bluuebunny/crossref_metadata_2025 huggingface dataset:
Collision induced dissociations of ions produced in the field free regions of a triple sector mass spectrometer
Authors: Maquestiau André , Meyrant Philippe , Flammang Robert
Published: May 2005

Molecular or fragment ions can be prepared by a large variety of reactions in the field free regions of a mass spectrometer; these reactions involve spontaneous dissociation as well as collision induced excitation of singly or doubly charged precursors. Some typical examples show the different means which can lead to a given ion and how they can be studied by collisional activation. It also appears that in most cases the use of a triple sector (E/B/E) mass spectrometer facilitates these experiments as interfering artefacts are suppressed.
Mass spectra of some thionocarbamates
Authors: Łożyński Marek
Published: May 2005

The mass spectra of a number O‐alkylthionocarbamates with two, one or no alkyl substituents on the nitrogen atom are presented and discussed. The main primary fragmentation pathways are McLafferty rearrangements, including the double so‐called protonated McLafferty rearrangement. Generally, rearrangement products give charge delocalized ions, which release hydroxyl or sulphydryl radicals and water or hydrogen sulphide, to produce stable fragments. It has been found that the position of alkyl moieties may be deduced on the basis of mass spectral fragmentation patterns.
Chemical ionization and electron impact mass spectra of thiosulfinates, thiosulfonates and sulfinyl sulfones
Authors: Freeman Fillmore , Angeletakis Christos N.
Published: May 2005

The chemical ionization and electron impact mass spectra of some thiosulfinates, thiosulfonates and sulfinyl sulfones have been studied. The electron impact mass spectra of four of the six thiosulfonates show molecular ions of less than 1%. Inconclusive evidence was obtained for sulfenyl sulfinate type intermediates in the electron impact spectra of thiosulfonates. The electron impact spectra of thiosulfonates were similar to those of thiosulfonates. The chemical ionization (isobutane) mass spectra of thiosulfinates and thiosulfonates generally show protonated molecular ions [MH]+as base peaks and [MH+1]+and [MH+2]+peaks.
Alkane elimination from ionized alkanols
Authors: Holmes John L. , Burgers Peter C. , Mollah Yousuf A.
Published: May 2005

The energetics, metastable characteristics and daughter ion structures for the loss of small alkane molecules from ionized 2‐propanol, 2‐butanol and 3‐pentanol have been examined in detail. [2‐Propanol]+˙ ions lose CH4 to generate the keto and enol forms of [C2H4O]+˙ and the same daughter ions are produced by loss of C2H6 from [2‐butanol]+˙. Ionized 3‐pentanol does not lose CH4 but readily eliminates C2H6 to produce the enol ion [CH3CHCHOH]+˙. The last reaction was shown to proceed by a simple 1,2 elimination mechanism in the μs time‐frame; isotope effects are also discussed.
Collisional activation study of cyclic polysulfides
Authors: Holzmann G. , Susilo R. , Gmelin R.
Published: May 2005

Cyclic polysulfides isolated from higher plants, model compounds and their electron impact induced fragment ions have been investigated by various mass spectrometric methods. These species represent three sets of sulfur compounds: C3H6Sx (x=1−6), C2H4Sx (x=1−5) and CH2Sx (x=1−4). Three general fragmentation mechanisms are discussed using metastable transitions: (1) the unimolecular loss of structural parts (CH2S, CH2 and Sx); (2) fragmentations which involve ring opening reactions, hydrogen migrations and recyclizations of the product ions ([MCH3]+, [MCH3S]+, [MSH]+ and [MCS2]+˙); and (3) complete rearrangements preceding the fragmentations ([MS2H]+ and [MC2H4]+˙). The cyclic structures of [M]+˙ and of specific fragment ions have been investigated by comparing the collisional activation spectra of model ions. On the basis of these results the cyclic ions decompose via linear intermediates and then recyclizations of the product ions occur. The stabilities of the fragment ions have been determined by electron efficiency vs electron energy curves.
Flowing afterglow studies of the reactions between negative ions and trimethylsilyl enol ethers. Regiospecific generation of gas phase enolate ions
Authors: Squires Robert R. , Depuy Charles H.
Published: May 2005

