bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fragmentation reactions of some aliphatic esters in the NCl(F−) and NCl(NH2−) mass spectra
Authors: Grützmacher Hans‐Fr. , Grotemeyer Barbara 
Published: May 2005

AbstractThe NCI(F−) and NCI(NH2−) mass spectra of a series of aliphatic acetates and of methyl and ethyl trimethylacetate have been obtained. The formation of fluoroenolate ions CH2COF− and of carboxamide anions RCONH− (R  CH3))CH3C). respectively, is observed besides formation of [M  H]− ions and carboxylate ions RCOO− (R  CH3, (CH3)3C). The relative intensities of the different anions depend on the structure of the ester molecules and on the primary reactant anions. Usually, the NCI(NH2−) spectra of the acetates are dominated by [M  H]− ions ([MD]− ions in the case of trideuteroacetates) fragmenting unimolecularly by elimination of an alcohol. The carboxylate ions are important fragments, too, but carboxamide ions are only observed with large intensities in the NCI(NH2− spectra of the trimethylacetates. The NCI(F−) spectra show much larger intensities of carboxylate ions and fluoroenolate ions. The mechanisms of the fragmentation reactions are discussed. The results indicate that most or even all of the fragment ions in the NCI(F− mass spectra of aliphatic esters are formed by addition‐elimination reactions via a tetrahedral intermediate, while competition between direct proton abstraction and addition‐elimination reactions occurs in the NCI(NH2−) mass spectra because of the higher basicity of NH2− resulting in an early transition state for direct proton abstraction.
A correlation between fragment intensity and critical energy in collisional activation of some ions produced by electron impact
Authors: Bursey Maurice M. , Harvan Donald J. , Ronald Hass J. , Becker Ernest I. , Arison Byron H. 
Published: May 2005

AbstractA Hammett correlation for ratios of intensities of collision induced fragments of [C4R4]+· ions from tetraphenylcyclopentadienones is predicted on the basis of statistical theory and observed in practice.
Mass spectral fragmentation and rearrangement of isatin derivatives
Authors: Peet Norton P. , Barbuch Robert J. 
Published: May 2005

AbstractMass spectral fragmentation pathways were formulated for 1‐alkylisatins, 1‐alkyl‐3‐arylimino‐2‐indolinones and 3‐arylimino‐2‐indolinons bearing no substituent at the 1‐position. Deuterium‐labelled and 13C‐labelled compounds were utilized in this study. An interesting rearrangement of the 1‐alkyl compounds, in which the 1‐alkyl substituent is incorporated into a fulvene ion, was established.
Accurate linked scans based on digital real time mass linearization and function generation
Authors: Friedli Felix 
Published: May 2005

AbstractA new, commercially available digital linked scan unit mass display/marker is presented operating in real time in a mass range of 0.0 to 1638.3 u without the need for a data system. The prerequisites and limitations of successful linked scans with their consequences for the new design are discussed. Examples give evience of the need for increased accuracy.
Experimental investigation of the molecular ions of the xylenes
Authors: Curtis J. M. , Boyd R. K. , Shushan B. , Morgan T. G. , Beynon J. H. 
Published: May 2005

AbstractA mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.
A relation between ion structures and experimental overall cross‐sections for collisionally activated decomposition
Authors: Van Tilborg M. W. E. M. , Van Thuijl J. 
Published: May 2005

AbstractCollisionally activated dissociation (CAD) mass spectra sometimes appear to be identical in spite of the fact that the precursor ion structures are known to differ. It is shown that determination of the experimental overall cross‐section for collisionally activated decomposition yields valuable extra information. After applying it to examples of known structure, [C4H5N]+·, [C5H5N]+· and [C5H5O]+, it is used to study a more complex problem, that of [C6H6]+· ions from four isomeric precursors.
The behavior of stereoisomeric ions in the gas phase: The Case of cyclohexane‐hexacarboxylic methyl esters
Authors: Audisio Guido , Grassi Maria , Daolio Sergio , Traldi Pietro 
Published: May 2005

AbstractNot only strong differences in relative abundances of product ions, but also different fragmentation pathways are observed in the electron impact mass spectrosopy of six stereoisomeric cyclohexanehexacarboxylic methyl esters. This unusual behaviour has been studied in detail with the aid of different ionization methyods, B/E and B2/E linked scans, exact mass measurements, deuterium labelling experiments and collisionally activated decomposition spectrometry. A close analogy between the isomerization observed under acidic conditions in condensed phase and that observed under chemical ionization (CH4) conditions is underlined.
Electron impact mass spectrometry of 4, 5‐dihydro‐1,2,4‐benzothiadiazepine‐1,1‐dioxide derivatives
Authors: Vettori Umberto , Lesma Giordano , Nali Micaela , Palmisano Giovanni 
Published: May 2005

