bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoionization studies of substituted trimethylamines
Authors: Loguinov Yuri , Takhistov Vyatcheslav V. , Vatlina Lidya P. 
Published: May 2005

AbstractIonization energies of substituted trimethylamines (CH3)2NCH2X, together with appearance energies of [M − X]+ ions, have been measured by the photoionization technique. The heats of formation for the following radicals have been derived (in kJ mol−1): C2H3˙ (+ 314), Ph. (+ 347), p‐CH3C6H4˙ (+ 326), HC2˙ (+ 494), (CH3)2NĊH2 (+ 134), NC˙ (+ 452), CF3. (− 435), (CH3)3Si˙ (+ 54.5). The heats of formation obtained for [(CH3)2NCH2]+ (+ 649) and (CH3)3Si+ (+ 610) lead to ionization energies of 5.35 eV for (CH3)2NĊH2 and 5.75 eV for (CH3)3Si˙.
On the heat of formation of [C6H4]+˙
Authors: Maccoll Allan , Mathur Deepak 
Published: May 2005

AbstractThe appearance energy of the [C6H4]+˙ ion from benzonitrile has been measured, using an electron monochromator. The value observed at onset, 12.54±0.03 eV, leads to a heat of formation of 1304±3 kJ mol−1. Possible reasons for widely divergent values reported previously are proposed.
The relative abundances of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{R}}_{\rm{1}} \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{O}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{R}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{O}} $\end{document} from R1R2CO, and the low voltage mass spectra of some methyl ketones
Authors: Maccoll Allan 
Published: May 2005

AbstractThe relative abundances of the ions formed by the loss of the larger and the smaller radical from RCOCH3 are interpreted in terms of the appearance energies of these fragments, calculated from the heats of formation of the relevant species. The appearance energies for the McLafferty rearrangement are also reported, as are the low voltage, low temperature mass spectra of propanone, butanone, pentan‐2‐one, pentan‐3‐one, 3‐methylbutan‐2‐one and 3,3′dimethylbutan‐2‐one.
Negative chemical ionization mass spectrometry of explosives
Authors: Bouma Willem J. , Jennings Keith R. 
Published: May 2005

AbstractThe negative chemical ionization mass spectra of nitrobenzene, ethylene glycol dinitrate and nitroglycerine have been obtained using various reagent ions. For nitrobenzene, [OH]− gives the [M − H]−, together with [M]−˙ ions formed by electron capture, but other reagent ions gave relatively low intensity adduct peaks. Ethylene glycol dinitrate and nitroglycerine gave abundant [M + X]− ions (X = NO2, NO3, Cl, Br, I), together with ions arising from the thermal decomposition of the samples in the heated inlet system. The rate of anion attachment to these compounds is much greater than that to related compounds having only one functional group, and it is suggested that this is due to the participation of the adjacent groups in the bonding between the substrate and anion.
Stereochemical effects in electron impact mass spectra of cis‐trans isomeric 1,2,4,5‐tetramethylcyclohexanes
Authors: Herzschuh R. , Mann G. , Werner H. , Mende Elke 
Published: May 2005

AbstractThe mass spectrometric fragmentation of the five cis‐trans isomeric 1,2,4,5‐tetramethylcyclohexanes is influenced by their configuration. The thermochemically stable isomers show a higher abundance of the [MCH3]+ ions and a lower abundance of the [MC2H5]+ ions than the strained isomers. The [MCH3]+/[MC2H5]+ intensity ratio correlates with the enthalpy difference ΔHisom and with the mean number of gauche arrangements ZgI of the stereoisomers.
Electron impact mass spectra of penitrem A, some derivatives and its analogues
Authors: Fellows Patricia A. , Kyriakidis N. , Mantle P. G. , Waight E. S. 
Published: May 2005

AbstractThe mass spectra of penitrems A‐E and some derivatives of penitrem A have been measured. Fragmentation pathways have been confirmed by use of the linked scan (B/E) technique and are consistent with the formulation of the compounds as analogues of paspalinine.
Kinetic and thermodynamic effects on intramolecular aromatic substitution in meta and para substituted benzalacetones
Authors: Schaldach Bernd , Grotemeyer Barbara , Grotemeyer Jürgen , Grützmacher Hans‐Friedrich 
Published: May 2005