Reactions of isomeric silyl enol ethers with fiuoride, amide or hydroxide ions in a flowing afterglow lead to the formation of relatively pure isomeric enolate anions. Isomeric enolates react specifically with neopentyl nitrite to give ionic products diagnostic of their structure.
Quantitative relationships between fragment ions and their relative intensities in electron impact mass spectrometry: VI—Hydroxy‐substituted tert‐alkylamines
Authors: Záhorszky U. I.
Published: May 2005

The influence of functional group interaction on the intensity ratios (Q) of product ions from α‐fission of ethyl‐tert‐alkylamines C2H5(C3H7)(HO(CH2)n)C NHC2H5, in which one side chain of the tert‐alkyl moiety is replaced by a hydroxyalkyl group of varying chain length, was investigated. It was found that only through‐bond interaction between the functional groups has a major influence on these ratios. By substitution of a hydrogen by a halogen atom in one side chain it was shown that the so‐called ‘ion mass effect’ is a degrees of freedom effect.
The fragmentation behavior of the endo‐ and exo‐octahydro‐4,7‐methano‐1H‐indene systems
Authors: Inman Roger C. , Servé M. Paul
Published: May 2005

The electron impact induced fragmentations of the endo‐ and exo‐octahydro‐4,7‐methano‐1H‐indene systems have been studied. The principal decomposition reactions have been elucidated by deuterium labelling. Two generic fragmentation patterns appeared: one involved the bisection of the molecule and the second involved the loss of various alkyl fragments.
Evidence for different reacting structures in the mass spectra of isomeric epoxides and aldehydes
Authors: Torroni Sandro , Foffani Maria Teresa , Sorriso Salvatore , Innorta Giuseppe
Published: May 2005

The metastable ion characteristics for common fragmentations of isomeric aromatic epoxides and aldehydes give indications for different reacting molecular ion structures. Some features of the fragmentation scheme of epoxides are discussed.
Application of emitter chemical ionization mass spectrometry to structural characterization of aminoglycoside antibiotics—2
Authors: Takeda Naohito , Harada Ken‐ichi , Suzuki Makoto , Tatematsu Akira , Kubodera Toshiya
Published: May 2005

Emitter chemical ionization mass spectra of several aminoglycoside antibiotics (pseudotrisaccharides) have been determined by using isobutane and ammonia as reagent gases. All mass spectra show the protonated molecule and nine characteristic fragment ions due to the cleavages of glycosidic linkages. These fragment ion peaks are shown to be useful for the structural characterization of compounds of this class. Fragmentation reactions have been confirmed by the shift technique with ammonia‐d3 as the reagent gas.
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

The 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

Collisionally 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

It 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

The 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

The 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

Fast 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

The 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

Commercial 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

The 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

The 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

Metastable 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

The 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

Intramolecular 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

A 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

Mechanisms 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

By 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.
Rearrangements in chemical ionization mass spectra
Authors: Kingston Eric E. , Shannon James S. , Lacey Michael J.
Published: May 2005

Rearrangements reported in the literature for positive ions formed by chemical ionization are briefly reviewed, with particular emphasis on illustrative examples of hydrogen and skeletal rearrangements.
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

Competitive 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

Twenty‐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

C5H10 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

The 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

n‐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

It 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

The 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

The [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

Isobutane 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

Halogenation 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

In 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

The 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.
Mass spectrometric studies of dithiophosphinato metal complexes
Authors: Heinz S. , Keck H. , Kuchen W.
Published: May 2005

Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L2 (L=Et2PS2−; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L3 (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal‐metal interaction is observed even under electron impact.
Comparison of ‘soft ionization’ techniques with electron impact mass spectrometry for desoxinojirimycin and folic acid derivatives
Authors: Wünsche C. , Benninghoven A. , Eicke A. , Heinen H.‐J. , Ritter H. P. , Taylor L. C. E. , Veith J.
Published: May 2005

