bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deuterium isotope effects and mechanism of the gas phase reaction [C3H7]+→[C3H5]+ + H2
Authors: Hvistendahl Georg , Uggerud Einar 
Published: May 2005

AbstractThe deuterium kinetic isotope effect and the deuterium isotope effect upon kinetic energy release have been calculated for the loss of H2 from the [C3H7]+ ion. The calculations are based on the transition state structure suggested recently from ab initio calculations on the reaction pathway. The results obtained are in good agreement with experimental data.
Bifunctional even‐electron ions. II. Fragmentation behaviour of aliphatic ω‐hydroxy and ω‐methoxy methoxonium ions
Authors: Záhorszky U. I. 
Published: May 2005

AbstractBifunctional methoxonium ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} -\mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OH}({\rm b}) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R} - \mathop {\rm C}\limits^ + ({\rm OCH}_3 ) - ({\rm CH}_2 )_{\rm n} - {\rm OCH}_3 ({\rm c}) $\end{document} (c) show as the main reactions those caused by functional group interaction, as has already been found for the analogous hydroxonium ions (g). Although there are similarities in the fragmentation behaviour of the isomeric ions b and g, their fragmentation pathways are different, proving b and g as distinct species. The dominant primary fragmentation for b and c is loss of CH3OH. The hydrogen migrations prior to this reaction have been established by deuterium labelling. The findings on the fragmentation behaviour of the bifunctional methoxonium ions have been extended to the general behaviour of hydroxy and alkoxy substituted alkoxonium ions.
Electron impact and chemical ionization mass spectra of bis(methoxycarbonyl) [2.2](2,5)pyridinophanes. Formation of quinolizinium ions under electron impact
Authors: Rentzea Marina , Hasselbach Hans‐Joachim , Staab Heinz A. 
Published: May 2005

AbstractFor four isomeric bis(methoxycarbonyl)[2.2](2,5)pyridinophanes differing only in the mutual orientation of the two nicotinic ester units, electron impact mass spectra were measured. The fragmentations observed distinguish surprisingly well between the isomers, depending on the transannular substitution pattern. Of special interest is that for one isomer the otherwise unimportant ion at m/z 298 is found as base peak. This ion is formed by expulsion of HCN from the molecular ion, transannular cycloaddition and aromatization to a stable quinolizinium ion. Fragmentation pathways of the isomers are compared, and chemical ionization and negative ion chemical ionization mass spectra are discussed.
Mass spectrometric synthesis—III Gas phase ion/molecule reaction between benzoic acid and some substituted phenols
Authors: Podda Gianni , Maccioni Antonio , Sturaro Alberto , Traldi Pietro 
Published: May 2005

AbstractThe reaction of benzoic acid with some substituted phenols, carried out in the chemical ionization source of a mass spectrometer and under high pressure conditions leads to phenyl benzoate. This has been proved by accurate mass measurements and collision activated dissociation mass‐analysed ion kinetic energy spectra. The intimate mechanisms of this reaction are discussed in detail.
A mass spectral study of stable neutral enols
Authors: Peake D. A. , Stanley J. , Kingsbury C. A. , Gross M. L. 
Published: May 2005

AbstractThe high‐resolution mass spectra of two stable enol tautomers, 4,6‐diethanoyl‐1‐methyl‐5‐phenyl‐3‐cyclohex‐ene‐1,3‐diol (2) and 4‐ethanoyl‐5‐hydroxy‐2‐(1‐hydroxyethylidene)‐5‐methyl‐3‐phenylcyclohexanone (3), and the corresponding diketone tautomer, 2,4‐diethanoyl‐5‐hydroxy‐5‐methyl‐3‐phenylcyclohexanone (1), are reported. Collisional activation of the molecular ions and major ionic fragments is used to assign decomposition pathways and to compare ion structures. Ionized 1 and 2 do not interconvert by a keto‐enol tautomerism, but isomerize to a common intermediate. This isomerization probably involves opening of the cyclohexanone ring and transfer of the enolizable hydrogen, and is followed by elimination of water. The radical cation of 3 does not interconvert with [1]+˙ and [2]+˙ Instead, [3]+˙ dissociates by loss of an acetyl radical and eliminates water via a higher‐energy pathway. As a result, the mass spectra of 1 and 2 are similar, whereas the mass spectrum of 3 is unique.
Thermospray ionization and tandem mass spectrometry of dyes
Authors: Ballard John M. , Betowski Leon D. 
Published: May 2005

