bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative chemical ionization spectra of aromatic acids and esters or are negative chemical ionization spectra of use only if one knows what one is looking for?
Authors: Stöckl D. , Budzikiewicz H. 
Published: May 2005

AbstractIt is shown that the appearance of negative chemical ionization spectra where the reactant gas is allegedly used only to produce low energy electrons is dependent upon instrumental parameters as well as the type of reactant gas used. Reactions with neutral or positive plasma particles, ion/molecule reactions of the substrate, and side reactions with ubiquitous trace impurities (O2, H2O) resulting in ions with masses above that of the molecular ion, as well as differing energy distributions of the thermal electrons which are of importance for the fragmentation behaviour can drastically influence the appearance of a mass spectrum.
Combined liquid chromatography time‐of‐flight mass spectrometry: An application of 252Cf fission fragment induced desorption mass spectrometry
Authors: Jungclas Hartmut , Danigel Harald , Schmidt Lothar , Dellbrügge Jörg 
Published: May 2005

AbstractA 252Cf fission fragment induced desorption mass spectrometer has been coupled on‐line to a high‐performance liquid chromatograph. The polar effluent (MeOHH2O) is introduced directly into a rough vacuum stage, where a thin sample of non‐volatile compounds is collected in a vacuum‐drying process (<1 cm3 min−1). The interface which spans the difference in operating pressure between the collection site and the ion source consists basically of a sample changing disk. Twelve discrete samples are collected consecutively and analysed, typically one per minute. The system has been tested for the quantitative analysis of some antitumor drugs in serum using homologous compounds as internal standards.
Cluster ion structures formed by positive and negative chemical ionization of lactic and other hydroxyacids
Authors: Li Zhong‐min , Kruger T. L. , Cooks R. G. 
Published: May 2005

AbstractBoth positive ion and negative ion chemical ionization mass spectra of hydroxycarboxylic acids (hydroxyethanoic acid, 3‐hydroxypropanic acid, 2‐hydroxypropanoic acid and 1‐phenyl‐1‐hydroxyethanoic acid) show intense oligomeric ions when the samples are evaporated into a chemical ionization source. The observation of oligomeric anionic and cationic species is unusual, and the parallel behavior observed between the positive and negative ion mass spectra is striking. These results are explicable in terms of evaporation of oligomers and their dehydration products from the hot probe, although gas phase clustering reactions of singly charged ions are not excluded. Hydrogen bonding and dehydration provide bonding within each cluster. The structures of the ions have been confirmed by recording the collision induced dissociations of individual cluster ions via their mass analyzed ion kinetic energy spectra. Temperature dependence of the chemical ionization mass spectra provides a method for distinguishing hydrogen bonding from covalent bonding and gives further structural information on the cluster ions.
The mass spectrometry of 4‐arylquinolizid‐2‐ones
Authors: Gołȩbiewski W. Marek 
Published: May 2005

AbstractThe fragmentation pathways of ten 4‐substituted quinolizid‐2‐ones were established using exact mass measurement, deuterium labelling and detection of metastable transitions. The base peak for most ketones was formed by cleavage of the C‐2C‐3 bond (α to the carbonyl group) and the benzylic C‐4N bond. The decompositions examined were compared with those of the Nuphar alkaloids.
Comparison of collisional activation spectra of some positive ions produced both by charge reversal of negative ions and by decomposition of positive ions
Authors: Lehman Thomas A. , Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald , Liotta Dennis , Waykole Liladhar 
Published: May 2005

AbstractThe charge reversal collision induced decomposition mass analyzed ion kinetic energy spectrum of allyl anion has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of allyl cation and found to be identical except for the presence of +2 ions formed by charge stripping in the spectrum of the [C3H5]+ ion. Likewise, the collision induced dissociation mass analyzed ion kinetic energy charge reversal spectrum of [CH3Se]− has been compared with the collision induced dissociation mass analyzed ion kinetic energy spectrum of [CH3Se]+ and found to be identical. A study of the pressure dependence of the collision induced dissociation mass analyzed ion kinetic energy spectrum of [C3H5]+ and [C3H5]− showed increasing fragmentation with increasing collision gas pressure, and suggests that a greater mean number of collisions converts more energy to internal modes in the collision induced dissociation mass analyzed ion kinetic energy experiment even at low pressures.
Analysis of peptides by means of a single focusing mass spectrometer equipped with a molecular beam solid analysis/fast atom bombardment source
Authors: Aubagnac Jean‐Louis , Devienne F. M. , Combarieu R. 
Published: May 2005

