bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometry of the triethylsilyl, tri‐n‐propylsilyl and tri‐n‐butylsilyl derivatives of some alcohols, steroids and cannabinoids
Authors: Harvey D. J. 
Published: May 2005

AbstractThe 25 eV mass spectra of the trialkylsilyl (R = Et, Pr, Bu) derivatives of several alcohols, steroids and cannabinoids are compared with those of the corresponding trimethylsilyl (TMS) derivatives. Abundant ions produced by elimination of one of the alkyl groups characterize most of the spectra. Although the presence of such ions is advantageous in certain cases, such as for single ion monitoring studies, the spectra usually contain fewer ions of diagnostic use than the spectra of corresponding TMS derivatives. Successive elimination of CnH2n fragments is also a feature of these spectra.
Studies in mass spectrometry. IV—Fragmentation of aryltriflates. Substituent effects on [ArO]+ ion abundances: Looking for a best suited electron energy in the steady state approach. Experimental evidence for the ‘through bond’ stabilization of aryl cations by meta electron donor Substituents
Authors: Derocque Jean‐Luc , Jochem Martin 
Published: May 2005

AbstractThe fragmentation patterns of 24 substituted phenyltrifluoromethanesulfonates has been determined by exact mass and metastable transition measurements. The influence of the ring substituent(s) on the abundance of the [ArO]+ ions has been investigated at low energies and a new standard parameter for plotting against Hammett's ó constants is proposed. The direct loss of CF3SO3 from the molecular ion of 3,5‐(diisopropyl)‐phenyl‐, 3,5‐(dicyclopropyl)phenyl‐ and 3,5‐di(α‐methylcyclopropyl)‐phenyl‐methanesulfonate, and further observations on the fragmentation processes of these compounds are consistent with M.O. calculations on the ‘through bond’ stabilization of the [Ar]+ σ state by meta electron donor substituents.
Spectrométrie de Masse de Benzylidène—Acétals d'Hexopyranosides
Authors: Bosso Claude , Defaye Jacques , Gadelle Andrée , Ulrich Jacques 
Published: May 2005

AbstractLa fragmentation en impact électronique est rapportée pour 46 benzylidéne‐acétals d'hexopyranosides, appartenant aux séries allo, altro, galacto, gluco, gulo et manno ainsi que pour quelques produits de leur oxydation partielle. Indépendamment de l'ion moléculaire toujours présent et fréquemment partie d'un triplet magnified image ainsi que la rupture bien connu C‐1C‐2, C‐4C‐5 et (Ph)CHO(C‐4), on retrouvé généralement deux types de ruptures complémentaires (C‐1C‐2, C‐3C‐4; C‐1O‐5, C‐2C‐3, dont l'intensité varie selon la substitution ou selon la fonctionnalisation de la molécule. Ces fragmentations permettent dans la majorité des cas l'assignation des substitutions sur des systémes du type 1,3,6‐trioxa‐bicyclo[4.4.0]décane. Les limitations de cette méthode sont discutées.
Spectrométrie de Masse d'Hétérocycles. VIII—Edude de Dérivés du Dioxasilolanne‐1,3,2
Authors: Lageot C. , Guillemonat A. 
Published: May 2005

AbstractL'étude de spectres de masse de dioxasilolannes‐1,3,2 montre que la présence de deux atomes d'oxygène simplifie notablement le nombre de fragmentations du cycle. Les principaux mécanismes conduisent à la formation d'ion ‘silylénoïdes’ à des ruptures en α et β du silicium ainsi qu'à des migrations d'hydrogène.
Electron impact induced alkyl‐group fragmentation on the acridine nucleus
Authors: Acheson R. M. , Aplin R. T. , Bolton R. G. 
Published: May 2005

AbstractThe fragmentation of simple alkyl acridines closely resembles that of the analogous quinoline derivatives. Interaction between the heteroatom and a 4‐alkyl substituent dramatically influences the fragmentation pattern with resultant γ‐cleavage or rearrangement to the heteroatom and corresponding elimination of an alkene fragment. The fragmentation of the 9‐chloroalkylacridines closely resembles that of the acridines with the loss of the clorine atom superposed on the alkylacridine fragmentation. Redistribution of the centre of apparent charge localization occurs for the acridones with a tendency for interaction with the 9‐position.
Conformational effects in the chemical ionization spectra of derivatives of isomeric 2,3‐dimethyl‐1,4‐cyclopentanediols
Authors: Claeys M. , Van Haver D. 
Published: May 2005