Abstractmeta and para substituted benzalacetones lose the substituents after electron impact in a multi‐step intramolecular aromatic substitution. The differences in the relative abundances of the benzopyrylium ions thus formed are not determined by the activation energies for the substituent losses but depend on a delicate balance between the thermodynamic stability of the intermediates involved and the rates of several H‐shifts within the intermediates (kinetic stability). The consequences for the analytical utility of intramolecular aromatic substitution are discussed briefly.
Unimolecular ethyl loss from metastable 13C labelled [C5H10O]+˙ ions with the oxygen on the middle carbon: An example for incomplete energy randomization?
Authors: Depke Gisbert , Schwarz Helmut 
Published: May 2005

AbstractThe investigation of 13C labelled 3‐pentanone cation radicals generated via isomerization of the corresponding [C5H10O]+˙ enol cation radicals demonstrates unambiguously that, in contrast to previous investigations, unimolecular ethyl loss from 13C labelled 3‐pentanone cation radicals is preceded by complete energy randomization.
The loss of ortho halogeno substituents from substituted thiobenzamide ions
Authors: Grützmacher Hans‐Fr. 
Published: May 2005

AbstractThe loss of ortho substituents (CH3, Cl, Br, I) from molecular ions of substituted thiobenzamides has been investigated by determination of the critical energy and kinetic energy released during this process to obtain some further insight into the corresponding reaction of N,N‐dimethylthiobenzamide ions. In contrast to the latter compounds the ortho methyl substituent is not eliminated from the molecular ions of o‐methylthiobenzamide, but the loss of ortho halogeno substituents occurs with identical reaction characteristics in both series of compounds. It is concluded that the loss of halogeno substituents from molecular ions in both series corresponds to a direct substitution reaction via a 4‐membered transition state.
A new linked scan for reversed geometry mass spectrometers
Authors: Boyd R. K. , Porter C. J. , Beynon J. H. 
Published: May 2005

AbstractA new linked scan is described by which fragmentations occurring in the second field free region of a two sector instrument can be monitored. The scan can be used only if the first stage allows selection of ions according to their masses. The magnetic sector and electric sector are scanned in unison so that the product B2E is maintained constant. A spectrum of all parents of a preselected daughter ion is obtained and the resolution depends only on the mass resolution of the magnetic sector.
Cationization of organic molecules under pulsed laser induced ion generation
Authors: Schueler B. , Feigl P. , Krueger F. R. , Hillenkamp F. 
Published: May 2005

AbstractMass spectra of various involatile organic compounds, obtained by surface analysis with a laser microprobe mass analyser are reported. Metal‐cationized quasimolecular ions of adenine, adenosine, 5‐adenylic acid and sucrose supported on metal foils were observed. Metal attachment can also be detected from mixtures of metal salts and the organic compounds. Silver‐cationized sugar molecules and atomic silver ions solvated by (H2O)x and (NH3)x (x = 1,2) have been found. The mass spectra are compared with those obtained by secondary ion mass spectrometry and similar techniques, discussing the processes of ion generation involved.
The mass spectra of some silver salts
Authors: Roberts Gerald D. , Edward White V 
Published: May 2005

AbstractFifteen of twenty‐four silver(I) carboxylates examined give useful electron impact mass spectra. The compounds vaporize at moderate temperatures, apparently mainly as dimer with traces of higher oligomer in only a few cases. The molecular ion for the dimer is generally weak or absent, with the most abundant silver containing ion being [Ag2(O2CR)]+ in most cases. Metastable defocusing and deuterium labeling experiments on silver acetate have established some of the fragmentation pathways. The reported loss of carbon dioxide from perfluorocarboxylates to give intense peaks for organosilver ions was not observed in this study. Attempts to obtain spectra on the silver salts of organic materials other than carboxylic acids were successful in several cases. Silver trifluoromethanesulfonate, although much less volatile, gives a spectrum and fragmentation very much like the carboxylates, whereas silver trifluoromethanethiolate gives a complex spectrum which suggests tetramer as a major gas phase species. Of three compounds examined which have silver to nitrogen bonding only silver(II) phthalocyanine is sufficiently volatile to give a spectrum without decomposition. The field desorption spectra of the four compounds examined all show the ions AgnXn − 1 for X=acetate (n=1 − 6), X=p‐chlorobenzoate (n=1 − 4), X=methanesulfonate (n=1 − 7) and X=p‐toluenesulfonate (n=1 − 5).
Electron impact and field desorption mass spectrometry of some macrocyclic‐acyclic polyether‐ester compounds
Authors: Auricchio Sergio , de Pava Orso Vajna , Traldi Pietro , Griffini Alberto 
Published: May 2005

