bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assigning structures to [C2H3O]+ ions
Authors: Terlouw Johan K. , Heerma Wik , Holmes John L. 
Published: May 2005

AbstractThe problem of assigning structures to [C2H3O]+ ions produced from a wide variety of precursor molecules has been readdressed. The identification of the acetyl cation, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{O}} $\end{document}, from metastable peak characteristics and collisional activation mass spectra appears to be straightforward. The structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{OH}} $\end{document} is also known to exist as a stable ion. A third ion, whose structure may be represented as \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{H}}_{\rm{2}} {\rm{CHO}} $\end{document} or magnified image has also been characterized.
Ion current surface for a double focusing mass spectrometer of reversed geometry
Authors: Lacey Michael J. , Macdonald Colin G. , Donchi Kevin F. , Derrick Peter J. 
Published: May 2005

AbstractIon currents obtained for fragmentations in a mass spectrometer of reversed geometry have been represented as three‐dimensional surfaces, which are termed ‘ion current surfaces’. In addition to ion current, useful dimensions of the ion current surfaces are a parameter ln(|ρ|) where ρ = (V0/V)(E/E0) and a parameter ln(|m*|) where m* = (V0/V)mB. Each ion reaction occurring in the source and flight path gives rise to a pattern of peaks and ridges on the surface. If the major features of the surface corresponding to each ion reaction are projected onto the zero ion current plane, they are disposed in a characteristic trapezoidal pattern. All simple and linked modes of scanning correspond to cross‐sections of the surfaces, and representing the scanning modes in this light facilitates the identification of ‘cross‐talk’.
Acid catalyzed aldol condensation in the gas phase
Authors: Wesdemiotis Chrysostomos , McLafferty Fred W. 
Published: May 2005

AbstractThe gas phase reaction of acetaldehyde with a Brønsted acid in a chemical ionization source yields protonated crotonaldehyde, as shown by its collisional activation mass spectrum. This is thus analogous to the well known aldol condensation in solution, in which the initial aldol adduct loses water to yield crotonaldehyde. The possibility of a common mechanism for the gas phase and solution reactions is discussed.
A study of the structures of decomposing and non‐decomposing [C4H5N]+˙ ions formed from different neutral species
Authors: Sakurai H. , Jennings K. R. 
Published: May 2005

Abstract[C4H5N]+˙ ions have been generated from eleven neutral species. From a study of their metastable transitions and the translational energy released in the fragmentation in which C2H2 is lost, it is concluded that [C4H5N]+˙ ions with sufficient energy to decompose do so from a common structure or mixture of structures when they are generated from crotonitrile, allyl cyanide, cyclopropyl cyanide, methacrylontrile, pyrrole, 2‐, 3‐ and 4‐hydroxypyridines and 2‐aminopyridine. The [C4H5N]+˙ ions formed from allyl isocyanide decompose from a different structure and those given by cyclopropyl isocyanide appear to decompose from a mixture of the two structures. Non‐decomposing [C4H5N]+˙ ions were investigated by means of their collision induced decomposition spectra using a B/E linked scan. Six different structures or mixtures of structures are suggested to explain these observations.
Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes
Authors: Herman Jan A. , Harrison Ale X. G. 
Published: May 2005

AbstractThe H2, N2/H2, CO2/H2, N2O/H2, CO/H2 and CH4 chemical ionization mass spectra of thirteen C8 to C11 alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]+ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane‐derived reagent system is estimated to be ∼556 kJ mol−1.
Thermal surface ionization of some complex salts
Authors: Schade U. , Stoll R. , Röllgen F. W. 
Published: May 2005

AbstractThermal ionization on the surface of a heated wire is applied to the volatilization products of alkali salts of carboxylic and sulfonic acids, and to quaternary ammonium salts. The mass spectra of the alkali salts exhibit almost exclusively cationized molecules. They provide evidence for the evaporation of intact clustered molecules even under conditions of a slow rate of evaporation of the salts. The method appears to be of interest for selective detection of alkali salts from complex mixtures. With the ammonium salts [R4N]+ ions are formed by thermal surface ionization of intact salt molecules. The evaporation of these molecules could be detected at rather low temperatures.
Comparison of the fragmentations and reactivities of positive and negative ions. Thiocarboxylate ions
Authors: Trenerry V. C. , Stone D. J. M. , Bowie J. H. , Clausen K. , Scheibye S. , Lawesson S.‐O. 
Published: May 2005

