bluuebunny/crossref_metadata_2025_split huggingface dataset:
Further correlations between fragment ion intensity and critical energy. Unimolecular covalent bond fragmentation
Authors: Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald , Becker Ernest I. , Arison Byron H. 
Published: May 2005

AbstractA correlation of fragment ion intensity with critical energy found in the collisional activation spectra of [C4Ph]+˙ ions produced by electron impact can also be found in the unimolecular mass‐analysed ion kinetic energy spectra of these ions. The P(E) functions of the unimolecular and collisionally activated ions should differ not only in width but also in structure and therefore, the hypothesis that P(E) functions do not have an important effect on these correlations is tested successfully.
The unimolecular and collisionally activated decompositions of fluorine‐substituted tetraphenyltetrahedrane ions on the microsecond time‐scale
Authors: Bursey Maurice M. , Harvan Donald J. , Hass J. Ronald 
Published: May 2005

AbstractUnimolecular and collision‐induced decomposition products of [C4(C6H5)2(C6H4F)2]+˙ generated from four unsymmetrical sources include [C14H10]+˙ and [C14H8F2]+˙ and so provide evidence for a tetrahedral intermediate. Other decompositions show substantial influence of the position of the ρ‐fluorophenyl ring on ion energy distributions. This influence may be related to the reported absence of peaks diagnostic for the tetrahedral intermediate from the spectrum of the equivalent ion from the appropriate 13C‐labeled analog. Alternatively the difference in spectra can be correlated with lifetimes of ions.
Mass spectral study of ring E of taraxasterol and compounds with similar ring substitution
Authors: Lee Hsiu‐Pu Daniel , Eichmeier Larry S. , Piatak David M. 
Published: May 2005

AbstractThe origin of the [M–69]+ and [M–111]+ signals in the mass spectrum of taraxasterol was studied through the use of C(18), (19), (21), (22) and/or (30) deuteriated derivatives. The generality of these signals for ring systems with an exocyclic methylene group and a methyl moiety on an adjacent carbon was verified with 2‐methylmethylenecyclohexane, 1‐methyl‐2‐methylene‐trans‐decalin, 1,10‐dimethyl‐2‐methylene‐trans‐decalin and some of their deuteriated derivatives. The most plausible mechanism for the formation of the [M–69]+ ion appears to involve cleavage of both bonds allylic to the exocyclic methylene group with a 1,3‐hydrogen transfer from the adjacent ring. Genesis of the [M–111]+ ion is more complicated but a five‐membered allylic ion generated from ring D is proposed.
Chemical synthesis inside the collision cell of a MS/MS system: 1—Formation of adduct ions between protonated esters and ammonia
Authors: Schmit J. P. , Dawson P. H. , Beaulieu N. 
Published: May 2005

AbstractAn evaluation of the TAGA 6000 tandem quadrupole MS/MS capabilities for the study of the formation of adduct ions is presented. It is shown that under chemical ionization conditions the protonated molecular ions of esters react with neutral ammonia inside the collision cell of the instrument to yield adduct ions. Under the same reaction conditions the molecular ions obtained under electron impact conditions do not yield any adduct. Although it is not yet clear whether the adduct structure is of the cluster or covalently bonded type, the experimental results argue mainly in favor of the latter. The center‐of‐mass energy range usable for the formation of adduct ions is narrow and an order of magnitude lower than the energy required for collision‐induced dissociation. However, despite the weak parent ion center‐of‐mass energies used, the spectra exhibit fragments characteristic of the adduct ion structures. Finally, by controlling the parent ion center‐of‐mass axial kinetic energy, the number of parent ions and the target thickness, it is possible to measure and control all the usual physicochemical parameters for adduct ion formation.
Mass spectral rearrangements of 3‐arylsulphonyl‐2‐arylthiopropenes and N‐(4′‐arylsulphonyl‐2′‐butynyl)‐N‐(4″‐arylthio‐2″‐butynyl)anilines
Authors: Glaspy P. E. , Hancock R. A. , Thyagarajan B. S. 
Published: May 2005