Seven desoxinojirimycin and three folic acid derivatives were investigated using the soft ionization techniques of desorption chemical ionization (DCI), laser desorption (LAMMA), field desorption (FD), secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB). The mass spectra were compared with electron impact (EI) spectra and interpreted in terms of their suitability for analytical purposes.
The reactions of metastable [C5 H10 O]+˙ ions with the oxygen on the second carbon
Authors: McAdoo David J. , Hudson Charles E. , McLafferty Fred W. , Parks Terry E.
Published: May 2005

Nearly all [C5H10O]+˙ isomers with the oxygen on the second carbon are shown to interconvert with each other and lose methyl and ethylene at the threshold for dissociation. The methyls contain the carbons from the 1‐ and 5‐positions with about equal frequency, and C(3) or perhaps C(4) about half as often as either terminal carbon. CH3 CH2 CH2 CO+ is formed by loss of the C(1) methyl and magnified image by loss of the C(5) methyl. Hydorgen transfer between C(5) and the oxygen and between the oxygen and C(4) are facile, and 1,2‐hydrogen transfers between C(3) and C(4) occur with high frequency. Extensive skeletal rearrangements also take placae by 1,2‐shifts between C(2), C(3) and C(4). We attribute the occurrence of teh three‐center shifts between C(2), C(3) and C(4) to the presence of considerable charge density on C(2) and C(3) in many of the [C5H10O]+˙ isomers. The isomerizations of [C5H10O]+˙ can be considered a mixture of free radical and carbocation reactions. Strong similarities exist between the isomerizations of metastable [C5H10O]+˙ ions with the oxygen on the second carbon and those of isomers of ionized butanoic acid, methyl butanoate and n‐butanal.
LAMMA mass spectra of β‐diketone, bis(benzoylacetone)ethylenediimine and bis(salicylidene)ethylenediimine complexes of some transition metals
Authors: Rohly Kenneth E. , Heffren John S. , Douglas Bodie E.
Published: May 2005

Complexes of 2,4‐pentanedione (acetylacetone, acac), [Cu(acac)2], [VO(acac)2] and [CO(acac)3], and the chromium(III) derivative of 3‐methyl‐2,4‐pentanedione (methylacetylacetone, meac), [Cr(meac)3], the ligands bis(benzoylacetone)ethylenediimine and bis(salicylidene)ethylenediimine, and their cobalt(II), nickel(II) and copper(II) chelates were analysed by laser desorption mass spectrometry (LAMMA) and compared to electron impact (EI) results. The positive ion LAMMA spectra generally reveal mostly small fragments, although metal cationization peaks are seen for most complexes. Negative ion LAMMA produce carbon clusters and some structurally important fragments.
Doubly charged ion mass spectra 8—alkenes
Authors: Appling J. R. , Musier K. M. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra of 23 alkenes have been measured using a double focusing Hitachi RMU‐7L mass spectrometer. Ion mass spectra were obtained using 100 eV electron energy and 3.2 kV ion accelerating voltage. Each 2E spectrum was determined using the olefinic compound under investigation as the target gas. In general, spectra are dominated by fragment ions which result from extensive hydrogen loss from the doubly charged molecular ion. Appearnce energies have been measured for intense fragment ions in each spectrum.
Ion–molecule reaction in the gas phase 4—Stereospecific nucleophilic substitution under ammonia chemical ionization conditions from diastereomeric methyl and benzyl ethers of 3‐hydroxy steroids
Authors: Tabet Jean‐Claude , Tondeur Yves , Hirano Yutaka , Wegmann Annemarie , Tecon Pierre , Djerassi Carl
Published: May 2005

