bluuebunny/crossref_metadata_2025_split huggingface dataset:
Desorption chemical ionization mass spectrometry of epimeric 3‐hydroxysteroids and derivatives. Stereoselectivity and nucleophilic substitution with ammonia
Authors: Tecon Pierre , Hirano Yutaka , Djerassi Carl 
Published: May 2005

AbstractThe desorption chemical ionization mass spectra, using ammonia as reagent gas, of several epimeric 3‐hydroxysteroids and their ether and carboxylic acid ester derivatives are reported. In the case of steroids possessing a Δ4‐ or Δ5‐3α‐benzoate moiety, stereospecific stabilization of the protonated molecular ion [M+H]+ is observed. This behavior is rationalized in terms of interaction of the double bond and the protonated benzoate group at C‐3. Nucleophilic substitution by NH3 is observed when a double bond is present in the vicinity of the substitution center. The nature and the stereochemistry of the leaving group influence this substitution reaction. Our results seem to indicate the operation of a two‐step mechanism (e.g. SN1 type reaction) rather than a SN2 type mechanism for the formation of the substitution ion [MOR+NH3]+.
Propanoyl ion formation from metastable [C3H6O]+˙ ions
Authors: Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractCollisionally activated spectra demonstrate that CH3CH2CO+ rather than \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 2} = {\rm CHCH = }\mathop {\rm O}\limits^{\rm + } {\rm H}$\end{document} is formed in the metastable losses of hydrogen from [C3H6O]+˙ ions with the oxygen on the first carbon. This provides another example of formation of an acyl ion following ‘ketonization’ prior to metastable decomposition.
Molecule/radical reactions prior to ionization under negative chemical ionization conditions
Authors: Stöckl Dietmar , Budzikiewicz Herbert 
Published: May 2005

AbstractIt is shown that alkyl radical species present in CH4 or iso‐C4H10 plasma can react with substrate molecules to give [M+CnH2n] species. These species become evident especially in negative chemical ionization as [M+CnH2n]−˙ and, less obviously, in positive chemical ionization as [M+CnH2n+1]+ ions which, for example in natural products chemistry, may be mistaken for a series of homologous compounds present in the sample.
Rearrangements and fragmentations of phenyl styryl sulfides: 1—Metastable ion spectra
Authors: Dijkstra P. J. , Weringa W. D. 
Published: May 2005

AbstractThe mass spectra of two isomeric phenyl styryl sulphides show abundant peaks for fragment ions formed after interesting and unusual rearrangements, e.g. loss of CHS˙ and C7H7˙. Information about these rearrangements was obtained by comparison of the metastable peak intensities and peak shapes with those of four isomers. It appears that isomerization reactions between the phenyl styryl sulfides and the isomers are possible and that most of the metastable ion fragmentations proceed via reacting configurations that are common to two or more of the compounds investigated. The results indicate that an earlier proposed mechanism for the fragmentation of phenyl vinyl sulfides is incomplete and only partly correct for the compounds studied. Metastable ion spectra were obtained using high voltage scans and constant B/E scans: a short comparison of the results obtained with the two methods is given.
The mass spectra of 1,1,1‐trichloro‐2,4‐pentanedione and its Al(III), Cr(III), Fe(III), Mn(II), Co(II) and Cu(II) complexes
Authors: Morris M. L. , Koob R. D. 
Published: May 2005

AbstractThe compounds 1,1,1‐trichloro‐2,4‐pentanedione, Cu(II)tca2, Co(II)tca2, Mn(II)tca2, Al(III)tca3, Cr(III)tca3 and Fe(III)tca3 (tca1,1,1‐trichloro‐2,4‐pentanedionato, [CCl3COCHCOCH3]−) have been prepared and their mass spectra have been obtained. The mass spectral results have been compared with findings for comparable fluorinated and nonhalogenated compounds. Comparisons are made in terms of internal redox reactions and hard and soft acid base theory. Rearrangement of chloride from ligand to metal accompanied by the elimination of CO or other neutral even electron fragments emerges as an important reaction for the ions of these compounds. While the internal redox reactions characteristic of all previous β‐diketonate complex mass spectra still occur, their importance appears reduced to some degree by the facility of the chlorine rearrangement.
Fast atom bombardment mass spectra of involatile naphthalene sulphonic acids and sulphonate salts
Authors: Monaghan John J. , Barber Michael , Bordoli Robert S. , Sedgwick R. Donald , Tyler Andrew N. 
Published: May 2005