AbstractThe use of a molecular beam solid analysis/fast atom bombardment source in conjunction with a single focusing mass spectrometer of limited specification is described for the identification of peptides. This ionization method is shown to have significant advantages for such analyses and the performance of the mass spectrometer is shown to be adequate for this work.
Mass spectrometry of dinucleotide analogues containing 6‐azauracil moiety
Authors: Zasada‐Parzyńska Alicja , Golankiewicz Krzysztof 
Published: May 2005

AbstractThe mass fragmentation of three dinucleotide analogues in which D‐ribose phosphodiester linkages were replaced by a three methylene unit chain has been investigated. The fragmentation pathways were proposed on the basis of high resolution data and metastable transitions. These compounds demonstrated a unique fragmentation with the formation of the fragment ion containing nitrogen at the end of the C3H6 chain.
Negative ion chemical ionization mass spectra of (η6‐arene)Cr(CO)3
Authors: Vaglio Gian Angelo , Volpe Paolo , Operti Lorenza 
Published: May 2005

AbstractThe negative ion chemical ionization mass spectra, with ammonia and methane as reagent gases, of the (η6‐arene)Cr(CO)3 complexes, where the arene is C6H5COCH3, C6H5COC2H5, C6H5COC3H7, C6H5COC(CH3)3, 2‐CH3C6H4COC3H7, C6H5COOCH3, C6H5CH3, 1,3,5‐(CH3)3C6H3 and C6H5CH2COC2H5, are reported. Similar behaviour is observed with the two reagent gases, but ammonia shows a much higher abundance for the ions produced by reactions of [NH2]− with sample molecules. The compounds containing the C6H5CO group display an abundant [M]− ˙, whereas the other compounds exhibit [MH]− as base peak, produced by ion/molecule reactions. A comparison of the negative ion chemical ionization mass spectra of the (η6‐arene)Cr(CO)3 complexes with those of the corresponding ligands shows the strong electron withdrawing power of the Cr(CO)3 group in the gas phase.
Electron impact mass spectra of bifunctional steroids. The interaction between ionic and neutral fragments derived from the same parent ion
Authors: Longevialle Pierre , Botter René 
Published: May 2005

AbstractApparent ‘long distance’ H transfers in the fragmentation of bifunctional steroids under electron impact result from an ‘intramolecular’ reaction between ionic and neutral fragments. These transfers are made possible by the independent rotation of the fragments and result from a compromise between their cross‐section and the velocity of separation of the fragments. They are compared with other processes previously described as involving the formation of a ‘complex’ between ionic and neutral fragments derived from the same parent ion.
Gas phase substitution under ammonia chemical ionization
Authors: Das K. G. , Swamy R. A. , van Thuijl J. , Onkenhout W. , Fraisse D. , Tabet J. C. 
Published: May 2005

AbstractEvidence for the isomerization of the [M + NH4]+ adducts of nitrobenzene and triphenylnitrocyclohexenes to the isonitroso derivatives in the first field free region has been obtained. The isomerized adducts undergo successive loss of ṄO and ȮH or NH3 to give ions corresponding to the substitution products. Mass analysed ion kinetic energy and collisionally activated dissociation/mass analysed ion kinetic energy data reveal that the adduct decomposes by similar pathways in the second field free region. In the ion source an addition elimination reaction and nucleophilic substitution contribute to the formation of the substituted product ion.
The nominal butyl ester ion in the mass spectra of long‐chain n‐alkyl esters: A postscript
Authors: Meyerson Seymour , Kuhn Eugene S. , Puskas Imre , Fields Ellis K. , Leitch Leonard C. , Sullivan Thomas A. 
Published: May 2005

Abstractn‐Octadecyl benzoate, taken as a model for long‐chain n‐alkyl carboxylates generally, loses C14H28 under electron impact to yield a product with the same elemental composition as the butyl benzoate molecular ion. This product retains quantitatively one hydrogen from C‐6, and seems to be formed as an oxygen‐protonated 4‐benzoyloxybutyl radical. It reacts further to lose H2O, in which deuterium labeling demostrates that the second hydrogen atom comes predominantly from C‐4. The intermediate reorganization, for which the driving force is presumably furnished by the instability associated with a primary radical, is pictured in terms of cyclization via bonding between the C‐4 radical site and the benzoyl carbon concerted with hydrogen migration via a 4‐membered quasicyclic transition state.
Cyclic organophosphorus compounds. XVIII—the mass spectroscopy of some 2‐amino‐1,3,2‐dioxaphosphorinans, cyclic phosphorodiamidates and phosphorodiamidothionates
Authors: Edmundson R. S. 
Published: May 2005