The ammonia chemical ionization (CI/[NH4+]) mass spectra of a series of diastereomeric methyl and benzyl ethers derived from 3‐hydroxy steroids (unsaturated in position 5 and saturated) have been studied. The adduct ions [M+NH4]+ and [MH]+ and the substitution product ions [M+NH4ROH]+ (thereafter called [MsH]+) are characterized by an inversion in their relative stabilites in relation to their initial configuration. [M+NH4]α+ and [MH]α+ formed from the α‐Δ5‐steroid isomers are stabilized by the presence of a hydrogen bond which is not possible for the β‐isomers. This stereochemical effect has also been observed in the mass analysed ion kinetic energy (MIKE) spectra of [M+NH4]+ and [MH]+. The MIKE spectra of [MsH]+ indicate that those issued from the β‐isomers are more stable than the one originating from the α‐isomers. This behavior is also observed in the first field free region (HV scan spectra) for [MH]+, [MsH]+ and [M+NH4]+ which are precursors of the ethylenic carbocations (base peak in the conventional CI/[NH4]+ spectra). Mechanisms, such as SN1 and SNi, have been ruled out for the formation of [MsH]+, but instead the data support an SN2 mechanism during the ion‐molecule reaction between [M+NH4]+ and NH3.
Mechanisms of ion formation in field desorption of oligosaccharides
Authors: Rogers David E. C. , Derrick Peter J.
Published: May 2005

Energy deficits have been measured for ions in the field desorption mass spectra of saccharides. Evidence is presented to show that monosaccharides, disaccharides and trisaccharides are volatile compounds, under the conditions of field desorption. It is proposed that the electric field plays an essential role in the desorption of [M+H]+ ions.
Mass spectral fragmentation pathways in 2,4,6‐trinitrotoluene derived from a MS/MS unimolecular and collisionally activated dissociation study
Authors: Robert Carper W. , Cameron Dorey R. , Tomer Kenneth B. , Crow Frank W.
Published: May 2005

The fragmentation pathways of 2,4,6‐trinitrotoluene have been examined using 15N and 2H isotopic labelling in conjunction with tandem mass spectrometry. Both the unimolecular and collisionally activated decomposition modes were investigated. Fragmentation pathways were established in both modes and isotopic shifts were used to determine the groups lost. The major pathways include the loss of OH or H2O, followed by the subsequent loss of NO or NO2. There is virtually no ring disintegration until the majority of the attached groups are lost.
Rearrangements and isomerism in the molecular ion of o‐methoxybenzoic acid
Authors: Gillis Richard G. , Porter Quentin N.
Published: May 2005

The molecular ion of o‐methoxy‐d3‐benzoic acid can undergo three different rearrangements and hydrogen/deuterium exchange between the functional groups. This can result in 14 isomers of the molecular ion before it decomposes giving fragments at m/z 105, 106, 107 and 108. Three types of isomer have been identified.
Mass spectroscopic fragmentation pathways of 1,8‐nonadiyne
Authors: Robbins Ronny Charles , Foster Norman George
Published: May 2005

Cleavage α to triple bonds in straight‐chain hydrocabons with only one triple bond is a very minor process. The mass spectrum of 1,8‐nonadiyne (mol. wt 120) shows strong peaks at around m/z91, which points to a major fragmentation pathway of cleavage α to triple bonds in straight‐chain diynes. This study attempts to explain this paradox. Through‐space interaction was indicated through the use of carbon‐13 labelling of the terminal carbon atoms in 1,8‐nonadiyne, 1,2,8,9‐13C‐1,8‐Nonadiyne and 3,7‐13C‐1,8‐nonadiyne were prepared to determine which carbon atoms were lost in the process of [M]+˙ and [M1]+ going to m/z91. These two molecules were chosen for ease of synthesis. Low‐resolution mass spectra and low‐voltage studies determined that a major portion of carbon atoms being lost were from the middle of the carbon chain. This points to a fragmentation pathway that results from through‐space interaction of the two terminal triple bonds. It is likely that ionization enhances this through‐space interaction of the two triple bonds.
Three new isomers of [C2H6O]+˙: The radical cations [CH3O(H)CH2]+˙, [CH3CHOH2]+˙ and a low‐energy isomer of unassigned structure
Authors: Burgers Peter C. , Holmes John L. , Terlouw Johan K. , van Baar Ben
Published: May 2005

