bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aktivierungsenergie und Mechanismus der intramolekularen Wasserstoff‐Wanderung bei Radikal‐Kationen von Keto/Enol‐Tautomeren in der Gasphase
Authors: Schwarz Helmut , Wesdemiotis Chrysostomos 
Published: May 2005

AbstractDie nicht zerfallenden Radikalkationen des Methylacetates [CH3COOCH3]+. und seiner Enolform [CH2C(OH)OCH3]+⋅ liegen aufgrund ihrer Stoßaktivierungsspektren in Potentialminima vor. Für zerfallende [C3H6O2]+ ‐Ionen wird belegt, daß der CH3O⋅ ‐Eliminierung aus [CH2C(OH)OCH3]+⋅ eine geschwindigkeitsbestimmende, symmetrieverbotene [1,3]‐Wasserstoffumlagerung vorgelagert ist. Der Alternativweg von zwei konsekutiven, formal symmetrieerlaubten [1.2]‐Wasserstoffverschiebungen spielt bei dieser Isomerisierung mit Sicherheit keine Rolle. In Abhängigkeit von der elektronischen Natur der Kationen (“open” “order” “closed” shell‐Systeme) liegt die Aktivierungsenergie solcher Umlagerungen im Bereich von 41–83 kcal · Mol−1.
Substituent effects in the mass spectra of benzoyl hetarenes
Authors: Grützmacher Hans‐Fr. , Schubert Ralf 
Published: May 2005

AbstractThe mass spectra of several benzoyl hetarenes, of 2‐benzoyl pyridines substituted at the phenyl and pyridyl group, respectively, and of phenyl substituted 2‐benzoyl pyrroles, have been studied with respect to the formation of benzoyl and hetaroyl ions. A correlation between the intensity of benzoyl ions, relative to molecular ion intensity, and the π‐electron density at the substituted carbon atom of the hetarene has been observed for benzoyl hetarenes. The relative intensities of (substituted) benzoyl ions of substituted 2‐benzoyl pyridines and 2‐benzoyl pyrroles are not easily related to substituent constants of Hammett equations. The relative ionization energies of phenyl substituted 2‐benzoyl pyridines, however, and the relative appearance energies of substituted benzoyl ions derived therefrom follow the σIP+‐constant of Bentley and Johnstone and the σ+‐constants of Brown, respectively.
Mass spectrometry of organic compounds of the group V Elements: VI—A new type of amine fragmentation under electron impact
Authors: Kostyanovsky R. G. , Voznesensky V. N. , Kadorkina G. K. , El'natanov Yu. I. 
Published: May 2005

AbstractA new type of amine fragmentation under electron impact is elucidated for proline, sarcosine and aspartic acid derivatives and aminomethylphosphines of the general formula R2NCH2X. Ordinary α‐cleavage affording the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_2 \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2} $\end{document} ion is suppressed by elimination of a neutral HX particle and [M ‐ HX]+ ion formation, or M‐HX neutral particle ejection and generation of an [HX]+ ion from [M]+˙. Such fragmentation is ensured by the presence of an α‐heteroatom (N, O, P, S) in one substituent (X) and a CO2R type delocalizing group in the α‐position of the other substituent (R2N).
Anionization of volatile molecules on the surface of electrolytic solutions exposed to high electric fields
Authors: Ott K. H. , Röllgen F. W. , Dähling P. , Zwinselman J. J. , Fokkens R. H. , Nibbering N. M. M. 
Published: May 2005

AbstractThe anionization of molecules supplied from the gas phase onto a negatively charged [Cl]− or [NO3]− ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO3) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]− and [NO3]− attachment and of some acids by proton abstraction is reported.
Metastable ion studies: XIII—the measurement of appearance energies of metastable peaks
Authors: Burgers Peter C. , Holmes John L. 
Published: May 2005

