bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of charge on hydroxyl loss from ortho‐substituted nitrobenzene ions
Authors: McLuckey Scott A. , Glish Gary L. 
Published: May 2005

AbstractAn abundant loss of hydroxyl in decompositions of ortho‐substituted nitroarene cations is commonly observed when the substituent contains one or more labile hydrogen atoms. The major loss of hydroxyl also takes place from many but not all of the corresponding molecular anions. Data are reported for the collisionally activated decompositions of the cations and anions of o‐nitrotoiuene, o‐nitrophenol and o‐nitroaniline. Data for some dinitro ions are also reported. The results can be rationalized on the basis of a greater degree of charge developed at the substituent in the transition state of the anions that leads to a rearranged ion. It is from this structure tint hydroxyl is lost via simple bond cleavage. This can be viewed most simply as a proton transfer from the substituent to the nitro group in the anion as opposed to hydrogen transfer in the analogous step for the cation. The degree to which hydroxyl loss occurs is therefore largely determined by the tendency for hydrogen (cations), or proton (anions), transfer from the substituent to the nitro group.
Comparison of the stable products formed by fast atom bombardment and γ‐irradiation of glycerol
Authors: Keough T. , Ezra F. S. , Russell A. F. , Pryne J. D. 
Published: May 2005

AbstractThe major end‐products formed by fast atom bombardment (FAB) and γ‐irradiation of glycerol have been identified using capillary gas chromatography/mass spectrometry. The product distributions differ dramatically. Products resulting from the recombination of either carbon‐centered or oxygen‐centered radicals are evident for both sources of irradiation. However, the major FAB‐generated products are formed by the recombination of carbon‐centered [G – H]· radicals with other carbon‐centered radicals while the major γ‐radiolysis products result from the recombination of oxygen‐centered [G–H]· radicals with lower‐weight carbon‐centered species. γ‐Radiolysis of an N2O‐saturated aqueous solution of glycerol, experimental conditions that strongly favor the formation of carbon‐centered [G – H]· radicals at the expense of the oxygen‐centered species, yielded some products that were identical to those produced by FAB of neat glycerol. Finally, the free radicals produced by γ‐radiolysis of glycerol were investigated by electron spin resonance spectroscopy and spin trapping with 5,5‐dimethyl‐1‐pyrrolne‐TV‐oxide. The presence of only the carbon‐centered free radical was established by this technique. The implications of these results are discussed.
Mass spectroscopy of natural products. XXIII, Comparative positive and negative ion mass spectral studies of scapanin‐type diterpenoidst
Authors: Schmidt Jiirgen , Huneck Siegfried , Franke Peter , Connolly Joseph D. 
Published: May 2005

AbstractThe mass spectral behaviour of 15 scapanin‐type diterpenoids (8α,12‐epoxylabdanes) was elucidated using accurate mass measurements and deuterium‐labelled derivatives. The results obtained allow a localization of the functional groups in the diterpenoid system. Furthermore, the negative ion mass spectra of the scapanin‐type diterpenoids are discussed and compared with the positive ion spectra.
Doubly charged ion mass spectra of alkyl‐substituted furans and pyrroles
Authors: Nelson P. R. , Kee Fung C. A. Fung , Sedgwick J. B. , Shields G. C. , Abbey L. E. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra of alkyl‐substituted furans and pyrroles were obtained using a double‐focusing magnetic mass spectrometer operated at 3.2 kV accelerating voltage. Molecular ions were the dominant species found in doubly charged spectra of lower molecular weight heterocydic compounds, whereas the spectra of the higher weight homologues were typified by abundant fragment ions from extensive decomposition. Measured doubly charged ionization and appearance energies ranged from 22.8 to 47.9 eV. Ionization energies were correlated with values calculated using self‐consistent field–molecular orbital techniques. A multichannel diabatic curve‐crossing model was developed to investigate the fundamental organic ion reactions responsible for development of doubly charged ion mass spectra. Probabilities for Landau–Zener type transitions between reactant and product curves were determined and used in the collision model to predict charge‐transfer cross‐sections, which compared favorably with experimental cross‐sections obtained using time‐of‐flight techniques.
Mass spectrometric investigation of benzyliderieaniline
Authors: Srzić Dunja , Čevizović Nada , Meić Zlatko 
Published: May 2005

