bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

meta 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

The 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

The 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

A 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

Mass 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

Fifteen 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

The 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

The 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

The 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

A 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

Alternative 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

It 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

The 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

The 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

The 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

Triple 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

Aerosols 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

Interpretation 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

Mass 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

The 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

The 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

The 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

Critical 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

Under 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.
The [MOH]+ ions of m‐ and p‐ethylnitrobenzene: A common structure?
Authors: Baldwin Michael A. , Bowley Heather J.
Published: May 2005

The structures of the [MOH]+ ions of m‐ and pethylnitrobenzene have been compared by measurements of metastable ion spectra, collisional activation spectra, kinetic energy releases and critical energies for the formation of these ions and their subsequent decomposition. Normalized rates of fragmentation of metastable molecular ions and metastable [MOH]+ ions have been compared for ion lifetimes up to 30 μs. The energy measurements fail to distinguish between the structures of the [MOH]+ ions, but the normalized fragmentation rates and the collisional activation spectra show their structures to be different.
Electron impact induced hydrogen rearrangements in (Z)‐ and (E)‐styryl alkyl sulfoxides
Authors: Liu Lilian Kao , Luo Fen‐Tair
Published: May 2005

Alkene elimination, alkyl loss, styryl and alkyl migrations to oxygen are the major fragmentations of (Z)‐ and (E)‐alkane‐sulfinyl‐2‐phenylethenes (cis‐ and trans‐styryl alkyl sulfoxides) under electron impact. Alkene elimination has been found to go through a McLafferty‐type hydrogen rearrangement to yield the benzylic carbon and the sulfinyl oxygen, respectively. This is the most facile and interesting process for compounds with longer alkyl chains (R⩾C3H7), and is a unique feature for styryl sulfoxides. Product ion analyses show the migrating aptitude to carbon and to oxygen to be qualitatively similar.
Pyrolysis reaction of carpronium chloride and its structurally related compounds. 1—electronic and steric effects on the orientation of the pyrolysis reaction
Authors: Ohya Kazumi , Yotsui Yasuhiko , Yamazaki Kenichi , Sano Mitsuji
Published: May 2005

The pyrolysis reaction of carpronium chloride and its structurally related compounds, which were trimethyl‐aminoalkyl acid alkyl esters involving two, three or four skeletal methylene groups, have been investigated by pyrolysis gas chromatography mass spectrometry. The results indicated that the reaction modes of these ammonium compounds were essentially dependent on the number of skeletal methylene groups, and secondarily on the length of the carbon chain of the ester group. These phenomena have been interpreted in terms of electronic and steric contributions for the ionic elimination reaction. The electronic and steric effects on the orientation of the reaction are discussed on the basis of the atomic population calculated by the CNDO/2 method.
Competing oxygen migrations in ortho nitro aromatic thioamides on electron impact
Authors: Ramana D. V. , Viswanadham S. K.
Published: May 2005

Interesting competitive oxygen migrations from the nitro group to the nitrogen and to the sulfur have been noticed during the mass spectral decomposition of ortho nitro aromatic thioamides on electron impact. The migration of the oxygen to the nitrogen of the thioamide function results in the formation of stable o‐nitrosothiobenzoyl cation. The other novel ortho effect noticed in the ortho isomers is the transfer of an oxygen from the nitro group to the sulfur followed by the ejection of SO from the molecular ions. A mechanism involving the initial oxygen migration to the sulfur through a favourable 6‐membered transition state followed by cyclization with the concomitant expulsion of SO is proposed for this process. Other interesting decomposition processes occurring as a consequence of this ortho effect have also been noticed. The proposed mechanisms for these processes are supported by mass analysed ion kinetic energy spectra and high voltage scans.
Quantitation of isomeric ion mixtures using collisional activation mass spectra
Authors: Proctor Christopher J. , McLafferty Fred W.
Published: May 2005

