bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and formation of gaseous [C4H5O]+ ions. IV—Ions derived from the cyclopropenium ion [C3H3]+
Authors: Terlouw Johan K. , Burgers Peter C. , Hommes Henk 
Published: May 2005

AbstractCharacterization of [C4H5O]+ ions in the gas phase using their metastable ion and collisional activation spectra shows that the three isomeric ions HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HOCH3, CH3O\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}CCH2 and OCH3 related to the two stable [C3H3]+ cations [HCCCH2]+ and are stable for ≥ 10−5s. In contrast to the formation of cyclopropenium ions, it is found that the methoxy cyclopropenium ion is not generated from acyclic precursor molecules. The small but significant intensity differences found in the collisional activation spectra of [C3H3]+ ions generated from HCCCH2I and HCCCH2Cl possibly indicate the presence of [C3H3]+ ions of different structures.
Mass spectral fragmentation of thioesters. 1—Identification of low energy, slow processes
Authors: Wood Gordon Walter , Kiremire Bernard T. 
Published: May 2005

AbstractA variety of thiol and thion esters, including acetates and benzoates with n‐butyl and β‐phenethyl alkyl groups, have been studied by electron impact mass spectrometry. Several rearrangement ions were documented and their persistence in low voltage and field ion spectra demonstrated. Among the significant ions found in the rich thion spectra, the most general requires O to S rearrangement of the alkyl group and subsequent cleavage to yield acyl ions (CH3CO or PhCO). This process is more important in longer chain compounds than in the methyl and ethyl homologues studied previously.
Effects of annulation on the mass spectral behavior of bicyclo[4.3.0]‐3‐nonene derivatives: Aldehydes
Authors: Tureček F. , Hanuš V. 
Published: May 2005

AbstractThe mass spectra of the title compounds depend markedly on ring annulation. On ionization, the cis‐annulated isomers lose alcohol and benzene regardless of the configuration of the alkoxyl. In the trans‐annulated isomers, the fragmentation is governed by the configuration of both the aldehyde and the alkoxyl groups. The role of non‐bonding interactions is discussed.
On the evaluation of ion source conditions for optimum sensitivity of chemical ionization
Authors: Morgan R. P. , Hayward E. J. , Steel G. 
Published: May 2005

AbstractThe best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS‐25 mass spectrometer. The best reagent gas pressure is shown to be different for each gas and is significantly lower than is usually reported in the literature.
Laser desorption mass spectrometry of thermally labile compounds using a continuous wave CO2 laser
Authors: Stoll R. , Röllgen F. W. 
Published: May 2005

AbstractA continuous wave CO2 laser has been used for the production of gaseous ions from organic sample layers. The long desorption times of a few seconds enabled a quadrupole mass spectrometer to be used for recording the mass spectra by signal accumulation. The laser desorption spectra of several thermally labile compounds are reported and discussed. The level of fragmentation is rather low. Molecular and fragment ions are formed almost exclusively by alkali ion attachment, even with acids. A particularly long desorption time of more than one minute has been observed with quarternary ammonium salts.
Mass spectroscopy of natural products. VI—Localization of functional groups in the hopane skeleton
Authors: Schmidt J. , Huneck S. 
Published: May 2005

AbstractThe mass spectral fragmentation of hopane derivatives with oxygenated substituents at C‐3, C‐6, C‐7, C‐15, C‐16 and C‐22 is discussed. It is shown, that the positions of functional groups in rings A and B or D and E respectively can be distinguished using several derivatives and deuterated analogues.
Mass spectrometric study of conjugated bifunctional acetylenes: 2—Ynals and ynones
Authors: Bachiri M. , Perros P. , Verneuil B. , Mouvier G. , Carlier P. 
Published: May 2005

AbstractThis study is based on results obtained by new techniques for observing metastable ions which make it possible to determine the fragmentation paths of conjugated ynals and ynones. For the ynals, the most interesting fragment is the [M–28]+˙ ion. For the ynones, when a McLafferty rearrangement is feasible, the ion arising therefrom is more abundant than the [MCO]+. ion. However, this elimination of a neutral CO molecule is quite important for the true acetylene ketones.
Chemical ionization mass spectrometry: Oligomerization reactions in tight ion sources
Authors: Hancock Richard A. , Thyagarajan B. S. , Walder Raymond 
Published: May 2005