AbstractThe mass spectral fragmentation of benzylideneaniline has been studied by deuterium labelling. Under electron impact, molecular ions undergo simple fission at the phenyl–N, phenyl–C and CN bonds, hydrogen migration reactions, and skeletal rearrangement fragmentations. Except in the skeletal rearrangement reactions, hydrogen scrambling does not feature in benzylideneaniline upon electron impact.
Mass spectra of phenoxyacetyl derivatives. Mechanism of loss of ‘CO’ from phenyl phenoxyacetates
Authors: Vairamani M. , Mirza Urooj Ali 
Published: May 2005

AbstractThe mechanism of loss of ‘CO’ in phenyl phenoxyacetates has been studied by collision‐induced dissociation spectra. Interesting ortho effects have been reported in the o‐methoxy and o‐nitro isomers.
Surface‐induced dissociation of isomeric [C5H6]+˙ ions
Authors: Mabud Md. A. , Ast T. , Cooks R. G. 
Published: May 2005

AbstractCollisions of [C5H6]+˙ ions of 25 eV tianslational energy with a surface result in dissociation, the extent of which depends upon the nature of the neutral precursor. A correlation between the degree of fragmentation and the reported degree of charge stripping upon gaseous collisions (R. Flammang et al, Org. Mass Spectrom. 20, 253 (1985)) supports the suggestion that mixtures of cyclic and linear structures in differing proportions are present in the [C5H6]+˙ ion beam.
A mass spectrometric study of dimethyl ester trimethylsilyl ether derivatives of some 3‐hydroxydicarboxylic acids
Authors: Svendsen John S. , Sydnes Leiv K. , Whist Jon E. 
Published: May 2005

AbstractThe fragmentation pathways for the dimethyl ester trimethylsilyl ether derivatives of some 3‐hydroxydicarboxylic acids have been found by using B/E 2nd B2/E linked scans and isotope substitution techniques. Most of the fragments are due to ionization at silicon, which induces a fragmentation pattern that intimately reflects the structure of the compounds.
Quantum mechanical investigation of effects in formation of carbonyl and thiocarbonyl cations. Part I. Fragmentation reactions of 1,2‐hemithiodione radical cations
Authors: Nevalainen Vesa , Vainiotalo Pirjo 
Published: May 2005

AbstractIn order to study decomposition reactions of ionic oxygen and sulphur‐containing compounds, such as hemithiodione radical cations, a quantum chemical investigation of the formation of formyl, thioformyl, acyl and thioacyl cations and radicals was performed. Calculations were carried out mainly at the 6–31G* level involving complete geometry optimizations. In the ionization of aldehydes and thioaldehydes, no important energy differences were found between the oxygen and sulphur analogues studied. A stepwise generation of formyl and thioformyl cations from formaldehyde and thioformaldehyde, by hydrogen atom abstraction followed by expulsion of unpaired electrons from the resulting radicals, showed the radicalization of formaldehyde to be only 12.6 kJ mol−1 more favoured than that of thioformaldehyde. The electron expulsion from formyl radical was 23.8 kJ mol−1 more favoured than that from thioformyl radical. Substitution of hydrogens of formyl and thioformyl groups by methyls lowered the total formation energies of carbonyl and thiocarbonyl cations 119.2 and 96.2 kJ mol−1. The formation energy difference between acyl and thioacyl cations was also very small.
High‐pressure collisional activation mass spectrometry of aromatic halides
Authors: Blom Karl , Munson Burnaby 
Published: May 2005

AbstractThe high‐pressure collisional activation mass spectra with methane as the reagent/collision gas are reported for five aromatic halides. The major decomposition of the protonated aromatic halides is hydrogen halide elimination. The energy‐resolved mass spectra and the chemical reactivities of fragment ions with the methane collision gas are used to establish dissociation pathways and structures of fragment ions. The high‐pressure collisional activation mass spectra are compared with conventional collisionally induced dissociation and chemical ionization mass spectra.
Loss of methyl from ionized 2‐hydroxy‐1,3‐butadiene
Authors: Turefček František , Maquin Francis , Hill Nicholas , Stahl Daniel , Gäumann Tino 
Published: May 2005

AbstractThe loss of methyl from unstable, metastable and collisionally activated [CH2CHC(OH)CH2]+˙ ions (1+˙) was examined by means of deuterium and 13C labelling, appearance energy measurements and product identification. High‐energy, short‐lived 1+˙ lose methyl groups incorporating the original enolic methene (C(1)) and the hydroxyl hydrogen atom (H(0)). The eliminations of C(1)H(1)H(1)H(4) and C(4)H(4)H(4)H(0) are less frequent in high‐energy ions. Metastable 1+˙ eliminate mainly C(1)H(1)H(1)H(4), the elimination being accompanied by incomplete randomization of the five carbon‐bound hydrogen atoms. The resulting [C3H3O]+ ions have been identified as the most stable CH2CHCO+ species. The appearance energy for the loss of methyl from 1 was measured as AE[C3H3O]+ = 10.47 ± 0.05 eV. The critical energy for 1+˙ → [C3H3O]+ + CH3˙ is assessed as Ec ⩽ 173 kJ mol−1. Reaction mechanisms are proposed and discussed.
Computer‐assisted composition analysis of unknown compounds by simultaneous analysis of the intensity ratios of isotope patterns of the molecular ion and daughter ions in low‐resolution mass spectra
Authors: Tenhosaari Aarni 
Published: May 2005