Recently Bass and Bowers have criticized methods for calculation of isomeric composition of gaseous ions based on mass spectra from collisionally activated dissociations (CAD). They fault values from this laboratory on the proportion of benzyl and tropylium ions calculated by two methods from product ion abundances. However, a careful remeasurement of the relevant yields of CAD product ions shows that neither calculation method affected the result outside experimental error, as the ion yields for at least 14 higher energy dissociations are insensitive to both isomeric identity and internal energy. Reducing the [C7H7]+ internal energy by 1.5 eV does give a 25% reduction in the ion yield for the lowest energy process, supporting the accepted recommendation that these be omitted for quantitative spectral comparisons. A calculation error was made in one of our previous reports on [C7H7]+, and corrected isomeric composition values are presented. The disparate values from recalculation by Bass and Bowers of other data from this laboratory on [C2H4O]+˙ ions are shown here to be consistent with the large experimental error of those measurements; the medians of their values are actually near the values originally reported. In direct contrast to their assertions, we find no evidence that previous calculation methods have produced misleading conclusions, or that the assumption of linear superposition of CAD spectra in ion mixtures has yielded unreliable results.
Stable C2H5X+˙ (X=Cl, Br) radical cations of structure [CH3CHXH+˙]: Their energetics and dissociation characteristics
Authors: Holmes John L. , Burgers Peter C. , Terlouw Johan K. , Schwarz Helmut , Ciommer Bernhard , Halim Herman
Published: May 2005

A new radical cation having the methyl carbene type structure [CH3CHClH]+˙ has been characterized in the gas phase. It is readily generated by the dissociative ionization [CH3CHCICO2H]+˙ → CO2+[CH3CHCIH]+˙. Its enthalpy of formation has been estimated to be 951 kJ mol−1, close to that of [CH3CH2CI]+˙. The principal fragmentation characteristics (loss of HCl and Cl˙) of the ion are discussed. A brief description of the bromo analogue [CH3CHBrH]+˙ is also given.
Further examples of skeletal rearrangements of the Wagner‐Meerwein type in chemical ionization mass spectrometry: The case of [C6H9]+ ions
Authors: Gäumann Tino , Houriet Raymond , Stahl Daniel , Tabet Jean‐Claude , Heinrich Nikolaus , Schwarz Helmut
Published: May 2005

The [C6H9]+ ions produced either via unimolecular H2O loss from 13 [C6H11O]+ precursors or direct protonation of 1,3‐ and 1,4‐cyclohexadiene have identical collisional activation mass spectra. The kinetic energy release data for the process [C6H11O]+→[C6H9]++H2O are also very similar (on average T0.5=24 meV) irrespective of the constitution of the precursor. From the proton affinities of 1,3‐cyclohexadiene (PA=837.2 kJ mol−1) using ion cyclotron resonance mass spectrometry the heat of formation of the [C6H9]+ ion is determined to 804.6 kJ mol−1. This value taken together with the results of molecular orbital calculations (MNDO) and the structure indicative losses of CH3. and C2H4 upon collisional activation suggest that the [C6H9]+ ion has the structure of the 1‐methylcyclopentenylium ion f and not that of the slightly less stable cyclohexenylium ion g. The generator of an easily interconverting system of isomeric [C6H9]+ ions is unlikely to be due to the high barrier separating the various isomers.
A photo‐ionization study of organosulfur ring compounds: Thiirane, thietane and tetrahydrothiophene
Authors: Butler James J. , Baer Tomas
Published: May 2005