AbstractA simple, accurate and reproducible method is described for measuring the appearance energy of a metastable peak. The method involves the comparison of the metastable peak intensity with that of a ‘standard’ metastable peak, over a small range of ionizing electron energies above their onsets. Six fragmentation processes whose reaction energetics are well established were selected to provide suitable calibrant metastable peaks. Results are also presented for fragmentations having large kinetic shifts and for some primary and secondary ion decomposition of current interest.
Stereochemistry of HOH and HOAc elimination from 1‐tetralol and 1‐acetoxytetralin radical cations
Authors: Groenewold G. S. , Gross M. L. 
Published: May 2005

AbstractWater and acetic acid eliminations from 1‐tetralin radical cations have been shown previously to be highly regiospecific 1,4 processes. Utilizing deuterium labeling, high resolution peak ratio measurements and metastable ion defocusing techniques, the stereochemistry of these processes has been investigated. cis‐4‐d1‐ and trans‐4‐d1‐1‐Tetralol both lose HOH and DOH in appreciable amounts; similarly, both acetoxy derivatives lose HOAc and DOAc. These results are interpreted in terms of an ionic epimerization which operates in competition with a stereospecific 1,4 elimination mechanism. A hydrogen exchange process which occurs between the 4‐carbon and the oxygen atom situated on the 1‐carbon of 1‐tetralol has also been observed. This process accounts for observed H/D ratios in the ethene elimination reaction of various deuterium labeled 1‐tetralols.
Quality control and evaluation of mass spectra
Authors: Milne G. W. A. , Budde W. L. , Heller S. R. , Martinsen D. P. , Oldham R. G. 
Published: May 2005

AbstractOver 1400 electron ionization mass spectra of selected organic compounds have been measured under carefully defined conditions. In this paper, the variables such as sample purity and spectrometer calibration that are controlled are described. The quality of the resulting spectra as well as the cost of the measurements is reported.
Fast atom bombardment mass spectrometry of butyloxycarbonyl protected (BOC) amino acids
Authors: Garner George V. , Gordon Derek B. , Tetler Lee W. , Sedgwick R. Donald 
Published: May 2005

AbstractThe positive and negative ion mass spectra of a series of BOC‐protected amino acids have been obtained using an FAB source. The spectra show characteristic features including a McLafferty type of rearrangement.
The structure of [C3H4N2]+· and [C5H5N2]+ ions formed from vinylimidazoles, studied by collisionally activated dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Houte J. J. , Van Thuijl J. 
Published: May 2005

AbstractMass spectra of the three isomeric vinylimidazoles have been compared and the structures of the fragment ions [C3H4N2]+· and [C5H5N2]+ have been investigated by collisionally activated dissociation mass spectrometry. The greater part of the non‐decomposing ions m/z 68 from 2‐vinylimidazole and from 2‐imidazolecarboxylic acid methyl ester, and a minor part of this ion formed from the free acid, all have the same structure: the imidazole ring system, with hydrogens at both nitrogen atoms but none at C(2). An analogous structure, with an ethyl group at C(2), is proposed for the m/z 93 ion from 2‐vinylimidazole.
Mass spectra of chlorinated aromatics formed in pulp bleaching 2—Chlorinated guaiacols
Authors: Knuutinen Juha , Korhonen Ilpo O. O. 
Published: May 2005

AbstractThe fragmentation of chlorinated guaiacols (2‐methoxyphenols) on electron impact has been studied. The most common fragmentation processes are interpreted and in some cases the small differences between spectra of positional isomers are explained. In addition to the well‐known alkyl‐oxygen fission (loss of methyl radical), metastable ion studies and deuterium labelling have indicated several new fragmentation pathways. The most characteristic are the formation of [MCH3HCl]+ and [MCH3Cl]+· ions. In general, however, the spectra of positional isomers are shown to be very similar.
Mass spectrometry of 7,7′,8,8′‐tetracyanoquinodimethane and of some of its radical anion salts
Authors: Mermilliod N. , Sellier N. 
Published: May 2005

