe fragmentation behaviour of a series of bifunctional hydroxonium ions C2H5C(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + {\rm H} $\end{document})(CH2)n‐CN (n = 0‐6), a n, has been investigated by electron impact mass spectrometry. The type of interaction‐induced reactions depend strongly on the chain distance between the oxonium and the cyano moiety, but the initial step in all cases is proton transfer from the hydroxy to the cyano group. The following selective primary fragmentations have been found: loss of C  NH (HCN) from a 0, loss of CH2,  C  NH from a 1, loss of HNCO from a 2‐a 4, loss of CH3CHC  O from a 4‐a 6, and loss of CO from a3. In addition, loss of NH3 and H2O, respectively, are observed as general fragmentations, except for the lowest homologues (a 0 and a 1). Mechanistic pathways of the selective reactions have been deduced with the aid of metastable ion spectra, high resolution, deuterium labelling and comparison of metastable ion spectra with those of independently generated ions.
Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 2—Salts
Authors: Van Vaeck L. , Bennett J. , van Espen P. , Schweikert E. , Gijbels R. , Adams F. , Lauwers W. 
Published: May 2005

AbstractLaser microprobe mass spectrometry (LMMS) has been applied systematically to a variety of organic polyfunctional molecules, covering a wide range of structures and polarities. The microprobe generally offers a combination of desorption under relatively mild conditions with abundant fragmentation. We attempted an empirical approach by tentative hypotheses about desorption and ionization in LMMS to consistently rationalize the detected fragments. The complementary nature of structural data, carried by positive and negative ions, is characteristic for LMMS results of non‐ionic compounds. The analysis of salts represents, traditionally, an ultimate test case for soft methods in organic mass spectrometry. Hence, by a selected series of compounds, we have tried to assess to which extent the presence of preformed ions becomes an asset for LMMS analysis and affects the amount, the accessibility or the distribution of organic information between positive and negative fragments.
Mass spectra of 2‐thioacylaminothiazoles, 2‐thioacylaminobenzothiazoles and their ‘fixed structure’ amino and imino tautomeric forms
Authors: Jagodziński Tadeusz S. , Terentiev Piotr B. 
Published: May 2005

AbstractThe fragmentation patterns of the thioacyl derivatives of 2‐aminothiazole and 2‐aminobenzothiazole and of their ‘fixed structure’ imino and amino tautomeric forms give evidence of the predominance of the imino tautomer in the molecular ions of the trifluorothioacetyl compounds. On the other hand, the M+˙ ions of the thioacetyl and thiobenzoyl derivatives are mainly the amino tautomers. A rearrangement with elimination of RCN and formation of the 2‐thiazolothione (2‐benzothiazolothione) ion is characteristic for ail the compounds investigated. Additional evidence for the interpretation of the main fragmentation paths is provided by the mass spectra of the N‐trideuteromethyl and N‐deuterated derivatives, high‐resolution mass spectrometry being used to determine the elemental composition of some selected peaks.
Extensive substituent scrambling in substituted diphenylacetylenes on electron impact
Authors: Ramana D. V. , Rama Krishna N. V. S. 
Published: May 2005

AbstractExtensive randomization of the substituents is found in mono‐ and disubstituted diphenylacetylenes under electron impact conditions. The study of diphenylacetylenes with a variety of substituents indicates that the electron‐withdrawing groups favour the substituent scrambling, AH the substituted diphenylacetylenes give an ion at m/z 176, having a common ion‐structure, arising as a result of the expulsion of a hydrogen radical and the substituent in monosubstituted diphenylacetylenes and the expulsion of both the substituents in disubstituted diphenylacetylenes. A ring‐expanded structure is postulated for this common fragment.
Multiply charged ions in ionspray tandem mass spectrometry
Authors: Siu K. W. M. , Gardner G. J. , Berman S. S. 
Published: May 2005

AbstractMultiply charged anions of some 30 species containing multiple carboxylic, sulphonic and/or phosphoric groups generated by ionspray were studied by using tandem mass spectrometry (MS/MS). Two trends emerged: (1) lower‐charged ions are preferentially evaporated, and (2) for more highly charged ions, evaporability is a function of ion size. Triply and quadruply charged ions were observed for azo dyes with molecular masses in the 700‐900 Dalton range. Daughter‐ion mass spectra of selected multiply charged ions are presented.
Unimolecular decomposition of ethoxytrimethylsilane
Authors: Herold David A. , Futrell Jean H. 
Published: May 2005