The gas phase heats of formation of several organosulfur cations were determined from thiirane, thietane and tetrahydrothiophene precursor molecules by photoionization mass spectrometry. Heats of formation at 0 K and 298 K are reported for the following ions: [H2CS]+˙, [H3CS]+, [C2H3S]+, [C2H4S]+˙, [C3H5S]+, [C3H6S]+˙, [C4H7S]+ and [C4H8S]+˙. The [C4H7S]+ (m/z 87), [C2H4S]+˙ (m/z 60), [C2H3S]+ (m/z 59), [C4H7]+ (m/z 55), [C4H6]+˙ (m/z 54) and [CH2S]+˙ (m/z 46) ions are produced from metastable tetrahydrothiophene ions at photon energies between 10.2 and 10.7 eV. Decay rates of internal energy selected parent ions to the m/z 60, 59, 55 and 54 fragments were measured by threshold photoelectron‐photoion coincidence, the results of which are compared to statistical theory (RRKM/QET) calculations. The [C2H4S]+˙ ion from tetrahydrothiophene is found to have the thioacetaldehyde structure. From the measured [C2H4S]+˙ onset a ΔH = 50±8 kJ mol−1 was calculated for the thioacetaldehyde molecule.
Characterization of isomeric [CH5P]+˙ and [C2H7P]+˙ radical cations and some [C2H6P]+ phosphonium ions in the gas phase by their collisional activation spectra
Authors: Weger E. , Levsen K. , Ruppert I. , Burgers P. C. , Terlouw J. K.
Published: May 2005

Collisional activation spectra were used to characterize isomeric ion structures for [CH5P]+˙ and [C2H7P]+˙ radical cations and [C2H6P]+ even‐electron ions. Apart from ionized methylphosphane, [CH3PH2]+˙, ions of structure [CH2PH3]+˙ appear to be stable in the gas phase. Among the isomeric [C2H7P]+˙ ions stable ion structures [CH2PH2CH3]+˙ and [CH2CH2PH3]+˙/[CH3CHPH3]+˙ are proposed as being generated by appropriate dissociative ionization reactions of alkyl phosphanes. At least three isomeric [C2H6]+ ions appear to exist, of which \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} - \mathop {\rm P}\limits^{\rm + } {\rm H = CH}_{\rm 2} $\end{document} could be identified positively.
Positive and negative ion mass spectrometric studies of dioximes of α‐diketones and their nickel complexes
Authors: Charalambous J. , Soobramanien G. , Stylianou A. D. , Manini G. , Operti L. , Vaglio G. A.
Published: May 2005

The positive and negative ion mass spectra of glyoxime, methylglyoxime, dimethylglyoxime, diphenyl glyoxime and of their nickel(II) complexes are reported. Both the positive and negative ion mass spectra of the dioximes show loss of OH˙ and H2O from the molecular ion to give fragment ions which probably have cyclic furazan type structures. The positive ion spectra of the complexes fragment mainly by loss of ligand radicals whereas the negative ion spectra show mainly loss of OH˙ and H2O.
Cyclic ions in the mass spectra of trimethylsilyl derivatives of substituted o‐dihydroxybenzenes
Authors: Horvat Robert J. , Senter Samuel D.
Published: May 2005

The mass spectra of trimethylsilyl (TMS) ethers/methyl esters of phenolic acids containing o‐dihydroxybenzene groups have base peaks at [M−119]+ instead of the usual [M−15]+ and [M−31]+ that are characteristic of TMS/methyl esters of monohydroxyphenolic acids. These ions, formed by the loss of 31+88 u from the parent ion, possess a cyclic moiety as proven by substitution of deuterium atoms for hydrogen atoms in the TMS groups of the methyl esters of 3,4,5‐trihydroxybenzoic (gallic), 3,4‐dihydroxybenzoic (protocatechuic) and β‐(3,4‐dihydroxyphenyl)propenoic (caffeic) acids. Although these cyclic ions are the base peaks in TMS‐derivatized o‐dihydroxyphenolic acid esters, similar ions represent intense peaks but not necessarily the base peak in other derivatized compounds such as 1,2‐dihydroxybenzene, 1,2‐dihydroxy‐3‐methyl‐ and 1,2‐dihydroxy‐4‐methyl‐benzenes and flavan‐3‐ols that possess o‐dihydroxybenzene groups. Compounds possession m‐ or p‐dihydroxybenzene groups do not form these cyclic ions; therefore, this procedure for derivatization and interpretation of mass spectra is valuable for the identification of compounds containing o‐dihydroxybenzene groups in complex mixtures of isomeric compounds.
Electron impact mass spectra of 3,5,7‐triaryl‐and ‐trialkyl‐4H‐1,2‐diazepines
Authors: Balaban Alexandru T. , Gheorghiu Mircea D. , Balaban Teodor Silviu
Published: May 2005