AbstractThe fragmentation pathways of some 4,5‐dihydro‐1,2,4‐benzothiadiazepine‐1,1‐dioxide derivatives are discussed on the basis of metastable transition data, exact mass measurements and labelling experiments. These compounds show several primary fragmentation processes: M  SO2, M  OH and one involving an intramolecular oxygen migration (M  CH3NO).
Electron ionization and chemical ionization mass spectra of pyridinium and isoquinolinium ylides
Authors: Bowen D. V. , Skett P. W. , Thorpe J. , Plunkett A. O. 
Published: May 2005

AbstractElectron ionization (EI) spectra and both positive and negative chemical ionization (CI) spectra have been obtained for four isoquinolinium ylides and two pyridinium ylides. Electron transfer reactions dominate the CI mass specra. The base peak in negative chemical ionization is the [M]−· ion, formed by electron capture. In the positive methane CI spectra the molecular ion, [M]+·, is relatively more intense than [MH]+ showing electron transfer to be the main positive ionization process. In the positive ammonia CI spectra, proton transfer to give [MH]+ is the main ionization process, but electron transfer is also observed. The EI spectra show fragmentations in which the aromatic nitrogen moiety retains the charge and fragmentation is by loss of radicals or small neutral molecules from the side‐chains. Radical driven reactions are proposed to explain these spectra.
Atmospheric pressure ionization mass spectrometry of the polychlorinated dibenzo‐p‐dioxins
Authors: Korfmacher Walter A. , Mitchum Ronald K. 
Published: May 2005

AbstractThe branching ratios for the reaction pathways of 39 polychlorinate dibenzo‐p‐dioxins (PCDDs) under oxygen negative chemical ionization/atmospheric pressure ionization mass spectrometric conditions were measured. These results demonstrated that the PCDDs could be separated into 14 groups by this technique. These results were compared with those reported previously for 14 PCDDs using oxygen negative chemical ionization mass spectrometry.
Translational energy release and stereochemistry of steroids 4—Epimeric 3‐keto and 3‐hydroxy steroids
Authors: Zaretskii Z. V. I. , Dan P. , Kustanovich Z. , Larka E. A. , Herbert C. G. , Beynon J. H. , Djerassi Carl 
Published: May 2005

AbstractThe translational energy, T, released during CH3˙ loss from the molecular ions of epimeric steroid ketones and from both molecular and [M‐H2O]+˙ ions of epimeric alcohols of the androstane, pregnane and cholestane series, differing in the mode of the A/B ring junction, has been measured. These data provide a simple and rapid method for identifying the configuration of the epimeric centres. Of the compounds studied, it is found in 3‐hydroxy steroids that the 5β‐isomers release the smaller amounts of translational energy for CH3˙ loss. In most of the 3‐keto steroids investigated, the opposite is found, i.e. the larger T values are observed for the 5β‐isomers. Exceptions occur when further keto groups are introduced at the 11‐ or 17‐positions. A small range of epimeric pairs of 17‐hydroxy, 17‐keto and 4‐keto steroids have also been studied, the 5β‐isomer giving the lower T value in each case. The importance of hydroxy and keto groups at the various sites within the steroid structure in determining the T values is discussed.
Ortho effect in the fragmentation of 2‐acetoxychalcones under electron impact
Authors: Mentlein Rolf , Vowinkel Erich 
Published: May 2005

Abstract2‐Acetoxychalcones decompose under electron impact conditions by loss of an acetoxy fragment to form flavylium ions. The effect is restricted to the ortho position and is reduced after hydrogenation of the chalcone double bond. The intense flavylium ion originates—as shown by specific labelling with 18O—from two different fragmentation lines: (a) direct loss of an acetoxy radical by cleavage of the phenolic ArO bond and (b) sequential elimination of ketene and a hydroxy radical.
Ion–molecule reaction in the gas phase 3—nucleophilic substitution of 17ξ‐R‐5α,14β‐androstane‐14,17ξ‐diols under [NH4]+ chemical ionization conditions1
Authors: Tabet J. C. , Bertranne M. , Beloeil J. C. , Stahl D. 
Published: May 2005