AbstractThe chemical ionization mass spectra of the trimethylsilyl and methylboronate derivatives of some isomeric 2,3‐dimethyl‐1,4‐cyclopentanediols have been determinded using methane and isobutane as reagent gases. The degree of loss of TMSOH or CH3B(OH)2 appears to be strongly dependent upon the stereochemistry of the 2,3‐dimethyl‐1,4‐cyclopentanediol moiety and permits differentiation between the structural isomers. The results obtained from the chemical ionization (isobutane) spectra of the methylboronates are in excellent agreement with those derived from infrared data.
Chemical ionization mass spectrometry: A method of estimating reagent gas pressure in the ion source based on kinetic data
Authors: Hancock Richard A. , Walder Raymond , Weigel Helmut 
Published: May 2005

AbstractConsequential upon determinations of kinetic rate constants of ion/molecule reactions in methane and isobutane, simple equations are presented from which the pressures of methane and isobutane in the ion source of chemical ionization mass spectrometers can be calculated. Account is taken of the design of the ion source and it is only necessary to determine two ion currents for each gas.
Charge distribution between formally identical fragments: The retro Diels‐Alder cleavage
Authors: Turecček F. , Hanuš V. 
Published: May 2005

AbstractThe electron impact induced retro Diels‐Alder cleavage of 4‐vinylcyclohexene, 1,4‐dimethyl‐4‐vinylcyclo‐hexene, limonene, dicyclopentadiene and dicyclohexadiene has been investigated using deuterium labelled analogues. With limonene, dicylopentadiene and dicyclohexadiene the charged diene fragments are produced with the same probability from both subunits of the molecular ion. With 4‐vinylcyclohexene and 1,4‐dimethyl‐4‐vinylcyclohexene, diene fragments containing the former vinyl group are charged preferentially. This small asymmetry of charge distribution was found to be independent of the ionizing energy. A new, qualitative rationalization is suggested to account for the unsymmetrical charge distribution in 4‐vinylcyclohexene and 1,4‐dimethyl‐4‐vinylcyclohexene. Metastable spectra and hydrogen scrambling are discussed.
Charge distribution between formally identical fragments: The McLafferty rearrangement
Authors: Tureček F. , Hanuš V. 
Published: May 2005

AbstractThe McLafferty rearrangement for 2,5‐diphenyl‐1‐hexene and its deuterium labelled analogues has been investigated. The α‐methylstyrene fragments originating from different parts of the molecular ion retain the charge with equal probability and afford identical metastable spectra. The geometry of the transition state is discussed.
Ion cyclotron resonance studies of alkylsilyl ions: V—The reactions of alcohols and ethers with the allyldimethylsilyl cation
Authors: Blair Ian A. , Trenerry V. Craige , Bowie John H. 
Published: May 2005

AbstractDiallyldimethylsilane provides a source of the allyldimethylsilyl cation in the ion cyclotron resonance spectrometer; reaction of this cation with alcohols (ROH) produces adducts which decompose by loss of C3H6 to yield the ion \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm Me}_2 \mathop {\rm S}\limits^{\rm + } {\rm i} - {\rm OR}} \right] $\end{document}. This elimination is thought to occur by a 1,5‐hydrogen shift, together with either stepwise or concerted silicon‐carbon bond cleavage. The corresponding aducts from ethers ROR1 (R1⩾R, R1⩾Et) first lose (R1H˙) and then undergo the elimination described above.
Mass spectra of some platinum clusters. Electron impact and field desorption studies of Ptn(CO)m(PR3)p complexes
Authors: Würminghausen Th. , Reinecke H. J. , Braunstein Pierre 
Published: May 2005

AbstractThe compounds Pt3(CO)3[P(C6H5)3]4 molecular weight 1717, Pt4(CO)5[P(C6H5)3]4 molecular weight 1968 and Pt5(CO)6[P(C2H5)3]4 molecular weight 1615 are thermally labile and are slowly solvolysed by tetrahydrofuran and acetone. They cannot be analysed by means of electron impact. Field desorption, however, shows the molecular ion and [MxCO]+˙ peaks.
High pressure mass spectrometry of some liquid chromatographic mass spectrometric reagents
Authors: Yinon Jehuda , Cohen Aviad 
Published: May 2005

AbstractPressure dependence of several reversed phase liquid chromatographic solvents, including methanol, acetonitrile and mixtures of methanol: water and acetonitrile: water has been investigated. Typical ions, [MH]+, [2M+H]+ and [3M+H]+, were recorded as function of source pressure and as a function of the amount of water in the mixture. Ion formation processes in methanol: water and acetonitrile: water are discussed. The influence of liquid chromatographic mass spectrometric solvent pressure on the mass spectra of samples has been demonstrated on an amino acid sample.
A 15N labelling, FD and FAB study of ammonia loss from protonated arginine molecules
Authors: Zwinselman J. J. , Nibbering N. M. M. , van der Greef J. , De Brauw M. C. Ten Noever 
Published: May 2005