Electron impact mass spectra of 3,5,7‐trisubstituted 4H‐1,2‐diazepines indicate that aryl substituents lead to N2expulsion while alkyl substitutents do not. A common fragmentation pattern is observed and discussed for all alkyldiazepines, most of which are newly reported compounds. Assignments are based on electron impact mass spectra of deuteriated substrates and high resolution mass spectra. A previous interpretation of N2expulsion is corrected.
The decompositions of metastable [C4H8O]+˙ ions and the [C4H8O]+˙ potential surface
Authors: McAdoo David J. , Hudson Charles E.
Published: May 2005

Collisionally activated decomposition (CA) spectra of [C4H8O]+˙ ions and the products of their metastable decompositions are used to refine a previously presented picture of the reactions of [C4H8O]+˙ ions. Metastable [C4H8O]+˙ isomers predominantly rearrange to the 2‐butanone ion and decompose by loss of methyl and ethyl, although up to 38% of the methyl losses take place by other pathways to form \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = {\rm{CHCH = }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H}}{\rm{.}} $\end{document}
. The CA spectra of many of the [C4H8O]+˙ ions with the oxygen on the first carbon are very similar, consistent with those ions isomerizing largely to common structures before or after collision. However, several of these ions have unique CA spectra, so they must remain structurally distinct from the majority of the [C4H8O]+˙ ions below energies required for decomposition. The CA spectra of ions with the oxygen on the second carbon are distinct from those of ions with the oxygen on the first carbon, so there is limited interconversion of the non‐decomposing forms of the two types of ions. A potential energy diagram for the reactions of metastable [C4H8O]+˙ ions is constructed from appearance energy measurements. As would be expected, the relative importances of most of the [C4H8O]+˙ isomerizations seem to be inversely related to the activation energies for those processes. Some parallels between the isomerizations of [C4H8O]+˙ ions and those of related ions are pointed out.
A fast atom bombardment and field ionization/field desorption study of some isomeric unsaturated dicarboxylic acids
Authors: Dallinga J. W. , Nibbering N. M. M. , Van Der Greef J. , Ten Noever De Brauw M. C.
Published: May 2005

Geometrically isomeric dicarboxylic acids, such as maleic and fumaric acid and their methyl homologues, and the isomeric phthalic acids, have been investigated using fast atom bombardment, field ionization and field desorption mass spectrometry. The most intense peak in the positive ion fast atom bombardment spectra corresponds with the [M + H]+ ion. This ion, when derived from the E‐acids, tragments either by successive loss of water and carbon monoxide or by elimination of carbon dioxide. In the case of the Z‐acids only elimination of water from the [M + H]+ ions is observed to occur to a significant extent. The same is true for the [M + H]+ ions of the isomeric phthalic acids, that is the [M + H] ions derived from iso‐ and terephthalic acid exhibit more fragmentation than those of phthalic acid. All these acids undergo much less fragmentation upon field ionization, where not only abundant [M + H]+ ions, but also abundant [M]+· ions, are observed. Upon field desorption only the [M + H]+ and [M + Na]+ ions are observed under the measuring conditions. Negative ion fast atom bombardment spectra of the acids mentioned have also been recorded. In addition to the most abundant [MH]− ions relatively intense peaks are observed, which correspond with the [M]−˙ ions. The fragmentations observed for these ions appear to be quite different from those reported in an earlier electron impact study and in a recent atmospheric pressure ionization investigation.
Conjugated Schiff's bases 16—Substituent effect on electron impact fragmentation of some 1‐oxa‐4‐azabutadienes1
Authors: Moskal Janusz , Moskal Alexandra , Nagraba Krzysztof
Published: May 2005