Abstract(1) Thiocarboxylate anions [RCOS]− formed by dissociative secondary electron capture are either stable or fragment to yield [R]−. (2) Thiocarboxylate cations [RCOS]+ formed by charge stripping from [RCOS]−, fragment to form [R]+, [COS]+. and [RCO]+ (not when R=CF3). (3) Aryl hydrogen scrambling is observed in the case of the thiobenzoate cation. Aliphatic hydrogen scrambling is not detected for the thiopropionate cation.
Charge stripping reactions of ions formed from methane, ammonia, water and hydrogen sulphide by protonation and by electron impact
Authors: Proctor C. J. , Porter C. J. , Ast T. , Bolton P. D. , Beynon J. H. 
Published: May 2005

AbstractThe minimum energy, Qmin, necessary to convert an ion m1+ to a doubly charged ion m12+ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]+ ions formed by chemical ionization in a high pressure source. Stable m12+ ions could not be formed in the case of [NH4]+, [NH]+˙, [H2O]+˙ and [OH]+. Even in these cases the value of Qmin could be estimated by studying the fragments formed from the unstable m2+ ions. In several cases, the energy required to form m12+ ions is less than the literature value for the ionization energy of m1+. This is discussed in terms of the possibility of the presence of excited states of m1+ in the present experiments.
Basic questions in mass spectrometry
Authors: Lorquet J. C. 
Published: May 2005

AbstractThe unimolecular dissociation of ionized molecules seldom consists in a direct bond cleavage where the reaction coordinate can be adequately represented by a simple bond stretch. The coordinate which controls the progress of the reaction is not always the reaction coordinate (defined as the degree of freedom whose extension leads to spatial separation of the molecular fragments). The specificity of a dissociation mechanism in a polyatomic species is due to its inherently multidimensional character, i.e. it requires participation of several degrees of freedom. It often consists of a sequence of elementary steps and is therefore controlled by several bottlenecks. The complicated and multistep nature of the reaction mechanism results in a natural tendency towards energy randomization. Radiationless transition from the initial upper electronic states to the ground state of the ion is not always very fast with respect to dissociation. A unimolecular reaction should be seen as a flux in phase space through a critical surface. A transition state corresponds to a surface of least flux, i.e. to a bottleneck of the reaction. For a given elementary step, several may exist, whose positions may vary with energy. The nature of these transition states is not immediately obvious. For instance, they do not necessarily coincide with saddle points or with rotational barriers.
Elimination of water from the molecular ion of cycloheptanol
Authors: Tureček František , Smutek Miloš , Hanuš Vladimír 
Published: May 2005

AbstractUnder electron impact cycloheptanol decomposes by four fragmentation paths: (1) α‐cleavage with subsequent losses of C1‐C5 fragments, (2) elimination of water, (3) loss of the hydrogen atom from C‐1 and (4) loss of the hydroxyl group. The mechanism of water elimination was investigated by means of deuterium labelling. 1,4‐Elimination of water predominates in cycloheptanol, with the stereospecific cis‐1,3‐elimination also being operative. The loss of water is preceded by extensive exchange of the hydroxyl hydrogen with those of the ring. This is attributed to a very facile transannular interaction of the hydroxyl group with the C‐3 to C‐6 positions that are made accessible due to conformational properties of the 7‐membered ring. A kinetic model is proposed, describing migrations of the ring hydrogen atoms.
Electron impact induced hydrogen migrations in organic molecules: IV—novel hydrogen transfers in alkyl o‐methoxybenzoates
Authors: Ramana D. V. , Sundaram N. 
Published: May 2005

AbstractSimultaneous hydrogen transfers—one from the methoxy group and the other from the alkyl group—to both the oxygen atoms of the ester function result in the formation of a common ion at m/z 152 in the alkyl o‐methoxybenzoates on electron impact. Expulsion of the formyl radical from this ion leads to a fragment resembling the protonated benzoic acid. Another novel feature in these compounds is the loss of H2O from the [MR]+ ion which arises through an ortho effect during a secondary fragmentation process.
High speed acquisition and data processing of peaks in the B‐E plane of a double focusing mass spectrometer
Authors: Warburton G. A. , Stradling R. S. , Mason R. S. , Farncombe M. 
Published: May 2005