AbstractA study of the metastable spectra from ethoxytrimethylsilane and the mass shifts of the deuterium‐labeled species permitted the rationalization of the fragmentation mechanism for forming all major ions in the mass spectrum. A new mechanistic pathway for the formation of [Si(CH3)3]+ (m/z 73) is demonstrated. A strong metastable ion for elimination of neutral acetaldehyde from the parent ion was observed despite the absence of a detectable daughter ion.
Positive electron impact and chemical ionization mass spectra of some nitramine nitrates
Authors: Rowley J. A. 
Published: May 2005

AbstractThe positive electron impact (EI) and isobutane chemical ionization (CI) mass spectra of six nitramine nitrates were studied with the aid of some accurate mass measurements. In the EI spectra, β fission relative to both the nitramine and nitrate ester is important. In the CI spectra a major ion occurs at [MH – 45]+ and was found to be mainly due to [M + 2H  NO2]+. All of the compounds except N‐(2 hydroxyethyl)‐N‐(2′,4′,6′‐trinitrophenyl)nitramine nitrate gave an [MH]+ ion. The [MH – 45]+ ion in the isobutane CI mass spectra of tetryl is also due to [M + 2H  NO2]+.
Stabilization of even‐electron ions in 4‐amino‐substituted cytosines. Appearance of the strong ortho effect between an aryl substituent and the pyrimidinyl ring
Authors: Plaziak Adam S. , Spychala Jaroslaw , Golankiewicz Krzysztof 
Published: May 2005

AbstractThe mass fragmentation of 4‐arylaminocytosine derivatives was investigated and it was found that the ortho effect is mainly responsible for the strong stabilization of even‐electron ions formed during fragmentation. The ortho effect in this class of compounds completely eliminates other possible fragmentation patterns. This effect disappears when the aryl substituent is separated from the 4‐amino group of the cytosine moiety by a methylene group.
Thermospray liquid chromatography/mass spectrometry of quaternary ammonium saltst
Authors: Vicchio Domenick , Yergey Alfred L. 
Published: May 2005

AbstractVarious esters of choline and carnitine have been shown to undergo fragmentation dependent on both the structures of the molecules and the vapor and block temperatures when subjected to thermospray ionization mass spectrometry. The fragments observed vary with the structure of the ester portion and the backbone of the molecules, and are consistent with the compounds undergoing three types of reactions: (1) carbon—nitrogen bond cleavage to tertiary amines and alkyl compounds, (2) hydrolysis of the ester linkage, forming alcohols and organic acids, and (3) deacylation of the molecules to form acids and the corresponding quaternary alkene. The general applicability of the carbon—nitrogen bond cleavage mechanism was studied with other classes of quaternary compounds, but the sole products consistently detected for pyridinium, benzyldimethyldodecylammonium and tetraalkylammonium salts were amines. The fragments observed for the esters of choline and carnitine and also the anticholinergic 2,2‐diphenyl‐4‐diisopropylaminobutyramide methiodide suggest that the mechanism of the thermospray fragmentation pathway is similar to that of the Hofmann elimination reaction.
Stereochemical effects in mass spectrometry: Part 8‐chemical ionization mass spectra of cyclic glycols and monosaccharides using formaldehyde dimethyl acetal as reagent gas
Authors: Tu Ya‐Ping , Chen Yao‐Zu , Chen Su‐Nian , Wang Mei‐Lan , Jing Zhi‐Zhong 
Published: May 2005

AbstractThe chemical ionization mass spectra of cyclic glycols and monosaccharides using formaldehyde dimethyl acetal as reagent gas have been studied. In the gas phase, the stereospecific reaction of methylene acetal formation was observed. From the relative abundances of the characteristic ions the stereoisomers of these compounds may be definitely distinguished.
Structures of decomposing and non‐decomposing gas‐phase [C4H6O]+· radical cations, and their [C2H2O]+· and [C3H6]+· product ions
Authors: Dass Chhabil , Gross Michael L. 
Published: May 2005

AbstractThe structures of gas‐phase [C4H6O]+· radical cations and their daughter ions of composition [C2H2O]+· and [C3H6]+· were investigated by using collisionally activated dissociation, metastable ion measurement, kinetic energy release and collisional ionization tandem mass spectrometric techniques. Electron ionization (70 eV) of ethoxyacetylene, methyl vinyl ketone, crotonaldehyde and 1‐methoxyallene yields stable [C4H6O]+· ions, whereas the cyclic C4H6O compounds undergo ring opening to stable distonic ions. The structures of [C2H3O]+· ions produced by 70‐eV ionization of several C4H6O compounds are identical with that of the ketene radical cation. The [C3H6]+· ions generated from crotonaldehyde, methacrylaldehyde, and cyclopropanecarboxaldehyde have structures similar to that of the propene radical cations, whereas those ions generated from the remainder of the [C4H6O]+· ions studied here produced a mixed population of cyclopropane and propene radical cations.
α‐Distonic ions as transient species in the reactions of metastable alkyl benzoate radical cations
Authors: Audier Henri Edouard , Milliet Arielle , Sozzi Georges , Hammerum Steen 
Published: May 2005

