bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies in negative ion mass spectrometry. XIII—Electron attachment to a series of Nickel(II) β‐diketonate complexes
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K. 
Published: May 2005

AbstractResults of electron attachment reactions and negative ion mass spectra are presented for a group of selected nickel(II) β‐diketonate complexes of formula Ni[R1COCHCOR2]2, where R1 is a perfluoroalkyl group and R2 either an alkyl or aryl group. Molecular negative ions together with ligand ions are the major contributors to the total ion currents for each compound, and the degree of fragmentation has been shown to be dependent on the substituents R1 and R2. Fragmentation schemes have been elucidated for all the major ion decomposition pathways, and all significant ions have been identified in the negative ion mass spectra of each compound. Bis(1,1,1‐trifluoro‐5,5‐dimethyl‐2,4‐hexanedionato) nickel(II), with R1CF3 and R2tert‐butyl is the complex which shows considerable potential for analytical quantitation in the negative ion mode, because of the stability of its negative molecular ion, the high negative ion yield given after electron attachment, as well as the volatility of the compound.
Mass spectrometry of condensed N‐heterocycles: II—A novel ortho effect in the electron impact induced fragmentation of some C‐(2‐nitrophenyl)‐azoles and ‐azoloazines
Authors: Könnecke A. , Lepom P. , Dörre R. , Lippmann E. , Herzschuh R. , Kralj B. , Stanovnik B. , Tišler M. 
Published: May 2005

AbstractHeterocycles containing an integrated 2‐nitrobenzaldehyde imine moiety produce ions of m/z 134 with high abundance under electron impact. As shown by kinetic energy release measurements these ions have the same structure in all the cases studied, identical to m/z 134 formed from the reference compound 2‐nitrobenzoylpiperidide. The mechanism of formation of m/z 134 most probably involves isomerization of its precursor ion to give a spiro intermediate, from which m/z 134 arises either synchronously or after a second isomerization. Both alternatives formally represent an oxygen transfer from the nitro group to the imino carbon via a 5‐membered transition state.
Ortho effects in schiff bases of diaminodicyanoethene
Authors: Holzmann G. , Rothkopf H. W. 
Published: May 2005

AbstractIn the electron impact mass spectra of azomethines derived from various substituted aromatic aldehydes and diarninodicyanoethene the superposition of two ortho effects concurring with the azomethine group is apparent: one involving the amino group of the diaminodicyanoethene part accounts for the cyclization to [C5H3N4]+ ions and the other involving ortho substituents of the benzylidene part which can interact with the azomethine moiety is responsible for specific fragment ions, suppressing the typical fragmentations of azomethines. The ortho effect was studied for the o‐nitro derivative by labelling experiments, analysis of metastable transitions and collisional activation comparing model ions, demonstrating that the specific [M‐H2O]+˙ and [C7H5NO2]+˙ ions are the result of cyclization processes.
Studies on the mechanism of electron impact induced SH radical loss from the diastereoisomeric 2‐dimethylamino‐2‐thiono‐4‐methyl‐1,3,2‐dioxaphosphorinanes
Authors: Stec W. J. , Zielińska B. , van de Graaf B. 
Published: May 2005

AbstractThe intensity differences between the [MHS]+ peaks in the mass spectra of diastereoisomeric 2‐dimethylamino‐2‐thiono‐4‐methyl‐1,3,2‐dioxaphosphorinanes have been rationalized in terms of fragmentation mechanisms and ion structures. Metastable characteristics together with D labelling experiments support these rationalizations.
Unimolecular decompositions of even‐electron ions
Authors: McLafferty F. W. 
Published: May 2005

AbstractFragmentations of even‐electron ions of lifetimes ≥10−5s caused by electron and chemical ionization and by collisional activation have been correlated. Proposed reaction classifications include: cleavage of one bond with charge migration; cleavage of one bond through cyclization‐displacement; cleavage of two bonds in a cyclic ion with charge retention; and cleavage of two bonds in an acyclic ion with rearrangement and charge retention. Such reactions are compared with those of odd‐electron ions; despite a higher tendency for rearrangement, the decompositions of a positive even‐electron ion, in particular as displayed in its collisional activation spectrum, have substantial utility for characterizing its structure.
Kinetic energy release and ion structure: [C6H6O]+˙
Authors: Maquestiau A. , Flammang R. , Glish G. L. , Laramée J. A. , Cooks R. G. 
Published: May 2005