AbstractAssociation of carbonyl compounds with protons to give cluster ions can be observed in conventional chemical ionization mass spectrometry. The variation of the relative ion currents of proton bound ‘dimers’ formed with acetone and methylethyl ketone have been examined as a function of ion source partial pressures. Multiple ion/molecule reactions with N‐methylol derivatives of amides and carbamates and repetitive losses of water give protonated oligomeric species. Ions having m/z values as large as 625 [M6H5H2O]+ have been detected in the chemical ionization spectrum of N‐hydroxymethylurethane (M).
The fragmentations of substituted cinnamic acids after electron impact
Authors: Schaldach Bernd , Grützmacher H.‐Fr. 
Published: May 2005

AbstractThe fragmentations of a number of cinnamic acids substituted at the phenyl ring have been studied with the aid of 70 eV mass spectra and mass analysed ion kinetic energy spectra. Evidence is presented that the formation of [C9H7O2]+ ions occurs by intramolecular aromatic substitution reactions. A mechanism is proposed for the energetically favourable loss of the substituents from meta and para positions of the phenyl ring. The analytical use of intramolecular aromatic substitution reactions is briefly discussed.
Mass spectral characteristics of the sulfur‐containing ketoxime carbamates thiofanox and metabolites
Authors: Corkins H. G. , Mannion J. J. , Storace L. 
Published: May 2005

AbstractDeuterium labeling and high resolution mass spectroscopy have been used to determine the modes of electron impact fragmentation of 3,3‐dimethyl‐1‐methylthio‐2‐butanone O‐[(methylamino)carbonyl]oxime, thiofanox and its metabolites, the sulfoxide and sulfone. The mass spectra of the corresponding oximes were also examined. The carbamates fragmented chiefly by two competing pathways—the loss of CH3NCO or the sulfur‐containing moiety. The favored process was dependent on the oxidation state at sulfur. Several unusual rearrangements were noted.
Mass spectrometric study of μ4‐oxohexa‐μ‐acetatotetrazinc, Zn4O(CH3CO2)6
Authors: Sipachev Viktor A. , Reshetova Lyudmila N. , Nekrasov Yurii S. , Sil'vestrova Svetlana Yu. 
Published: May 2005

AbstractThe electron impact mass spectrum of Zn4O(CH3CO2)6 isostructural to Be4O(CH3CO2)6 studied earlier is reported. The principal fragmentation paths of both compounds involve the elimination of M(CH3CO2)2 where M is Zn, Be, or (CH3CO)2O. Further fragmentations proceed by the losses of CH2CO and H2O. The spectrum of Zn4O(CH3CO2)6 contains intense doubly charged ions. The results obtained are interpreted in terms of stereochemical considerations.
Direct mass spectrometric analysis of the 18O/16O ratio in sulfur‐containing organophosphorus compounds
Authors: Reimschüssel Wladyslaw , Paneth Piotr 
Published: May 2005

AbstractHigh precision measurements of the 18O/16O ratio in bis‐(5,5‐dimethyl‐2‐oxo‐1,3,2‐P‐dioxaphosphorinanyl)‐sulfide and P1‐oxo‐P2‐thiono(5,5‐dimethl‐1,3,2‐dioxaphosphorinanyl)oxidee have been carrid out using a Finnigan 4000 mass spectrometer.
Program for elemental analysis using low or medium resolution mass spectra
Authors: Kavanagh Peter E. 
Published: May 2005

AbstractA program, called ELANAL, has been written in basic which computes all possible empirical formulae for a molecular ion or a fragment ion containing up to eleven common elements. The program then calculates the expected intensities of the peaks following the molecular or fragment ion due to heavier isotopes in the formulae. These calculated intensities are compared with the intensities in an experimentally determined mass spectrum.
A study of some cations formed in the ammonia chemical ionization of ketones using mass analysed ion kinetic energy spectrometry
Authors: Maquestiau André , Flammang Robert , Nielsen Lawrence 
Published: May 2005