AbstractA technique is described whereby a double focusing mass spectrometer is scanned under data system control to obtain a map of the intensity of the signal transmitted through the collector slit as a function of the electrostatic analyser and magnetic analyser field strengths. Results of processing programs are given, which allow various types of scans within the map to be extracted and presented.
Mass spectrometry of metal compounds: II—mass spectrometric studies of [CF3EMn(CO)4]2, [CF3EFe(CO)3]2(E = S, Se), CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5
Authors: Chaudhuri M. K. , Dasgupta H. S. , Roy N. , Khathing D. T. 
Published: May 2005

AbstractThe electron impact induced mass spectra of [CF3SMn(CO)4]2, [CF3SeMn(CO)4]2, [CF3SFe(CO)3]2, [CF3SeFe(CO)3]2, CF3SeFe(CO)2C5H5and CF3SCr(NO)2C5H5are reported. These compounds exhibit weak molecular ion peaks and undergo preferential loss of CO or NO groups. The CO or NO free fragments suffer typical loss of ECF2(E = S, Se) with the simultaneous shift of F from carbon to metal. The ions [FFeC5H5]+and [FCrC5H5]+in the spectra of the cyclopentadienyl compounds prefer expulsion of π‐cyclopentadienyls. The pyrolysis effects on the spectra of the compounds have been studied. An increase in temperature eases the expulsion of ECF2groups from all the compounds and favors the formation of [Fe(C5H5)2]+and [Cr(C5H5)2]+in the cyclopentadienyl compounds.
Doubly charged ion mass spectra: III—N‐alkanes
Authors: Jones B. E. , Abbey L. E. , Chatham H. L. , Hanner A. W. , Teleshefsky L. A. , Burgess E. M. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra have been obtained for 15 n‐alkane hydrocarbons. Spectra were measured using a Nier‐Johnson geometry Hitachi RMU‐7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from CC bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n‐alkanes were [C2H4]2+, [C3H2]2+, [C4H3]2+, [C5H2]2+, [C6H6]2+, [C6H8]2+, [C7H6]2+, [C7H8]2+, [C8H6]2+ and [C8H8]2+. Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.
Doubly charged ion mass spectra: IV—chlorinated and brominated alkanes
Authors: Hanner A. W. , Abbey L. E. , Bostwick D. E. , Burgess E. M. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra have been obtained for 42 chlorinated and brominated n‐alkane (methyl through octyl) hydrocarbons. A double focusing Hitachi RMU‐7L mass spectrometer, operated at 1.6kV accelerating voltage, has been used to measure the spectra. Molecular doubly charged ions have not been observed. Intense fragment ions have been produced from extensive H and halogen loss as well as CC bond rupture of the parent molecule. The most abundant ions in the doubly charged ion spectra observed in this investigation resulted from reactions of [Cl]2+˙, [Br]2+˙, [CCL2]2+, [C2H2Cl]2+˙, [C3H2]2+, [C3HCl]2+, [C3HBr]2+, [C4H3]2+˙, [C4H4]2+, [C4H6Br]2+˙, [C4H8Br]2+˙, [C5H2]2+, [C6H6]2+, [C6H8]2+ and [C7H8]2+. The prominent doubly charged fragment ions formed by electron impact of the smaller halogenated alkanes generally contained halogen, whereas ions of the type [CnHx]2+ were dominant in the spectra of higher molecular weight mono‐ and dihalogenated alkanes. Appearance energies of several ions have been measured. A geometry optimized quantum mechanical SCF treatment has been used to compute energies, charge densities and structures of doubly charged halogenated alkane ions.
Review paper: Design of a mass and ion kinetic energy spectrometer for organic chemical work
Authors: Beynon J. H. , Harris F. M. , Green B. N. , Bateman R. H. 
Published: May 2005