AbstractIt is shown that, contrary to a recent report, the kinetic energy release for CO loss from phenol does not decrease as the ion accelerating voltage is decreased. In fact, an increase is observed which is attributed, at least in part, to greater discrimination against off‐axis ions at low voltage. The kinetic energy release data do not demand the tautomerization of ionized phenol before decarbonylation.
The use of two linked scanning modes in alternation to analyse metastable peaks
Authors: Lacey Michael J. , Macdonald Colin G. 
Published: May 2005

AbstractAnalyses of masses and relative kinetic energies for metastable peaks may be achieved by the use in alternation of two types of linked scans of the electric sector voltage and magnetic field. The method is demonstrated by an appraisal of hydrogen exchange in molecular ions of 2‐methyl‐[2H3]‐benzoic acid.
Charge stripping mass spectra: A method for identifying isomeric [C5H8]+˙ and [C3H6]+˙ ions
Authors: Holmes John L. , Terlouw Johan K. , Burgers Peter C. , Rye Robin T. B. 
Published: May 2005

AbstractCharge stripping (collisional ionization) mass spectra are reported for isomeric [C5H8]+˙ and [C3H6]+˙ ions. The results provide the first method for adequately quantitatively determining the structures and abundances of these species when they are generated as daughter ions. Thus, loss of H2O from the molecular ions of cyclopentanol and pentanal is shown to produce mixtures of ionized penta‐1,3‐ and ‐1,4‐dienes. Pent‐1‐en‐3‐ol generates [penta‐1,3‐diene]+˙. [C3H6]+˙ ions from ionized butane, methylpropane and 2‐methylpropan‐1‐ol are shown to have the [propene]+˙ structure, whereas [cyclopropane]+˙ is produced from ionized tetrahydrofuran, penta‐1,3‐diene and pent‐1‐yne.
Mass spectrometric fragmentation of S‐(1‐aryltetrazol‐5‐yl)‐monothiocarbonic acid esters
Authors: Löster Heinz , Herzschuh Rainer , Lippmann Eberhard 
Published: May 2005

AbstractThe mass spectra of S‐(1‐aryltetrazol‐5‐yl)‐monothiocarbonic acid esters have been studied. The stability of the ester molecular ions is lower than the stability of the corresponding 1‐aryl‐5‐mercaptotetrazoles. Substituents at the phenyl group increase the stability, whereas the influence of the ester alkyl groups is very small. The esters undergo fragmentation via four different fragmentation pathways. The elimination of carbon dioxide is influenced by an ‘ortho effect’ of the substituents.
Metastable peak study in methylactophenone isomers
Authors: Rabbih M. A. , Selim Ezzat T. M. 
Published: May 2005

AbstractThe relative intensity of the metastable peaks at 70 eV appearing at m/z 105.7 and 69.6 in the mass spectra of methylacetophenone isomers, as well as the kinetic energy (T1/2) released with the peaks at 14 and 70 eV respectively, are reported. The profile of all the metastable peaks studied has been found to be approximately flat‐topped. For the same transition it is found that the kinetic energy released with the metastable peaks formed by unimolecular decomposition of the three isomers decreases from the ortho to the para isomer. In addition, the kinetic energy released during the same transition is found to be roughly directly proportional to their corresponding intensity ratios. This result, together with the observation that the energy released with each metastable peak decreases by lowering the electron energy, may reveal the role of the internal energy of the reacting ions in producing the kinetic energy associated with the metastable peaks produced from methylacetophenone isomers.
Electron impact induced intramolecular hydrogen transfer reactions in polymethylene glycol di‐p‐toluenesulfonates
Authors: Blane Pierre‐Alain , Gülaçar Fazil O. , Buchst Armand 
Published: May 2005

AbstractThe mechanisms of formation of the ionized acid and the protonated acid fragments in the electron impact induced fragmentation of the title compounds were investigated. The well known mechanisms of hydrogen transfer through mono‐ and bicyclic transition states that occur in the molecular ions of carboxylic esters are not the main pathways giving rise to these fragments. The major component of the m/z 172 peak corresponding formally to ionized p‐toluenesulfonic acid in fact has a different structure; its formation involves a complex mechanism including a double hydrogen transfer reaction.
Mass spectrometric studies of 2‐nitrosophenols
Authors: Charalambous J. , Fysh R. R. , Herbert C. G. , Johri M. H. , Shutie W. M. 
Published: May 2005

