bluuebunny/crossref_metadata_2025_split huggingface dataset:
The study of ionic fragmentation by photoelectron‐photoion coincidence spectroscopy
Authors: Dannacher Josef 
Published: May 2005

AbstractSince its invention, a decade ago, photoelectron‐photoion coincidence spectroscopy has continuously provided extremely important information on ionic fragmentation processes. The outstanding reputation of the technique is essentially founded on the fact that internal energy selected cations can be studied. In striking contrast to the importance of the method and to the reliability of the data obtained, only about 150 coincidence studies have been published up to now. This is due to the rather intricate experimental technique involved and, probably even more, to the main drawback of this method, i.e. the enormous length of time involved in the measurements. The systems investigated so far are comprehensively compiled in the present article. The two experimental variants currently in use, termed fixed and variable wavelength technique, are compared. Evidence for the complementary character of the two experimental versions is presented. It is recalled that the primary source of information is in any case a time‐of‐flight distribution. The different ways of analysing these distributions are summarized and the accuracy of the derived results is discussed. The current state of the art is exemplified by reviewing the outcomes for a number of selected examples. The presented results on di‐, tri‐ and tetra‐atomic cations reveal clearly the more recently achieved experimental progress. Data on such smaller ionic species are particularly useful for studying predissociation mechanisms, a domain which becomes more and more accessible to modern ab initio calculations of fragmentation pathways. The reported results for O2+ and CO2+ reveal that branching ratios for the formation of electronically and vibrationally excited dissociation products can now be quantified for sufficiently small systems. The possibility of distinct behaviour of isoenergetic molecular ions depending on the method of preparation is outlined in the case of formaldehyde cation. The same cation is used to exemplify a puzzling isotope effect originating in a rate‐determining radiationless transition that precedes a significantly faster dissociative step. A variety of data on larger systems grouped according to topic are critically reviewed. The determination and accuracy of rate‐energy functions is discussed, at first for the case of a single decay channel; then the analogous analysis for a series of competing fragmentations is outlined. The importance of competitive radiative and non‐radiative/dissociative depletion of an excited electronic state is pointed out.
The substituent effect on the single and double hydrogen atom transfer reactions in para‐substituted benzoic acid isobutyl esters
Authors: Tobita Seiji , Tajima Susumu , Tsuchiya Toshikazu 
Published: May 2005

AbstractThe substituent effect on the single and double hydrogen atom transfer reactions in para‐substituted benzoic acid isobutyl esters has been investigated by electron impact mass spectrometry. Electron‐donating substituents favour formation of the [MC4H8]+˙ ion generated by single hydrogen atom transfer reaction (McLafferty rearrangement), whereas electron‐withdrawing substituents favour formation of the [MC4H7]+ ion generated by double hydrogen atom transfer reaction. In the case of the latter compounds, the m/z56 ([C4H8]+˙) ion, which is generated by single hydrogen atom transfer reaction with charge migration, is very intense, while in the former compounds, the m/z56 ion is very weak. These observations can be reasonably explained on thermochemical grounds based on the sum of the standard heats of formation of the fragments.
Isomerization of [C6H5C3H5O]+˙ ions: The case of 1‐phenylpropenol
Authors: Denhez J. P. , Audier H. E. 
Published: May 2005

AbstractAppearance energy and kinetic energy release measurments together with isotopic labelling have shown that the meastable molecular ion of 1‐phenylpropenol isomerizes into those of cinnamic alcohol and 3‐phenylpropanal prior to loss of ketene. 13C labelling and thermodynamic considerations prove that the rearrangement of 1‐phenylpropenol occurs by an ‘ortho attack’ leading to bicyclic intermediates. Statistical hydrogen exchanges are observed prior to fragmentation. The isomerization mechanisms are discussed.
Differentiation of polycyclic aromatic hydrocarbons using electron capture negative chemical ionization
Authors: Buchanan Michelle V. , Olerich Geraldine 
Published: May 2005

AbstractA number of isomeric polycyclic aromatic hydrocarbons may be distinguished using electron capture negative chemical ionization when methane is used as a buffer gas, including benzo[a]pyrene and benzo[e]pyrene. The ionization behavior of these compounds may be predicted, on the basis of their electron afinities, allowing compounds to be distinguished without the use of standards.
Mass spectrometry of bis‐quinolizidine alkaloids: Lactams of sparteine and α‐isosparteine
Authors: Majchrzak‐Kuczyńska U. , Wiewiórowski M. , Wyrzykiewicz E. 
Published: May 2005