AbstractThe positive ion field desorption (FD) spectrum of arginine taken at the best anode temperature only contains a peak due to [M+H]+ ions. At higher emitter temperatures a considerable amount of fragmentation is induced and the [M+HNH3]+ ions become most abundant. Specific 15N labelling reveals that the eliminated ammonia molecule, exclusively, contains one of the terminal nitrogen atoms of the guanidyl group. This also applies to the ammonia loss from metastably decomposing [M+H]+ ions. The positive ion fast atom bombardment (FAB) spectrum shows more fragmentation than the FD spectrum. In contrast with the FD results, the [M+H]+ ions generated upon FAB with ion lifetimes <10−6 s eliminate both ammonia containing one of the terminal nitrogen atoms of the guanidyl group and ammonia containing the α‐amino group in the ratio of 1.35, as found by 15N labelling. The metastably decomposing [M+H]+ ions, however, eliminate only the former ammonia molecule. In the negative ion FD and FAB spectra no other peak than that corresponding to the [MH]− ion is observed. Some attention has been paid to the thermal degradation of arginine on the basis of a few Curie‐point pyrolysis experiments.
The dynamical theory of energy partition. Loss of a hydrogen atom from the hydroxymethylene radical cation
Authors: Donchi Kevin F. , Derrick Peter J. 
Published: May 2005

AbstractThe translational energy releases accompanying fromation of H˙ and [CHO]+ from [CHOH]+˙, H˙ and [CDO]+ from [CDOH]+˙, D˙ and [CHO]+ from [CHOD]+˙ and D˙ and [CDO]+ from [CDOD]+˙ have been calculated from the widths at half‐height of the respective metastable peaks. The energy releases for [CHOD]+˙ and [CDOD]+˙ are similar to each other in magnitude, but are both significantly larger than those for [CHOH]+˙ and [CDOH]+˙. These differences are discussed in terms of the dynamical theory of energy partition. The larger energy releases for decompositions giving D˙ are attributed to larger proportions of the kinetic energy being associated with the departing D˙ in the transition states, as compared to H˙ in the transition states for the decompositions yielding H˙.
A mass spectrometry/mass spectrometry investigation of the nature of [C10H10]+˙, [C9H7]+ and [C10H8]+˙ gas phase ions
Authors: Dass Chhabil , Gross M. L. 
Published: May 2005

AbstractAdditional evidence for the rearrangement of the 1‐ and 3‐phenylcyclobutene radical cations, their corresponding ring‐opened 1,3‐butadiene ions and 1,2‐dihydronaphthalene radical cations to methylindenetype ions has been obtained for the decomposing ions by mass analysed ion kinetic energy spectroscopy (MIKES). The nature of the [C9H7]+ and [C10H8]+˙ daughter ions arising from the electron ionization induced fragmentation of these [C10H10]+˙ precursors has been investigated by collisionally activated dissociation (CAD), collisional ionization and ion kinetic energy spectroscopy. The [C9H7]+ produced from the various C10H10 hydrocarbons are of identical structure or an identical mixture of interconverting structures. These ions are similar in nature to the [C9H7]+ generated from indene by low energy electron ionization. The [C10H8]+˙ ions also possess a common structure, which is presumably that of the maphthalene radical cation.
Quantitative determination of compounds in mixtures by B2E=constant linked scans
Authors: Walther Hansjörg , Schlunegger Urs Peter , Friedli Felix 
Published: May 2005

AbstractThe B2E = constant linked scan is shown to be an excellent tool for quantifications with reversed geometry mass spectrometers. Deuterium‐labelled analogues may be used as internal standards, thus providing very simple clean‐up procedures. The principle is demonstrated with the example of chloro‐substituted benzoic acid methyl esters. Possible interferences arising from isotope peaks are discussed. The method is applied to the quantification of caffeine in beverages.
Formation of ketone ions upon the loss of CH2O from ionized esters
Authors: Lin Thomas , Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractUnimolecular and collision‐induced decompositions of the products of CH2O loss from propyl propanoate and butyl butanoate demostrate that the respective products are the 3‐pentanone and 4‐heptanone ions.
The dichotomy of methyl loss from 2‐methylalkane molecular ions
Authors: Wolkoff Peder , Holmes John L. , Lossing F. P. 
Published: May 2005