AbstractUnder Ammonia chemical Ionization conditions the source decompositions of [M + NH4]+ ions formed from epimeric tertiary steroid alchols 14 OHβ, 17OHα or 17 OHβ substituted at position 17 have been studied. They give rise to formation of [M + NH4H2O]+ dentoed as [MHsH]+, [MsHH2O]+, [MsHNH3]+ and [MsHNH3H2O]+ ions. Stereochemical effects are observed in the ratios [MsHH2O]+/[MsHNH3]+. These effects are significant among metastable ions. In particular, only the [MsH]+ ions produced from trans‐diol isomers lose a water molecule. The favoured loss of water can be accounted for by an SN2 mechanism in which the insertion of NH3 gives [MsH]+ with Walden inversion occurring during the ion‐molecule reaction between [M + NH4]+ + NH3. The SN1 and SNi pathways have been rejected.
Collisionally induced dissociative ionization of neutral products from unimolecular ion fragmentations. 1—Neutral product structures
Authors: Burgers Peter C. , Holmes John L. , Mommers Alexander A. , Szulejko Jan E. , Terlouw Johan K. 
Published: May 2005

AbstractA method is described for the investigation of the structure of neutral products from the unimolecular (metastable) dissociative ionizations of mass selected ions, by means of the collisionally induced dissociative ionization of the neutral species themselves. The neutral species, with kilovolt translational energies, enter a positively charged collision cell situated in the second field free region of a standard ZAB‐2F mass spectrometer. Dissociative ionization of the neutrals results therein from their collisions with He target gas. The resulting ions are analysed by means of the electric sector and the relative ion abundances are shown to be structure characteristic. For such experiments the neutral flux should be c. ≥ 0.5% of the selected precursor ion flux; the collision gas pressure must be insufficient to cause significant precursor ion fragmentation in the field free region preceding the collision cell. It was shown that HNC is generated in the fragmentation of aniline molecular ions, whereas HCN is the neutral product in the dissociative ionizations of pyridine, benzonitrile and benzyl cyanide. The neutral radical [C, H3, O˙] formed together with [CH3CO]+ from ionized methyl acetate has the structure ˙CH2OH, but that from the analogous fragmentation of the methyl propanoate molecular ion has the structure CH3O˙. Allyl radicals were shown to be generated from [(CH3)2CHCH2OH]+˙ together with [CH3OH2]+ ions.
Matrix effects in the fast atom bombardment protonation of carbohydrates
Authors: Puzo Germain , Prome Jean‐Claude 
Published: May 2005

AbstractFAB positive mass spectra of trehalose in the presence of different matrices such as glycerol, diethanolamine (DEA) and triethanolamine (TEA) are presented and discussed. Protonated and solvated protonated trehalose ions are observed, of which the relative abundance changes with the liquid matrix used. MIKE spectra of the protonated molecular ions solvated by the matrix show unambiguously that desolvation contributes to the formation of protonated molecular ions. It is shown that the decomposition of these complexes is mainly controlled by the relative proton affinities of the analysed sample and the matrix.
Mechanism of CO loss for protonated 1‐indanone and isomeric [C9H9O]+ ions
Authors: Audier Henri E. , Milliet Arielle 
Published: May 2005

AbstractIn order to establish the mechanism of CO loss occurring during metastable decomposition of protonated 1‐indanone, fragmentations of monocyclic [C9H9O]+ isomers have been studied. These ions of known structure were prepared by CI protonation and fragmentation of the corresponding acids chlorides. It is demonstrated that the wide component of the [MHCO]+ metastable peak induced by protonated 1‐indanone fragmentation is the result of fragmentation of the [C6H5CH2CH2CO]+ isomer ion.
Mass spectrometry of β‐keto aldehydes: Novel hydroxyl transfer reactions
Authors: Kulkarni P. S. , Kamath S. V. , Kamath H. V. , Kulkarni Sheshgiri N. 
Published: May 2005

AbstractThe mass spectral fragmentation of 2,3‐diaryl‐3‐oxo‐1‐propanals has been investigated by low electron energy, metastable defocusing and shift techniques. The o‐nitro group strongly interacts with α‐cleavage reactions of the carbonyl group. The cyclization/elimination processes, accompanied by oxygen and hydroxyl transfer in the mass spectra of o‐nitro‐β‐keto aldehydes, are preceded by hydrogen abstraction by the nitro group.
Chemical ionization mass spectra of alkylphenol and linear alcohol polyethoxylates
Authors: Stephanou Euripides 
Published: May 2005