AbstractThe mass spectral fragmentations of 2‐oxosparteine (lupanine), 2‐oxo‐α‐isosparteine (α‐isolupanine), 15‐oxosparteine, 17‐oxosparteine and 10‐oxosparteine (aphylline) are reinvestigated and discussed. Fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed. The fragmentation assignments are not consistent with those previously reported in the literature. Many fragment species of the same m/z (low‐resolution spectra) are composed of two or three fragment ions of different elemental compositions (high‐resolution spectra). The obtained data create a safe basis for distinguishing structural and stero isomers.
Structure and fragmentation of dimethyl methylphosphonate and trimethyl phosphite
Authors: Holtzclaw James R. , Wyatt Jeffrey R. , Campana Joseph E. 
Published: May 2005

AbstractThe structures and fragmentation pathways of two isomeric organophosphorus esters, dimethyl methylphosphonate (DMMP) and trimethyl phosphite (TMP) have been determined. The long‐lived, low‐energy molecular ions of DMMP were found to undergo a keto‐to‐enol isomerization prior to collision‐induced dissociation. This isomerization was established through the comparison of the collision spectra from DMMP, TMP, isotopically labeled DMMP and a model precursor ion. Electron ionization and charge exchange reactions were used to study the isomerization as a function of the internal energy of the molecular ion. The structure of the TMP molecular ion retained the structure of the neutral molecule. The daughter ion spectra of the isomeric fragment ions from DMMP and TMP were used to infer the fragment ion structures. Negative ions of DMMP and TMP were also studied, and their collision spectra were found to be indistinguishable.
Mass spectral analysis of Schiff bases derived from 1,1,1‐trifluoro‐2,4‐pentanedione and Bis(3,3′‐aminopropyl)amine and bis(3,3′‐aminopropyl)methylamine and their copper(II) and nickel(II) complexes
Authors: Morris M. L. , Koob R. D. 
Published: May 2005

AbstractMass spectra have been obtained for bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)amine, bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylamine, bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)aminocopper(II), bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)aminonickel(II), bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylaminocopper(II) and bis(5,5,5‐trifluoro‐4‐oxopentan‐2‐N‐propylene)methylaminonickel(II) using a Varian‐MAT CH5 mass spectrometer. The first two compounds are seen to fragment primarily in the trimethylene chain γ to the middle nitrogen although fragmentation is seen at a variety of other sites as well. Lower molecular weight ions form a significantly larger fraction of the total ion intensity for the methylated middle nitrogen compound than for its non‐methylated analog. In the metal complexes of these Schiff bases, the metal exerts its influence in two ways. The primary cleavage site inthe trimethylene bridge is β, rather than γ, to the middle nitrogen, and other fragments are produced which are ascribable to ligand to metal electron transfer.
Fast atom bombardment mass spectrometry of alkali metal fluorides and chlorides; a comparison of the solid salt and glycerol matrix spectra
Authors: Miller Jack M. , Theberge Roger 
Published: May 2005

AbstractThe Fast Atom Bombardment (FAB) mass spectra of the alkali metal chlorides (Na, K, Cs) and fluorides (Na, K, Rb, Cs) were obtained from solids and a glycerol matrix, using a fast atom bombardment source. From solids the fluorides exhibited an ion abundance enhancement of the well‐known [M(MF)4]+ cluster, which decreased with increasing cation size. A gradual decrease in the n=4 enhancement was observed as the salt was diluted with glycerol. In the chlorides only sodium chloride showed the n=4 relative enhancement. The mass spectra of the salts from a glycerol matrix at molar ratios of 1:1 to 1:10 showed that the spectra of the 1:1 solutions were similar to those from the solids, while glycerol adducts were found to increase with increasing glycerol concentration. A [M(MX)n(gly)]+ species that featured successive losses of HX was observed. It has not been established whether HX losses take place in solution, in the surface/vacuum interface and/or whether gas phase reactions might be responsible for the observation of the [M(MX)n(gly)–y HX]− species in the mass spectra of the MX/glycerol system.
Fragmentation of trimethylsilyl derivatives of 2‐alkoxyphenols: A further violation of the ‘even‐electron rule’
Authors: Krauss Dietlinde , Mainx Hans Georg , Tauscher Bernhard , Bischof Peter 
Published: May 2005