AbstractWe present mass spectrometry experiments on tetracyanoquinodimethane (TCNQ), deuteriated TCNQ and on some TCNQ salts. Apart from the usual nitrile fragmentation, at least two original features appear in the spectra. The first is the formation of TCNQ dimers, as evidenced by their molecular peaks and their fragmentation. The second aspect concerns the spectra of the ammonium salts, which show that hydrogen or alkyl groups add to TCNQ before its decomposition, leading to new fragments (as m/z 141).
Gas phase protonation and subsequent dissociations in β‐amino alcohols as a function of exoergicity and interfunctional distance
Authors: Houriet Raymond , Rufenacht Hermann , Stahl Daniel , Tichy Milos , Longevialle Pierre 
Published: May 2005

AbstractThe gas phase protonation of β‐amino alcohols and subsequent water loss is investigated in an ion cyclotron resonance spectrometer. It is found that the loss of water is correlated with the formation of oxonium ions (OH protonation). A relationship is found between the extent of internal stabilization at short interfunctional distance in protonated amono alcohols and the exoergicity of protonation required to induce the loss of a water molecule.
Stereochemical effects in mass spectrometry: 2—Chemical ionization mass spectra of some cyclic glycols and mono‐ and di‐saccharides using trimethyl borate as reagent gas
Authors: Suming Hua , Yaozu Chen , Longfei Jiang , Shuman Xue 
Published: May 2005

AbstractThe chemical ionization mass spectra of cyclic glycols and mono‐ and di‐saccharides using trimethyl borate as reagent gas have been studied. In the gas phase, the trimethyl borate ions react stereospecifically with molecules of cis‐cyclic glycols to form characteristic ions, from which the stereochemical isomers of 1,2‐cyclopentanediols, 1,2‐cyclohexanediols and mono‐ and di‐saccharides can be definitely distinguished.
A combined time‐resolved and stereospecific deuterium labelling study of the elimination of methanol from the molecular ion of methoxycyclohexane
Authors: Molenaar‐Langeveld Tineke A. , Nibbering Nico M. M. 
Published: May 2005

AbstractIt is shown by field ionization kinetics in combination with both site‐specific and stereospecific D‐labelling that the loss of a molecule of methanol from the molecular ion of methoxycyclohexane can occur via 1,4‐ and 1,3‐eliminations. The 1,4‐elimination predominates at molecular ion lifetimes of ≥10−10.1 s. It is found that ∼19% of this reaction channel corresponds to a stereospecific cis‐elimination, whereas the remaining 81% is only site‐specific. At molecular ion lifetimes of between 10−10 and 10−9 s, a very sudden increase of the 1,3‐elimination is observed at the expense of the 1,4‐elimination. A stereospecific loss of methanol, however, is not observed at all for the 1,3‐elimination within the limits of error. Possible intermediates and reaction pathways, which can account for the observations made, are discussed.
Charge reversal of the conjugate base of formamide
Authors: Kiplinger Jeffrey P. , Maynard Andrew T. , Bursey Maurice M. 
Published: May 2005

AbstractCharge reversal collisional activation mass spectremetry of negative ions has been used in conjunction with positive ion collisional activation to investigate several isomeric [H2, C, N, O]+ ions. Generation of m/z 44 ions from formamide, acetamide, JV‐methylformamide, acetaldoxime and by charge reversal of the [M–1]− ion formed from formamide yields several different isomeric structures. Charge reversal of the conjugate base of formamide appears to yield a mixture of singlet and triplet H2NCO+ ions; experiments with deuterium‐labeled compounds have been used to support this. Ab initio molecular orbital calculations indicate that the triplet ion is a stable structure, existing in a potential minimum 390.6 kJ mol−1 above the ground state singlet.
The ethyl halides: Stable neutral and radical cation isomers [C2, H2, X] where X = F, Cl, Br, I
Authors: Blanchette Marcia C. , Holmes John L. , Lossing F. P. 
Published: May 2005