AbstractThe key intermediates to the fragmentation of metastable methyl and ethyl benzoate radical cations are α‐ and β‐distonic isomers of the molecular ions. The α‐distocic isomers are also formed by fragmentation of longer chain alkyl benzoates, but may not be long‐lived, stable species. Rearrangement of the α‐distonic ions prior to fragmentation can take place, but (re)formation of the benzoate molecular ions does not occur.
Characterization of cyclotrimethylenetrinitramine (RDX) by pyrolysis H2O/D2O atmospheric‐pressure chemical ionization tandem mass spectrometry
Authors: Snyder A. Peter , Liebman Shirley A. , Schroeder Michael A. , Fifer Robert A. 
Published: May 2005

AbstractThe oxidative pyrolysis‐atmospheric‐pressure chemical ionization tandem mass Spectrometry (Py‐APCI MS/MS) of Cyclotrimethylenetrinitramine (RDX) was investigated under various sample introduction conditions. Subambient (0.97 atm) as opposed to ambient (0.98 atm) pressure (1 atm = 101325 kPa) facilitated the appearance of new pyrolysis mass spectral ions, including m/z 44. Deuterated decomposition products from [2H]RDX contained amide groups and, depending on the ion source pressure, significant differences in the degree of proton‐deuterium exchange occurred on the amide groups. The D2O Py‐APCI MS/MS method also confirmed and extended the analogous H2O APCI information from RDX, [2H]RDX and pure standards. The m/z 44 decompositon species was identified as protonated dimethylimine, [H3CNCH2]+ as opposed to its primary amine isomer, [H3CC(H)NH]H+, which contains an acidic proton. It was determined that m/z 60 is due to protonated N‐methylformamide and acetaldoxime, [H3CC(H)NOH]H+.
Low‐energy fragmentations of five isomeric [H3, C, N, O2] +· ions
Authors: Sirois M. , Holmes J. L. , Hop C. E. C. A. 
Published: May 2005

AbstractThe low‐energy fragmentation characteristics of the [H3,C,N,O2]+· isomers [H3CNO2]+· (a), [H2CN(O)OH]+· (b), [H3CONO]+· (c), [HC(O)NHOH]+· (d) and [HC(OH)NOH]+· (e) were studied in detail by metastable ion mass spectrometry. In agreement with most earlier observations, appearance energy measurements established the potential energy surface of the isomers a, b and c, showing the intricate interrelations between them. It was concluded that a isomerizes into b prior to fragmentation by loss of ·OH and H2O and into c before loss of ·H and H3CO· moreover, the reverse reactions do not take place on the metastable time‐frame. The dominant metastable process for isomers d and e (obtained via HCN loss from glyoxime) was generation of [H2NOH]+·. For isomer e this process was proposed to involved a rate‐determining isomerization into d. It was concluded that isomers d and e do not intercommunicate with ions a, b and c prior to fragmentation. Neutralization‐reionization mass spectrometry indicated that the enol form of formohydroxamic acid as well as the keto counterpart are stable in the gas phase.
Interlaboratory comparison of limits of detectic in negative chemical ionization mass spectrometry
Authors: Arbogast B. , Budde W. L. , Deinzer M. , Dougherty R. C. , Eichelberger J. , Foltz R. D. , Grimm C. C. , Hites R. A. , Sakashita C. , Stemmler E. 
Published: May 2005