AbstractThe design of a mass spectrometer for the determination of the structural formulae of organic compounds is discussed. The ion‐optical characteristics of electric and magnetic sectors and also of quadrupole mass analysers are considered and the additional information that can be gleaned when such components are combined in various ways is listed. The advantages of using collision cells for inducing fragmentation of selected ion species are listed including those that result when the collision cell is floated at an electrical potential different from that of the incident ion beam. Important performance characteristics are the resolution with which a particular ion may be selected and the resolution with which daughter ions formed from it can be separated. It is concluded, that for instruments comprising three analysing units together with the appropriate collision cells, the most versatile combinations and those with the highest performance are an arrangement consisting of a magnetic sector followed by an electric sector, this being followed either by a further magnetic sector or a quadrupole. The properties of these two systems are compared in detail.
The elimination of carbon monoxide from molecular ions of phenol and other [C6H6O]+˙ isomers
Authors: Walther H. J. , Eyer H. , Schlunegger U. P. , Porter C. J. , Larka E. A. , Beynon J. H. 
Published: May 2005

AbstractPhenol and five acyclic isomeric compounds have been investigated using electron impact and field ionization techniques, mass analysed ion kinetic energy spectrometry and collision induced dissociation mass analysed ion kinetic energy spectrometry. The kinetic energy release data corresponding to the elimination of carbon monoxide from the molecular ions show that at least two structures of the reactant ion are involved. The electron impact and field ionization collision induced dissociation mass analysed ion kinetic energy spectra indicate that under electron impact conditions, the phenol ion partially isomerizes to another ion structure. An isomerization of about 40% to the structure of cis‐2‐hexen‐4‐yn‐1‐al is in good accordance with the spectral data.
Collision induced dissociations of ions produced in the field free regions of a triple sector mass spectrometer
Authors: Maquestiau André , Meyrant Philippe , Flammang Robert 
Published: May 2005

AbstractMolecular or fragment ions can be prepared by a large variety of reactions in the field free regions of a mass spectrometer; these reactions involve spontaneous dissociation as well as collision induced excitation of singly or doubly charged precursors. Some typical examples show the different means which can lead to a given ion and how they can be studied by collisional activation. It also appears that in most cases the use of a triple sector (E/B/E) mass spectrometer facilitates these experiments as interfering artefacts are suppressed.
Mass spectra of some thionocarbamates
Authors: Łożyński Marek 
Published: May 2005

AbstractThe mass spectra of a number O‐alkylthionocarbamates with two, one or no alkyl substituents on the nitrogen atom are presented and discussed. The main primary fragmentation pathways are McLafferty rearrangements, including the double so‐called protonated McLafferty rearrangement. Generally, rearrangement products give charge delocalized ions, which release hydroxyl or sulphydryl radicals and water or hydrogen sulphide, to produce stable fragments. It has been found that the position of alkyl moieties may be deduced on the basis of mass spectral fragmentation patterns.
Chemical ionization and electron impact mass spectra of thiosulfinates, thiosulfonates and sulfinyl sulfones
Authors: Freeman Fillmore , Angeletakis Christos N. 
Published: May 2005

AbstractThe chemical ionization and electron impact mass spectra of some thiosulfinates, thiosulfonates and sulfinyl sulfones have been studied. The electron impact mass spectra of four of the six thiosulfonates show molecular ions of less than 1%. Inconclusive evidence was obtained for sulfenyl sulfinate type intermediates in the electron impact spectra of thiosulfonates. The electron impact spectra of thiosulfonates were similar to those of thiosulfonates. The chemical ionization (isobutane) mass spectra of thiosulfinates and thiosulfonates generally show protonated molecular ions [MH]+as base peaks and [MH+1]+and [MH+2]+peaks.
Alkane elimination from ionized alkanols
Authors: Holmes John L. , Burgers Peter C. , Mollah Yousuf A. 
Published: May 2005

AbstractThe energetics, metastable characteristics and daughter ion structures for the loss of small alkane molecules from ionized 2‐propanol, 2‐butanol and 3‐pentanol have been examined in detail. [2‐Propanol]+˙ ions lose CH4 to generate the keto and enol forms of [C2H4O]+˙ and the same daughter ions are produced by loss of C2H6 from [2‐butanol]+˙. Ionized 3‐pentanol does not lose CH4 but readily eliminates C2H6 to produce the enol ion [CH3CHCHOH]+˙. The last reaction was shown to proceed by a simple 1,2 elimination mechanism in the μs time‐frame; isotope effects are also discussed.
Collisional activation study of cyclic polysulfides
Authors: Holzmann G. , Susilo R. , Gmelin R. 
Published: May 2005