AbstractThe mass spectra of trimethylsilyl (TMS) ethers of 2‐methoxyphenols show abundant [M–30]+˙ ions originating from consecutive loss of two methyl radicals. This is illustrated by comparison of the accurate mass‐measured and linked‐scan spectra of the TMS derivatives of 2‐methoxyphenol (guaiacol), 4‐hydroxy‐3‐methoxybenzaldehyde (vanillin) and 3‐(4‐hydroxy‐3‐methoxyphenyl)‐2‐propenoic acid methyl ester (ferulic acid methyl ester) with those of the TMS derivatives of phenol, 4‐hydroxybenzaldehyde, 3‐(4‐hydroxyphenyl)‐2‐propenoic acid methyl ester (p‐coumaric acid methyl ester), 3‐methoxyphenol and 4‐methoxyphenol. This distinctive ortho effect is valuable in the identification of isomeric phenolic compounds. In the spectra of the TMS derivatives of 2‐ethoxyphenol and 2‐propoxyphenol the sequential loss of two radicals is less pronounced, because elimination of the side‐chain and a methyl group with rearrangement and hydrogen migration is competitive.
McLafferty reactions in even‐electron ions?
Authors: Zollinger M. , Seibl J. 
Published: May 2005

AbstractWithin the scope of a comparative study of the reactivities of odd‐ versus even‐electron ions, the possible significance of the well‐known McLafferty reaction for structural analysis in even‐electron ions is investigated. In order not to compare reactions of different types with one another, a selective set of experimentally verifiable features is specified which must be met by a degradation reaction to justify its classification as a true McLafferty process. The literature is critically reviewed in the light of this restrictive specification and some ambiguous examples have been reinvestigated, applying modern techniques of selective metastable ion scrutiny together with specific 2H labelling. Only in a few specific cases are even‐electron ions found to decay in a McLafferty fashion according to the postulated criteria, indicating a rather limited effectiveness of the reaction as a source of structural information in this field. Fundamental problems in unequivocally pinning down a very specific mechanistic course of a reaction are encountered in spite of using sensitive new techniques of measurement.
Main fragmentation routes of functionally substituted cyclopropenes under electron impact
Authors: Domnin I. N. , Lakshin A. M. , Misharev A. D. , Takhistov V. V. , König W. A. 
Published: May 2005

AbstractThe behaviour of substituted cyclopropenes under electron impact is to a large extent determined by the presence of the unsaturated three‐membered ring which is capable of efficient delocalization of the positive charge. The loss of one of the substituents at the C(3) position of the small ring is characteristic for the fragmentation of cyclopropenes; the loss of the substituent which is less electron donating occurs preferentially. The presence of substituents with heteroatoms on the three‐membered ring may lead to changes in the fragmentation scheme characteristic for the specific set of substituents.
A spurious [CH5]− ion: Problems with negative chemical ionization quadrupole instrument
Authors: Poppe A. , Schröder E. , Budzikiewicz H. 
Published: May 2005

AbstractIt is shown that in a quadrupole mass spectrometer set up for negative chemical ionization, positive ions can be formed between the ionization chamber and the analyser both by electron impact and by chemical ionization. These ions will be registered together with negative ions formed in the ion source if the instrument is equipped with a positive and a negative conversion dynode and may reach the secondary electron multiplier even if the negative conversion dynode is disconnected.
Low‐energy, low‐temperature mass spectra. 5‐alkanals
Authors: Maccoll Allan , Mruzek Margaret N. 
Published: May 2005

AbstractThe low‐energy, low‐temperature mass spectra of thirteen alkanals are reported and their predominant modes of fragmentation discussed in terms of energetics. Characteristic of this class of compounds is the very high proportion of odd‐electron ions in the mass spectra, namely [M  CMH2m]+˙, [M  H2O]+˙ and [M  H2O  CmH2m]+˙.
High‐Resolution electron impact mass spectrometry of five novel organoiron complexes
Authors: Lay Jackson O. , Allison Neil T. , Yongskulrote W. , Ferede R. 
Published: May 2005

AbstractThe high resolution mass spectra of five novel η1‐R substituted Fe(II)(CO)2 η5‐C5H5 complexes are reported. Fragmentation behavior common to all the studied compounds is noted, as well as some ligand‐specific fragmentation. Fragment ions associated with ligand recoordination, ligand substituent transfer and inter‐ligand bond formation are noted. The role of the electron density around the metal center, and in particular the ‘18‐electron’ configuration, on the fragmentation of these compounds is discussed.
Mass spectra and stereochemistry of alkylsubstituted 2,2‐diphenyl‐1,3‐dioxa‐2‐germacyclohexanes
Authors: Gren A. I. , Yasinenko N. E. , Timofeev O. S. , Zagorevskii D. V. 
Published: May 2005