AbstractThe mass spectra of 2‐nitrosophenols are independent of the insertion temperature, suggesting that the compounds either do not exhibit tautomerism in the vapour phase or that the enthalpy of isomerization is low. However, their fragmentation patterns suggest tautomerism in the molecular ion.
The mass spectral rearrangements of 1,6‐bis(arylsulfenyl)‐2,4‐hexadiynes and 1,6‐bis(arylsulfonyl)‐2,4‐hexadiynes
Authors: Thyagarajan B. S. , Glaspy P. E. , Baker E. , Brown Peter 
Published: May 2005

AbstractThe mass spectral. behavior of 1,6‐bis(arylsulfenyl)‐2,4‐hexadiynes and 1,6‐bis(arylsulfonyl)‐2,4‐hexadiynes were examined. The sulfenyl derivatives extruded the hexadiynyl moiety with the formation of ArSSAr fragments. The sulfonyl derivatives, on the other hand, showed no extrusion of the hexadiyne fragment but an expulsion of SO2 and even two SO2 units.
The electron impact mass spectrometry of some para substituted trans‐2‐styryl‐6‐carboxychromones. An unusual cleavage of the chromone ring
Authors: Tonani Roberto 
Published: May 2005

AbstractThe electron impact mass spectrometry of some para substituted trans‐2‐styryl‐6‐carboxychromones shows a new fragmentation of the chromone ring in addition to the well known retro Diels‐Alder reactions with and without hydrogen transfer. The observed primary fragments are supported by metastable transitions and exact mass measurements.
Stereochemical applications of mass spectrometry. II—Chemical ionization mass spectra of isomeric dicarboxylic acids and derivatives
Authors: Harrison Alex. G. , Kallury R. Krisha Mohan Rao 
Published: May 2005

AbstractThe H2 and CH4, chemical ionization mass spectra of the cis dicarboxylic acids, maleic and citraconic acid, show much more extensive loss of H2O from [MH]+ than the trans isomers, fumaric acid and mesaconic acid. Similarly, esters of maleic acid show a much more facile loss of ROH (R=alkyl or phenyl) from [MH]+ than do esters of fumaric acid. Similar differences are observed in the chemical ionization mass spectra of the isomeric phthalic and isophthalic acids and derivatives, where the ortho isomers show more extensive fragmentation of [MH]+ than the meta isomers. The facile fragmentation of [MH]+ for the cis and ortho isomers is attributed to ROH elimination involving interaction between the two carboxylate functions and forming the stable cyclic anhydride structure for the fragment ion. By contrast ROH elimination from [MH]+ for the trans and metu isomers requires a symmetry‐forbidden [1,3]‐H migration in the carboxyl protonated species and cannot lead to the cyclic anhydride structure. The chemical ionization mass spectra of cis and trans cyclohexane‐1,2‐dicarboxylic acids are essentially identical and show extensive fragmentation of the [IMH]+ ion. Experiments using deuterium labelling show extensive carboxyl group interactions for both isomers. The chemical ionization mass spectra of maleanilic and phthalanilic acids and of the related anhydrides and imides also are reported, as are the electron impact mass spectra of diphenyl maleate, diphenyl fumarate, diphenyl phthalate, maleanilic acid and phthalanilic acid.
Mass spectrometry of aryl substituted di‐ and trisiloxanes
Authors: Swaim Robert E. , Weber William P. , Boettger Heinz G. , Evans Margaret , Bockhoff Frank M. 
Published: May 2005

AbstractThe mass spectra of arylpentamethyldisiloxanes, sym‐diaryltetramethyldisiloxanes and 1,5‐diaryl‐1,1,3,3,5,5‐hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M‐15]+ ions is important. Phenylpentamethyldisiloxane, sym‐tetramethyldiphenyldisiloxane and 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M‐15]+ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH3)2SiO] and phenylmethylsilanone [PhCH3SiO] to yield daughter siliconium ions. The [M‐15]+ ion of sym‐tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M‐15]+ ion of 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di‐ and trisiloxanes discussed.
Chemical ionization mass spectrometry of dimethyl acetals and diethyl dithioacetals of aldopentoses and aldohexoses, and the influence of stereochemical configuration
Authors: Blanc‐Muesser Michèle , Defaye Jacques , Foltz Rodger L. , Horton Derek 
Published: May 2005