AbstractUnder electron impact the title compounds undergo skeletal rearrangement in addition to the anticipated modes of cleavage. The 3‐arylsulphonyl‐2‐arylthiopropenes readily eliminate sulphur dioxide. Other modes of fragmentation include rearrangement to a bisaryl sulphide moiety and sulphone‐sulphinate rearrangement. The formation of a bisaryl sulphide ion is analogous to the behaviour of the isomeric trans‐1‐arylsulphonyl‐2‐arylthiopropenes. N‐(4′‐Arylsulphonyl‐2′‐butynyl)‐N‐(4″‐arylthio‐2″‐butynyl) anilines do not undergo any of the skeletal rearrangements mentioned above, but display the concerted loss of the arylsulphonyl and arylthio moieties. Similar eliminations have been observed from the analogous bis‐sulphides and bis‐sulphones.
Analysis of carbohydrates by fast atom bombardment mass spectrometry: 2—Influence of the matrix and the nature of the alkaline cations in the attachment process of an alkaline cation to a disaccharide molecule
Authors: Puzo G. , Promé J. C. 
Published: May 2005

AbstractThe fast atom bombardment (FAB) ionization process of a non‐reducing disaccharide by an attachment reaction with an alkaline cation has been investigated according to the nature of both the matrix (glycerol, diethanolamine, triethanolamine) and the alkaline cation (lithium, sodium, potassium, rubidium, caesium). We have established that one way of forming the cationized disaccharide molecular ions, [disaccharide‐cat]+, is by a desolvation reaction from the cationized solvated disaccharide molecular ions, [disaccharide‐cat‐matrix]+. This process, which has been established by mass‐analysed ion kinetic energy (MIKE) spectral analysis of the solvated species, is shown to be drastically affected by the nature of the involved matrix but only slightly by the alkaline cation. The variations in the relative abundances of the disaccharide cationized molecular ions compared to their solvated clusters in the FAB mass spectra, due to the matrix employed, have been explained according to the unimolecular dissociation of the solvated clusters examined by MIKE analysis. However, the variations in the abundance of the disaccharide cationized molecular ions in relation to the alkaline cation used—a higher sensitivity has been observed for lithium, sodium and potassium alkaline cations—have been explained in terms of the cations available at the target surface for the attachment process to the sugar molecule, and by a ligand exchange reaction between the matrix and the disaccharide.
In‐beam ionization by alkali ion attachment applying a two‐filament ion source
Authors: Schmelzeisen‐Redeker G. , Giessmann U. , Röllgen F. W. 
Published: May 2005

AbstractA simple ion source was constructed for in‐beam ionization by alkali ion attachment. A wire probe covered with sample was placed near an alkali ion emitter prepared from a mixture of silica gel and alkali halides. The ionization of various thermally labile compounds and of mixtures was investigated. Na+ proved to be the most suitable alkali ion for cationization. For monosaccharides experiments revealed the elimination of water upon ionization by Li+ attachment. The experimental set‐up was also examined for measuring the heat of sublimation of organic solids.
The behaviour of stereoisomeric ions in the gas phase: 2—Negative and positive chemical ionization of cyclohexanehexacarboxylic methyl esters
Authors: Audisio Guido , Grassi Maria , Traldi Piero , Daolio Sergio 
Published: May 2005

AbstractThe positive ion chemical ionization (CI (isobutane)), negative ion chemical ionization (NICI) electron attachment (CH4, He) and NICI (OH−) spectra of the title compounds have been studied in detail with the aid of deuterium‐labelled derivatives. The obtained results show that under CI conditions the stereospecificity is retained. Interesting correlations with the condensed phase epimerization yields are emphasized.
Provitamin D and vitamin D isomerizations in the mass spectrometer. Translational energy release and collision‐induced dissociation studies
Authors: Zaretskii Z. V. I. , Kingston E. E. , Beynon J. H. , Lauber R. , Schlunegger U. P. 
Published: May 2005