AbstractThe chemical ionization mass spectra of some tert‐octylphenol ethoxylates and linear alcohol ethoxylates have been determined using methane and ammonia as reactant gases. Proton, [C2H5]+ and [C3H5]+ adducts were observed with attachment on the ring as well as on the oxyethylene chain for the tertiary octylphenol ethoxylates. Proton and [NH4]+ addition reactions were also observed. Alkyl ion and olefin displacement reactions were also important fragmentations. Hydride abstraction and proton, [C2H5]+, [C3H5]+ and [NH4]+ attachment were the most important reactions occurring for the linear alcohol ethoxylates.
Mass spectrometry in structural and stereochemical problems. 2617—The effect of stereochemistry on the course of the characteristic ring D fragmentation of steroid hydrocarbons
Authors: Patterson Donald G. , Haley M. J. , Midgley I. , Djerassi Carl 
Published: May 2005

AbstractThe ring D cleavage of the sterol skeleton with loss of carbon atoms 15, 16 and 17 together with the side‐chain is one of the most characteristic and structurally useful mass spectral features of steroids. It has been tacitly assumed that the hydrogen rearrangements accompanying this process are not sensitive to stereochemical changes. Using deuterium labeling it has now been demonstrated that the stereochemistry at various positions of the nucleus, notably 8, 9 and 14, strongly affects this process. Possible rationalizations for this unexpected observation are presented.
The site of gas phase cation attachment. The protonation, methylation and ethylation of morpholine, thiomorpholine and 1,4‐thioxane
Authors: Burinsky David J. , Campana Joseph E. 
Published: May 2005

AbstractThe attachment of gaseous positive ions ([H]+, [CH3]+ and [C2H5]+) to morpholine, thiomorpholine and 1,4‐thioxane, through chemical ionization, has been studied by collision spectroscopy. The daughter ion spectra of the ion/molecule reaction products were compared to those of model ions, generated by fast‐atom bombardment of corresponding quaternary ammonium salts, in order to determine the preferred site of reaction for the protonation and alkylation of these multifunctional nucleophilic compounds. For novel entities with no model precursors, the site of cation attachment was postulated on the basis of characteristic fragmentations and trends established by the study of other bifunctional heterocycles. The site of protonation followed predicted trends in proton affinity differences for the various heteroatoms (N>S>O), and the alkyl ion reactivities followed differences in electronegativity or nucleophilicity (S>N>O).
Collision energy effects in tanden mass spectrometry as revealed by a proton‐bound dimer ion
Authors: McLuckey S. A. 
Published: May 2005

AbstractMass spectra resulting from collision‐induced decomposition of the proton‐bound dimer of iso‐propylamine and sec‐butylamine have been obtained as a function of laboratory collision energy over the range 10‐6000 eV. The ratio of the two principal fragment ions from the dimer ion measured as a function of collision energy is compared with the ratio expected as a function of internal energy as calcualted based on the statistical theory of mass spectra. This comparison indicates that the average energy deposited into the dimer ion upon collision reaches a maximum at a collision energy of ∼70 eV. The average internal energy of the ions at this collision energy is ∼4.3 eV. Other fragment ions which arise from higher energy decompositions are also observed in the spectra at much lower intensities. The relative intensities of these fragments indicate that the probability for large energy transfers are highest at ke V collision energies. These observations are interpreted on the basis of differences in the postcollision internal energy distributions resulting from keV and eV collisions.
Mass spectrometry of aryl‐substituted benzoylcyclopropanes
Authors: Guziec Frank S. , Luzzio Frederick A. , Yu T. J. , Vouros Paul 
Published: May 2005

AbstractThe electron impact and chemical ionization mass spectra of several benzoylcycloprpanes carrying a wide variety of ring substituents were examined. Cleavage of the benzoyl‐cyclopropyl CC bond was a dominant process in the spectra of the compounds. Retention of the positive charge with either the benzoyl or the cyclopropyl moiety was influenced by the electron‐donating properties of the ring substituents. The stereoselectivity of hydrogen abstraction in the elimination of ArH groups was evaluated using deuterium‐labelled analogs.
A mass spectrometric study of the pyrolysis of gibberellic acid
Authors: Greathead Roger J. , Mason Rod S. , Jennings Keith R. , Page Janet A. , Pryce Robert J. 
Published: May 2005