AbstractFast Atom Bombardment mass spectra of a range of involatile naphthalene sulphonic acids and sulphonates are presented. Excellent spectra are obtained for the mono‐, di‐ and the previously unexamined trisulphonated compounds. The relative value of positive and negative ion spectra for the study of these species is discussed. The results are shown to be superior to those obtained by other mass spectrometric methods.
The study of C1C3 monosubstituted alkyl benzenes by the inverse convolution of first differential ionization efficiency curves
Authors: Selim Ezzat T. M. , Helal A. I. 
Published: May 2005

AbstractThe electron impact ionization efficiency curves for the parent ions and the [C7H7]+ fragment ion formed from monosubstituted alkyl benzenes (RCH3n‐C3H7) have been studied by applying the inverse convolution technique of Vogt and Pascual to the first derivative ionization efficiency curves of the ions. Ionization and appearance energies measured for the ions at threshold are in good agreement with recently published photoionization values. Structures in the ionization efficiency curves (higher energy processes) are also reported for about 4 e V above threshold. The heats of formation calculated for [C7H7]+ fragment ions obtained from toluene and ethyl benzene at threshold are equal to 864 and 865 kJ mol−1 respectively, and are consistent with the tropylium structure. However, for the [C7H7]+ fragment ion obtained from n‐propyl benzene at threshold the calculated heat of formation is equal to 923 kJ mol−1 and probably corresponds to a benzyl structure.
Instrumental parameterization for optimum use of commercial direct inlet systems
Authors: Traldi Pietro , Vettori Umberto , Dragoni Franco 
Published: May 2005

AbstractCommercial direct insertion probes generally do not operate under ideal conditions required for direct inlet systems, with the consequence of large decomposition effects for thermolabile compounds. Instrumental parameters for two different probes are given which indicate that under the best conditions a molecular distillation occurs with drastic reduction of pyrolysis processes.
Inverse stereochemical effects in the mass spectra of carboalkoxycyclopropylsilanes
Authors: Vékey Károly , Tamás József , Czira Gábor , Dolgy Igor E. 
Published: May 2005

AbstractThe electron impact induced decomposition of the cis and trans isomeric pairs of five 1‐trialkylsilyl‐2‐alkoxy‐carbonylcyclopropanes were investigated. Compared with carbon analogues, the silicon atom inhibited ring opening and dramatically altered the fragmentation. The main primary decomposition routes were alkyl loss from silicon, and trialkylsilyl ion formation as well as trialkylalkoxysilane elimination. An unexpected inverse stereochemical effect was found for this latter reaction which was far less significant for the cis isomers, where the interacting SiQ3 and OR groups are close to each other, than for the trans isomers. This is explained by assuming a hidden silicon‐oxygen bond formation, which is possible only in the cis isomers for geometric reasons. This interaction favours alkyl elimination over other fragmentations, and has a marked effect on the further decomposition of the [M—alkyl]+ ions, where observed differences in abundance as great as three orders of magnitude are accounted for.
Electron impact mass spectra of meliacins
Authors: Madhusudanan K. P. , Saikia B. , Goswami B. N. , Mathur R. K. 
Published: May 2005

AbstractThe electron impact mass spectra of some new meliacins and their derivatives are discussed. The major fragmentation modes include the functional group losses, the different ring cleavages and the loss of the furan residue as neutral fragments. A mechanism for the loss of the furan moiety from the molecular ion is discussed in detail with the help of deuterium labelling, high resolution and metastable data.
Relative stabilities of the methyltropylium and α‐phenylethyl cations
Authors: Barbalas Michael P. , McLafferty Fred W. 
Published: May 2005

AbstractMetastable decomposition of ethylbenzene molecular ions should yield [C8H9]+ ions of nearly threshold energies. Mass spectral data from collisionally activated dissociation of these ions show them to be mainly the methyltropylium (a) isomer, which is also that formed from 7‐methylcycloheptatriene and isopropylbenzene. Combined with the threshold photoionization studies of McLoughlin, Morrison and Traeger, this establishes a as the most stable [C8H9]+ isomer. This is more stable than the α‐phenylethyl isomer (b), which can be formed from α‐bromoethylbenzene molecular ions; higher energy b ions appear to isomerize to a.
A field ionization and collisionally activated dissociation/charge stripping study of some [C9H10]+˙ ions
Authors: Lay J. O. , Gross M. L. , Zwinselman J. J. , Nibbering N. M. M. 
Published: May 2005