AbstractCollision‐induced dissociation mass‐analysed ion kinetic energy spectrometry and translational energy release studies have established that provitamin D3 (7‐dehydrocholesterol), provitamin D2 (ergosterol), vitamin D3 and vitamin D2 isomerizations in the mass spectrometer occur at the fragment ion level leading to [MH2OCH3]+ ions of identical structure. It was found that the reaction, [M]+˙→[MH2O]+˙, plays a central role in these isomerizations.
Doubly charged ion mass spectra of organophosphorus compounds
Authors: Appling J. R. , Burdick G. W. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra have been obtained for 11 organophosphorus compounds. Methane has been used as a target gas to increase the probability of single electron transfer collisions in the first field‐free region of an Hitachi RMU‐7L mass spectrometer. In general, the spectra of organophosphorus compounds do not exhibit molecular ions but are dominated by fragment ions, many of which must be formed by rearrangement processes. A geometry‐optimized self‐consistent field molecular orbital method has been employed to compute energies and structural parameters for prominent ions. In addition, a diabatic curve crossing model has been used to examine the single electron transfer reactions responsible for intense ions in the doubly charged ion mass spectra. Appearance energies measured for ions prominent in the 2E spectra of organophosphorus compounds have ranged from 23 to 38 eV.
Chemical ionization mass spectrometry of doxylamine and related compounds
Authors: Korfmacher Walter A. , Holder Claude L. , Freeman James P. , Mitchum Ronald K. , Gosnell Aubrey B. 
Published: May 2005

AbstractThe chemical ionization mass spectrometric (CIMS) analysis of doxylamine, N,N‐dimethyl‐2‐[1‐phenyl‐1‐(2‐pyridinyl)ethoxy]ethanamine, and related compounds, using both ammonia and methane as reagent gases, is discussed. The two reagent gases did not produce the same major fragment ion for doxylamine. Mechanisms for the fragmentation of doxylamine under either ammonia or methane CIMS conditions are proposed. The mechanisms explain the observation of an m/z 182 fragment ion for doxylamine analyzed under methane CIMS conditions and an m/z 184 product ion detected under ammonia CIMS conditions.
Translational energy release and stereochemistry of steroids 6—Contribution of the 18‐ and 19‐methyl groups to the translational energy release for the angular methyl loss in unsaturated steroids
Authors: Zaretskii Z. V. I. , Kustanovich Z. , Kingston E. E. , Beynon J. H. , Lauber R. , Schlunegger U. P. , Djerassi Carl 
Published: May 2005

AbstractThe translational energy, T, released during angular methyl loss from the molecular ions of unsaturated steriod hydrocarbons and alcohols, containing the double bond in the position allylic to either the 19‐CH3 or 18‐CH3 group, has been measured. The different contributions of the two angular methyl groups to the overall T value for the [M]+˙→[MCH3]+ reaction are discussed.
The unimolecular dissociation of protonated phenyl ethers formed by chemical ionization
Authors: Meyrant Philippe , Flammang Robert , Maquestiau André , Kingston Eric E. , Beynon John H. , Liehr Joachim G. 
Published: May 2005

AbstractA series of phenyl ethers with cyclic and acyclic olefins has been observed to form proton‐bound complexes on protonation under chemical ionization conditions with methane as the reagent gas. The competitive dissociations of these complexes have been studied by ion kinetic energy spectrometry and the measured branching ratios have been correlated with the relative stabilities of the product species.
Mass spectrometric studies on cyclo‐ and poly‐phosphazenes: 4—Attempts at mass spectrometrically induced polymerization of cyclotriphosphazenes substituted with primary and secondary amines
Authors: Gleria Mario , Audisio Guido , Daolio Sergio , Vecchi Enrico , Traldi Pietro 
Published: May 2005