Three new [C2H6O]+˙ ions have been generated in the gas phase by appropriate dissociative ionizations and characterized by means of their metastable and collisionally induced fragmentations. The heats of formation, ΔHf0, of the two ions which were assigned the structures [CH3O(H)CH2]+˙ and [CH3CHOH2]+˙ could not be measured. The third isomer, to which the structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = \mathop {\rm C}\limits^{\rm .} {\rm H} \cdot \cdot \cdot \mathop {\rm H}\limits^ + \cdot \cdot \cdot {\rm OH}_{\rm 2} $\end{document} is tentatively assigned, was measured to have ΔHf0 = 732±5 kJ mol−1, making it the [C2H6O]+˙ isomer of lowest experimental heat of formation. It was found that the exothermic ion–radical recombinations [CH2OH]++CH3˙→[CH3O(H)CH2]+˙ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm + } {\rm HOH + H}^{\rm .} $\end{document}→[CH3CHOH2]+˙ have large energy barriers, 1.4 and ⩾0.9 eV, respectively, whereas the recombinations yielding [CH3CH2OH]+˙ have little or none.
Optimization of operating conditions for desorption chemical ionization mass spectrometry
Authors: Takeda Naohito , Harada Ken‐ichi , Suzuki Makoto , Tatematsu Akira
Published: May 2005

Optimization of the operating conditions for desorption chemical ionization (D/CI) mass spectrometry has been evaluated on the production of molecular ion species as well as structurally informative fragment ion species with sucrose as a main model compound. Among various parameters examined, it was found that configuration and heating rate of the emitter wire were significantly concerned with the desorption efficiency, while chamber temperature played an important role on the control of the fragmentation process rather than the desorption process. Therefore, the conditions for optimal molecular ion species are quite opposed to those for optimal fragment ion species. The former can be achieved by the use of the highest heating rate combined with the lowest chamber temperature. Under the optimal operating conditions, a 20 ng sample of sucrose is adequate for recording a clear mass spectrum with good reproducibility, where [M·NH4]+ (m/z 360) is the base peak and the glycosyl ion [S·NH3]+ (m/z 180) also has moderate abundance (rel. int., 40%).
Structure of gas phase [C5H6]+˙ ions
Authors: Flammang Robert , Meyrant Philippe , Maquestiau André , Kingston Eric E. , Beynon John H.
Published: May 2005

Charge‐stripping spectra have been used to differentiate ionized cyclopentadiene from its acyclic isomers. The minimum amounts of translational energy lost during the charge‐stripping processes and the relative charge‐stripping efficiencies, which are also structurally important parameters, have been measured for these ionic species. [C5H6]+˙ ions, formed by dissociative ionization of various precursors in the ion source are found, usually, to be a mixture of cyclic and acyclic ions. In contrast, [C5H6]+˙ ions, derived from the dissociation of metastable molecular ions from a series of organic compounds, have the cyclopentadienyl structure. This structure was confirmed by collision‐induced dissociation of ions formed in the first field‐free region of a triple sector mass spectrometer.
The Claisen rearrangement of protonated allyl phenyl ether
Authors: Kingston Eric E. , Beynon John H. , Liehr Joachim G. , Meyrant Philippe , Flammang Robert , Maquestiau André
Published: May 2005

Molecular protonated ions of allyl phenyl ether undergo a Claisen rearrangement both in the ion source and along the flight path. The rearranged ions undergo fragmentation, the predominat loss being ethene, and only a small contribution from loss of carbon monoxide is observed. Collision‐induced dissociation spectra are used to verify the structures of the daughter ions. These spectra, together with other evidence of an acid‐induced ortho rearrangement, allow a mechanism to be proposed for the ethene loss. In contrast, molecular protonated ions of propargyl phenyl ether lose exclusively carbon monoxide.
Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane
Authors: Clemens David , Munson Burnaby
Published: May 2005