AbstractStepwise replacement of O in 1,3‐dioxa‐2‐phospha(V)‐cyclohexanes (or related ring systems) by NR (R=H or Me) leads to an increase in the stability of the hetero‐ring ions produced under electron impact conditions. In the case of the 2‐phenoxy derivatives, there is also an increased abundance of [MPhO]+ or [MPhOH]+ ions, and, for the 2‐sulphides, a reduction in the abundance of [M‐S]+˙ and [M‐SH]+ ions, with a concurrent increase in that of [M‐PhS]+ ions. Such trends have been correlated with ultraviolet photoelectron spectral data on a qualitative basis.
Electron impact mass spectrometry of the acetates of zinc, magnesium, cobalt and manganese
Authors: Marshall G. L. 
Published: May 2005

AbstractThe electron impact mass spectra of the acetates of zinc, magnesium, cobalt and manganese have been investigated using a direct inlet probe. Volatile tetrahedral complexes are produced on heating, and ions of the form [M4(OCOCH3)6O]+˙ (M = Co and Mn) and [N4(OCOCH3)5O]+ (N = Zn or Mg) are observed. A mixture of magnesium and cobalt acetates produces ions of the form [MgnCo4–n(OCOCH3)6O]+˙.
Ion chemistry of phthalamic acids. 2—mass spectral retrosynthesis of phthalanilic acids and structure analysis of [C8H6NO2]+ ions from N‐cyclohexylphthalamic acid and [MH]+ of N‐cyclohexylphthalimide
Authors: Selva Antonio , Traldi Pietro , Ventura Paolo , Servadio Vittorino 
Published: May 2005

AbstractUnder electron impact o‐phthalanilic acids show the retrosynthetic reaction previously described for other phthalamic acids. As primary amine derivatives they undergo thermal and electron impact induced water loss. Like the molecular ions of the related phthalimides, their [MH2O]+˙ do not give [C8H6NO2]+ fragments, which are obtained from the N‐cyclohexyl derivative. The structure of such fragments is investigated by collisionally activated mass analysed ion kinetic energy spectra, and compared with the [MH]+ of phthalimide, obtained by chemical ionization with CH4 or NH3 and assumed to be possible models.
Doubly charged ion mass spectra. 7—acetylenes
Authors: Appling J. R. , Jones B. E. , Abbey L. E. , Bostwick D. E. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra of 20 aliphatic and 3 aromatic acetylenic compounds have been measured using a double focusing Hitachi RMU‐7L mass spectrometer. Spectra were obtained using 100 eV ionizing electron energy and 3.2 kV ion accelerating voltage. In general, the spectra of aliphatic type acetylenic compounds were dominated by fragment ions formed by extensive H loss from doubly charged molecular ions. Intense molecular ions were observed in the doubly charged ion spectra of phenyl‐substituted acetylenes. Total product ion intensities for doubly charged ion spectra of acetylenic compounds were found to be smaller, in general, than the total product ion intensity observed in the benzene doubly charged ion mass spectrum. Measured appearance energies of intense product ions ranged from 24 to 47 eV. A geometry optimized quantum mechanical self‐consistent field molecular orbital treatment was employed to compute energies and structural parameters of prominent ions in the doubly charged ion mass spectra of acetylenic compounds.
The role of the field in field desorption fragmentation of polyethylene glycol
Authors: McCrae Christine E. , Derrick Peter J. 
Published: May 2005

AbstractThe degree of fragmentation induced during field desorption of polyethylene glycol increases as the potential between emitter and cathode is raised. This fragmentation is explained as field dissociation. The shape of the envelope of pseudomolecular ion peaks depends upon temperature but not upon field. It is suggested that the desorption of pseudomolecular ions proceeds over barriers whose heights are dependent upon the electric field strength.
Electron impact induced water elimination from hydroxyamides. 2—N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline and N‐Methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline
Authors: Steiner B. , Schumann D. , Naumann A. 
Published: May 2005