AbstractThe electron impact mass spectrometric behaviour of a series of macrocyclic‐acyclic polyether‐ester compounds containing an isoxazole, benzene or pyridine ring is discussed in detail with the aid of exact mass measurements and metastable ions (linked scans B/E and B2/E). The nature of unusual [M+H]+ species, present in the crown moieties only, is elucidated by means of low electron energy measurements and labelling experiments. The field desorption spectra show only intense peaks corresponding to [M+H]+ species and rule out the presence of dimeric moieties.
Unusual mass spectrometric fragmentation of N,N′‐diethyl‐N,N′‐diphenylurea
Authors: Hanuš V. , Horák Z. , Tolman V. 
Published: May 2005

AbstractThe electron impact mass spectrum of N,N′‐diethyl‐N,N′‐diphenylurea contains the ion m/z 164 which is of low abundance at normal energy of ionizing electrons but prominent at 15‐20eV. The mechanism of its formation has been revealed by means of labelled compounds. It is rationalized in terms of an unusual formation of styrene lost as a neutral molecule.
The chemical ionization mass spectrometry of RDX
Authors: Zitrin Shmuel 
Published: May 2005

AbstractThe fragmentation pathways of RDX in chemical ionization mass spectrometry have been rationalized, using data from different reagent gases, including CD4 and iso‐C4D10. The dependence of spectra taken with different gases on the acid strength of the reactant ions in the gases is accounted for.
Quantitative 252Cf plasma desorption mass spectrometry for pharmaceuticals: A new approach to coupling liquid chromatography with mass spectrometry
Authors: Jungclas Hartmut , Danigel Harald , Schmidt Lothar 
Published: May 2005

AbstractA 252Cf plasma desorption mass spectrometer has been set up to analyse thin layers of non‐volatile organic samples. Molecular and fragment ions were produced and their mass was determined by a time‐of‐flight measurement. A novel interface combines a high‐performance liquid chromatograph with the 252Cf plasma desorption mass spectrometer in a twofold way: introducing the effluent continuously through a capillary inlet in the on‐line liquid chromatography mass spectrometry mode or transferring already prepared samples through a vacuum lock into the mass spectrometer in the off‐line liquid chromatography+mass spectrometry mode. The off‐line mode has been applied for the quantitative analysis of pharmaceuticals in blood using stable isotope labelled standards.
Losses of isobaric neutral species from molecular ions of isomeric nitroanisoles
Authors: Macdonald Colin G. , Lacey Michael J. 
Published: May 2005

AbstractAlternative losses of the isobaric neutral species CH2O and NO˙ have been assessed for molecular ions of isomeric nitroanisoles fragmenting in the ion source and the first field free region of a double focusing mass spectrometer. Mass analyses of the primary fragment ions indicate that specific loss of CH2O occurs from molecular ions of 2‐nitroanisole, while specific loss of NO˙ occurs from molecular ions of 3‐nitroanisole. Although the peak due to [MNO]+ ions is negligible in the mass spectrum of 2‐nitroanisole, evidence is presented to show that they are transient intermediates in the consecutive fragmentation for loss of the elements of CNO2 from the molecular ions.
A fourier transform ion cyclotron resonance study of the mechanism of formation of protonated dimethyl ether from methanol by use of naturally occurring 18O
Authors: Kleingeld J. C. , Nibbering N. M. M. 
Published: May 2005

AbstractIt is shown that ejection of mass selected ions of high abundance from the cell of a Fourier transform ion cyclotron resonance spectrometer permits the study of ion/molecule reactions of ions of very low abundance. Methanol is used as an illustration. Ejection of all ions with the exception of the 18O labelled protonated methanol molecules, present at natural abundance, shows that the protonated dimethyl ether molecules in this system are formed mainly by an SN2 displacement reaction.
The structures and formation of [C4H6N]+ ions 2—ion structures derived from 2‐methylpropanenitrile
Authors: Sarneel Maria M. , Heerma Wigger , Dijkstra Geo 
Published: May 2005

AbstractThe loss of a hydrogen atom from ionized 2‐methylpropanenitrile is preceded by a drastic rearrangement of the molecular ion. The result of this fragmentation is the generation of two stable structurally different [C4H6N]+ ions, formed via different pathways. Their structures can be established by a careful comparison of the metastable ion spectra, collision activation spectra, and charge stripping spectra from the compound and its three deuterium labeled analogues and from [C4H6N]+ ions generated from reference compounds via electron impact ionization or in selected ion/molecule reactions.
Studies in chemical ionization mass spectrometry: V—localization of homoconjugated triene and tetraene units in aliphatic compounds
Authors: Brauner A. , Budzikiewicz H. , Boland W. 
Published: May 2005