AbstractA microcomputer program has been developed which calculates compositions of unknown compounds by using the intensity ratios of isotope patterns in low‐resolution electron impact mass spectra. The patterns originating from the molecular ion, recognizable daughter ions, and ions from common neutral fragment losses are simultaneously used for the composition analysis, thus improving the reliability compared to previously published methods. The method is most suitable for analysing spectra of compounds giving intense, well‐shaped and separate peak patterns of daughter ions. The program is also able to analyse the compositions of the analytically useful compounds of boron.
Desorption due to charge exchange in low‐energy collisions of organofluorine ions at solid surfaces
Authors: Vincenti M. , Cooks R. G. 
Published: May 2005

AbstractCollisions of organofluorine ions at a metal surface result in efficient emission of adsorbate species as gas‐phase ions. The experiments are done at 120° scattering angle in a hybrid (BQ) mass spectrometer; the primary ions, mass‐selected by a magnetic sector (B), are allowed to collide with a target at a selected kinetic energy in the tens of eV range and the emitted ions are mass‐analyzed using a quadrupole mass filter (Q). It is proposed that the impinging ions undergo neutralization accompanied by desorption of hydrocarbon ions and that the amount of internal energy deposited in the desorbed ions is strongly dependent on the collision energy and affects their degree of fragmentation. Competing processes include reflection and fragmentation of the colliding particle, along with such ion/adsorbate reactions as hydrogen atom abstraction by the fluorinated ion. Small even‐electron ions, such as [CHF2]+ and [C2H2F]+ are more effective in promoting chemical sputtering of the surface adsorbate as compared to larger ions (e.g. [C3F5]+) and odd‐electron ions (e.g. [C2F4]+˙ and [C2HF2]+˙). At low energies some odd‐electron fluorinated ions undergo collision without any secondary ions being emitted from the surface. In these cases the parent ions are apparently neutralized, but without sufficient energy transfer to cause hydrocarbon ion desorption. Non‐fluorinated organic ions yield fragment ions and ion/surface reaction products under the condition of these experiments, but do not cause significant desorption of hydrocarbon ions.
Mass spectrometric investigation of some [1]benzopyrano[3,4‐c]pyrazole and [1]benzopyrano[4,3‐d]isoxazole derivatives
Authors: Kostova Ivanka N. , Mollova Nevena N. 
Published: May 2005

AbstractThe fragmentation behaviour of some [1]benzopyrano[3,4‐c]pyrazole and [1]benzopyrano[4,3‐d]isoxazole derivatives under electron impact is described.
Internal energy requirements for remote site fragmentation
Authors: Wysocki Vicki H. , Bier Mark E. , Cooks R. Graham 
Published: May 2005

AbstractAttempts to induce remote site fragmentation by using low‐energy collisional activation with a neutral target gas or with a surface (surface‐induced dissociation) are reported. These data, in conjunction with knowledge of the internal energy deposition associated with these activation methods, provide information on the amount of internal energy needed to promote remote site fragmentation in selected compounds. The internal energy required for remote site fragmentation of lithiated oleyl alcohol was recently estimated to be 1.3–1.9 eV. Our experiments suggest that internal energies much greater than 2 eV are required to produce detectable remote site fragmentation in several different ions, including lithiated oleyl alcohol, n‐dodecylbenzenesulfonate anion, stearylsulfate anion, stearate anion and protonated octadecylamine. The results also suggest that the internal energy required to record spectra which show remote site fragmentation is compound‐dependent, i.e. strongly dependent on the nature of the ionic group.
Mass spectral fragmentation pathways in phthalate esters. A tandem mass spectrometric collision‐induced dissociation study
Authors: Yinon Jehuda 
Published: May 2005