AbstractThe structures of the major adduct ions formed in ammonia chemical ionization of thirteen aliphatic and aromatic ketones have been studied by mass analysed ion kinetic energy spectrometry. The [M+NH3+H]+ ion is shown to have a protonated carbinolamine structure, [M+2NH3+H]+ to be a protonated carbinolamine with hydrogen‐bonded ammonia and [2M+NH3+H]+ to be, at least in part, a protonated carbinolamine with hydrogen‐bonded ketone. These structures may imply a nucleophilic addition of ammonia at the carbonyl of the ketone‐ammonium ion complex. An unusual hydroxy migration is seen in the internal rearrangement of the [2M+NH3+H]+ ion leading to the formation of a protonated imine.
Bond breaking energy in collision induced dissociation: A study of carbon cage fragmentation in cubane, kepone and mirex
Authors: Lehman Thomas A. , Harvan Donald J. , Hass J. Ronald 
Published: May 2005

AbstractCollision induced dissociation of the carbon cage compounds cubane, kepone and mirex breaks the cage structures. The energy available for bond breaking is thus not less than about 9 eV, and the time between energy acquisition and subsequent unimolecular fragmentation is long enough that the available energy can be concentrated in three bonds to the same carbon atom. Collision induced dissociation mass‐analyzed ion kinetic energy spectra of [C5Cl6]+˙ from mirex and from hexachlorocyclopentadiene are virtually identical, and similar for [C6H6]+˙ ions from cubane and benzene.
Chemical ionization and electron impact mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes
Authors: Shaw Charles J. , Kane Vinayak V. 
Published: May 2005

AbstractThe methane and isobutane chemical ionization mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.
The constant neutral linked magnetic field electric sector scan
Authors: Haddon William F. 
Published: May 2005

AbstractA linked magnetic field‐electric sector scan for which (B/E)\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {1 - E} $\end{document} is constant selectively records first field free region metastable peaks representing loss of the same neutral fragment. The constant neutral metastable ion spectra produced by this scan should provide information about the presence and location of particular functional groups beyond that which is available from focused mass spectra. Constant neutral linked scans can be obtained consecutively with focused spectra and with B/E and B 2/E linked scans by simple extension of a computerized B‐E scanning method developed previously.
Some PhCNO‐containing molecules; mass spectral similarity and molecular diversity
Authors: Deem M. L. 
Published: May 2005

AbstractSome diverse compounds possessing a PhCNO unit cleave the NO link upon electron impact to give [PhCN]+˙. Different and especially significant modes of NO scission occur in metastable processes when the oxygen atom of the PhCNO group is exocyclic to a heterocyclic nitrogen atom. Upon electron impact, rupture of the NO bond in PhCNO‐containing molecules generally dominates over 1,3‐dipolar cycloreversion, which generates the radical cation of benzonitrile oxide. Stable PhCNO‐containing molecules survive competing fragmentations in the ion source to produce [M+H]+ ions of moderate relative intensity. Other ions, which are larger than [M]+ are implicated where M is PhCHNOR. Several values of m/z for metastable ions are common to compounds which have a PhCNO moiety. These m/z values generally derive both from a parent ion with m/z⩽105 and from a PhCNO moiety.
Mass spectrometric studies of organophosphorus compounds: III—Remarkable migration of chalcogen on electron impact of organophosphorus compounds
Authors: Keck Helmut , Kuchen Wilhelm , Mahler Hans F. 
Published: May 2005

AbstractThe mass spectra of several dibenzo (d.f)‐1,3,2,‐dioxaphosphorepines of the type magnified image where X=0, S, Se and R=2,2′‐biphenylylene, have been studied. Dibenzochalcogen ions [RX]+˙ stemming directly from [M]+˙ were observed with high intensities, indicating specific migration of X from phosphorus to carbon with simultaneous destruction of the dioxaphosphorepine ring. Simple cleavage of PY as usually observed in similar organophosphorus compounds is not a common process here.
Mass spectrometry of diaziridines: 1—Rearrangements of the molecular ion of 1‐benzyl‐3,3‐dimethyldiaziridine and identification of some daughter ions using collisional activation
Authors: Mintas Mladen , Mayer Klaus K. 
Published: May 2005