AbstractThe correlations between electron impact induced formation of fragment [M  C6H6]+˙ from alkyl‐substituted 2,2‐diphenyl‐1,3‐dioxa‐2‐germacyclohexane (1) and the peculiarities of the molecular structures were found. Benzene elimination is regiospecific and stereoselective, resulting from the abstraction of an axial phenyl group and a hydrogen atom from the C‐4 or C‐6 position of the ring.
Enhancement of negative ion currents by argon/CO2 mixtures in an electron impact ion source
Authors: Lauber R. , Schlunegger U. P. 
Published: May 2005

AbstractArgon and mixtures of argon with carbon dioxide in the range of 1–50% have been used as moderator gases for negative ion production in an electron impact ion source of a VG ZAB‐2F mass spectrometer. The enhancement of quasi‐molecular anion ([M – H]−) currents of oxygen‐containing samples has been studied. It is a function of the composition of moderator gas mixture, moderator gas pressure, and sample pressure in the ion source. Most intensive quasi‐molecular anion currents have been observed at a pressure in the ion source of c. 2.5 × 10−5 Torr (measured by the ion gauge remote from the ion source of the ZAB‐2F) using a moderator gas mixture of 10% CO2 in argon. Fragmentation of the samples may be increased by increasing the concentration of CO2 in the moderator gas.
Ortho effect of the nitro group in the fragmentation of 1‐phenyl‐3‐nitrophenyl‐2‐pyrazolines
Authors: Srzić D. 
Published: May 2005

AbstractElectron impact mass spectra and mass‐analysed ion kinatic energy spectra of the title compounds are discussed. The characteristic fragment ions of the ortho isomer are shown by high resolution and kinetic energy release measurements to involve the transfer of hydrogen to the nitro group and oxygen from the nitro group to the pyrazoline carbon.
Ammonia in the ion source. II. Clustering with aromatic nitro compounds
Authors: Gillis Richard G. 
Published: May 2005

AbstractUnder positive ion chemical ionization conditions with ammonla at relatively low pressure, aromatic nitro compounds do not form [M + H]+ ions but often form ionic clusters [M + NH4]+ and [M + N2H7]+. Nitrobenzene forms a cluster [2M + NH4]+ and aniline, formed by nucleophilic substitution, leads to a cluster [anilinium ion + nitrobenzene]+. The dinitrobenzenes form [M + NH4]+ clusters and show evidence of nitroaniline formation and clustering. 1,3,5‐Trinitrobenzene gives little indication of clustering or of substitution. The six isomers of trinitrotoluene appear to be stabilized by the methyl group and form clusters up to [M + N3H10]+. Nucleophilic substitution leads to dinitrotoluidines, which also form clusters with ammonium ions.
Mass spectra of isomeric monothiopyrophosphates
Authors: Kamiński R. , Paneth P. , Reimschüssel W. 
Published: May 2005

AbstractThe main fragmentation patterns of the phosphorus‐containing moiety of bis(5,5‐dimethyl‐2‐oxo‐1,3,2‐dioxaphosphorinanyl) sulphide, 3, and its isomer P‐oxo‐P'‐thiono‐bis(5,5‐dimethyl‐1,3,2‐dioxaphosphorinanyl) oxide, 4, are presented. Isotope studies with 18O, 36S, 34S and 2H indicate that compound 3 undergoes an extensive isomerization prior to fragmentation. The mechanism of this isomerization must involve interaction of at least two molecules, as shown by isotope scrambling experiments.
Isomerization and fragmentation of methylfuran ions and pyran ions in the gas phase
Authors: Spilker Rudiger , Grutzmacher H.‐F. 
Published: May 2005

