bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pyrones: V—The mass spectra and fragmentation mechanisms of some 3(5)‐methoxy‐4‐pyrones
Authors: McGillivray David L. , Poulton Gerald A. 
Published: May 2005

AbstractThe mass spectra of methyl kojate (2‐hydroxymethyl‐5‐methoxy‐4H‐pyran‐4‐one), two deuterated analogues and 14 related 3(5)‐methoxy‐4‐pyrones have been studied. These compounds fragment according to a common mechanism, initiated by primary rearrangement of the molecular ion(s). Guidelines which indicate the presence of 3(5)‐methoxy‐4‐pyrones and allow structural determinations to be made from their mass spectra are presented. For the majority of substituents studied, the nature of the substituent has no major effect upon the fragmentation pattern; the cyano group does. The hydroxy counterparts of the above compounds are readily converted for analysis by simple methylation.
The dependence of collision induced fragmentation pattern on the internal energy of the precursor ion
Authors: Porter C. J. , Proctor C. J. , Beynon J. H. 
Published: May 2005

AbstractA Method is presented whereby product organic ions formed as the result of fragmentation of metastable ions can be selected on the basis of their internal energies. The method requires requires angular collimation of the beam of reactant ions issuing from the ion source and that the fragmentation of the metastable ions is studied in the first field free region of a reversed geometry double focusing mass spectrometer. The product ions that make up the metastable peak are allowed to fall on the intermediate resolving slit and, by adjusting the magnet current over a small range, ions contained in different regions of the peak can be allowed into the second field free region. It is shown that the position of an ion within the metastable peak correlates with its internal energy, ions near the edges of the peak being the least excited. The ions entering the second field free region can be investigated by collisional activation. This has been done for molecular ions of p‐chlorophenol, methylbenzoate, benzaldehyde, m‐chlorotoluene and n‐butane. The in which the collision induced fragmentation pattern varies with internal energy of the ions is illustrated.
Thermal desorption of quasimolecular ions
Authors: Stoll R. , Röllgen F. W. 
Published: May 2005

AbstractThe thermal desorption of [M + Alkali]+ quasimolecular ions from a heated metal surface is reported for some alkali salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. No quasimolecular ion could be detected from sucrose. With benzo[15]crown‐5 the desorption of [M + Na]+ ions takes place even below the threshold temperature for thermionic emission of alkali ions. In addition, the desorption of intact [B(C6H5)4]− ions from a layer of NaB(C6H5)4 is reported.
Bifunctional interaction and its effect on the esterification of dicarboxylic acids in chemical ionization mass spectrometry
Authors: Wengang Chai , Guanghui Wang , Zhiling Xu , Jiongguang Pan , Shumin Duan 
Published: May 2005

AbstractThe chemical ionization mass spectra of different dicarboxylic acids, including saturated and unsaturated aliphatic, aromatic, hydroxyl and amino‐substituted dicarboxylic acids, have been studied using pure methanol as the reagent gas. Biomolecular monoesterification and diesterification product ions [M+15]+ and [M+29]+, and adduct ion [M+33]+, were observed, in addition to the protonated molecule [MH]+ and unimolecular water elimination product ions. The formation of a protonated molecule with bridged intramolecular hydrogen bond, and its effect on the esterification of dicarboxylic acids is discussed. Geometric isomers, such as maleic and fumaric acid, and ortho and meta isomers of phthalic acids can be distinguished from each other by methanol chemical ionization mass spectra. When ethanol was used as the reagent gas, similar mass spectra of some dicarboxylic acids were obtained.
Charge reversal of three alkylamide ions: Free nitrenium ions
Authors: Bursey Maurice M. , Harvan Donald J. , Parker Carol E. , Darden Thomas A. , Hass J. Ronald 
Published: May 2005

AbstractThe methylnitrenium, ethylnitrenium and dimethylnitrenium ions are prepared by charge reversal collisional activation (CR CA) of the corresponding negative ions; their collisional activation mass spectra are shown to support the assigned structures. MINDO/3 energies are used to evaluate relative energies of [CH4N]+ and [C2H6N]+ isomers, and to determine whether unstable forms rearrange spontaneously to stable ones. As in other examples, charge reversal here generates cations that do not exist in an energy well, but their transient existence is established because their fragmentation is more rapid than their rearrangement to a more stable form.
Mass and kinetic energy spectrometries of alkylketenes
Authors: Maquestiau A. , Flammang R. , Pauwels P. 
Published: May 2005