AbstractIntense rearrangement processes involving migrations of hydrogen atoms and the phenyl group were observed in the electron impact induced fragmentation of 1‐benzyl‐3,3‐dimethyldiaziridine. The following ions are observed: (i) m/z 146: a two‐step fragmentation involving hydrogen transfer followed by loss of NH2; (ii) m/z 119: C—N1 bond fission followed by a 1–4 phenyl shift and loss of CH3N2; (iii) m/z 106: a process involving reciprocal hydrogen migration between the methyl and benzylic methylene groups; (iv) m/z 58: hydrogen transfer from benzylic methylene and subsequent loss of PhCHN. The origin of these ions has been confirmed by measurements of metastable transitions in 1‐benzyl‐3,3‐dimethyldiaziridine, and on specifically deuterated and substituted diaziridines. The structure of the ions at m/z 119 and m/z 106 has been deduced by means of collisional activation spectrometry.
Structure and formation of some [C4H5O2]+ ions generated by radical losses in pseudo simple cleavage reactions
Authors: Terlouw Johan K. , Burgers Peter C. , Schwarz Helmut 
Published: May 2005

AbstractCharacterization of some [C4H5O2]+ ions in the gas phase using their collisional activation mass spectra shows that the isomeric ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O,} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HC} \equiv {\rm C} - \mathop {{\rm C}({\rm OH}){\rm OCH}_3 }\limits^ + $\end{document} are stable for t⩾10−5 s. Of these, ions of structure were generated by the site specific gas phase protonation of γ‐crotonolactone with isobutane or methanol as chemical ionization reagent gases. These results and those derived from measurements on some 2H, 13C and 18O labelled [C4H5O2]+ product ions, were used to study the mechanisms of unimolecular radical elimination reactions, viz. (1) loss of CH3˙ from [trans‐methyl crotonate], (2) loss of H˙ from [methyl acrylate]+˙, (3) loss of H˙ from [cyclopropane carboxylic acid]+˙ and (4) loss of CH3˙ from [1,3‐dimethoxypropyne]+˙. It is concluded that none of these losses occur by simple bond cleavage. Mechanisms are presented which account for the observation that the first three reactions yield product ions of structure whereas the ions generated by reaction (4) have structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}. It is further proposed that a minor fraction of the [M‐CH3]+ ions from ionized trans‐methyl crotonate is generated via a rearrangement process which yields ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}.
The computer processing and interpretation of mass spectral information. VII—identification of ions in terms of structural symbols
Authors: Sukharev Yu. N. , Sizoi V. F. , Molgachova N. S. , Nekrasov Yu. S. 
Published: May 2005

AbstractA new version of the AELITA‐F program for computation of a monoisotopic spectrum and identification of the ion composition as a collection of elements or as structural fragments is described. A technique is proposed for specifying a priori information on the compound in a ‘hybrid’ form which combines structural fragments of the molecule and individual chemical elements. This version permits the elimination of redundant information and reduces the requirements of computer resources. The program effectiveness is increased by reducing the number of ions to be generated. The format in which the mass spectral information is read out is more comprehensible to a chemist.
Cyclization of dimethyl oxalate upon electron impact
Authors: Liehr J. G. , Larka E. A. , Beynon J. H. 
Published: May 2005

AbstractIsotope labelling experiments and also consecutive fragmentation investigations of metastable ions, a novel technique in mechanistic studies, have been carried out to elucidate structure and genesis of the m/z 45 ions from dimethyl oxalate as well as dimethyl carbonate. It is shown that the formation of the m/z 45 ions, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{O}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document}, in the mass spectra of these compounds arises via single step processes. Mechanisms involving hydrogen transfer and subsequent formation of cyclic intermediates which then collapse to give \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{O}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} directly from molecular ions are suggested. No evidence was found for a two‐step fragmentation route to m/z 45 from the molecular ions of either dimethyl oxalate or dimethyl carbonate.
The fragmentation of the ions of nonan‐4‐one: A study by triple quadrupole mass spectrometry
Authors: Yost R. A. , Enke C. G. 
Published: May 2005

AbstractThe fragmentation pathways for the ions generated by electron impact from nonan‐4‐one have been studied using low energy collision induced dissociation in a triple quadrupole mass spectrometer. Over 400 fragmentation pathways have been identified. These results are compared with data from earlier ion kinetic energy spectrometry studies of nonan‐4‐one which employed metastable decompositions.
Mass spectrometry of thio analogues of pyrimidine bases: 2‐alkoxycarbonylalkyl‐thiouracils
Authors: Wyrzykiewicz E. , Buczek J. , Golankiewicz K. 
Published: May 2005