AbstractThe kinetic energy release for methyl loss from the molecular ion of 2‐methylpentane increases c. twofold over the time‐range 1–15 μs. This result from a mixture of secondary and tertiary pentyl cations. The appearance energy showed that at threshold (and long times) only tertiary ions are formed. The molecular ion of 2‐methylhexane produces tertiary hexyl ions by loss of methyl at threshold, but in the μs time‐frame only secondary hexyl ions appear to be formed, because the kinetic energy release is small and independent of the observation time.
Chemical ionization of ethylene dibromide with ammonia gas
Authors: Cairns Thomas , Siegmund Emil G. 
Published: May 2005

AbstractUnder ammonia chemical ionization conditions, a fragment ion of ethylene dibromide undergoes a nucleophilic substitution reaction which is demostrated to be highly pressure‐dependent upon the reagent gas concentration. This reaction is strongly influenced by the stability of the intermediate carbonium ion and the ability of the substituted product ion to be stabilized by intramolecular hydrogen bonding.
Solvent‐derived metal oxides in electrospray mass spectrometry of metal salt solutions
Authors: Cheng Z. L. , Siu K. W. M. , Guevremont R. , Berman S. S. 
Published: May 2005

AbstractThe electrospray mass spectra of MX2and MX3salts (where X is typically halide or nitrate) in protic and aprotic solvents, and solvent mixtures were examined. Comparisons of species responses with equilibrium aqueous solution concentrations were made. For MX2salts, a good correlation between MOH+ response and MOH+ solution concentration was observed under conditions where the collision energy was nominally zero. Cu(II) is easily reduced in acetonitrile to Cu(I); Cu(I) was the principal species observed in the electrospray mass spectrum of Cu(II) in acetonitrile whereas Cu(II) was the principal species observed in that of Cu(II) in dimethyl sulphoxide. Gas‐phase reactions between solvated clusters produced by electrospray and a second solvent vapour were examined. M3+clusters were the principal ions observed when an aqueous solution of MX3was sprayed in the presence of aprotic solvent vapours.
Formation of· CH2CH2CO + and C2H6+· in the metastable decompositions of ionized ethyl formate
Authors: Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractThe products of the metastable decompositions of ionized ethyl formate (a) are characterized. The loss of water from a produces ·CH2CH2CO+, a rarely reported product. Loss of H appears to produce CH2=CHC(OH). The third decomposition is an unusual formation of C2H. This work demonstrates that a previous supposition that isomerization to different intermediates is involved in the losses of ethene and of water from a is correct.
Analysis of amino acid mixtures by plasma desorption mass spectrometry
Authors: Hoppilliard Yannik , Mauriac Christine 
Published: May 2005

AbstractPlasma desorption mass spectrometry (PDMS) was investigated as a means of analysing mixtures of three, four and five amino acids in both positive‐ and negative‐ion modes. Fifteen mixtures were tested; each mixture contained equimolar amounts of selected amino acids. The PD mass spectra exhibited MH+ and [M – H]− molecular ions for all the aminoacids with different desorption–ionization yields. The spectra were more easily interpreted in the negative‐ than the positive‐ion mode. The desorption order of the amino acids was progressively established by comparing the molecular ion desorption–ionization yields for each mixture. This desorption order was well correlated in both the positive‐ and negation‐ion modes with the acid–base thermodynamic data for the amino acids in the gas phase. This observation gives some insight into the desorption–ionization mechanisms under PDMS conditions.
Predicting mold flow for unsaturated polyester resin sheet molding compounds
Authors: Silva‐Nieto R. J. , Fisher B. C. , Birley A. W. 
Published: May 2005

AbstractImproved products can be obtained from sheet molding compounds (SMC) if due regard is given to the geometry of the molding charge relative to the product shape. For example, it is possible to position designed charge shapes in the mold to produce moldings without weld‐lines and without substantially altering the initial fiber orientation of the SMC matrix. This paper describes theoretical and experimental work which has developed a charge shape calculation procedure for molding two‐dimensional SMC components weld‐line free without substantially altering the SMC‐matrix glass fiber orientation. The two main parts of the work are; (i) The theoretical development of a charge shape calculation procedure for molding symmetrical and unsymmetrical plaques. This includes a mathematical description of the compression flow process, which is used to determine flow front development from mold‐cavity pressure and velocity distributions. (ii) The results of experimental work which test the mathematical description of the compression flow process, and charge shape calculation procedure. These results include mold pressure measurements from an instrumented mold, fiber distribution and orientation measurements, and SMC‐material tensile strength properties.
Impact fracture of glass‐flake reinforced polypropylene
Authors: Vu‐Khanh T. , Fisa B. 
Published: May 2005