AbstractReal‐time analysis of alkylketenes synthesized by flash vacuum thermolysis (FVT) of acid chlorides has been performed by mass spectrometric techniques using a triple sector (E/B/E) spectrometer. The major high energy reactions of the molecular ions consist of β‐cleavages relative to the CC bond of the ketene function, followed by decarbonylation. The unimolecular reactions of the metastable molecular ions are often different as shown by collisional activation of the fragment ions produced in a field‐free region of the spectrometer and also from estimated heats of formation.
A study of [C7H8]+˙ and [C7H8]2+ ions formed from different precursor molecules
Authors: Rabrenović M. , Brenton A. G. , Ast T. 
Published: May 2005

AbstractOn the basis of unimolecular and collisionally activated decompositions, as well as their charge stripping behaviour, [C7H8]+˙ and [C7H8]2+ ions from a variety of precursors have been studied. In particular, structural characteristics of molecular ions of toluene, cycloheptatriene, norborna‐2,5‐diene and quadricyclane have been compared to those of [C7H8]+˙ and [C7H8]2+ rearrangement fragment ions obtained from n‐butylbenzene, 2‐phenylethanol and n‐pentylbenzene. Severe interferences from [C7H7]2+˙ ion fragmentations have been observed and rationalized.
The collisionally induced dissociation of allyl and 2‐propenyl cations
Authors: Burgers Peter C. , Holmes John L. , Mommers Alexander A. , Szulejko Jan E. 
Published: May 2005

AbstractPure [CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} ions are generated only in metastable fragmentations of [CH2CHCH2X]+˙, X=Cl, Br, I, and [CH3CXCH2]+˙, X=Br, I, respectively. For ion source generated [C3H5]+ ions there is some structural interconversion. The structure characteristic feature of their collisional activation mass spectra is the ratio m/z 27 ([C2H3]+): m/z 26 ([C2H2]+˙). For \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} the ratio is only weakly dependent upon the translational energy of the ion. For [CH2CHCH2]+, the ratio rises sharply as translational energy is reduced, from 0.9 at 8 kV to c. 3 at 1 kV. [CH2CHCH2]+ ions generated by charge reversal of [CH2CHCH2]− show higher ratios, resulting from their lower average internal energy content. It must therefore be emphasized that [C3H5]+ ion structure assignments should only be made using reference data which apply to specific experimental conditions. [C3H5]+ daughter ion structures for a number of well‐known fragmentations have been established. The heat of formation of the 2‐propenyl cation was measured to be 969±5 kJ mol−1. Labelling experiments show that at low internal energies, allyl cations do not undergo atom randomization in c. 1–2 μs; high internal energy ions of longer lifetime (c. 8 μs) show complete atom randomization. H˙ atom loss from [13CH3CHCH2]+˙ has been shown to generate [13CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {}^{{\rm{13}}}{\rm{CH}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{CH}}_{\rm{3}} $\end{document} without any skeletal rearrangement.
The energy surface for isomeric [C2H3O]+ ions: Further experimental evidence
Authors: Tureček FrantišEk , McLafferty F. W. 
Published: May 2005

AbstractMass spectra from collisionally activated dissociation (CAD) of [C2H3O]+ ions, including isotopically labeled analogs, provide further information on the isomers [CH3CO+] (a), [CH2CO+H] (b), [+CH2CHO] (c) and (d). Our data generally support the recent conclusions from theory by Radom and coworkers and from experiment by Terlouw, Holmes and coworkers. Most acetyl‐containing molecular ions form a ions in high purity only at low energies, consistent with isomerization of higher energy molecular ions to form the more stable enol which dissociates to b. Isomer d, prepared from (CICH2)2CHOH, undergoes facile hydrogen scrambling, presumably through a degenerate 1,2‐hydrogen shift. Theory suggests that c undergoes spontaneous isomerization to a and d; although [C2H3O]+ ions from BrCH2CHO appear to consist of a and ∼15% d, the latter are formed without substantial hydrogen scrambling.
Collision‐induced dissociation of ester enolate ions using fourier transform mass spectrometry
Authors: Froelicher Stephen W. , Lee Robert E. , Squires Robert R. , Freiser Ben S. 
Published: May 2005

AbstractA series of ester enolates was investigated by the technique of collision‐induced dissociation (CID) using a Fourier transform mass spectrometer. Two primary modes of fragmentation were observed which led to CID products characteristic of the acyl and alkoxyl moieties of the ester enolates. An investigation of the fragmentation mechanism revealed that the primary fragmentation mode appears to be a sensitive function of the structure and the proton affinities of the two possible product ions. In most cases the anion (ketenyl or alkoxide) with the lower proton affinity was observed as the threshold product, suggestive of a proton‐bound dimer intermediate. Interesting secondary dissociations were observed to occur from the primary product ions, as alkoxide ions fragmented to enolate ions or other stabilized anions.
The reaction of the trichloromethylium ion with olefins
Authors: Stone John A. , Moote Nancy Joan 
Published: May 2005