AbstractSixteen commercial dye samples and three liquid wastes from organic pigment and dye manufacture have been characterized without prior chromatography by thermospray ionization and low energy collision‐activated dissociation of protonated molecules using a triple quadrupole mass spectrometer. Many samples contained precursors of the dyes and other by‐products of the synthesis. Many of these components were identified by collision‐activated dissociation experiments and by inspection of the chemistry of dye manufacture. Detection limits of 20–200 ng in the positive ion mode were obtained for seven dyes of the anthraquinone, triarylmethane, xanthene, coumarin, azo and sulfonated azo dye classes. Under conditions of negative ionization, detection limits for an anthraquinone dye and a sulfonated azo dye were about one order of magnitude higher.
The involvement of neutral species in the NO− → O+ charge inversion reaction
Authors: Kingston R. G. , Brenton A. G. , Guilhaus M. , Beynon J. H. 
Published: May 2005

AbstractIntermediates in the overall charge inversion reaction NO− → O+˙ (la), have been found to be O and NO˙ neutrals, and NO+ ions. The intermediates involved have been characterized by various mass spectrometric techniques; for example, inducing the steps of the reaction in separate field‐free regions allows the peaks for the consecutive reactions NO− → NO+ → O+˙ (II) to be recorded free from interference. However, to observe the involvement of a neutral intermediate, techniques such as floating the collision cell and applying a voltage to a deflector plate in front of the collision cell have been employed. Utilizing these methods allows a peak to be obtained due to one or both of the processes, NO− → NO˙ → O+˙ (IIIa) and NO− → O+˙ (IIIb), which cannot be separated. It is shown that the peak for the overall reaction NO− → O+˙ can be modelled and reconstructed by addition of peaks, in a ratio of 1:3, produced by reactions II and III. This provides a reasonable account of the peak shape, in particular, of the tails of the peak which correspond to fragmentations involving large translational energy releases of up to 10 eV.
Ionization by fast atom bombardment—A chemical lonization (matrix) process in the gas phase?1
Authors: Schröder E. , Münster H. , Budzikiewicz H. 
Published: May 2005

AbstractIt is proposed that ion formation from non‐ionic substrates under fast atom bombardment occurs essentially by chemical ionization in the gas phase by a matrix plasma. Corroborating experiments regarding the matrix plasma are presented.
Structures of gas phase C5H8 radical cations: A collisional ionization study
Authors: Dass Chhabil , Peake David A. , Gross Michael L. 
Published: May 2005

AbstractCollisional ionization (charge stripping) and charge exchange ionization spectrometry were utilized to determine structures of fourteen cyclic and acyclic C5H8 radical cations, including ionized 1,2‐ 1,3‐, 1,4‐ and 2,3‐pentadienes (‐PD), isoprene, 1‐ and 3‐methylcyclobutenes (1‐ and 3‐MCB), 3‐methyl‐1,2‐butadiene (3‐M‐1,2‐BD), methenecyclobutane (MECB), cyclopentene, 3‐methyl‐1‐butyne (3‐MB), 1‐ and 2‐pentynes and vinylcyclopropane (VCP). The pressure of the charge exchange reagent gas in the ion source was adjusted to generate ions of different energy contents. The structures of the C5H8 ions are energy dependent, and their isomerization reactions can be monitored as a function of the amount of internal energy deposited by charge exchange. 1,3‐PD, isoprene and cyclopentene radical cations are identified as stable ion structures. 1‐MCB, 3‐M‐1,2‐BD and 3‐MB radical cations isomerize to isoprene ions, whereas ionized VCP, 3‐MCB, 1,2‐PD, 2,3‐PD, 1,4‐PD, 1‐pentyne and 2‐pentyne ultimately isomerize to the [1,3‐PD]+˙. Thermodynamic arguments are invoked to corroborate these isomerization reactions. The critical energies of the isomerizations are also estimated.
Electron impact and chemical ionization mass spectra of 2,2‐diphenyl‐3‐arylcyclobutanone oximes. Formation of ion m/z 167
Authors: Sudhakar Reddy G. , Smith Grant Gill 
Published: May 2005

AbstractThe electron impact (EI) and chemical ionization (CI) spectra of 2,2‐diphenyl‐3‐aryl cyclobutanone oximes (1–5) are reported. Formation of diphenylmethyl cation at m/z 167 is a major fragmentation process in both EI and CI spectra. Labelling studies established that the hydrogen involved in this rearrangement transfers from the NOH group and not from cyclobutane ring positions. The [M + 3]+ ions are formed under CI conditions as a result of CN double bond reduction. An interesting secondary kinetic isotope effect is observed in the formation of ion e at m/z 183 in both EI and CI spectra. Other characteristic fragmentation pathways occurring in the EI and CI spectra of these compounds are outlined.
Gas phase glycosidic cleavage of oxynions from alkyl glycosides
Authors: Prome Jean‐Claude , Aurelle Hélène , Prome Danielle , Savagnac Arlette 
Published: May 2005