AbstractThe following isomers of the ethyl halide molecular ions have all been shown to be stable species in the gas phase: [CH2CH2FH]+˙; [CH3ClCH2]+˙ (ΔHf° = 1012 kJ mol−1); [CH3CHClH]+˙ (ΔHf° = 971 kJ mol−1); [CH2CH2ClH]+˙; [CH3BrCH2]+˙ (ΔHf° = 1058 KJ mol−1); [CH3CHBrH]+˙ (ΔHf° = 995 kJ mol−1) and [CH2CH2BrH]+˙.Neutralization–reionization mass spectrometry, employing Xe as the electron transfer target gas and O2 as the target gas for reionization, indicated that the ylides CH3ClCH2 and CH3BrCH2 could not be generated by such means. However, the species CH3CHClH, CH2CH2ClH and CH2CH2BrH (and possibly CH3CHBrH) were unambiguously identified.
Internal reactions of ion–neutral complexes from some disubstituted protonated benzaldehydes and acetophenones
Authors: Grützmacher Hans‐Fr. , Thielking Gerhard 
Published: May 2005

AbstractProtonated benzaldehydes ‘a’ and protonated acetophenones ‘b’, substituted by a methoxymethyl group, a hydroxy‐methyl group and a mercaptomethyl group, respectively, in position 3, in addition to a methoxymethyl side chain at position 5, have been prepared by electron impact induced dissociation from the corresponding benzylic alcohols. The spontaneous fragmentations of metastable ions of ‘a’ and ‘b’ have been investigated with the aid of specifically deuterated derivatives. Large signals arc observed for the loss of methanol induced by a proton migration across the aromatic ring. The competing loss of H2O and H2S, respectively, from the second side chain is less abundant, in agreement with the smaller PA's of HO and HS groups. The elimination of HCOX and CH3COX (X = OCH3, OH, SH), respectively, from ‘a’ and ‘b’ is also observed. The label distributions for these reactions are in agreement with a mechanism corresponding to an internal reaction of [CHO] + and [CH3CO] +, respectively, with the functional group of the side chains in an intermediary ion–neutral complex. In addition, fragmentations are observed arising from reactions between the two side chains at positions 3 and 5. The D labelling proves specific reactions without any H/D exchange and thus reaction channels separated from the methanol loss. The results are explained by internal ion‐molecule reactions in an intermediary ion‐neutral complex of a methoxymethyl cation, a hydroxymethyl cation and a mercaptomethyl cation, respectively, formed by a protolytic bond cleavage of the side chains.
A reinvestigation of the collisional activation mass spectra of [C7H7]+ ion mixtures
Authors: Buschek J. M. , Ridal J. J. , Holmes J. L. 
Published: May 2005

AbstractThe collisional activation (CA) mass spectra of the two isomeric [C7H7]+ ions, benzyl and tropyl, have been reassessed. The structure‐characteristic feature of their CA mass spectra, the m/z 77:74 abundance ratio, has been confirmed as 3.15 ± 0.2 for benzyl cations and lowered to 035 ± 03 for tropyl ions. Benzyl–tropyl cation mixture analyses were made and were in general agreement with earlier CA results, but still disagree with the results of ion cyclotron resonance experiments. The behavior of toluene molecular ions close to their dissociation threshold to [C7H7]+ + H˙ was examined; for metastable [C7H8]+˙ ions an approximately 55:45 benzyl:tropyl ratio was found. Observations are discussed in relation to photoionization and photoelecrron‐photoionization coincidence studies, both of which predict high tropyl ion contents at low energies. However, at the lowest energies attainable in this study the benzyl content failed to fall below 50% and it is concluded that toluene molecular ions do not generate tropyl cations at their dissociation limit.
Energetics of retro‐Diels–Alder fragmentation in limonene as characterized by surface‐induced dissociation, and energy‐ and angle‐resolved mass spectrometry
Authors: Vincenti Marco , Horning Stevan R. , Cooks R. Graham 
Published: May 2005