AbstractThe extent of isomerization of [C9H10]+˙ ions, with lifetimes of approximately 10−11 and 10−6 s has been investigated using field ionization, collisionally activated dissociation and charge stripping techniques. The [C9H10]+˙ ions which were investigated included the molecular ions of α‐methylstyrene, β‐methylstyrene, o‐methylstyrene, m‐methylstyrene, p‐methylstyrene, indan, cyclopropylbenzene, allylbenzene and the product of water loss from 3‐phenylpropanol. The field ionization spectra of all the C9H10 hydrocarbons were different indicating that isomerization to a common ion structure had not occurred to a measurable extent for ions with lifetimes of approximately 10−11 s. Collisionally activated dissociation and charge stripping results indicated that most of the [C9H10]+˙ ions continued to maintain unique ion structures (or mixtures of structures) at ion lifetimes of 10−6 s. Possible exceptions are the [C9H10]+˙ ions from allylbenzene and cyclopropylbenzene which gave indistinguishable collisionally activated dissociation and charge stripping spectra.
Methyl transfer in field desorption mass spectrometry of ammonioalkanecarboxylate hydrochloride salts
Authors: Wood Gordon W. , Collacott Ronald J. 
Published: May 2005

AbstractIntramolecular methyl transfer has been observed previously in pyrolysis electron impact mass spectra of complex ammonioalkanecarboxylates. We present here field desorption mass spectra results of more simple N,N,N‐trimethylammoniocarboxylate hydrochloride salts and their N,N,N‐perdeuterotrimethylammonium analogs in which we observe methyl transfer. We demonstrate that mechanisms for this and other fragmentation and rearrangement processes are dependent on anode heating current. Addition of the protonating agent p‐toluenesulfonic acid suppresses most ions except the protonated molecular ion.
Reaction gas chromatography/mass spectrometry. 2—the use of catalytic on‐line dehydrogenation for the investigation of alcohols by gas chromatography/mass spectrometry
Authors: Mikaya A. I. , Smetanin V. I. , Zaikin V. G. , Antonova A. V. , Prostakov N. S. 
Published: May 2005

AbstractA method for structure determination of aliphatic alcohols within mixtures is described. It involves the use of a vapour phase dehydrogenation micro‐reactor (Cu, 300°C) located between the chromatographic column and the mass spectrometer or between the injection port and the column. Since primary and secondary alcohols are converted into corresponding carbonyl compounds, they can be readily differentiated from tertiary alcohols and dialkyl ethers. An examination of the mass spectra of alcohols and carbonyl compounds permits the determination of molecular mass, the location of hydroxyl group and the determination of branching at the β‐carbon atom.
The mechanisms of decomposition of the 1‐ and 2‐phenyltetralin radical cations
Authors: Gallagher James J. , Chess Edward K. , Arghestani Saleh M. , Gross Michael L. 
Published: May 2005

AbstractMechanisms for decomposition of 1‐ and 2‐phenyltetralins were investigated using low resolution mass spectrometry and metastable ion techniques. Four primary decompositions were observed for 1‐phenyltetralin radical cations: (1) the loss of C6H6 via a 1,4‐elimination; (2) the elimination of ethene via competing losses from carbons 3 + 4 and carbons 2 + 3; (3) the loss of C8H8, probably through a stepwise Diels‐Alder cycloreversion to expel styrene; and (4) the loss of methyl radical involving carbon 2 and possibly carbon 4. Three major decompositions were observed for 2‐phenyltetralin radical cations: (1) the loss of C8H8, possibly through a Diels‐Alder cycloreversion to expel styrene; (2) the loss of C6H6 via a 1,3 elimination; and (3) the loss of methyl radical from carbon 1. Various exchange reactions occur prior to these losses, but they proved to be incomplete even for metastable ions.
On the formation of protonated acetic acid from ionized n‐alkanoic acids in the gas phase
Authors: Halim Herman , Schwarz Helmut , Terlouw John K. , Levsen Karsten 
Published: May 2005

AbstractBy means of collisional activation mass spectrometry and semi‐empirical molecular orbital calculations (MNDO) it is shown that the [C2H5O2]+ ions from metastable molecular ions of n‐pentanoic and hexanoic acid have the structure of carbonyl protonated acetic acid [CH3C(OH)2]+. The MNDO calculated geometries of this ion and some other isomeric forms are given together with the ΔHf0 values.
Competitive electron impact induced methylene imine elimination from methyl‐ and dimethylamino N‐heterocycles. 1—substituted melamines
Authors: Michie Preston D. , Johnson Bruce M. 
Published: May 2005