AbstractA collision‐induced dissociation study of a series of phthalate esters was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the phthalates were determined in the electron impact mode. Two major daughter ions are formed, one by a McLafferty rearrangement and hydrogen transfer and the other by loss of an alkoxy radical Another major daughter ion, at m/z 149—which is the base peak in the electron impact mass spectra of most phthalate esters—is being formed through four alternate pathways.
[C7H7] radicals studied by neutralization reionization mass spectrometry; the ortho‐tolyl to benzyl radical rearrangement
Authors: Buschek J. M. , Holmes John L. 
Published: May 2005

AbstractThe collision‐induced dissociation characteristics of the benzyl, tropyl and tolyl cations which serve to identify these [C7H7]+ isomers (the m/z 74–77 relative abundances) were not preserved in their neutralization‐reionization (NR) mass spectra. However, analyses of mixtures of the [C7H7]+ isomers made by comparison of NR mass spectra gave similar results to those obtained from collisional activation (CA) mass spectra. The radicals produced by electron transfer from Xe to tolyl cations were not observed to rearrange to benzyl radicals on the time‐scale of the NR experiment, a result in conflict with other gas‐phase studies.
Fragmentation of ligands and stability of inorganic skeletons in the mass spectra of polynuclear beryllium and zinc complexes
Authors: Sipachev Viktor A. , Nekrasov Yurii S. 
Published: May 2005

AbstractElectron impact induced fragmentations of 12 beryllium and zinc μ4‐oxohexa‐μ‐acido and μ4‐oxopenta‐μ‐acido‐μ‐alkoxo complexes containing carboxylato, fluoro‐ and chloroacetato, alkoxo and nitrato groups as ligands are discussed. The spectra are interpreted in terms of a model of weakly interacting fragments. It is demonstrated that in the systems under consideration, structural rather than electronic factors play the determining role in the stabilization of fragment ions. All the spectra are dominated by terra‐ and trinuclear complex cations containing OM4 and OM3 (M = Be, Zn) units, respectively. Their relative abundances correlate with the number of ligand vibrational degrees of freedom, being independent of ligand electronic characteristics.
Stereochemical effects in mass spectrometry. 7. Determination of absolute configuration of some organic molecules by reaction mass spectrometry
Authors: Chen Yao‐Zu , Li Hung , Yang Hou‐Jun , Hua Su‐Ming , Li Hai‐Quan , Zhao Fan‐Zhi , Chen Nen‐Yu 
Published: May 2005

AbstractIt was found that in the chemical ionization (isobutane) mass spectra of some asymmetric secondary alcohols and α‐amino acids, when a pair of enantiomers (such as R‐ and S‐2‐phenyIbutyric anhydride, R‐ and S‐mandelic acid, R‐ and S‐2‐methylbutanoic acid or R‐ and S‐α‐phenyl ethyl amine) were used as reaction reagents, the relative abundances of characteristic ions formed by the stereoselective reaction between sample and reagent of the same configuration were much higher than those ions formed by the sample and a reagent of a different configuration. The absolute configuration of the sample molecule may be predicted by examination of mass spectra of the sample measured with R‐ and S‐reagent respectively. This approach proved to be a convenient way for determination of the absolute configurations of organic molecules on a micromole level by mass Spectrometry.
Protonation of some cyclopropylarenes in the gas phase
Authors: Galli Carlo , Speranza Maurizio 
Published: May 2005

AbstractThe capability of the cyclopropyl group to conjugate with Unsaturated systems or to delocalize an adjacent positive charge is compared with that of a double bond, and is tested by the determination of the gas‐phase basicity (GB) of various methyl‐substituted cyclopropylbenzenes, α‐methyl styrenes, and biphenyls by Fourier‐transform ion cyclotron resonance. The site of the gas‐phase protonation in the cyclopropylbenzene is established at the three‐membered ring, based on analogy with the trends of GBs in the styrene system upon methyl substitution at the aromatic meta and para positions. The diverse nature of the conjugative interaction of a cyclopropyl group and of a double bond toward an aromatic ring is manifested, instead, in the different behaviour toward a steric perturbation. The cyclopropyl group adopts the bisected conformation in cyclopropylbenzene, because it tolerates the steric perturbation of a methyl group, intentionally placed in the ortho position, more easily than the double bond, which adopts a coplanar conformation in the isomeric α‐methyl styrene.
Cationated cyclopropanes as reaction intermediates in mass spectra: an earlier incarnation of ion‐neutral complexes
Authors: Meyerson Seymour 
Published: May 2005