AbstractElectron impact induced water elimination from the metastable molecular ions of N‐acetyl‐ and N‐benzoyl‐4a‐hydroxydecahydroquinoline mainly follows a formal [1,2] elimination. The initiating and ratedetermining step in the reaction is the hydrogen rearrangement from C‐8a onto the carbonyl group. The transferred hydrogen is subsequently lost, together with the hydroxyl group. The almost complete absence of H2O loss from both diastereomers of N‐methyl‐4a‐hydroxy‐2‐oxodecahydroquinoline confirms that the reaction can only proceed when the carbonyl group is able to function as ‘hydrogen carrier’ by occupying positions in the vicinity of both a hydrogen and the hydroxyl function.
Collisionally activated dissociation spectra of protonated methyl N‐alkanoates studied using a triple quadrupole
Authors: Sun Wing‐Fung , Dawson P. H. 
Published: May 2005

AbstractThe collisionally activated dissociation (CAD) spectra of protonated methyl n‐alkanoates CH3 (CH2)nCOOCH3 with n = 1−9 were studied using a triple quadrupole. The influence of hydrocarbon chain length and collision energy on characteristic fragment ions such as those due to the loss of methanol was examined. It was found that most characteristic fragment ions became less important in the CAD spectra with increasing chain length of the esters and finally disappeared in the higher members of the series. Special care would have to be taken when trying to use such neutral losses in analysis for identifying the presence of a certain class of compounds.
Ortho effects in organic molecules on electron impact: XI—the interesting ortho effect of the methoxy group in o‐methoxy aromatic thioamides
Authors: Ramana D. V. , Viswanadham S. K. 
Published: May 2005

AbstractIt has been noticed that the major part of the loss of ṠH from the molecular ion of most of the o‐methoxythioamides results from an ortho effect of the methoxy group. Comparison of the MIKE spectra of the [MSH]+ of 1‐(2‐methoxyphenylthioxomethyl)piperidine and 1‐(2‐methoxyphenylthioxomethyl)pyrrolidine with the MIKE spectra of [MSH]+ of the corresponding unsubstituted compounds, reported earlier, indicated two parallel pathways for the formation of [MSH]+ in the o‐methoxy compounds. In the first pathway, as has been noticed in thioamides in general, the loss of ṠH involves the migration of either the α‐hydrogen in the amine moiety or the hydrogen attached to nitrogen. In the second pathway, the migration of a hydrogen from the o‐methoxy group to the sulphur atom followed by ejection of SH from the molecular ion leads to a stable cyclized ion. Interesting secondary fragmentations as a consequence of this ortho effect have also been noticed.
Mechanism for semiquinone formation in the oxygen negative chemical ionization mass spectrometry of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin
Authors: Mitchum Ronald K. , Korfmacher Walter A. , Althaus James R. 
Published: May 2005

AbstractThe high toxicity of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (2,3,7,8‐TCDD) has led to the development of selective and highly sensitive quantitative methods for mass spectral analysis. Analytical selectivity has been demonstrated for the oxygen negative chemical ionization (ONCI) reaction of TCDD in an oxygen‐rich plasma. While the reaction product (4,5‐dichloro‐1,2‐benzoquinone anion) of 2,3,7,8‐TCDD and oxygen is well known, the mechanism of its formation has not been studied thoroughly. In this report the results of a study involving the reaction of 18O2 with 2,3,7,8‐TCDD under high pressure and low pressure ONCI conditions are reported. A mechanism is proposed which is compatible with the observation that one 18O atom is incorporated into the product anion.
Mass spectra of some tetrasubstituted 4,4′‐biisoxazoles and 4,4′‐methylendiisoxazoles
Authors: Filipović‐Marinić N. , Sušnik‐Rybarski I. 
Published: May 2005

AbstractThe behaviour of some tetrasubstituted 4,4′‐biisoxazoles and 4,4′‐methylendiisoxazoles under electron impact has been investigated by means of high and low resolution mass spectrometry. The determination of metastable transitions and accurate masses of important fragment ions has led to the construction of fragmentation schemes. Specific skeletal rearrangement processes are discussed and it is proposed that they proceed through azirine and oxazole intermediates.
Mass spectra of halogenated esters 6—Methyl esters of some trihalogenated propanoic and butanoic acids
Authors: Korhonen Ilpo O. O. 
Published: May 2005