AbstractCyclic polysulfides isolated from higher plants, model compounds and their electron impact induced fragment ions have been investigated by various mass spectrometric methods. These species represent three sets of sulfur compounds: C3H6Sx (x=1−6), C2H4Sx (x=1−5) and CH2Sx (x=1−4). Three general fragmentation mechanisms are discussed using metastable transitions: (1) the unimolecular loss of structural parts (CH2S, CH2 and Sx); (2) fragmentations which involve ring opening reactions, hydrogen migrations and recyclizations of the product ions ([MCH3]+, [MCH3S]+, [MSH]+ and [MCS2]+˙); and (3) complete rearrangements preceding the fragmentations ([MS2H]+ and [MC2H4]+˙). The cyclic structures of [M]+˙ and of specific fragment ions have been investigated by comparing the collisional activation spectra of model ions. On the basis of these results the cyclic ions decompose via linear intermediates and then recyclizations of the product ions occur. The stabilities of the fragment ions have been determined by electron efficiency vs electron energy curves.
Flowing afterglow studies of the reactions between negative ions and trimethylsilyl enol ethers. Regiospecific generation of gas phase enolate ions
Authors: Squires Robert R. , Depuy Charles H. 
Published: May 2005

AbstractReactions of isomeric silyl enol ethers with fiuoride, amide or hydroxide ions in a flowing afterglow lead to the formation of relatively pure isomeric enolate anions. Isomeric enolates react specifically with neopentyl nitrite to give ionic products diagnostic of their structure.
Quantitative relationships between fragment ions and their relative intensities in electron impact mass spectrometry: VI—Hydroxy‐substituted tert‐alkylamines
Authors: Záhorszky U. I. 
Published: May 2005

AbstractThe influence of functional group interaction on the intensity ratios (Q) of product ions from α‐fission of ethyl‐tert‐alkylamines C2H5(C3H7)(HO(CH2)n)C NHC2H5, in which one side chain of the tert‐alkyl moiety is replaced by a hydroxyalkyl group of varying chain length, was investigated. It was found that only through‐bond interaction between the functional groups has a major influence on these ratios. By substitution of a hydrogen by a halogen atom in one side chain it was shown that the so‐called ‘ion mass effect’ is a degrees of freedom effect.
The fragmentation behavior of the endo‐ and exo‐octahydro‐4,7‐methano‐1H‐indene systems
Authors: Inman Roger C. , Servé M. Paul 
Published: May 2005

AbstractThe electron impact induced fragmentations of the endo‐ and exo‐octahydro‐4,7‐methano‐1H‐indene systems have been studied. The principal decomposition reactions have been elucidated by deuterium labelling. Two generic fragmentation patterns appeared: one involved the bisection of the molecule and the second involved the loss of various alkyl fragments.
Evidence for different reacting structures in the mass spectra of isomeric epoxides and aldehydes
Authors: Torroni Sandro , Foffani Maria Teresa , Sorriso Salvatore , Innorta Giuseppe 
Published: May 2005

AbstractThe metastable ion characteristics for common fragmentations of isomeric aromatic epoxides and aldehydes give indications for different reacting molecular ion structures. Some features of the fragmentation scheme of epoxides are discussed.
Application of emitter chemical ionization mass spectrometry to structural characterization of aminoglycoside antibiotics—2
Authors: Takeda Naohito , Harada Ken‐ichi , Suzuki Makoto , Tatematsu Akira , Kubodera Toshiya 
Published: May 2005

AbstractEmitter chemical ionization mass spectra of several aminoglycoside antibiotics (pseudotrisaccharides) have been determined by using isobutane and ammonia as reagent gases. All mass spectra show the protonated molecule and nine characteristic fragment ions due to the cleavages of glycosidic linkages. These fragment ion peaks are shown to be useful for the structural characterization of compounds of this class. Fragmentation reactions have been confirmed by the shift technique with ammonia‐d3 as the reagent gas.