AbstractThe reactions of [CCl3]+ with ethylene, 1‐hexene, cyclopentence, cyclohexene and styrene have been studied in a field‐free, high‐pressure ion source by time‐resolved ion collection following a short ionizing pulse of electrons. Ethylene is completely unreactive, while addition of [CCl3]+ to the olefinic bond of the other compounds is followed by loss of one or more HCl molecules to give unsaturated cations. Only styrene forms a stable adduct [MCCl3]+ which is an arenium ion produced by addition to the aromatic ring. Rate constants for the reaction of [CCl3]+ have been determined and show that whereas reaction with styrene occurs at almost every ion‐molecule collision, with 1‐hexene and cyclopentene only 15% of the collisions lead to reaction.
Electron impact mass spectrometry of some 2,3‐dihydro‐1‐benzofuran‐3‐acetic acids
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Daolio Sergio , Traldi Pietro , Vecchi Enrico 
Published: May 2005

AbstractThe mass spectrometric behaviour of four 2,3‐dihydro‐1‐benzofuran‐3‐acetic acids has been studied in detail with the aid of exact mass measurements, linked scans, collisionally activated decomposition, mass analysed ion kinetic energy spectra and labelling experiments. Unusual fragmentation pathways are emphasized for which mechanisms are proposed.
Further mass spectral studies of flavones
Authors: Guidugli F. H. , Ardanaz C. E. , Kavka J. , Garibay M. E. , Joseph‐Nathan P. 
Published: May 2005

AbstractFurther evidence supporting the structure of the [M − 1]+ ion found in the mass spectrum of flavone as being the [dibenzo‐β‐tropolone − H]+ species was obtained by comparison of linked scan measurements performed in flavone, 3‐deuteroflavone, 5,6,7,8‐tetradeuteroflavone, 2′,3′,4′,5′,6′‐pentadeuteroflavone and dibenzo‐β‐tropolone. This fragmentation process has also been demonstrated in the case of 3‐methoxyflavone by high‐resolution measurements, deuterium labelling, metastable decompositions and evaluation of the subspectra of 9‐methoxyfluorenol, fluorenone and biphenylene. The structure of the ion at m/z 181 in the spectrum of flavone was found to be the [2‐phenylbenzoxetane − 1]+ species.
Oxidation reactions in triterpenes under chemical ionization conditions
Authors: Madhusudanan K. P. , Singh Chandan , Fraisse D. 
Published: May 2005

AbstractFrom a collisional activation spectral study it has been found that certain triterpene alcohols with an ursane or oleanane skeleton undergo oxidation to the corresponding ketones under chemical ionization (NH3) conditions giving rise to abundant [M + NH4  2]+ ions. Mass‐analysed ion kinetic energy and B2/E scan results indicate that both [M + NH4]+ and [M + N2H7  2]+ ions contribute to the formation of the [M + NH4  2]+ ion.
Thermochemistry of HCOS+ and HCS2+
Authors: McAllister Trevor , Taylor Peter R. , Scarlett Margaret 
Published: May 2005

AbstractHeats of formation for HCOS+ and HCS2+, obtained from high‐quality ab initio calculations, have been used to determine the thermochemistry of several reactions which may form these ions in interstellar clouds or mass spectrometer experiments. Radiative association of HCO+ or HCS+ with either O or S may be important in interstellar clouds, whereas proton transfer from H3+ or HCO+ to CS2 or COS may be a means of synthesizing these ions by mass spectrometry. In the latter case, the relevant heats of formation are: HCS2+(1A1) 1042 kJ mol−1 and HCOS+ (1A′) 996 kJ mol−1.
The correlation of the intensities of the M+˙ and [M − H]+ ions in electron impact mass spectra of cyclic acetals and thioacetals containing a phenylalkoxyester group
Authors: Konopski Leszek , Masłosz Józef 
Published: May 2005

AbstractThe correlation between the intensities of the M+˙ and [M − H]+ ions of 47 cyclic acetals and thioacetals of alkyl formylphenoxyacetates and propionates as well as the fragmentation patterns in the vicinity of the molecular ion are discussed. The characteristic differences between the spectra of 1,3‐dioxolanes, 1,3‐oxathiolanes, 1,3‐dithiolanes and 1,3‐dioxanes are presented.
Hydride abstraction in fast atom bombardment
Authors: Baldwin Michael A. , Welham Kevin J. , Toth Istvan , Gibbons William A. 
Published: May 2005