AbstractThe mutual interconversion of the molecular ions [C5H6O]+ of 2‐methylfuran (1), 3‐methylfuran (2) and 4H‐pyran (3) before fragmentation to [C5H5O]+ ions has been studied by collisional activation spectrometry, by deuterium labelling, by the kinetic energy release during the fragmentation, by appearance energles and by a MNDO calculation of the minimum energy reaction path. The electron impact and collisional activation mass spectra show clearly that the molecular ions of 1–3 do not equilibrate prior to fragmentation, but that mostly pyrylium ions [C5H5O]+ arise by the loss of a H atom. This implies an irreversible isomerization of methylfuran ions 1 and 2 into pyran ions before fragmentation, in contrast to the isomerization of the related systems toluene ions/cycloheptatriene ions. Complete H/D scrambling is observed in deuterated methylfuran ions prior to the H/D loss that is associated with an iostope effect kH/kD = 1.67–2.16 for metastable ions. In contrast, no H/D scrambling has been observed in deuterated 4H‐pyran ions. However, the loss of a H atom from all metastable [C5H5O]+ ions gives rise to a flat‐topped peak in the mass‐analysed ion kinetic energy spectrum and a kinetic energy release (T50) of 26 ± 1.5 kJ mol−1. The MNDO calculation of the minimum energy reaction path reveals that methylfuran ions 1 and 2 favour a rearrangement into pyran ions before fragmentation into furfuryl ions, but that the energy barrier of the first rearrangement step is at least of the same height as the barrier for the dissociation of pyran ions into pyrylium ions. This agrees with the experimental results.
Mass spectrometric studies of cyclopropanes with electronegative substituents. Indication of methoxy group randomization in (±) dimethyl 2‐methoxy‐3,3‐dimethylcyclopropane‐1,1‐dicarboxylate
Authors: Kolsaker Per , Kvarsnes Arnfinn , Storesund Hans‐Johan 
Published: May 2005

Abstract(±) 2‐Methoxy‐3,3‐dimethylcyclopropane‐1,1‐carboxylate was studied by electron impact and chemical ionization mass spectrometry. By using selective deuteration of the methyl groups, it was established that extensive randomization of the methoxy groups takes place prior to the decomposition of the molecular ion.
Low‐energy mass spectra of some aliphatic ketones
Authors: Abbatt Jonathan A. , Harrison Alex G. 
Published: May 2005

AbstractThe charge exchange mass spectra of a selection of C5‐C7 ketones have been measured using [CS2]+˙, [COS]+˙ and [N2O]+. as reagent ions. The low energy charge exchange with [CS2]+˙ or [COS]+˙ provides simple primary ion mass spectra, which readily permit structure elucidation in contrast to metastable ion spectra. In several cases, isomer distinction is easier from the charge exchange mass spectra than from the electron impact mass spectra. The energy transfer from [N2O]+˙ is sufficiently high for complex spectra resembling electron impact mass spectra to be obtained.
The behaviour of stereoisomeric ions in the gas phase: 3—The case of homosubstituted bicyclooctenes
Authors: Grassi Maria , Audisio Guido , Traldi Pietro 
Published: May 2005

AbstractIn the electron impact mass spectroscopy of four 2,3,5,6‐bicyclo(2.2.2)–7‐octenetetramethoxycarbonyl stereoisomers differences in relative abaundances of product ions and also different fragmentation pathways are observed. The stereospecificity is retained also under positive ion chemical ionization (CI(methane), CI(isobutane)) and negative ion chemical ionization (NICI) (OH−) conditions. Interesting correlations between fragmentation and molecular symmetry are suggested.
Discrimination of isomers by liquid ionization mass spectrometry with techniques of collisional activation and adduct ion formation
Authors: Niki Yoshiko , Tsuchiya Masahiko 
Published: May 2005

AbstractLiquid ionization mass spectrometry is a soft ionization technique used with liquid samples under atmospheric pressure. It facilitates the handling of reagents and the observation of ion–molecule reactions in the ion source. The differentiation of isomers by characteristic fragment ions, for example those resulting from asymmetrical cleavage of a cyclobutane ring, and by molecular adduct ion formation was studied. The samples studied were cyclobutane derivatives, alkyl 4‐(3‐oxo‐3‐pIienyl‐l‐aIkenyl)benzoate dimers, and reagents having two functional groups were used to produce adduct ions to clarify the difference between isomers. The reagents act on a sample molecule at two functional groups to form hydrogen bonds. Some correlations were observed between the structure of the sample and the relative abundances of molecular adduct ions and also fragment ions produced by collisionally activated dissociation.
Mass spectra of some 1‐(6′‐substituted‐4′‐methyl‐2′‐quinolyl)‐3‐methylpyrazol‐5‐ols and their 4‐substituted analogues
Authors: Singh Shiv P. , Vaid Radhe K. , Prakash Om 
Published: May 2005

AbstractElectron impact induced fragmentation of some 1‐(6′‐substituted‐4′‐metbyI‐2′‐quinolyI)‐3‐methylpyrazoI‐5‐ols follows a route where the pyrazole moiety is preferentially cleaved with successive losses of two moieties of 41 u. High‐resolution measurements have established that the first loss is due to the Ċ2HO moiety, which necessitates an intramolecular hydrogen transfer followed by ring fission. The resultant ion loses CH3CN in a subsequent step. The origin of many fragment ions was traced with the use of B/E linked‐scan spectra.