AbstractIonized limonene and related isomeric compounds have been examined by collisional activation at both gaseous and solid targets. The gas‐phase collision‐induced dissociation (CID) experiments were performed as a function of collision energy and scattering angle and the surface‐induced dissociation (SID) experiments as a function of collision energy, in order to vary systematically the internal energy deposited in the molecular ion. The virtual absence of retro‐Diels–Alder (RDA) fragmentation upon conventional CID, as compared to its importance in the electron impact (EI) mass spectrum, the subject of a study by Boyd and coworkers, was confirmed. However, as the ion internal energy was increased by raising the collision energy or the scattering angle, RDA fragmentation was observed and it became a dominant mode of fragmentation for SID at collision energies in the range of 25–50 eV. The energy deposited into the colliding ion in the SID technique is compared with that deposited upon CID in the eV and keV energy ranges and upon EI. The order obtained is: SID > EI > low‐energy, multiple‐collision CID > high‐energy, single‐collision CID > low‐energy, single‐collision CID. The distribution of energies in SID is narrower than in the other techniques. High internal energies are accessible by increasing the scattering angle in CID; however, this is accompanied by an increase in the width of the internal energy distribution, and it is therefore not possible to channel fragmentation predominantly into RDA by this method. It is concluded that RDA fragmentation of limonene is a high‐energy process and that this is the explanation for its behavior. Isomerization, occurring through 1,3‐hydrogen migrations of the molecular ions of limonene, isolimonene, terpinolene and α‐terpinene, was investigated and long‐lived molecular ions of the first three compounds were found to maintain distinct structures.
Fragmentation characteristics of trialkylphosphane oxides, R3P(O)
Authors: Keck Helmut , Kuchen Wilhelm , Kühlborn Sabine 
Published: May 2005

AbstractFragmentation characteristics of trialkylphosphane oxides, R3P(O) (R: Et, n Pr, n Bu) are given and discussed. For phosphane oxides with substitutents R > Et fragmentations within the alkyl groups and ‘conventional’ McLafferty rearrangements are observed. The results of a structure determination for radical cations [C2H7PO]+˙ (m/z 78) and [C4H11PO]+˙ (m/z 106) obtained by collisional activation mass spectrometry are reported.
Triterpenoids. Part IV. Mass spectrometry of pentacyclic triterpenoids: 18β‐ and 18α‐11‐oxooleanolic acid derivatives
Authors: Wyrzykiewicz E. , Wrzeciono U. , Zaprutko L. 
Published: May 2005

AbstractThe mass spectral fragmentation of five pairs of 18β‐ and 18α‐11‐oxooleanolic acid derivatives 1a, 1b–5a, 5b are investigated and discussed. Fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed, The obtained data create a safe basis for distinguishing the above‐mentioned 18 diastereomers.
Sulphonylium ions in the gas phase
Authors: Chatgilialoglu C. , Guerra M. , Pelli B. , Traldi P. 
Published: May 2005

AbstractElectron impact mass spectrometry was used to investigate the fragmentation of a series of arenesulphonyl chlorides. Sequential losses of a chlorine atom and sulphur dioxide from the molecular ions occurred and the reverse of these reactions had small critical energies that were generally unaffected by the ring substituent. However, an interesting intramolecular cyclization reaction occurring on the ortho‐nitro derivative is discussed with the aid of kinetic energy release measurements on this derivative and on a model compound. Appearance energy measure ments combined with multiple scattering Xα calculations led to an estimate of the sulphur‐chlorine bond strength in benzenesulphonyl chloride.
Analyzer scan modes for hybrid mass spectrometers
Authors: Glish Gary L. , McLuckey Scott A. 
Published: May 2005

AbstractThe scan modes that can be used to obtain daughter ion, parent ion, and constant neutral‐loss spectra on hybrid mass spectrometers are derived for instruments with a quadrupole combined with a magnetic and/or electric sector. All combinations of sector/quadrupole and quadrupole/sector instruments are discussed. The advantages or lack thereof of the various scans are presented with respect to operation, resolution and potential artifacts.
Gas‐phase chemistry of electron deficient organometallic anions: the reactions of [Cr(CO)3]− ˙ and [Cr(CO)4]− ˙ with aldehydes, ketones, esters and ethers
Authors: Gregor I. K. 
Published: May 2005