AbstractChemical ionization mass spectra have been recorded for the title compounds having the four pentose configurations and the eight hexose configurations, with ammonia and isobutane as the reagent gases. The ammonia mediated spectra display [NH4]+ capture ions with successive loss of one or two molecules of methanol (acetals) or ethanethiol (dithioacetals), whereas when isobutane was the reagent gas, loss from the protonated acetals of one or two molecules of methanol and of water, and loss from the protonated dithioacetals of one or two molecules of ethanethiol and of water were featured. Significant differences in the ion intensities as a function of stereochemistry in the precursor are noted, and are discussed in terms of the ease of formation of cyclic fragment ions.
Rule‐based mass spectrum prediction and ranking: Applications to structure elucidation of novel marine sterols
Authors: Lavanchy Andre , Varkony Tomas , Smith Dennis H. , Gray Neil A. B. , White William C. , Carhart Raymond E. , Buchanan Bruce G. , Djerassi Carl 
Published: May 2005

AbstractA novel, computer aided approach to the interpretation of mass spectra is documented by its application to a series of recently isolated marine sterols. The method consists of construction of biosynthetically plausible candidate structures, prediction of their major mass spectral fragmentation paths using class‐specific rules derived from a training set of known compounds, and a system of ranking candidate structures based on a comparison of the predicted and observed spectra.
Electron impact studies: CXXXI—Ion cyclotron resonance studies of ambident nucleophiles. The reaction between the thioacetate anion and thioacetic anhydride. A further example of a negative ion McLafferty rearrangement
Authors: Trenerry V. Craige , Bowie John H. 
Published: May 2005

AbstractThe [MeCOS]− ion undergoes reaction with neutral thioacetic anhydride in an ion cyclotron resonance cell to yield an adduct [M+MeCOS]− which decomposes principally by loss of CH2CS, thus establishing the occurrence of nucleophilic attack through O at the carbonyl centre.
Ion/molecule reactions of ammonia and methylamine with chloro‐ and nitrobenzene. A comparison of chemical ionization and ion cyclotron resonance experiments
Authors: van der Hart W. J. , Luijten W. C. M. M. , van Thuijl J. 
Published: May 2005

AbstractIt is shown by ion cyclotron resonance measurements that ion/molecule reactions, leading to substitution or reduction product ions from chloro‐ and nitrobenzene with the title amines, are those between the molecular ions [RNH2]+ or [C6H5X]+˙ and their respective counterparts C6H5X or RNH2. The protonated reagent gas ions [RNH3]+ are not involved in these reactions. In the case of nitrobenzene, adduct ions [C6H5NO2·RNH3]+ do not decompose within the time scale of the measurements. The results obtained are compared with those found under chemical ionization conditions.
Mechanisms of unimolecular fragmentations of odd‐electron cations in the gas phase: The importance of intramolecular hydrogen migration for [odd]+˙ → [even]+ transitions
Authors: Schwarz Helmut 
Published: May 2005

AbstractEighteen quite different examples are discussed in which the unimolecular elimination of a given radical X˙ from an odd‐electron cation cannot be described as a one‐step process. Despite the fact that the radical X˙ eliminated is already present as a structural unit in the decomposing ions, the product analysis and structure determination of the even‐electron ion formed, the investigation of the energetics of the reaction, the analysis of stereochemical factors, and the determination of kinetic isotope effects reveal that the eliminations must be characterized as two‐ or multi‐step reactions. In all cases investigated, the process commences with a specific (intramolecular) hydrogen transfer to a suitable acceptor function. In this way a reactive radical site is created which induces the actual dissociation step (elimination of X˙) by simultaneous double bond formation. Due to the fact that the hydrogen migration takes place within the charge carrying part of the cation radical and that the migrated hydrogen atom remains there throughout the whole process, the intervention of a H‐migration cannot be traced directly by appropriate mass shifts in the spectra of 2H labelled precursors. However, the methods mentioned above can be applied to reveal the details of the reaction mechanism, and the term ‘hidden’ hydrogen migration induced dissociation is suggested to recognize the particular rǒle of H‐rearrangements to trigger radical eliminations from odd‐electron cations in the gas phase.
Electron impact induced fragmentation of 4‐alkyl derivatives of 2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane and the corresponding 1‐oxides, 1‐sulfides and 1‐selenides
Authors: Kenttämaa Hilkka , Enqvist Jouni 
Published: May 2005