The electron impact fragmentation patterns of some 1‐oxa‐4‐azabutadienes have been determined and supported by the corresponding metastables. The effect of substituents on this fragmentation has been investigated. Satisfactory correlation of intensity ratios of the peaks characterizing the primary fragmentation versus the Brown and Okamoto σ+ substituent parameters has been found. The relationship between the substituent parameters and the dissociation energy ED,C(3)‐C(5), estimated with the help of appearance energies has been considered.
Further investigation of the mass fragmentation of dinucleotide analogues containing the 6‐azauracil moiety
Authors: Jankowska Jadwiga , Golankiewicz BożEnna , Golankiewicz Krzysztof
Published: May 2005

The mass fragmentation of four dinucleotide analogues in which uracil and 6‐azauracil derivatives are connected by a trimethylene bridge is discussed. The fragmentation pathways have been proposed on the basis of high resolution data and metastable transitions. The distinct influence of alkyl substituents in the 5‐position of the uracil moiety on the fragmentation pathway has been observed and a novel fragmentation of 6‐azapyrimidine ring noted.
The isomerization of 1,4‐cyclohexadiene ions to the 1,3‐cyclohexadiene structure as studied by photodissociation
Authors: Van Velzen P. N. T. , Van Der Hart W. J.
Published: May 2005

Photodissociation experiments in a trapped ICR cell show that at low ionizing energies about two‐thirds of the molecular ions of 1,4‐cyclohexadiene have isomerized to the 1,3‐cyclohexadiene structure. The major fraction of the remaining ions isomerizes by a reaction with the parent neutral.
Secondary ion mass spectrometry of some promazines and photochemistry of chlorpromazine in glycerol
Authors: Dung Dao Viet , Marien J. , De Pauw E. , Decuyper J.
Published: May 2005

SIMS using 6 keV Cs+ ions has been performed on glycerol solutions of various promazines. Fragmentation patterns are compared to those obtained by other ionization methods. The photochemical degradation of chlorpromazine has been observed directly in the glycerol droplet, showing the potentiality of SIMS for the direct study of photochemical reactions in solution.
The elimination of masses 27 and 28 from the [MOH]+ ion of 2‐nitrotoluene
Authors: Herbert C. G. , Larka E. A. , Beynon J. H.
Published: May 2005

The expulsion of neutral fragments of masses 27 and 28 from metastable [M  OH]+ ions derived from 2‐nitrotoluene has been observed. The relative abundances of the resulting fragment ions, together with the kinetic energy released in each process, has been compared with similar fragmentation of [C7H6NO]+ ions derived from other precursor molecules. In this way, the nature of the neutral fragments and the structure of the [M  OH]+ ions from 2‐nitrotoluene has been investigated. The most likely structure is the 1,2‐benzisoxazolenium cation although the coexistence of other structures cannot be ruled out on the present evidence.
Investigation of the relative stability of positive alkali halide cluster ions generated by fast atom bombardment
Authors: Morgan T. G. , Rabrenović M. , Harris F. M. , Beynon J. H.
Published: May 2005

The stabilities of alkali halide cluster ions [M(MX)n]+ (M  Li, Na, K, Rb, Cs; X  F, Cl, Br, I) have been studied by measuring the fragment ion yields following dissociation of the ions in the second field free region of a ZAB‐2F mass spectrometer. Extractable cluster ions were observed for certain values of n. It was found that the stabilities of the neutral fragment species formed are also of importance in determining the fragmentation rates. Possible configurations of M and X in the stable ions are discussed.
Structures and relative energies of gas phase [C3H7O]+ ions
Authors: Nobes Ross H. , Radom Leo
Published: May 2005