AbstractThe oxyanion [MH]− from several methylglycosides were generated by fast atom bombardment and their decomposition was studied by mass‐analysed ion kinetic energy spectrometry. The main decomposition pathway is the loss of methanol. The hydroxylic hydrogen arises by proton transfer from the hydroxyl groups of the sugar. In the gluco‐series, no anomeric effect is found. The absence of either the hydroxyl groups at C‐2 or C‐6 does not inhibit the glycosidic cleavage. However, the blocking of both the hydroxyl groups at C‐4 and C‐6, by a benzylidene group or two methyl groups, inhibit completely the glycosidic cleavage. From these results, it is proposed that the glycosidic cleavage occurs after opening the sugar ring by a vicinal attack of an oxyanion at C‐6 or C‐4 to the C‐5 carbon atom. Then, the ionized hemi‐acetals fragment into a methanolate anion and a 5,6‐ or 4,5‐anhydrosugar which exchange another proton before their separation into charged and neutral species.
Electron impact mass spectra of some new macropolycycles
Authors: Constantin E. , Kotzyba‐Hibert F. H. , Lehn J. M. , Traldi P. 
Published: May 2005

AbstractMass spectra of some macropolycycles have been studied. Normal and metastable (B/E) mass spectra are presented. The fragmentation patterns and the structures of the main ions are discussed.
Charge transfer reactions of organic ions containing oxygen: Correlation between reaction energetics and cross sections
Authors: Shields G. C. , Steiner P. A. , Nelson P. R. , Trauner M. C. , Moran T. F. 
Published: May 2005

AbstractCross sections for charge transfer reactions of organic ions containing oxygen have been obtained using time‐of‐flight techniques. Charge transfer cross sections have been determined for reactions of 2.0 to 3.4 keV ions produced by electron impact ionization of oxygen containing molecules such as methanol, ethanal and ethanol. Experimental cross section magnitudes have been correlated with reaction energy defects computed from ion recombination energies and target ionization energies. Large cross sections are observed for reacting systems with small energy defects.
Laser desorption fourier transform mass spectra of ascorbic and isoascorbic acids
Authors: Coad Peter , Coad Raylene A. , Yang Cathy L. C. , Wilkins Charles L. 
Published: May 2005

AbstractPositive and negative ion laser desorption Fourier transform mass spectra of ascorbic acid, isoascorbic acid, and their sodium and potassium salts have been determined. A number of differences between these spectra and previously reported laser microprobe mass analyzer (LAMMA) spectra are found. In contrast with earlier results, m/z 175 anions are present in all negative ion spectra, as are cluster ions. Thus, it should not be concluded that the radical salts are electroneutral, as claimed in the earlier study.
Electron impact induced fragmentations of some 2,2‐disubstituted 1,3‐dithiolanes
Authors: Vainiotalo Pirjo , Nevalainen Vesa 
Published: May 2005

AbstractElectron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.
The reactions of the ions [XC]+, [X2C]+·, [X3C]+· and [X4C]+· (where X = H or F) with ethene and propene
Authors: Robinson J. N. , Tedder J. M. 
Published: May 2005

AbstractThe reaction of C1 ions with ethene and propene has been studied in the gas phase using a triple quadrupole mass spectrometer.
Ion chemistry of α‐diazoketones. 1. A collissional activation study of 1‐diazo‐3‐phenoxypropan‐2‐one upon elecgtron impact
Authors: Selva Antonio , Ferrario Francesco , Saba Antonio 
Published: May 2005

AbstractThe gaseous ionic products of 1‐diazo‐3‐phenoxypropan‐2‐one upon electron impact show that cyclization reactions, which have counterparts in condensed‐phase chemistry, occur in competition with a mass spectral Wolff type rearrangement.
Structure and fragmentation of [C6H13O]+ ions formed by chemical ionization
Authors: Weiss Mathania , Crombie Richard A. , Harrison Alex. G. 
Published: May 2005