AbstractData are presented on the limits of detection for a series of nine compounds in negative chemical ionization (NCI) mass spectra obtained in five different mass spectrometers: Finnigan 4000 with a 4500 ion source, Kratos MS‐80, Hewlett‐Packard 5985 and two Finnigan 4500s. The nine compounds undergo either resonance capture or dissociative capture of an electron at optimum energies ranging from 0.0 to 1.1 eV. The limits of detection generally increased with increasing optimum electron energy. The limit of detection as a function of optimum electron capture energy is expected to provide information about the electron energy distribution in the ion sources. The data showed scatter within and between instruments. The scatter is believed to be due primarily to reactions with low levels of adventitious gases such as oxygen in the ion source. The data also suggested wide variations in electron energies between the instruments. The variation in the electron energy distribution is thought to have been caused by variations in the ion optical fields within the instruments. These results suggest that the requirements for reproducibility in NCI mass spectra at the limit of detection are rigorous control of trace gases in the ion source, control of the electric fields within the source including ion optical fields that penetrate the source aperture control of pressure, temperature and other factors that influence NCI mass spectra.
Flash‐vacuum pyrolysis of 1‐acylbenzotriazole: Direct observation of cyclopenta‐2,4‐dienylidenemethaneimines by tandem mass spectrometry and low‐temperature infrared spectrometry
Authors: Maquestiau André , Beugnies Didier , Flammang Robert , Freiermuth Beat , Wentrup Curt 
Published: May 2005

AbstractA real‐time analysis of the flash‐vacuum pyrolysis products of 1‐acetylbenzotriazole (1) and 1‐benzoylbenzotriazole (2) was performed by tandem mass Spectrometry. In the temperature range 500‐600 °C, these compounds lose nitrogen, yielding N‐acetyl‐ and N‐benzoylcyclopenta‐ 2,4‐dienylidenemethaneimines (10 and 17, respectively). At higher pyrolysis temperatures, 1 gives 2‐methylbenzoxazole, cyanocyclopentadiene, methylcyanocyclopentadiene(s), benzonitrile and ketene, which were identified by collision‐activated dissociation mass Spectrometry. Low‐temperature infrared experiments confirmed the pyrolytic transformation 1(2) → 10(17) at mediated temperatures.
Collisional activation spectra of the adduct ions of 1,2,3‐triarylpropenones under ammonia chemical ionization conditions
Authors: Madhusudanan K. P. , Durani S. , Kapil R. S. , Fraisse D. 
Published: May 2005

AbstractUnder ammonia chemical ionization (CI) conditions triarylpropenones undergo hydrogen radical‐induced olefinic bond reduction on metal surfaces, resulting in [M + 2H + NH4]+ ions corresponding to the ammonium adduct of the saturated ketone. The decomposition of the adduct ions, [MNH4]+ and [M + 2H + NH4]+, was studied by collision‐induced dissociation mass‐analysed ion kinetic energy (CID‐MIKE) spectroscopy in a reverse geometry instrument. From the CID‐MIKE spectra of the [MNH4]+, [M + 2H + NH4]+, [MND4]+ and [M + 2D + ND4]+ ions it is clear that the fragmentation of the adduct ions involves loss of NH3 followed by various cyclization reactions resulting in stable condensed ring systems. Elimination of ArH and ArCHO subsequent to the loss of NH3 and formation of aroyl ion are characteristic decomposition pathways of the [MNH4]+ ions, whereas elimination of ArCH3 and formation of [ArCH2]+ are characteristic of the [M + 2H + NH4]+ ions of these propenones.
Evidence for metal surface catalysed reduction of unsaturated carboxylic acids under negative ion chemical ionization
Authors: Vairamani M. , Saraswathi M. , Rao G. K. Viswanadha 
Published: May 2005

AbstractUnsaturated carboxylic acids have been found to undergo hydrogenation in the presence of methanol prior to ionization. Z‐Isomers are found to undergo more facile reduction than the E‐isomers in the case of two pairs of dicarboxylic acids studied.
Rearrangements and fragmentations of metastable [C13H9S]+, [C14H11]+, [C13H11]+ and [C8H7S]+ ions
Authors: Rietjens Marcel , Oudman Drewes , Weringa Wilke D. 
Published: May 2005

Abstract[C13H9S]+, [C14H11]+, [C13H11]+ and [C8H7S]+ ions with unknown structures were generated from two [C14H12S]+·precursor ions by fragmentation reactions that must be preceded by extensive rearrangements. Ions with the same compositions, each with several initial structures, were prepared by simple bond‐breaking reactions. Metastable characteristics were compared for each of the four types of ions. It was found than in all cases fast isomerization reactions occur prior to fragmentation, so that no information about the unknown ion structures could be obtained by comparison of the observed fragmentations of metastable ions.
Determination of the fragmentation mechanisms of organophosphorus ions by H2O and D2O atmospheric‐pressure ionization tandem mass spectrometry II—dialkyl alkylphosphonate ions
Authors: Snyder A. Peter , Harden Charles S. 
Published: May 2005