AbstractThe electron impact fragmentations of several derivatives of 2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane have been examined by means of high resolution and metastable ion analysis. The principal fragmentation route for bicyclophosphites, phosphates and phosphorothionates involves a loss of formaldehyde, followed by a loss of the PO2X and HPO2X groups (X = ‐, O, S). The behaviour of phosphoroselenates is quite different, due partly to the favoured loss of selenium from the molecular ion before further fragmentation. Fragmentation through CO bond breaking and a rearranged molecular ion is dependent on the exocyclic chalcogen atom (‐, O, S, Se) on phosphorus. The reactions have been rationalized in terms of 1‐ and 4‐substitutions.
Studies of consecutive reactions of organic ions in a reversed geometry mass spectrometer
Authors: Proctor C. J. , Kralj B. , Brenton A. G. , Beynon J. H. 
Published: May 2005

AbstractOver thirty consecutive reactions of a type m1+ → m2+ → m3+ have been studied in a variety of organic compounds using a reversed geometry mass spectrometer. Two field free regions allow the separation of the two steps that make up the consecutive reaction sequence. Translational energy release measurements are used in the comparison of m2+ ions formed as a result of a high energy process in the ion source with m2+ ions formed as a product of a metastable decomposition. In some cases the structures of such ions have been found to be different. Examples have also been found where consecutive fragmentations of metastable ions do not occur although, when higher energy ions within the source are studied, the two‐step reaction does take place. Furthermore, it has been found that a control over ion internal energy may be achieved by selecting portions of a peak due to the fragmentation of a metastable ion. Unimolecular reactions may then be used to study the reactivity of such ‘energy‐selected’ ions; collision induced reactions can be used to study the structure of both the reactive and unreactive energy selected ions.
Mass spectral fragmentation of metal dithiocarbamate complex salts
Authors: Dias Jerry Ray , Zigon Majda , Gomiscek Sergej 
Published: May 2005

AbstractA summary of the mass spectra of metal dithiocarbamate complex salts (ML2 and ML3) is presented. Only divalent metal dithiocarbamate ions without an electronic configuration containing an inert s‐orbital electron pair exhibited both expulsion of a ligand radical (L) and the neutral even electron species (L–H) generated from the ligand via hydrogen transfer to the metal‐containing fragment ion. Divalent metal dithiocarbamate ions can be generated either by direct electron impact ionization of gas phase ML2 molecules or ionization of ML3 molecules followed by loss of a ligand radical. A highly stable sp2 hybridized, gas phase ion of a monobidentate lead dithiocarbamate complex is proposed.
Nicotinates as derivatives for the mass spectrometric investigation of long chain alcohols
Authors: Vetter W. , Meister W. 
Published: May 2005

AbstractThe mass spectra of the nicotinates of two methyl branched and one unsaturated long chain alcohol were compared with the mass spectra of the underivatized alcohols and of their trimethylsilyl ethers. It is shown that the structure of the chain is much more clearly shown by the spectra of the nicotinates than in the other spectra.
Chemical ionization mass spectra of selected C3H6O compounds
Authors: Bowen Richard D. , Harrison Alex G. 
Published: May 2005

AbstractThe chemical ionization mass spectra of five isomers of C3H6O (acetone, propionaldehyde, oxetane, propylene oxide and allyl alcohol) have been determined using a variety of reagent gases (H2, D2, N2/H2, CO2/H2 and CO/H2). The [C3H7O]+ ions produced by protonation of these isomers undergo very similar reactions to those reported for analogous [C3H7O]+ metastable ions; however, decomposing ions generated by chemical ionization appear to have somewhat higher internal energies. The results of 2H labelling studies (D2 reagent gas or labelled analogues of C3H6O) indicate that protonation occurs mainly on oxygen and are consistent with previous investigations of metastable oxonium ions. The protonated acetone ion is particularly stable, in agreement with the higher activation energies for fragmentation of this isomer than for other [C3H7O]+ structures. As the calculated heat of protonation of C3H6O is reduced by changing the reagent gas, so the extent to which fragmentation occurs decreases. This is discussed in the context of competition between fragmentation and collisional stabilization of the excited [C3H7O]+* ion. It is concluded that on average a large fraction (approaching 1) of the exothermicity of the protonation reaction resides in the [C3H7O]+* ions produced initially.