Ab initio molecular orbital calculations have been carried out for 17 possible isomeric [C3H7O]+ structures. Optimized geometries have been obtained with a split‐valence basis set and improved relative energies determined with polarization basis sets and with incorporation of electron correlation. The results agree well with available experimental data. In particular, (CH3)2COH+, CH3CH2CHOH+, CH3CHOCH3+, CH3CH2OCH2+,
equation image
and
equation image
have been confirmed as low‐energy isomers. Six additional structures appear to be energetically accessible and to offer a reasonable prospect for experimental observation. These are CH2CHCH2OH2+, CH2C(CH3)OH2+, CH3CHCHOH2+, CH2CHOHCH3+,
equation image
and
equation image
.
The heats of formation of some protonated olefinic carbonyl compounds: [C5H9O]+ and [C4H7O2]+ ions
Authors: Bouchoux G. , Hoppilliard Y. , Jaudon P. , Houriet R.
Published: May 2005

The proton transfer equilibrium reactions involving 3‐penten‐2‐one, 3‐methyl‐3‐buten‐2‐one, crotonic acid and methacrylic acid were carried out in an ion cyclotron resonance (ICR) spectrometer. The semiempirical method MNDO, used to estimate the heats of formation for 14 protonated [C5H9O]+ and [C4H7O2]+ ions and the energetic aspect of the fragmentations of metastable [C6H12O]+. and [C6H12O2]+. ions, leads to the conclusion that the ions corresponding to protonation at the carbonyl oxygen are the most stable. Thus the experimentally determined heats of formation of protonated olefinic carbonyl compounds can be attributed to the following structures: [CH3COHCHCHCH3]+ (δHf = 490 KJ mol−1), [CH3COHC(CH3)CH2]+ (δHf = 502 KJ mol−1), [HOCOHCHCHCH3]+ (δHf = 330 KJ mol−1) and [HOCOHC(CH3)CH2]+ (δHf = 336 KJ mol−1).
Mechanism for the formation of [M–1]+ in flavones
Authors: Guidugli F. H. , Pestchanker M. J. , Kavka J. , Joseph‐Nathan P.
Published: May 2005

The electron impact induced fragmentations of flavone have been studied with the aid of high resolution measurements, metastable decompositions and deuterium labelling. Based on the obtained data a mechanism for the formation of the [MH]+ ion is proposed and further substantiated from the study of substituted flavones.
Effects of stereoisomerism on the electron impact fragmentation of some compounds with an eburnane skeleton1
Authors: Czira Gábor , Tamás József , Kalaus György
Published: May 2005

The mass spectra of five sets of stereoisomers possessing an eburnane basic skeleton (vincamine, vincaminic acid ethyl ester, deoxyvincamine, deoxyvincaminic acid ethyl ester, apovincaminic acid ethyl ester and all their possible epimers) have been compared. All of the epimers, among them the 3H‐β isomers, not studied formerly, have characteristically different electron impact spectra. For vincamine and its epimers similar differences were also found in the argon charge exchange ionization, mass‐analysed ion kinetic energy and collisionally activated mass‐analysed ion kinetic energy spectra. The main effects of stereoisomers on the abundance ratios clearly indicated the occurrence of some highly stereospecific or stereoselective decomposition processes. Conclusions concerning the mechanism of these reactions, based on the normal and metastable ion spectra as well as on some energetic data for the epimers, have also been drawn. For several fragment ions the observed unexpected abundance differences seem to be rationalized in terms of the competing effects of other decomposition processes of higher stereoselectivity.
An energy‐resolved study of the fragmentation of ionized 1‐Penten‐3‐ol
Authors: Zwinselman Jan J. , Harrison Ale X. G.
Published: May 2005

A detailed energy‐resolved study of the fragmentation of CH2CHCH(OH)CD2CD3 (1‐d5) has been carried out using metastable ion studies and charge exchange techniques, combined with collision‐induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1‐d5 rearranges to the 3‐pentanone structure and fragments by loss of C2H5 or C2D5 leading to the acyl structure, [CH3CH2CO]+ or [CD3CD2CO]+, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C2D5 by direct cleavage, leading to [CH2CHCHOH]+, becomes the dominant fragmentation reaction. As a result the [C3H5O]+ ion seen in the electron impact mass spectrum of 1‐penten‐3‐ol has predominantly the protonated acrolein structure.
Structural identification of fatty acid methyl esters by collision spectra of their [M  H]− species
Authors: Bambagiotti A. Massimo , Coran Silvia A. , Giannellini Valerio , Vincieri Franco F. , Daolio Sergio , Traldi Pietro
Published: May 2005