AbstractIn this paper, the mass spectrometric behaviour of cyclophosphazenes substituted with primary and secondary amines is investigated, together with the mass spectrometric polymerization pattern of these compounds. While it is not possible to achieve the mass spectrometric polymerization of hexa(anilino)cyclotriphosphazene, ion–molecule reactions take place in the case of hexa(piperidino)‐ and hexa(morpholino)cyclotriphosphazenes, which lead to the formation of hexameric species. Evidence is given that pentasubstituted cyclophosphazenephosphorus cations are the species responsible for the oligomerization process.
Mass spectra of some high molecular weight tetra(alkyl)silanes
Authors: Onopchenko Anatoli , Sabourin Edward T. , Danner David A. 
Published: May 2005

AbstractThe mass spectra of tetra(alkyl)silanes having one short and three long alkyl groups were recorded (C20C32). These silanes did not give molecular ions, and the dominant course of fragmentation involved the loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups, followed by elimination of alkenes. The loss of alkyl groups followed the sequence iso‐Pr>Et, Pr,… C14H29» Me. With alkyl groups longer than hexyl, a rearrangement was observed in which n‐alkanes were eliminated from the base ion. When the alkyl group was hexyl, the alkane eliminated was methane; when the alkyl group was heptyl, ethane was expelled; with octyl, it was propane; and with decyl, n‐pentane was expelled. Deuterium labeling showed that at least two modes of rearrangement were occurring.
Substitution reactions under NH3 chemical ionization conditions in cis‐/trans‐1,2‐dihydroxybenzosuberans
Authors: Madhusudanan K. P. , Prasad Mohan , Rastogi Shri Nivas , Fraisse D. 
Published: May 2005

AbstractThe nucleophilic substitution reaction under NH3 chemical ionization (CI) conditions in cis‐ and trans‐1,2‐dihydroxybenzosuberans (1–4) has been studied with the help of ND3 CI and metastable data. The results indicate that in the parent diols 1 (cis) and 2 (trans), the substitution ion [MsH]+, is produced mainly by the loss of H2O from the [MNH4]+ ion (SNi reaction) while in their 7‐methoxy derivatives 3 and 4, the ion‐molecule reaction between [MOH]+ and NH3 seems to be the major pathway for the formation of [MsH]+. The substitution ion from 1 and 2 and the [MH]+ ion from trans‐1‐amino‐2‐hydroxybenzosuberan give similar collision‐induced dissociation mass‐analysed ion kinetic energy spectra. Interestingly, their diacetates do not undergo the substitution reaction.
Mass spectra of phenoxyacetyl derivatives
Authors: Vairamani M. , Ishratullah K. , Reddy D. M. , Rao G. K. Viswanadha 
Published: May 2005

AbstractThe electron‐impact‐induced mass spectra of substituted N‐phenylphenoxyacetamides are discussed. The structure of the rearrangement ion at m/z 108 is investigated and compared with the molecular ion of anisole by metastable ion and corrected collisionally activated dissociation spectra.
The effect of para‐substitution on the mass spectra of arylsulphonate esters of neopentanol
Authors: Mamer Orval A. , Padmapriya Abeysinghe A. , Just George 
Published: May 2005

AbstractThe mass spectra of several para‐substituted benzenesulfonic and benzoic esters of unlabelled and 1,1‐d2‐neopentyl alcohol are examined and compared. Evidence is presented of migration of the aryl group from the sulfur to an oxygen atom in the molecular ions of the sulfonic esters. The nature of the fragmentation processes and the occurrence of metastable ions for these processes are both much more dependent upon the polarity of the para substituent in the case of the sulfonates than for the benzoates. Elimination of C5H10 occurs from the molecular ion of the p‐methoxysulfonate with transfer to the residual ion of a hydrogen atom selected randomly from the alkyl fragment, while in the case of the p‐aminosulfonate, incomplete randomization is demonstrated.
Stereoisomeric effects on mass spectral fragmentations of chloronorbornanones
Authors: Rothwell A. P. , Cooks R. G. , Singh T.‐V. , De Cárdenas L. , Morrison H. 
Published: May 2005