AbstractThe mass spectral fragmentation of twelve new 2‐alkoxycarbonylalkylthio substituted derivatives of uracils is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions are proposed. It has been found that the basic mass spectral fragmentation of these compounds is due to cleavage of SC, OC and CC bonds of the alkoxycarbonylalkylthio group.
Mechanisms of formation of [MHCO]+ and [MC6H5CO]+ ions from isomers of 1,4‐benzodioxin derivatives
Authors: Bouchoux Guy , Dagaut Jacques 
Published: May 2005

AbstractIt is demonstrated that phenyl and benzocyclobutenyl derivatives of 1,4‐benzodioxin interconvert before fragmentation at low internal energy. The mechanisms of the two major fragmentations (HCO and C6H5CO losses) are investigated by means of kinetic energy release determination and appearance energy measurements. From these experiments it is concluded that the fragment ions possess a dibenzopyran structure.
Reduction of trinitroaromatic compounds in water by chemical ionization mass spectrometry
Authors: Yinon Jehuda , Laschever Miriam 
Published: May 2005

AbstractA reduction process was found to occur in the ion source when observing the chemical ionization mass spectra of a series of trinitroaromatic compounds, using water as reagent. The [MH–30]+ ions in the CI mass spectra were due mainly to the reduction of the compounds to their corresponding amines. This was proved by using D2O as reagent: the [MH–30]+ ions were shifted to [MD–28]+ ions. The trinitroaromatic compounds investigated included 1,3,5‐trinitrobenzene, 2,4,6‐trinitrotoluene, 2,4,6‐trinitro‐m‐cresol, 2,4,6‐trinitroaniline (picramide) and 2,4,6‐trinitrophenol (picric acid).
Atmospheric pressure chemical ionization negative mass spectra of the dinitrotoluene isomers
Authors: Asselin Michel J. F. , Paré Jocelyn J. R. 
Published: May 2005

AbstractThe atmospheric pressure chemical ionization of the dinitrotoluene isomers in ambient air was studied with a quadrupole mass spectrometer operating in the negative mode. The isomers can be grouped on the basis of the product ions: 2,5‐, and 2,6‐ and 3,5‐dinitrotoluene give the molecular anion with little fragmentation; 2,3‐ and the 3,4‐dinitrotoluene behave similarly but with more extensive fragmentation; 2,4‐dinitrotoluene gives the quasimolecular [DNT − H]− ion with little fragmentation. The results are discussed in terms of the molecular structure of the isomers.
Four isomers of [C3H8O]+˙ distinguished by collisional activation
Authors: Crow Frank W. , Gross Michael L. , Bursey Maurice M. 
Published: May 2005

AbstractCollisional activation of the molecular ions of 1‐propanol, 2‐propanol and methyl ethyl ether, and of the m/z 60 ion from 1,2‐dimethoxyethane provides evidence for four distinct forms of [C3H8O]+˙. Collision induced decompositions may be explained either by simple cleavages, by cyclic processes involving adjacent substituents, or by bicyclic processes of adjacent substituents. Evidence for a form of [C3H8O]+˙ in which charge and radical site are separate is assembled from the spectra.
Studies of consecutive reactions of quinones in a reversed geometry mass spectrometer
Authors: Proctor C. J. , Kralj B. , Larka E. A. , Porter C. J. , Maquestiau A. , Beynon J. H. 
Published: May 2005

AbstractConsecutive reactions involving the ejection of molecules of carbon monoxide from quinone systems have been studied. Using a reversed geometry double focusing mass spectrometer, the individual steps of a consecutive reaction may be separated into different field free regions. The structure of ions formed in the ion source may be compared with those formed from the fragmentation of metastable ions in a field free region by studying differences in the pattern of translational energies released when they break. In the case of anthraquinone it is found that two structures exist for the [MCO]+˙ ion. Critical energy measurements strengthen this argument. Furthermore, 18O labelling has been used to distinguish between the loss of carbon monoxide from different positions on the molecular ion of 1‐hydroxyanthraquinone.
A study of the tautomerism of 5‐as‐triazinones by mass spectrometry
Authors: Daunis Jacques , Djouai‐Hifdi Laila , Pigière Christian 
Published: May 2005

AbstractThe tautomeric equilibria of variously substituted 5‐triazinones have been studied by comparing their mass spectra with those of their methylated derivatives. The results for 6‐methyl‐5‐triazinone have been confirmed by comparison with the mass analysed ion kinetic energy spectra of ions generated from N‐ethyl derivatives. The equilibria are dependent upon the nature of the substituents in the 3‐ and 6‐positions.