AbstractThe impact resistance of glass‐flake reinforced polypropylene was analyzed over a wide range of loading rates and glass‐flake concentrations. It was found that the dynamic fracture toughness, Kd, of the composite is strongly rate‐dependent. When impact velocity is increased, Kd first decreases, attains a minimum value, and then increases with impact speed. The increase in Kd with loading rate is attributed to the blunting effect at the crack tip, induced by adiabatic heating. The addition of glass flakes substantially increases the dynamic fracture toughness of polypropylene. The increase in Kd with glass‐flake content is also more pronounced when the loading rate is increased. The blunting effect was found to increase with glass‐flake concentration up to 30 percent by weight, leading to a stronger increase in Kd with glass‐flake content from 0 to 30 percent. Above 30 percent, the blunting effect diminishes with concentration.
Mechanical performance of various nylon 6 composites formed by in‐situ polymerization of caprolactam
Authors: Goettler Lloyd A. , Neff Willard J. 
Published: May 2005

AbstractThis paper describes the fabrication and mechanical characterization of composites made by incorporating various types of glass as bead or fiber into an activated caprolactam melt, which is then caused to anionically polymerize to a nylon 6 resin. Three types of composites are discussed and compared under separate headings: glass bead filled, sheet reinforced with a random fiberglass mat, and sheet reinforced with a unidirectional fiberglass mat that is studied under transverse loading to emphasize the role of the nylon 6 matrix resin. High molecular weight, better wet‐out and adhesion to the reinforcement, and cold drawing of the polycaprolactam resin lead to homogeneous cavitation that increases composite toughness in comparison to epoxy or other nylon matrices of equivalent stiffness.
Unique orientation of lamellae in film processed poly (phenylene sulfide)
Authors: Huo Peter Pengtao , Chung Jerry Sengshiu , Cebe Peggy 
Published: May 2005

AbstractThe morphology of poly(phenylene sulfide), PPS, obtained as processed film has been studied using wide angle X‐ray scattering (WAXS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). A unique morphology has been identified in the original film. The spherulites are very small in size and possess a cylindrical symmetry with their lamellae oriented on the edge. In these processed PPS films, the a‐axis of the lattice is preferentially aligned perpendicular to the film plane, while the b and c axes are predominantly in the film plane. In the PPS isothermally crystallized from the melted, original film, there is no such preferential orientation. Thermal analysis of the original and melt crystal‐lized PPS shows that while the degree of crystallinity is about the same, the nature of the amorphous phase in the two materials is different. In the original film, we did not observe a heat capacity increment at a glass transition temperature by DSC, indicating that all of the amorphous phase belongs to the category of rigid amorphous phase. In the melt crystallized PPS, a distinct glass transition was seen, though only a portion of the amorphous phase becomes mobile at Tg. The differences in orientation and mobility of the amorphous phase in the original film compared to melt crystallized PPS are explained by the different thermal processing procedures used for the two materials.
Crystallization behavior and effect of thermal treatment on fracture performance of glass flake reinforced polypropylene
Authors: Denault J. , Vu‐Khanh T. 
Published: May 2005

AbstractIn this work, the role of the interface and matrix morphology in determining the fracture behavior of glass flake reinforced polypropylene is investigated. Differential scanning calorimetric analysis shows that silane coupling agent modifies the crystallization behavior of the polypropylene matrix. Silane treated glass flakes prepared by dry blending are found to induce nucleation and decrease the rate of development of the crystalline entities during the crystallization process. This effect is attributed to the physisorbed layer of silane on the glass flakes. The effect of matrix morphology on the fracture performance is analyzed by fracture mechanics. An increase in matrix crystallinity in pure polypropylene and in glass flake/polypropylene composites leads to a reduction in the maximum crack growth resistance. The lower ductility of a more crystalline matrix results in a reduction of the energy dissipated in the matrix stretching and, therefore, a concomitant decrease in the fracture energy. Although the effect of matrix morphology seemed to be important in the case of pure polypropylene and untreated glass flake polypropylene composites, this effect is found to be negligible for the silane treated composites. Nevertheless, microscopic observation of the fracture surfaces of silane treated composites also revealed a reduction in the ductility of the matrix in highly crystalline samples. An improvement in the matrix‐filler interface seems to inhibit the effect of matrix morphology on the fracture behavior of glass flake/polypropylene composites.