AbstractCompetitive intramolecular expulsion of methylene imine is evaluated for heterocyclic methylamino and dimethylamino substituents using selectively labelled N2,N2,N4‐trimethylmelamine. In this compound methylene imine expulsion from the dimethylamino group is favored by more than 2:1 over loss from the methylamino group. The effects of other fragmentations and hydrogen randomisation are estimated independently using methylmelamines with each of the groups as the sole source of methylene imine loss.
Tetraalkylammonium cations in electron impact mass spectrometry
Authors: Isa Kimio , Yamada Yayoi 
Published: May 2005

AbstractTwenty‐five tetraalkylammonium halide salts were investigated by means of electron impact mass spectrometry. In all cases, corresponding ammonium cations have been detected at low electron energy. Moreover, [C+M]+ have been detected (where C and M denote ammonium cation and molecule, respectively) for both symmetrical salts and iodine salts. Quaternary ammonium salts are considered to be more stable than believed previously.
A Study of C5H10 radical cations by collisionally activated dissociation, charge stripping, and low energy ion‐molecule reactions
Authors: Miller D. L. , Gross M. L. 
Published: May 2005

AbstractC5H10 radical cations generated from a variety of olefins and cycloalkanes were investigated by collisionally activated dissociation, charge stripping, and low energy ion‐molecule reactions. It has been determined that all of the isomers studied can be distinguished by charge stripping, whereas collisionally activated dissociation and the ion‐molecule reactions are less informative. The radical cations from cyclopentane, methylcyclobutane and substituted cyclopropanes retain their cyclic structures for at least a fraction of the population having lifetimes in the microsecond range.
Mass spectrometric synthesis. 1—the reaction of catechol with 2,4‐dimethyl‐2,3‐pentadiene
Authors: Podda Gianni , Maccioni Antonio , Vettori Umberto , Daolio Sergio , Traldi Pietro 
Published: May 2005

AbstractThe reaction of catechol with 2,4‐dimethyl‐2,3‐pentadiene, carried out in the chemical ionization chamber of a VG ZAB2F mass spectrometer, has been studied with respect to the partial pressure of the reacting species. The structure of the reaction product, 2,2‐diisopropyl‐1,3‐benzodioxole, has been proved by exact mass measurements, B/E linked scans, labelling experiments and collisionally activated dissociation mass analysed ion kinetic energy spectra.
CI(NO) spectra of n‐Alkyn‐1‐ols1
Authors: Brauner A. , Budzikiewicz H. 
Published: May 2005

Abstractn‐Alkyn‐1‐ols show fragmentation patterns which are influenced by the length of the chain and by the relative positions of the hydroxyl group and triple bond, and which allow a localization of the site of unsaturation.
Structure of [C3H5O]+ ions produced from unimolecular decomposition of several [C4H8O]+˙ metastable ions
Authors: Bouchoux G. , Hoppilliard Y. , Flammang R. , Maquestiau A. , Meyrant P. 
Published: May 2005

AbstractIt is demonstrated by means of collisionally activated decomposition (CAD) that [C3H5O]+ originating from metastable [C4H8O]+˙ ions are either acylium [C2H5CO]+ (a) or hydroxycarbenium [CH2CHCHOH]+ (b). Butanone gives exclusively a but 2‐methyl‐2‐propen‐1‐ol, 2‐buten‐1‐ol, 3‐buten‐1‐ol, butanal and 2‐methylpropanal lead to ion b. Both structures a and b are produced from 3‐buten‐2‐ol. These results are discussed in conjunction with experimental and calculated (MINDO/3) thermodynamic data.
Metastable ion and induced stable ion fragmentation of isomeric 5‐methyl‐3‐tolyl‐1,2,4‐oxadiazoles
Authors: Nielsen Lawrence T. , Srivastava R. M. , e Silva Lẽda M. M. 
Published: May 2005

AbstractThe electron ionization fragmentation patterns of 5‐methyl‐3‐(o‐, m‐ and p‐tolyl)‐1,2,4‐oxadiazoles (1a—c) have been examined by metastable ion and high resolution mass spectrometry. The o‐tolyl isomer loses CO and C2H2O from the metastable molecular ion whereas the m‐ and p‐tolyl isomers lose only CH3CN thus indicating a strong ortho effect in directing the fragmentation in 1a. Slight differences between o‐, m‐ and p‐tolyl isomers in the collisional activation fragmentation of stable [C7H6N]+ ions suggest that structural differences exist even after a series of extensive rearrangements of the molecular ions. Metastable ion kinetic energy (MIKE) and collisional activation (CA) spectra were very helpful in providing valuable information about many fragments.
Structural determination of [C7H7O]+ ions in the gas phase by ion cyclotron resonance spectrometry
Authors: Cassady Carolyn J. , Freiser Ben S. , Russell David H. 
Published: May 2005