AbstractUnder fast atom bombardment conditions, compounds having long alkyl chains may exhibit [M − H]+ as the major quasimolecular ion species, which can lead to incorrect assignment of molecular masses. It is shown that for a long‐chain ether the loss of the hydride occurs from the hydrocarbon chain remote from the oxygen. This effect may yield information concerning ionization mechanisms in fast atom bombardment/mass spectrometry.
Mass spectrometry of charge‐transfer complexes of 7,7′,8,8′‐tetracyanoquinodimethane‐π‐donor systems
Authors: Kurono Sadamu , Tani Takeshi , Hirano Takashi , Tsujimoto Kazuo , Ohashi Mamoru 
Published: May 2005

AbstractElectron impact (El) ionization and positive and negative liquid secondary ion mass Spectrometry (pLSIMS and nLSIMS) of eight charge‐transfer complexes of 7,7′,8,8′‐tetracyanoquinodimethane (TCNQ)‐aromatic systems and of the individual π‐donors and ‐acceptors was examined. The El spectra exhibited the molecular ions of both the donor and the acceptor of each complex. The molecular ion of the π‐donor was observed in pLSIMS using m‐nitrobenzyl alcohol (NBA) if its oxidation potential is lower than 1.2 V, but when the oxidation potential is higher than 1.9 V, no molecular ion was detected. On the other hand, nLSIMS exhibited the molecular ion of TCNQ in all cases. Participation of an excited state of NBA in the ionization process is suggested.
Mass spectrometry of thio analogues of pyrimidine bases: Correlation of the intensities of the M+˙ and the [M – ˙SH]+ ions of 2‐alkylthiouracils
Authors: Wyrzykiewicz E. , Bartkowiak G. 
Published: May 2005

AbstractThe mass spectral fragmentations of eight 2‐alkylthiouracils with C10, C12, C16 and C18 in the alkylthio group were investigated. Fragmentation pathways are proposed on the basis of accurate mass and matastable transition measurements. The correlation between the intensities of the M+˙ and [M ‐ ˙SH]+ ions of 36 2‐alkylthiouracils is discussed. The data obtained create the basis for distinguishing structural isomers.
Ion–molecule reactions of [ketene]+˙ as a diagnostic probe for distinguishing isomeric alkenes, alkynes and dienes: A study of the C4H8 and C5H8 isomeric hydrocarbons
Authors: Dass Chhabil , Stout Charles B. 
Published: May 2005

AbstractThe gas‐phase ion–molecular reactions of [ketene]+˙ with a number of isomeric alkenes, alkynes and dienes were studied by using tandem mass spectrometry. Ketene was reacted with C4H8 (but‐1‐ and −2‐ene and 2‐methylpropene) and C5H8 unsaturated hydrocarbons (isoprene, penta‐1,3‐ and −1,4‐diene, pent‐1‐ and −2‐yne, cyclopentene and methylenecyclobutane) in a high‐pressure chemical ionization source of a tandem mass spectrometer. The collisionally stabilized ion–molecule adducts were analyzed by use of collisionally activated dissociation (CAD) spectra. The three C4H8 alkenes were distinguishable on the basis of the distinct CAD spectra of their adducts with ketene. Similarly, the CAD data for the corresponding adducts derived from the C5H8 hydrocarbons point to different structures for the C5H8 compounds.
[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines
Authors: Stemmler Elizabeth A. 
Published: May 2005

AbstractThe N2 negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [M + 11]−˙. This addition is also observed in the N2 positive chemical ionization (PCI) mass spectra. An ion at [M – 15]− is found in the NICI spectra of aminoaromatics such as aniline, 1‐ and 2‐aminonaphthalene and 1‐ and 2‐aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [M + 11]−˙, [M – 15]−˙ and [M + 11]+˙ ions result from the ionization of analytes altered by surface‐assisted reactions. Experiments with 15N2, [15N] aniline, [2,3,4,5,6‐2H5] aniline and [13C6] aniline show that the [M + 11]−˙ ion corresponds to [M + N – 3H]−˙. The added nitrogen originates from the N2 buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N2 PCI mass spectrum of aniline suggest that the neutral product of the surface‐assisted reaction is 1,4‐dicyanobuta‐1,3‐diene. Experiments with diamino‐substituted aromatics show analogous reactions resulting in the formation of [M – 4H]−˙ ions for aromatics with ortho‐amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.
Collision‐induced decompositions of [M – H]− and [M + Li]+ ions from fast atom bombardment of dinucleoside phenylphosphonates
Authors: Madhusudanan K. P. , Katti S. B. , Hashmi S. A. N. 
Published: May 2005