AbstractDiethyl methylphosphonate (DEMP), diisopropyl methylpbosphonate (DIMP), diethyl isopropylphosphonate (DEIP) and diethyl ethylphosphonate (DEEP) were characterized by H2O and D2O atmospheric pressure ionization tandem mass Spectrometry (API‐MS/MS). Collision‐induced dissociation (CID)/fragmentation pathways included alkyl ions by direct cleavage, alkyl radical and water loss processes and McLafferty and McLafferty‐type rearrangements by six‐ and five‐membered ring transition states, respectively. D2O API proved particularly useful in that certain decomposition pathways (i.e. water and methanol neutral losses) had a statistical distribution as to the loss of an acid deuteron and proton(s). This phenomenon was manifested by two pairs of ions in the D2O API daughter‐ion mass spectrum for each phosphonate compound (e.g. both m/z 79/80 and 65/66 for DEMP and DIMP). The observed ion intensity ratios for these pairs of ions served as guides in the determination of their predicted ion relative abundance ratios and CID decomposition pathways.Water neutral losses as opposed to ether and alcohol neutral losses were favored for most of the protonated organophosphonate molecular ion decomposition schemes.
Isomerization and fragmentation of aliphatic ether radical cations: Interconversion of distonic ions and cyclopropane intermediates
Authors: Audier Henri Edouard , Sozzi Georges , Milliet Arielle , Hammerum Steen 
Published: May 2005

AbstractThe reactions of propyl ether radical cations close to threshold are initiated by (reversible) formation of γ‐disitonic isomers, R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document} (H)CH2CH2CH2·. The three methylene groups in these ions lose their positional identity by ring closure/ring opening via [cyclopropane + alcohol]+· intermediates. Extensive hydrogen exchange occurs within the C3‐chain. When R is not methyl the γ‐distonic isomer undergoes further intramolecular hydrogen atom transfer reactions that lead to formation of α‐ and β‐distonic ions. The α‐distonic isomers expel ethyl and propyl radicals by CO bond cleavage.
Single and double hydrogen migration in the fragmentation of 3‐methyl‐2‐butyl trifluoroacetate
Authors: Fǎrcaşiu Dan , Miller Glen , Hsu Chang S. 
Published: May 2005

AbstractThree of the main oxygen‐containing fragments resulting from 3‐methyl‐2‐butyl trifluoroacetate (11) had been identified previously as the 1‐triflnoroacetoxyethyl cation (m/z 141, 12, product of simple cleavage), and the products of single (m/z 142) and double hydrogen transfer (m/z 143, protonated ethyl trifluoroacetate). Collisionally activated dissociation of m/z 142 and the isotopomers resulting from 11‐2‐d, 11‐1‐d3, 11‐5,6‐d6, and 11‐18O2 has established that m/z 142 is the oxygen protonated 1‐trifluoroacetoxyethyl free radical (17) formed by hydrogen shift irom a γ‐methyl group to oxygen in the molecular ion, rather than in a complex (18) between 12 and the 2‐propyl free radical, as expected based on a mechanistic model existing in the literature. The second hydrogen transferred originates in the other γ‐methyl group; its migration may occur, but does not have to, in the complex between 17 and a molecule of propene, prior to dissociation of the two fragments. Collision‐activated dissociation has now shown that the m/z 140 ion observed in the spectrum is the molecular ion of vinyl trifluoroacetate, possibly formed by a hydrogen transfer from 12 to the 2‐propyl radical in the complex 18. The hydrogen migration to oxygen exhibits no isotope effect, whereas the transfers to carbon atoms exhibit small primary and α secondary kinetic isotope effects. Exclusive migration of the tertiary hydrogen from C(3) occurs in the formation of 2‐methylbutene cation radical (m/z 70) from the molecular ion. The hydrocarbon ion fragments and the heteroatom‐containing fragments are formed from 11 by disjoint pathways.
Ring opening reaction of protonated polyfluorinated benzenes in the gas phase. A theoretical MNDO study
Authors: Hrušák Jan 
Published: May 2005

AbstractThe MNDO calculations of protonated polyfluorobenzenes [Ph‐Fn]H+ indicate the possibility of a relatively free migration of the hydrogen proton with energy barriers of 125–145 kJ mol−1. At a higher degree of substitution (n) the protonation of the ipso carbon atom occupied by fluorine becomes energetically feasible, along with analogous migrations of fluorine, which, however, are energetically the most advantageous (ΔEa ∼ 230 kJ mol−1). In addition to bridged fluoronium ions, relatively stable cyclic intermediates were also found, which make possible a rearrangement to the difluoromethylenecyclopentadienyl cation and thus the elimination of CF2 observed in collision‐induced dissociation mass spectra.