AbstractThe [C7H7O]+ ions from a series of compounds have been studied using ion cyclotron resonance spectrometry. The techniques employed in this gas phase ion structure determination of [C7H7O]+ were photodissociation, ion‐molecule reactions, and collisionally activated dissociation using a Fourier transform mass spectrometer (FTMS‐CAD). In addition to the low energy FTMS‐CAD results, high energy CAD data obtained with a sector mass spectrometer is also provided. Evidence was found for five unique [C7H7O]+ structures, including the hydroxybenzyl ion, the hydroxytropylium ion, the protonated benzaldehyde ion, the methylaryloxy ion and the phenyl methylene ether ion. Ion‐molecule reactions, invovling both proton transfer and methylene transfer, provided the most unambiguous results and yielded qualitative and quantitative evidence for the five structures. However, a combined approach using the three techniques was necessary to identify all of the structures. The tropylium form of [C7H7O]+ was found to absorb strongly at 305 nm, while the protonated benzaldehyde ion was found to have a strong absorption band at 305 nm and a weak band at 370 nm. The proton affinity of 2,4,6‐cycloheptatrienone was determined to be 918±8 kJ mol−1, which is considerably lower than a previously reported value. In addition, deprotonation reactions of the methylaryloxy ion yielded a proton affinity of 871±14 kJ mol−1 for 4‐methylenecyclohexa‐2,6‐diene‐1‐one.
Chemical ionization mass spectrometry of crown ether acetals using isobutane as reagent gas
Authors: Hancock Richard A. , Walder Ray , Weigel Helmut , Gold Victor , Sghibartz Cristian M. 
Published: May 2005

AbstractIsobutane chemical ionization mass spectrometry of crown ether acetals (M), derived from ethanal, give [MH]+ ions from which species corresponding to 44 u are successively eliminated. Mechanisms are presented in which these units correspond to (i) ethanal and (ii) oxirane. An accompanying process is the elimination of ethyne. Similar reactions occur in the chemical ionization mass spectrometry of benzo crown ether acetals.
Isotopic distribution of the polyhaloorganics formed from the halogenation of haloorganics with isotopically enriched halogens
Authors: Tanner D. D. , Ruo T. S. , Kosugi J. 
Published: May 2005

AbstractHalogenation reactions, both brominations and chlorinations, of haloorganics lead to di‐ or often polyhalogenated products. A major mechanistic question concerning these reactions always remains unanswered; whether they proceed by direct substitution or whether they proceed by a process involving an elimination‐readdition sequence. The question can be answered by carrying out the reactions using isotopically enriched halogen. A method of analysis has been devised, using high resolution mass spectrometry, which determines the isotopic distribution in each of the individual halogen atoms. The details of this procedure are presented in this report and examples of its use from several mechanistic investigations are presented.
Graphical aids and scanning modes for tandem mass spectrometry
Authors: Macdonald Colin G. , Lacey Michael J. 
Published: May 2005

AbstractIn tandem mass spectrometry, where typically one analyser is used to study the reactions of ions selected by another analyser from a mixture leaving the ion source, the output contains an additional dimension of information compared to that from conventional mass spectrometry. The increase in dimensionality tends to make the results less easy to assimilate and interpret, but the difficulties may be overcome in large measure by presenting the results in an appropriate graphical form. This review deals with the use of graphical representations of three‐dimensional data to display the results of experiments in tandem mass spectrometry. Perspective diagrams or contour maps can be used to show the identity of the parent and daughter ions for all of the reactions occurring in a tandem mass spectrometer, including reactions of positive ions, reactions of negative ions and charge inversion reactions. A graphical approach is particularly valuable when double focusing mass spectrometers are used for tandem mass spectrometry, because it can make it much easier to establish the origin of the ions contributing to an observed peak and thus to determine whether interference is occurring. Factors bearing on the choice of a coordinate system are discussed. Relationships characterizing the more important simple and linked scanning modes are listed and the features to which they correspond in two selected coordinate systems are shown. Factors that influence the resolution of neighbouring peaks by sector field tandem mass spectrometers are discussed.
The isomerization mechanism of alkylamines: Structure of [C2H6N]+ and [C3H8N]+ fragment ions
Authors: Audier H. E. , Milliet A. , Sozzi G. , Denhez J. P. 
Published: May 2005

AbstractThe MIKE spectra of amines RCH2NH2 containing more than five carbon atoms exhibit m/z 44 and m/z 58 peaks. The structures of these [C2H6N]+ and [C3H8N]+ ions have been established by collisional activation spectra. The results are in agreement with the fragmentation mechanisms previously proposed.