Negative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass‐analysed ion kinetic energy spectra of [M  H]− species, obtained by OH− reaction with a selection of six C18 fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.
Intermolecular O‐methylation during EIMS of quaternary methoiodides of isoquinoline alkaloids
Authors: Huang Zhi‐Heng , Zhu Ji‐Ping , Zhou Yun‐Li
Published: May 2005

Quaternary methoiodides of tetrahydroprotoberberine (THB) alkaloids (1‐8) tend to undergo preionization degradation in the mass spectrometer at elevated temperatures. Different reaction pathways have been found in relation to the structure of the substance studied. Permethylated alkaloids, e.g. tetrahydropalmatine‐CH3I (8), give predominantly the Hofmann degradation intermediates and the fragment ions derived therein, while the alkaloids with free phenolic group(groups), as exemplified by scoulerine‐CH3I (1), show a greater tendency to be methylated by an intermolecular CH3 transfer mechanism: magnified image The latter process has been systematically studied and the mechanism substantiated through comparison of the spectra of analogous series, B/E linked scan and CD3 labelling. Similar behaviour has been observed in bisbenzyltetrahydroisoquinoline alkaloids.
Loss of methyl from [H2CC(OH)CH3]+˙ ions prepared by electron impact ionization of unstable 2‐hydroxypropene
Authors: Tureček František , Hanuš Vladimír
Published: May 2005

Unstable 2‐hydroxpropene was prepared by retro‐Diels‐Alder decomposition of 5‐exo‐methyl‐5‐norbornenol at 800°C/2 × 10−6 Torr. The ionization energy of 2‐hydroxypropene was measured as 8.67±0.05 eV. Formation of [C2H3O]+ and [CH3]+ ions originating from different parts of the parent ion was examined by means of 13C and deuterium labelling. Threshold‐energy [H2CC(OH)CH3]+˙ ions decompose to CH3CO++CH3˙ with appearance energy AE(CH3CO+) = 11.03 ± 0.03 eV. Higher energy ions also form CH2COH+ + CH3 with appearance energy AE(CH2COH+) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C2H3O]+ ions containing the original methyl group and [CH3]+ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate‐determining isomerization [H2CC(OH)CH3]+˙ →[CH3COCH3]+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.
Kinetic energy release in metastable ions from β‐keto esters
Authors: Moldovan Zaharie , Palibroada Nicolae , Mercea Victor , Mihǎilescu Gheorhe
Published: May 2005

The kinetic energy release, T, in metastable ion transitions accompanying the main fragmentation reaction by electron impact has been determined for methyl‐, ethyl‐ and propyl‐pivaloyl acetates. The measurements have been made using a MAT 311 mass spectrometer with inverse Nier–Johnson geometry, by high voltage and mass‐analysed ion kinetic energy methods. The peak width at 50% height has been used in the calculations. The T values and the shape of the metastable peaks are correlated to reaction types and to the alcohol radical.
Stereochemical effects in the electron impact mass spectra of cis–trans isomeric 1,2,3,5‐tetramethylcyclohexanes and some trimethylcyclohexanes
Authors: Herzschuh R. , Mann G. , Rennecke D.
Published: May 2005

The mass spectra of 10 isomeric trimethylcyclohexanes and six cis–trans isomeric 1,2,3,5‐tetramethylcyclohexanes are discussed. 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 log of the intensity ratio for loss of methyl and ethyl from the molecular ions correlates well with the strain energies and with the mean number of gauche arrangements of the stereoisomers.