AbstractThe collision‐induced decompositions of the [M – H]− and [M + Li]+ ions of a few dinucleoside phenylphosphonates were studied using fast atom bombardment and linked scanning at constant B/E. Deprotonation takes place on the base or sugar moieties. The [M – H]− ion decomposes mainly by cleavage on either side of the phosphonate linkage, leading to the formation of mononucleotide fragment ions and also by cleavage of the basesugar bond. Rupture of the 3′‐phosphonate bond is preferred. Unlike the normal charged nucleotides, these neutral nucleotides do not eliminate a neutral base from the [M – H]− ion. However, the mononucleotide fragment ions which can have the charge on the phosphorus oxygen eliminate neutral bases by charge‐remote fragmentation. The 4,4′‐dimethoxytrityl (DMT)‐protected nucleotides show the additional fragmentation of loss of DMT. Li+ attachment can occur at several sites in the molecule. As observed for the [M – H]− ion, the major cleavage occurs on either side of the phosphonate bond in the fully deprotected nucleotides, cleavage of the ester bond on C(3′) being preferred. Cleavage of the 5′‐phosphonate bond is not observed in the DMT‐protected nucleotides. Many of the fragmentations observed can be explained as arising from charge‐remote reactions.
An epoxy resin‐elastomer system for filament winding
Authors: Rinde J. A. , Mones E. T. , Moore R. L. , Newey H. A. 
Published: May 2005

AbstractTests characterizing an epoxy system that contains 5 percent rubber and is suitable for wet‐filament winding are described. The resin is a bisphenol‐A rubberized epoxy diluted with an aliphatic diglycidyl ether and cured with an aromatic amine. The viscosity and pot life were measured and the progress of cure was monitored so an optimum cure could be chosen. Mechanical tests were performed on the cured resin. The low viscosity (0.95 Pa's) and long pot life (29.3 h) make for ease of processing. A cure cycle of 1.5h at 90°C plus 2 h at 130°C gives a cured resin having a glass transition temperature of 104°C. The heat‐cured material has a tensile strength of 76.1 MPa and a modulus of 2.43 GPa. Kevlar 49 composites of 60‐, 65‐, and 70‐volume‐percent fiber were prepared and tested. Results are presented and compared to two other Kevlar 49/epoxy composites.
Interfacial interactions and the properties of filled polymers: I. Dynamic‐mechanical responses
Authors: Boluk M. Y. , Schreiber H. P. 
Published: May 2005

AbstractThe dynamic mechanical responses of rutile‐filled, chlorinated polyethylene (CPE) were studied as a function of temperature, of filler loading, and of filler surface condition. An objective was to establish the influence of matrix‐filler interactions on mechanical properties. Necessary information on potential interactions between matrix and filler was obtained from inverse gas chromatographic data, in the form of an acid‐base interaction parameter, Ω. The damping peak in filled CPE compounds was depressed by the pigment, as called for by theoretical models. The magnitude of the effect exceeded expectations, however, and clearly depended on the strength of interfacial interactions. These were consistent with the acid‐base ranking of CPE and the various rutiles, as given by Ω. It has been postulated that in the presence of acid‐base interactions, an immobilized layer of polymer in the vicinity of solid particles increases the effective particle dimension, thereby accounting for the observed variations in relative damping. Additional effects of matrix‐filler interaction were noted in the variation of storage moduli with loading and temperature. Again, the effects tend to be more pronounced when significant specific interactions between matrix and solid are operative. These observations point to the inadequacy of existing models as interpretative bases for dynamic mechanical properties in systems with significant specifie interactions among their components.
Electrical properties of exfoliated‐graphite filled polyethylene composites
Authors: Wang Y. S. , O'Gurkis M. A. , Lindt J. T. 
Published: May 2005

AbstractAn experimental study has been carried out to prepare and characterize high density polyethylene‐based composites filled with exfoliated graphite particles of varied aspect ratios. It has been demonstrated that the dielectric constant of the composite correlates with the in situ volumetric fraction of the compressible exfoliated filler particles. The dielectric constant has been found to range from 2.23 to 125. The minimum electrical resistivity of the composites obtained was 0.1 Ω.cm at a graphite content of 40 percent by volume. The use of these composites is intended in electromagnetic radiation interference (EMI) shielding.