AbstractThe homoconjugated triene (‘linolenic acid unsaturation’) and tetraene (‘arachidonic acid unsaturation’) pattern can be readily recognized and localized in aliphatic compounds by chemical ionization (NO) mass spectrometry. This method may be used for the screening of biological material, especially in food analysis.
Metastable fragment ions from carbinolamine ethers
Authors: Longevialle P. , Bouchoux G. , Kapnang H. , Charles G. , Maquestiau A. , Flammang‐Barbieux M. , Flammang R. 
Published: May 2005

AbstractThe secondary decomposition of fragment ions produced by electron impact of carbinolamine ethers was studied by mass analysed ion kinetic energy spectrometry. A new case was observed of ions of the same structure leading to the same fragments through different mechanisms competing in the metastable time frame and accompanied by a different partitioning of the excess energy (internal vs translational). The role of a fractional positive charge localized at saturated centres in the reactivity of these gaseous organic ions is discussed.
The use of triple quadrupoles for sequential mass spectrometry: 1—The instrument parameters
Authors: Dawson P. H. , French J. B. , Buckley J. A. , Douglas D. J. , Simmons D. 
Published: May 2005

AbstractTriple quadrupoles are becoming widely used in sequential mass spectrometry. The observed spectra are very dependent upon the choice of instrument parameters such as the gas target density, the mode of operation of the central quadrupole, and the direct current levels of the quadrupoles (rod‐offsets) which determine the collision energy and the maximum mass resolutions in each analysing quadrupole. The influence of each of the instrument parameters is discussed with examples of experimental measurements of performance, and the optimum choice of modes of operation is determined.
Mass spectra of polar organic compounds in aqueous solutions introduced into an inductively coupled plasma
Authors: Houk Robert S. , Fassel Velmer A. , Svec Harry J. 
Published: May 2005

AbstractAerosols of 1.5% aqueous solutions of glycine, glucose and tartaric acid were introduced into an atmospheric pressure inductively coupled plasma that served as the ion source of a quadrupole mass spectrometer. Protonated water cluster ions were the major ions observed during nebulization of deionized water. Protonated molecular ions were observed at count rates in the range 1000‐10000 counts s−1. Detection limits for [MH]+ ions of glycine, glucose and tartaric acid were 100, 2000 and 160 μg ml−1, respectively. Numerous fragment ions of the above compounds were observed. Both the number of fragment peaks and their count rates decreased as the forward power supplied to the plasma increased.
Unimolecular slow decompositions of [CnH2n+1O]+ ions
Authors: Záhorszky U. I. 
Published: May 2005

AbstractInterpretation of the metastable ion transitions found in normal electron impact mass spectra of appropriate compounds, shows that ions (C4 to C13) of structures \documentclass{article}\pagestyle{empty}\begin{document}${\rm R - CH = }\mathop {\rm O}\limits^{\rm + } {\rm H} $\end{document}, (a), \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}^{\rm 1} ({\rm R}^{\rm 2} ){\rm C = }\mathop {\rm O}\limits^{\rm + } {\rm H}$\end{document} (b), and \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}^{\rm 1} ({\rm R}^{\rm 2} ){\rm C = }\mathop {\rm O}\limits^{\rm + } {\rm R}^{\rm 3}$\end{document} (c) are clearly distinguishable from each other (R = alkyl). Within the latter series c those ions with R3 = methyl and R3>methyl exhibit totally different behaviour. Low homologues are shown to behave exceptionally. Therefore, general conclusions drawn from their reactions must be regarded with caution. Except for these low homologues, ions b and c only isomerize within their groups, but not to each other or to other acyclic ‘oxonium’ ions. Ions a probably have a minor pathway to isomerize to b, and ions c with R3>methyl were found not to isomerize at all prior to slow decompositions.
Mass spectrometry of some new 2‐substituted 10‐N‐(aminoacyl)phenothiazines
Authors: Morosawa Shiro , Kamal Sudarshan , Dandiya Prem C. , Sharma Hoshyari L. 
Published: May 2005