AbstractThe structure and fragmentation of eight [C6H13O] + ions formed by protonation of C6H12O carbonyl compounds in the gas phase have been investigated using isotopic labeling and metastable ion studies to investigate the fragmentation reactions and collisional dissociation studies to probe ion structures. Protonated 3‐methyl‐2‐pentanone and protonated 2‐methyl‐3‐pentanone readily‐interconvert by pinacolic‐retro‐pinacolic rearrangements; the remaining six ions represent stable ion structures, although in many cases fragmentation is preceded by pinacolic‐type rearrangements. Unimolecular (metastable ion) fragmentation of the [C6H13O] + species occurs by elimination of H2O, C3H6, C4H8 and C2H4O. The last three elimination reactions appear to occur through the intermediacy of a proton‐bound complex of a carbonyl compound and an olefin, with the proton residing with the species of higher proton affinity on decomposition of the complex.
Mass spectrometry of 1,3,4‐thiadiazolo thiacrown ethers
Authors: Pappalardo Sebastiano , Occhipinti Salvatore 
Published: May 2005

AbstractThe mass spectra of two homologous series of 1,3,4‐thiadiazolo thiacrown ethers possessing one or two heterocyclic subunits, respectively, have been correlated and compared with those of closely related open‐chain analogues. The prevailing feature in the spectra of these macrocycles is the presence of homologous series of ions, which formally correspond to the sequential loss of C2H4O units from appropriate precursors. The majority of these ions have been rationalized in terms of structure and mechanism of formation by assuming an electron impact induced isomerization process (via H migration) of the molecular ion to several competing linear structures prior to fragmentation. Metastable peak analysis and high‐resolution measurements provide support for the postulated fragmentation mechanisms and product ion structures.
Multidimensional computer evaluation of mass spectra
Authors: Neudert R. , Bremser W. , Wagner H. 
Published: May 2005

AbstractThe increasing importance of spectroscopic methods as an analytical tool in industry, combined with the trend to automatize spectrometers, demands new standards in the quantity and quality of spectrum interpretation. Suitable computer programs should be able to predict structural features from mass spectral properties. The knowledge base is a structure‐oriented mass spectral data collection consisting of some 42000 spectra and topologies. The comparison of selected mass spectral properties such as similarity, neutral losses and ion series of the unknown with the equivalent properties of the library spectra results in a set of corresponding structures. Subsequent substructure analysis yields a histogram of substructure frequencies containing information about their statistical relevance. The relevant substructure set may be recombined to produce a structure proposal, as is demonstrated for 1‐acetyl‐2‐methoxy‐4‐trimethylsilyioxybenzene. In a second example, the relevant substructures derived by the interpretation system are used as input for the 13C‐NMR substructure generator. This procedure reduces the solution space of the structure prediction algorithm considerably. Besides the spectrum interpretation, additional possibilities are available. The substructure search enables us, for example, to look for mass spectrometric reaction centres. Beyond that, substructure analysis is applicable to the determination of structural features typical of certain combinations of neutral losses and/or characteristic fragments.
The chemical ionization mass spectra of 2‐tert‐butyl‐substituted 1,3‐cycloalkanediol diacetates and dimethyl ethers
Authors: D'Haenens L. , Van De Sande C. C. , Schelfaut M. , Vandewalle M. 
Published: May 2005

AbstractThe chemical ionization (CI) mass spectra of the 2‐tert‐butyl‐substituted 1,3‐cyclopentane‐ and 1,3‐cyclohexanediol diacetates and dimethyl ethers have been determined using isobutane and methane as reagent gases. From the differences in the spectra of these compounds, it clearly follows that steric and conformational effects are expresssed in the CI mass spectra. The relative impact of these effects, however, is strongly dependent on diol derivatization and 2‐alkyl substitution.
Chemical ionization mass spectrometry with amines as reactant gases. V—Amine chemical ionization mass spectrometry of flavonoid glycosides
Authors: Mollova N. N. , Bankova V. S. , Popov S. S. 
Published: May 2005

AbstractThe chemical ionization mass spectra of flavonoid glycosides (O‐glycosides, C‐glycosides and acetylated glycosides) have been investigated. Triethylamine, ethylenediamine, diethylamine, methylamine and ammonia were used as reactant gases. The fragmentation mechanism is discussed, and the perspectives for establishing the molecular weights of glycosides, aid the nature of both the sugar residue and the aglycone, are outlined.
Destabilized carbenium ions. Secondary and tertiary α‐acetylbenzyl cations and α‐benzoylbenzyl cations
Authors: Dommröse Anne‐Marie , Grützmacher Hans‐Friedrich 
Published: May 2005