AbstractStereoelectronic factors allow facile Cl˙ atom loss from the exo‐6‐chloro‐2‐norbornanone radical cation but not from the endo‐6‐epimer. The predominant primary reaction in the endo‐6 and in the exo‐5 and endo‐5 compounds is HCl elimination. While CI˙ elimination occurs with skeletal reorganization, HCl loss, at least in part, does not. The 5‐chloro isomers undergo a regiospecific McLafferty rearrangement which occurs relatively slowly in competition with Cl˙ and HCl loss. The use of energy‐resolved forms of tandem mass spectrometry provides considerable detail regarding the unimolecular fragmentations of these gaseous ions.
Identification of two separate mechanisms for HCN loss from gas phase quinoline cations
Authors: Baldwin Michael A. , Langley G. John 
Published: May 2005

AbstractCritical energy measurements on 13C‐labelled quinolines show that the energy requirement for elimination of H(C‐2)N from metastable ions is lower than that for H(C‐3)N elimination, the critical energies being 4.03 ± 0.05 eV and 4.17 ± 0.05 eV, respectively. It is also shown that involvement of C‐2 and C‐3 in unimolecular HCN elimination from ions in the second field‐free region is greater, by factors of approximately 3 and 2 respectively, than would be anticipated for elimination following complete carbon randomization.
Mass spectra of 1‐(2′‐hydroxy‐5′‐alkylphenyl)‐1‐alkanone (E)‐oximes
Authors: Łozyński Marek , Krzyzanowska Ewa 
Published: May 2005

AbstractThe mass spectra of 1‐(2′‐hydroxy‐5′‐alkylphenyl)‐1‐ethanone (E)‐oximes 1–6 and 1‐(2′‐hydroxy‐5′‐methylphenyl)‐1‐alkanone (E)‐oximes 7–12 are given and the major fragmentation pathways discussed. The simultaneous loss of water and alkyl moieties from the molecular ion indicates that a skeletal rearrangement take place and a cycloheptatrienyloheterocyclic system is formed. The McLafferty rearrangement, γ‐fission in the side aliphatic chain and oxygen expulsion are discussed with evidence being drawn from accurate mass measurements, metastable ions and comparison with mass spectral data of related compounds.
Proton affinities by reactant ion monitoring: Triphenyl group Va compounds
Authors: Tran Vinh Thi , Munson Burnaby 
Published: May 2005

AbstractProton affinities of a series of triphenyl Group Va compounds have been determined by bracketing using reactant ion monitoring: (C6H5)3N = 904 ± 8 kJ mol−1, (C6H5)3P = 968 ± 5 kJ mol−1, (C6H5)3As = 904 ± 8 kJ mol−1 and (C6H5)3Sb = 846 ± 8 kJ mol−1. The large difference in substituent effect of phenyl for hydrogen between As or P and N may result from overlap of the 2p orbitals of N with the sp2 orbitals on the ring carbons and lack of overlap for P or As. Proton affinities of phenylalkylphosphine oxides are essentially the same, 904 ± 8 kJ mol−1, independent of alkyl group.
Electron impact and ammonia chemical ionization mass spectra of n‐azabicyclo[m.2.0]alkan‐(n + 1)‐ones (m = 3–6, n = 6–9)
Authors: Pihlaja Kalevi , Vainiotalo Pirjo , Bernáth Gábor , Göndös György , Gera Lajos 
Published: May 2005

AbstractElectron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low‐resolution, high‐resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7‐azabicyclo[4.2.0]octan‐8‐one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k‐2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙.
Laser desorption mass spectrometry of squaric acid and its salts
Authors: Byrd Gary D. , Fatiadi A. J. , Simons D. S. , White V E. 
Published: May 2005