AbstractMass spectral studies of some typical 2‐substituted 10‐N‐(aminoacyl)phenothiazines of biological interest are reported. Some commonly occurring phenomena, like McLafferty cleavage, followed by rearrangement and desulphuration, have been observed. The molecular ion peak is not the base peak in any of these compounds. The nature of the substituent present in the phenothiazine nucleus seems to govern the point of cleavage in the side chain of these derivatives. The latter subsequently determines the appearance of the base peak. Dechlorination takes place via a free radical mechanism while defluorination occurs through the fluorotropylium system. Dehydration has also been observed in one case.
13C labelling study of the interconversion of ethylbenzene, 7‐methylcycloheptatriene and p‐xylene ions
Authors: Grotemeyer Jürgen , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractThe isomerization of the molecular ions of ethylbenzene, 7‐methylcycloheptatriene and p‐xylene by skeletal rearrangement prior to the formation of [C7H7]+ ions has been investigated by using 13C labelled compounds. The results obtained for ions generated by 70 eV and 12 eV electron impact, and fragmenting in the ion source, the 1st field free region and the 2nd field free region, respectively, are compared with those obtained from D labelled derivatives. It is shown that at long reaction times metastable p‐xylene ions lose a methyl radical after scrambling of all C atoms and H atoms, while the unstable molecular ions in the ion source react by specific loss of one of the methyl substituents. Both unstable and metastable ethylbenzene ions fragment by two competing mechanisms, one corresponding to specific loss of the terminal methyl group, and the other involving scrambling of all C and H atoms. These results are discussed by use of a dynamic model developed for the mutual interconversion and fragmentation of the molecular ions of ethylbenzene, methylcyclo‐heptatriene and p‐xylene. The experimental results can be explained by an equilibrium between metastable methylcycloheptatriene ions and p‐xylene ions with sufficient energy for skeletal rearrangement, while about 40% of the metastable ethylbenzene ions fragment after rearrangement to methylcycloheptatriene ions and about 60% of the ethylbenzene ions rearrange further to xylene ions before fragmentation. Metastable methylcycloheptatriene ions, mainly lose a methyl group without a skeletal rearrangement, however, because the rearranged ions are kinetically trapped as ‘stable’ xylene ions or ethylbenzene ions.
Beckmann rearrangement in benzophenone oxime, a mass spectrometric study
Authors: Majer J. R. , Azzouz A. S. P. 
Published: May 2005

AbstractThe isomerization of benzophenone oxime to benzanilide, previously observed to take place in the ion source of a mass spectrometer and attributed to a Beckmann type rearrangement of the benzophenone oxime molecule ion, has been shown to occur by a thermal mechanism prior to ionization. Mass spectrometric evidence is supplemented by infrared spectrophotometric examination of solid samples and shows that in the solid state, at room temperature, benzophenone oxime has a lifetime of about 600 h.
Internal energy effects in collision induced dissociation spectra
Authors: van Koppen Petra A. M. , Illies Andreas J. , Liu Shuying , Bowers Michael T. 
Published: May 2005

AbstractThe effect of the precursor ion internal energy on the branching ratios obtained from collision induced dissociation fragmentation patterns was examined for [NH3]+ and [C2H4N]+. The ion internal energy was changed by varying both the chemical ionization reagent gas and the ion source pressure. Effects observed in the collision induced dissociation fragmentation patterns as a function of the ion source pressure are explained by the reaction exothermicities and by collisional deactivation of internally excited ions (at high pressure).
Barrier to 1,3‐sigmatropic shift in odd electron ions. A MINDO/3 study of H, OH, CH3 and C6H5 migration
Authors: Hoppilliard Y. , Bouchoux G. 
Published: May 2005

AbstractCritical energies for 1,3‐R sigmatropic migrations (RH, OH, CH3 and C6H5) have been calculated by means of the MINDO/3 method. This investigation was carried out for the system [RCH2CHCH2]+˙ and the results indicated that hydroxyl group migration is energetically favoured (critical energy = 53 kJ mol−1). Calculations are also presented for [3‐buten‐2‐ol]+˙ isomerizations. The lowest energy pathway is related to the [2‐buten‐1‐ol]+˙; the corresponding critical energy for OH migration is equal to 33 kJ mol−1 in this case.
Comparison of the mass spectra of 6‐thiotheophyllines and 6‐sulfinytheophyllines
Authors: Bergmann Felix , Rahat Miriam , Frank Arie , Deutsch Joseph 
Published: May 2005

AbstractUnder electron impact, 6‐thiotheophyllines eliminate various fragments from the pyrimidine moiety. In a retro Diels‐Alder reaction, they lose the fragment XCNCH3 from positions 1 and 2 of the pyrimidine ring. In 6‐sulfinyltheophyllines, the sulfinyl group is the main target for fragmentation; it can lose either oxygen or sulfur, and the abundance of [M—16]+ and [M—32]+ is much higher than the abundance of the molecular ion. Elimination of the sulfur atom of the 6‐sulfinyl substituent, with retention of its oxygen, may be explained by intermediate formation of a ring. All further fragmentations of the 6‐sulfinyl derivatives proceed by a primary loss of oxygen or sulfur, followed by elimination of fragments from the pyrimidine moiety, similar to the primary processes, observed in the mass spectra of the 6‐thiotheophyllines.