AbstractThe appearance a decade ago of the concept of ion‐neutral complexes as intermediates in unimolecular decompositions constituted a major advance in mechanistic interpretation of mass spectra. The concept, however, was not new; it goes back to the introduction of the cationated cyclopropane in the mid‐1950s. Its development did not occur via a smooth progression; rather, its history bridges a sharp discontinuity. The early workers, in a curious historical quirk, failed to generalize on the idea beyond complexes in which the neutral component is cyclopropane or a closely related species. Hence it took an independent rediscovery of the concept to usher in the rapid growth and wide application that characterize its present stage of development.
Rearrangement reactions of the molecular ions of some substituted aliphatic oxiranes
Authors: Grützmacher Hans‐Friedrich , Pankoke Doris 
Published: May 2005

AbstractThe fragmentation reactions of glycidic methyl ester (1) and of its derivatives (2–6) substituted by one, two and three methyl groups, respectively, at the oxirane ring, of the corresponding glycidols (7–12), and of the glycidyl ethers (13–16) in the 70 eV mass spectra have been studied using isotopic labelling and mass‐analysed ion kinetic energy spectrometry. It is shown that the typical reaction of these aliphatic oxirane radical cations carrying a nucleophilic methoxy group and hydroxy group, respectively, at the side chain corresponds under high‐energy conditions to a rearrangement by a methoxy group or a hydroxy group migration to the β‐carbon atom of the oxirane moiety. This rearrangement is very likely mediated by the isomerization of the molecular ions into distonic ions via CC bond cleavage within the oxirane ring.
Doubly charged porphyrin ion tandem mass spectrometry: Implications for structure elucidation
Authors: Beato Brian D. , Yost Richard A. , Quirke J. Martin E. 
Published: May 2005

AbstractUnder electron ionization (EI) conditions, porphyrins yield unusually high intensities of doubly charged molecular and fragment ions. These doubly charged ions offer unique opportunities for the structure elucidation of porphyrins by tandem mass spectrometry (MS/MS). First, they fragment to a greater extent than the corresponding singly charged ions under both EI/MS and EI/MS/MS conditions. Second, doubly and singly charged porphyrin ions often fragment via different pathways, and can therefore yield different structural information. This paper describes several ways in which analyses of doubly charged porphyrin ions with a triple quadrupole tandem mass spectrometer can be useful in structure elucidation of porphyrins. The effect of the metal atom on the fragmentation of metalloporphyrins in an EI source is demonstrated by correlating the extent of doubly charged fragment ion formation to a stability index. Doubly charged porphyrin ions are shown to yield predominantly doubly charged daughter ions upon collisionally activated dissociation (CAD), and are also shown to fragment to a greater extent than corresponding singly charged porphyrin ions. Advantages and disadvantages of doubly charged porphyrin ion MS/MS for structure elucidation are discussed.
Collisionally activated dissociation of some pyridinium cations: Novel fragmentation pathways
Authors: Katritzky Alan R. , Watson Clifford H. , Dega‐Szafran Zofia , Eyler John R. 
Published: May 2005

AbstractThree novel collisionally induced dissociation pathways, additional to the usual formation of pyridine or pyridinium cation, are described for laser‐desorbed N‐substituted pyridinium cations. Particularly prevalent is the formation of an ion of m/z 94, corresponding to [PyCH3]+. Doubly charged pyridiniums tend to lose H+, and one example of the apparent formation of the neutral radical C5H6N˙ is reported.
Unimolecular and collision‐induced dissociation reactions of peracetylated methyl glucopyranoside
Authors: Guevremont Roger , Pathak Ved P. , Wright Jeffrey L. C. 
Published: May 2005

AbstractThe mechanism of the collision‐induced fragmentation of peracetylated methyl‐α‐D‐glucopyranoside was investigated using deuterium‐labelled acetates and sequential mass spectrometry. Loss of the substituent at C(1), the anomeric carbon, yields an ion of m/z 331, [C14H19O9]+. This ion further dissociates via two pathways, the first including m/z 271, [C12H15O7]+, 169, [C8H9O4]+ and 109, [C6H5O2]+, and the second including m/z 211, [C10H11O5]+, 169, [C8H9O4]+ and 127 [C6H7O3]+. The first path proceeds via loss of acetate at C(3), followed by a single‐step concerted loss of acetates from C(2) and C(4), and ending with loss of acetate from C(6). The second path proceeds predominantly via loss of acetates from C(3) and C(4), elimination of ketene from the C(2)‐acetate and finally loss of ketene from the acetate at C(6). This path is also characterized by an ill‐defined series of parallel decomposition reactions involving acetates from other sites on the molecule. At low collision energy, and in the absence of collision gas (unimolecular reaction conditions), the former pathway predominates; m/z 331 dissociates via loss of acetate at C(3), followed by a single‐step concerted loss of acetates from C(2) and C(4).