AbstractThe laser desorption mass spectrometry of the oxocarbon squaric acid (3,4‐dihydroxy‐3‐cyclobutene‐1,2‐dione) and its salts of the form A2C4O4 (A = cation) is described. Both positive and negative ion spectra were obtained. The positive ion spectrum of the acid is characterized by an ion corresponding to loss of CO from [M + H]+. The negative ion spectrum shows an intense [M − H]− peak in addition to a dimer species. The alkali salt spectra contain [M + A]+ in the positive mode and [M − A]− and an intense [C4HO4]− in the negative mode. The smaller alkali salts also have an [M + H]+ adduct ion. Unlike the alkali squarates, the ammonium salt shows ions corresponding to losses of neutrals from the molecular adduct in the positive ion spectrum and a dimer species in the negative ion spectrum. Molecular weight information was obtained in all cases. A (bis) dicyanomethylene derivative of potassium squarate was also studied. Some field desorption mass spectrometry results are presented for comparison.
Mass spectra of some 2‐(4′‐butyl‐3,′5′‐dimethylpyrazol‐1′‐yl)‐6‐substituted benzothiazoles
Authors: Singh Shiv P. , Vaid Radhe K. 
Published: May 2005

AbstractThe fragmentation of the title compounds on electron impact has been studied and the major processes interpreted. The base peak invariably appears at [M  43]+ whose origin from the butyl chain has been traced with the help of metastable ion studies and accurate mass measurements. Loss of methyl cyanide, involving the decomposition of the pyrazole moiety, is observed only from the fragment ions.
Ortho effects in organic molecules on electron impact 13—mechanism of decarboxylation in o‐carboxy heteroaromatics
Authors: Ramana D. V. , Kartha T. R. Gopinathan 
Published: May 2005

AbstractExpulsion of CO2 from the molecular ions of the 2‐(2‐carboxyphenyl) derivatives of benzoxazole, benzothiazole and benzimidazole gives rise to the base peaks on electron impact. The proposed mechanism for this fragmentation process, involving the anchimeric assistance of the heteroatom by the initial abstraction of the H˙ from the carboxyl group followed by the expulsion of CO2 from the molecular ions, is supported by the study of the linked scan spectra.
Structure analysis of the propionic–pentafluoropropionic anhydride derivatives of norepinephrine and serotonin
Authors: Barker Steven A. , Tolbert Lelland C. , Brown George B. 
Published: May 2005

AbstractGas chromatographic/mass spectrometric analysis was used for the examination of norepinephrine and serotonin derivatives formed from their sequential reaction with propionic anhydride and pentafluoropropionic anhydride. The structures of the resulting derivatives were determined by the analysis of the mass spectra of the proteo and deutero homologs and by nuclear magnetic resonance spectroscopy. Mechanisms for the synthesis and electron impact fragmentation of these derivatives are proposed.
Mass spectrometry of analogues of pyrimidine bases: 2‐ and 4‐alkylthio‐5‐halogenouracils
Authors: Stobiecki Maciej 
Published: May 2005

AbstractThe electron impact induced mass fragmentations of 16 new 2‐ and 4‐alkylthio‐5‐chloro‐ and 2‐ and 4‐alkylthio‐5‐bromouracils are presented. The elucidation of the fragmentation pathways is described. The fragmentation routes have been confirmed by accurate mass measurements and metastable transitions. It has been found that the position of uracil ring thiation may be deduced on the basis of the mass spectral fragmentation patterns.
Electron impact mass spectrometry of some 2‐methyl‐2‐aryl‐ and 2‐methyl‐2‐alkyl‐1,3‐dithianes
Authors: Sturaro Alberto , Traldi Pietro 
Published: May 2005

AbstractThe electron impact mass spectrometric behaviour of four 2‐methyl‐2‐aryl‐ and two 2‐methyl‐2‐alkyl‐1,3‐dithianes is described and discussed in detail, with the aid of exact mass measurements, linked scans and mass‐analysed ion kinetic energy spectrometry. The mechanism of the primary HS2˙ loss, as well as those of the more unusual fragmentation pathways, are given.