Mixtures of 50% tetramethylsilane (TMS) and methane have been found to give [M+73]+ adduct ions and structurally useful fragment ions for many oxygen‐ and nitrogen‐containing organic compounds. All of the reagent ions in TMS react with polar compounds. The high‐pressure TMS chemical ionization spectra of many simple oxygenated compounds are in agreement with predictions from ion chemistry of (CH3)3Si+ obtained by ion cyclotron resonance experiments at very low pressures, but differences are noted. Sensitivities for oxygen‐, nitrogen‐, and sulfur‐containing compounds with TMS as the reagent gas appear to be approximately the same.
Electron impact induced ortho effects in 2‐nitro‐substituted aromatic sulphides containing 2‐pyridyl, 2‐(5‐methylthio‐1,3,4‐thiadiazolyl) and/or 2‐(4‐methyl‐1,3,4‐thiadiazolinyl‐5‐thione) moieties
Authors: Pappalardo Sebastiano , Di Grazia Michele
Published: May 2005

The most significant mass spectral features of 14 title compounds are discussed with the aid of deuterium labelling experiments. The decomposition patterns of these compounds are strongly affected by several competing ortho effects, due to the interaction of the nitro function(s) with neighbouring electron‐poor N‐heterocycles. Very intense polycyclic ions are produced via addition‐elimination reactions by loss of simple radicals (H˙, OH˙, NO2˙) from the molecular ion, followed by the ejection of neutral molecules (HNO2,CH3SCN or CH3NCS). In addition, primary or secondary intramolecular oxygen transfers, preceded or not by hydrogen migration, from the nitro group to the imino carbon via spirocyclic intermediates, are generally observed. Minor skeletal rearrangements, triggered by single or multiple intramolecular oxygen transfer to the bridgehead sulphur atom, followed by SO or SO2 ejection, are also noticed.
Mass spectrometric study on 2‐amino‐as‐triazino[6,5‐c]quinoline and some of its derivatives
Authors: Vékey K. , Tamás J. , Berényi E. , Benkó P.
Published: May 2005

Electron impact induced fragmentations of 2‐amino‐as‐triazino[6,5‐c]quinoline and its 2‐methylamino, 2‐dimethylamino and 2‐benzylamino analogues have been investigated. The main primary decomposition route of both the singly and the doubly charged molecular ions is the N2 loss. For the singly charged ions the critical energy of this reaction is 110±10 kJ mol−1 and the kinetic energy release is 61±4 kJ mol−1. For the doubly charged ions these values are 90±10 kJ mol−1 and 5±2 kJ mol−1, respectively, indicating a significantly different reaction profile. The further fragmentation of [MN2]+˙ ions consists of radical eliminations from the 2‐amino group with cleavages of the α‐ and β‐bonds. Here a significant substituent effect is eliminations found suggesting an intramolecular cyclization reaction with a substituent migration. D and 15N labelling experiments have shown a minor extent of randomization of the labelled atoms and the occurrence of other hidden skeletal rearrangements during the fragmentation.
Matrix effects in fast atom bombardment mass spectrometry of cationic iridium(III) and rhodium(III) coordination complexes
Authors: Divisia‐Blohorn B. , Kyriakakou G. , Ulrich J.
Published: May 2005

Fast atom bombardment mass spectra of cationic iridium(III) and rhodium(III) coordination complexes (M+Cl2L2, X−; where the ligand L is a dinitrogenous aromatic system) have been obtained with thioglycerol, glycerol or tetraglyme as a matrix. Two kinds of reactions, initiated by particle bombardment, have been discovered between these complexes and the matrix. First, with thioglycerol one or two chlorine atoms are substituted by a thioglycerol radical, more rapidly for rhodium compounds; secondly, when the ligand L possesses a diazo function, this function is hydrogenated depending on the ability of the matrix to generate hydrogen radicals by bombardment.