AbstractThe secondary α‐acetylbenzyl and α‐benzoylbenzyl cations, as well as their tertiary analogues, have been generated in a mass spectrometer by electron impact induced fragmentation of the corresponding α‐bromoketones. These ions belong to the interesting family of destabilized α‐acylcarbenium ions. While primary α‐acylcarbenium ions appear to be unstable, the secondary and tertiaiy ions exhibit the usual behaviour of stable entities in a potential energy well. This can be attributed to a ‘push‐pull’ substitution at the carbenium ion centre by an electron‐releasing phenyl group and an electron‐withdrawing acyl substituent. The characteristic unimolecular reaction of the metastaible secondary and tertiary α‐acylbenzyl cations is the elimination of CO by a rearrangement reaction involving a 1,2‐shift of a methyl group and a phenyl group, respectively. The loss of CO is accompanied by a very large kinetic energy release, which gives rise to broad and dish‐topped peaks for this process in the mass‐analysed ion kinetic energy spectra of the corresponding ions. This behaviour is attributed to the rigid critical configuration of a corner‐protonatei cyclopropanone derivative and a bridged phenonium ion derivative, respectively, for this reaction. For the tertiary α‐acetyl‐α‐methylbenzyl cations, it has been shown by deuterium labelling and by comparison of collisional activation spectra that these ions equilibrate prior to decomposition with their ‘protomer’ derivatives formed by proton migration from the α‐methyl substituent to the carbonyl group and to the benzene ring.
Studies in chemical ionization mass spectrometry part. XVI: Are the reactions of aliphatic cc double bonds with NO+ governed by remote functional groups?
Authors: Budzikiewicz H. , Schneider B. , Busker E. , Boland W. , Francke W. 
Published: May 2005

AbstractIt is shown that the characteristic fragments observed by Malosse and Einhorn (Adv. Mass Spectrom. 1369 (1986)) in the CI(NO) spectra of alkenyl acetates and related compounds (cleavage of the double bond and formation of an acyl ion), which had not been reported, for alkenes and alkenoic acids, for example, are actually formed from all straight‐chain olefinic compounds (the only exceptions being where the double bond is too close to one of the ends of the chain). Their relative abundance may, however, vary from almost zero to 100%, and it is highly dependent on experimental parameters (e.g. the source temperature and even the type of instrument used). Apparent inconsistencies in the data reported in the literature could thus be resolved.
Electron impact mass spectrometry of hemiterpenoid tricyclic quinoline alkaloids
Authors: Sturaro Alberto , Traldi Pietro , Bravo Pierfrancesco , Viani Fiorenza , Resnati Giuseppe 
Published: May 2005

AbstractThe mass spectral behaviour of some quinoline‐type alkaloids, 3,4‐dihydro‐2H,5H‐pyrano[3,2‐c]quinolin‐5‐ones, isomeric 3,4‐dihydro‐2H,5H‐pyrano[2,3‐b]quinolin‐5‐ones and 2H,5H‐pyrano[3,2‐c]quinolin‐5‐ones, was studied in detail with the aid of linked scans, exact mass measurements and collisional spectrometry. The occurrence of a partial isomerization of the differently annulated isomers to a common, open‐chain structure is discussed.
Selective surface ionization of quaternary salts on a platinum filament
Authors: Van Gemmeren U. , Röllgen F. W. 
Published: May 2005

AbstractSurface ionization of quaternary ammonium and pyridinium salts evaporated onto a platinum filament has been investigated. The experiments reveal a high selectivity for the formation of intact cations from these salts with virtually no fragmentation up to about 1000 K, and a low level of fragmentation up to about 1300 K, while even at higher temperatures the ionization of volatile non‐ionic compounds such as trialkyl amines is largely suppressed. The fragmentation of quaternary cations at higher temperatures is attributed in part to decomposition reactions in a two‐dimensional ion trap on the surface formed by the image force of the ions. For some compounds and mixtures, evidence is presented of the exchange of alkyl groups for cations as a thermal reaction prior to volatilization of the salts. The surface ionization technique appears promising for selective detection of quaternary salts from complex mixtures.
Mass spectral studies of naphthoflavones
Authors: Guidugli F. H. , Kavka J. , Garibay M. E. , Santillan R. L. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe electron impact induced fragmentations of the five possible naphthoflavones have been studied with the aid of low‐ and high‐resolution measurements, metastable decompositions and isotope labelling using either deuterium or carbon‐13 atoms. All compounds show both the direct expulsion of a CO residue from the carbonyl group and the retro Diels–Alder cleavage. The abundant [M–H]+ ion has been formulated as the substituted β‐tropolone species, which, in the case of β‐naphthoflavone, is in competition with a pentacyclic species arising from the elimination of H‐5 as evidenced in the spectrum of 5‐d‐β‐naphthoflavone. Other previously unsuspected ions are also in evidence.