AbstractReactions in the gas phase of the 13‐ and 15‐electron radical anions [Cr(CO)3]− ˙ and [Cr(CO)4]− ˙ with a series of 27 aldehydes, ketones, esters and ethers have been examined. Sequential alkane eliminations and metal‐bonded CO ligand displacements were the principal reactions identified for the RCHO/[Cr(CO)3]− ˙ systems with the latter reaction also common to the RCHO/[Cr(CO)4]− ˙ systems. While [Cr(CO)4]− ˙ was generally unreactive towards ketones R · R'CO, the principal products identified for [Cr(CO)3]− ˙/ketone reactions were the metal‐decarbonylated species, respectively [R · R'CO · Cr(CO)x]− ˙ with x = 0–3, and [R · (R' ‐ H2)CO · Cr(CO)2]− ˙. The reaction of [Cr(CO)3]− ˙ with esters RCOOR' proceeds via metal insertion into the alkoxy CO bond to give end products of the type [R'O · Cr · R(CO)2]− and [R'OCr(CO)3]− while the sole ionic products of dialkyl ether/[Cr(CO)3]− ˙ reactions were identified as the alkoxytricarbonylchromium species [RO · Cr(CO)3]−.
Fragmentation and rearrangement patterns of phospho‐ureas. Possible consequences for biotin activation
Authors: Belghith Hachemi , Blonski Casimir , Klaébé Alain , Périé Jacques , Roussel Jean 
Published: May 2005

AbstractAnalysis by electron impact and metastable ions (MIKE technique) of the fragmentation patterns for one acyclic and two cyclic N‐phosphorylated ureas reveals for the first case an isomerization from nitrogen to the ureido oxygen atom of the phosphoryl group and subsequent fragmentation. For the other two cases, fragments result from PN bond breaking and ring‐opening. Possible involvement in the biotin‐ATP activation process is discussed.
Mass spectra of substituted pyrrolidine‐N‐oxyl radicals
Authors: Jerkovich Gyula , Hankovszky H. Olga , Hideg Kálmán 
Published: May 2005

AbstractElectron impact mass spectra of 65 pyrrolidine‐N‐oxyl derivatives have been assigned on a ‘peak‐to‐subgraph’ basis. On average, 50% of the total ion current is represented by structurally significant fragments associated with the nitroxide group. Secondary fragmentation is, as a rule, of a minor importance (30%), and fragments due to functional groups other than NO· seldom contribute more than 10% of the total ion current An enhanced specificity of fragmentation is observed when one or more of the 2,2, 5,5‐methyl groups is replaced by a longer aliphatic chain or an aromatic group.
Gas‐phase ion–molecule reactions in dilute mixtures of dimethyl ether in krypton. Bimolecular and clustering reactions
Authors: Illies Andreas J. 
Published: May 2005

AbstractThe results of high‐pressure variable‐temperature and variable ionizing electron energy studies of gas‐phase ion‐molecule reactions of dimethyl ether in krypton are presented. Near the ionization threshold a series of peaks corresponding to (CH3OCH3)nH+ (n = 1‐4) clusters are observed. At higher ionizing electron energies, two new series of peaks appear, corresponding to [CH3OCH2]+(CH3OCH3)n and [(CH3)3O]+ (CH3OCH3)n clusters. The onium ion, [(CH3)3O]+, has been previously reported at elevated temperatures under methane chemical ionization conditions. It was suggested that the onium ion is formed by reaction of (CH3)2OH+ with CH3OCH3 with subsequent elimination of methanel, i.e. by fragmentation of an adduct ion. The present results strongly suggest that, under our conditions, [CH3OCH2]+ rather than thermal (CH3)3OH+, is the precursor to [(CH3)3O]+.