AbstractThe mass spectral fragmentation of trihalogenated methyl esters, formed in the reactions of monochlorinated methyl propenoates and 2‐butenoates with Cl2, BrCl and Br2, have been investigated. In most cases α‐cleavage gives the base peak, [COOCH3]+, the peaks originating from the subsequent losses of one or two halogen atoms also being abundant. The primary loss of a halogen atom is more prominent in the C4 derivatives, Br˙ and Cl˙ being preferentially lost from the 2‐ and 3‐positions, respectively. The McLafferty rearrangement yields in one case the base peak; the 2‐halo compounds could in general be distinguished by that fragmentation. Typical for all 2‐bromo‐substituted methyl butanoates studied is the base peak, [C3H3]+, at m/z 39, and for some 3‐halo compounds the peaks at m/z 95, [C2H4ClO2]+ and 139, [C2H4BrO2]+.
Phosphoric amides. 7—Mass spectrometry of phosphoric amido esters: Fragmentation patterns and migratory aptitudes
Authors: Davidowitz Bette , Modro Tomasz A. 
Published: May 2005

AbstractMass spectra of 38 organophosphorus compounds, containing both phosphate ester (P(O)OR) and phosphoramidate (P(O)NR′R″) functional groups, were recorded and discussed. Attention was focused on PN bond cleavage, which can involve simple fission, fission accompanied by hydrogen migration from the ester group and fission accompanied by the migration of the ester R group to the departing nitrogen atom. Fragmentations characteristic for the N(β‐chloroethyl) derivatives (phosphorylated nitrogen mustards) are also presented.
The mass spectra of nitrosulphanilamides. Observation of thermally generated products from 4‐(piperidylsulphonyl)‐2‐nitroacetanilide
Authors: Abdel‐Halim A. M. , Bilton J. N. , Waight E. S. 
Published: May 2005

AbstractIn addition to the expected electron impact induced fragmentation, the mass spectra of substituted nitrosulphanilamides, such as 4‐(piperidylsulphonyl)‐2‐nitroacetanilide, exhibit peaks due to imidazoles, imidazole‐N‐oxides and furazans, which are formed thermally in the spectrometer ion source.
A study of the electron impact induced retro‐diels‐alder process with selected 5,6,6a, 7,12,12a‐hexahydrobenzo[a]anthracenes
Authors: Bobenrieth M.‐J. , Levy L. A. , Hass J. R. 
Published: May 2005

AbstractThe mass spectra of 5,6,6a,7,12,12a‐hexahydrobenzo[a]anthracene and 2‐methoxy, 3‐methoxy‐, 4‐methoxy and 1‐methyl‐4‐methoxy derivatives are reported. Among the fragment ions observed under electron impact ionization, [C8H8]+· and [MC8H8]+· can be generated by a retro‐Diels‐Alder process. Studies of metastable ion reactions show these ions to be formed by fragmentation directly from the molecular ion. The CA spectra of the [C8H8]+· ions from the subject compounds were compared with spectra from ions of the same composition from various sources. From these data, kinetic energy release measurements and stereochemical considerations, it is concluded that these ions are formed by a stepwise, rather than a concerted mechanism.
Field ionization and electron impact mass spectra of cycloolefins
Authors: Rang Silvia , Strenze Tiiu , Müürisepp Mati , Eisen Olaf 
Published: May 2005

AbstractThe field ionization mass spectra of monosubstituted cyclopentenes and cyclohexenes with C1‐C7 n‐alkyl and C4‐C5 isoalkyl substituents in positions 1 and 3 have been investigated and compared with the previously reported electron impact mass spectra of these compounds. The cleavage of the CC bond β to the double bond in the non‐isomerized molecular ion was found to be a typical degradation reaction of the higher homologues in the strong electric field. So, by means of the field ionization mass spectra, the >C1 alkyl substituent can be readily located in the parent molecule. The electron impact mass spectra exhibit a less specific fragment ion distribution for positional isomers due to the extensive molecular ion isomerization prior to decomposition, but provide useful information on the ring size. For structure determination it is appropriate to use both ionization techniques.
Collision dissociation study of negative ion chemical ionization (OH−) fragments of bornyl C4C5 esters
Authors: Selva Antonio , Traldi Pietro , Massimo Bambagiotti A. 
Published: May 2005

AbstractCollisional activation spectra show interesting and specific dissociations which demonstrate the retention of structural identity not only of carboxylate anions discussed in a previous paper, but also of other fragments obtained from bornyl C4C5 esters under negative chemical ionization mass spectral conditions with OH− as reactant ions.