AbstractThe behaviour of gibberellic acid (GA3) under electron impact and chemical ionization conditions has been examined. The tendency of GA3 to undergo pyrolysis by the loss of the elements of water and carbon dioxide has been identified. Two methods of sample introduction can be used to minimize the occurrence of this pyrolysis. Accurate mass measurement allows the composition of the pyrolysis product to be determined and metastable techniques confirm the structure of this product to be epi‐allogibberic acid rather than its isomer allogibberic acid. This result corrects a misconception in the literature and illustrates the advantage of metastable methods compared with accurate mass measurements, for the determination of small structural differences within a molecule.
Electron capture negative ion and positive ion chemical ionization mass spectrometry of polychlorinated phenoxyanisoles
Authors: Campbell Jo‐Anne B. , Griffin Donald A. , Deinzer Max L. 
Published: May 2005

AbstractSeveral polychlorinated phenoxyphenols with three to nine chlorine atoms were examined as their methyl ethers by electron capture negative ion and positive ion chemical ionization and electron impact mass spectrometry. In chemical ionization studies methane, hydrogen, nitrogen, helium and argon were used as reagent gases. Selected compounds were also examined with deuteriomethane, ammonia and deuterioammonia as reagent gases. Utilization of chemical ionization spectra in conjuction with electron impact spectra provides substantial structural information about these compounds. Chemical ionization spectra provide information about chlorine atom substitution. The position of phenoxy substitution can be established from electron capture negative ion and positive ion spectra.
Rearrangement reactions in the positive and negative ion mass spectra of clausmarin A
Authors: Madhusudanan K. P. , Shoeb Aboo 
Published: May 2005

AbstractThe positive and negative ion mass spectra of clausmarin A, a naturally occurring tetracyclic coumarin, have been studied. The base peaks in the positive and negative ion spectra correspond to the complementary ions at m/z 143 and m/z 255, respectively, formed by a rearrangement reaction. The fragmentation pathways have been elucidated with the help of exact mass measurements and in situ deuterium labelling.
Collision‐induced dissociation of negative ions in the gas phase: [Aryl S]−, [aryl SO]− and [aryl SO2]−
Authors: Bowie John H. , Stringer Michael B. 
Published: May 2005

AbstractCollision‐induced dissociation of the ions [ArS]−, [ArSO]− and [ArSO2]− has uncovered a rich and varied ion chemistry. The major fragmentations of [ArS]− are complex and occur without prior ring hydrogen scrambling: for example, [C6H5S]−→[C2HS]− and [HS]−; [p‐CD3C6H4S]−→[C6H4S]−˙, [CD3C4S]− and [C2HS]−. In contrast, all decompositions of [C6H5CH2S]− are preceded by specific benzylic and phenyl hydrogen interchange reactions. [ArSO2]− and [ArSO2]− ions undergo rearrangement, e.g. [C6H5SO]−→[C6H5O]− and [C6H5S]−; [C6H5SO2]−→[C6H5O] −. The ion [C6H5CH2SO]− eliminates water, this decomposition is preceded by benzylic and phenyl hydrogen exchange.
Fast atom bombardment mass spectrometry of salts of substituted methylene bisphosphonic acids and other analogues of pyrophosphoric acid
Authors: Hutchinson David W. , Semple Graeme 
Published: May 2005

AbstractFast atom bombardment mass spectra have been obtained of salts of analogues of inorganic pyrophosphoric acid, e.g. substituted methylene bisphonates, and positive ion fast atom bombardment mass spectrometry (FABMS) has proved to be more successful than negative ion FABMS for the analysis of these salts. Owing to the low molecular weight of these analogues, FAMBS of the free acids and the sodium salts does not always give results which are easy to interpret as interference by peaks from the matrix can occur. However, the potassium salts in a 60% glycerol matrix, when bombarded by argon atoms, give good FAB spectra which are relatively free of interfering peaks.
Mass spectroscopy of natural products. 20—Quinazoline carboxylic acids 4—Comparative positive and negative ion mass spectroscopic studies of 3,4‐dihydroquinazolin‐4‐on‐3‐ylalkanoic acids and 3,4‐dihydro‐1,2,3‐benzotriazin‐4‐on‐3‐ylalkanoic acids
Authors: Schmidt Jürgen , Süsse Manfred , Johne Siegfried 
Published: May 2005

AbstractThe mass spectroscopic behaviour of 3,4‐dihydroquinazolin‐4‐on‐3‐ylalkanoic acids and 3,4‐dihydro‐1,2,3‐benzotriazin‐4‐on‐3‐ylalkanoic acids was studied under positive and negative ionization. The differences in fragmentation both between the ionization modes and between the two heterocyclic systems are discussed by using some 15N‐labelled derivatives.