bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations
Authors: Das K. G. , Reddy G. Sudhakar , Wolfschütz R. , Schwarz H. 
Published: May 2005

AbstractEvidence for the gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations directly or through common intermediates has been obtained from chemical ionization/collisional activation and kinetic energy release data.
Electron impact mass spectra of 2‐(2‐pyridyl)methylene‐1,3‐dicarbonyl compounds: Unusual abundance of the [M + 1]+ ion and the effect of stereochemistry
Authors: Pohjala Esko K. , Nieminen Antti O. K. 
Published: May 2005

AbstractElectron impact mass spectra of 2‐(2‐pyridyl)methylene‐1,3‐dicarbonyl compounds and related heteroaryl species have been investigated. In 3‐(2‐pyridyl)methylene‐2,4‐pentanedione, its 6′‐methyl and 6′‐methoxycarbonyl derivatives and in E‐ and Z‐ethyl 3‐oxo‐2‐(2‐pyridyl)methylenebutanoates the base peak arises from the loss of methyl radical from the molecular ion to produce a 3‐oxo‐3H‐indolizinium ion. A marked difference is observed in the behaviour of the geometric isomers of the keto esters. The diketones and E‐keto ester carrying a 2‐pyridyl substituent and ketone functionality on the same side of the carbon‐carbon double bond exhibit an unusually high [M + 1]+/[M]+˙ ratio (about 2.5) under normal ionization conditions (pressure 10–100 μPa). This abnormality is a function of pressure only and independent of temperature. In the case of the Z‐keto ester, the corresponding malonate, 3‐ and 4‐(2‐pyridyl)methylene‐2,4‐pentanediones, and 2‐furyl, 2‐thienyl and phenyl diketone analogues, the ratio does not differ much from that due to the natural isotope abundance. Results for 1,1,1,5,5,5‐hexadeuterio‐2‐(2‐pyridyl)‐methylene‐2,4‐pentanedione (strong M + 2 peak) suggest one mass unit transfer as an intermolecular proton shift from a methyl group to give a 3‐hydroxy‐3‐methyl‐3H‐indolizinium ion. This real mass spectrometric phenomenon is a unique example of low pressure self‐chemical ionization.
Photodissociation of gaseous [C5H8]+˙ ions
Authors: Wagner‐Redeker W. , Levsen K. 
Published: May 2005

AbstractPhotodissociation permits the distinction of four isomeric [C5H8]+˙ ions (ionized 2‐pentyne, 1,2‐pentadiene, 1,3‐pentadiene and cyclopentene) which cannot be identified via collisional activation spectrometry. Both the relative cross‐section for photodissociation and the relative abundance of the photodissociated fragments can be used to characterize the ion structure. Furthermore, upper and lower limits for the barrier for interconversion between 1,3‐pentadiene and the other isomers can be determined.
Secondary ion mass spectra of oligopeptides
Authors: Kambara Hideki , Hishida Shinzaburo , Naganawa Hiroshi 
Published: May 2005

AbstractSecondary ion mass spectrometry for oligopeptides, such as tri‐tetra‐, penta‐ and hexapeptides, and bioactive peptides, are presented. Quasimolecular ions and cationized molecules were observed, together with many kinds of fragments, which were helpful in structural assignments. Secondary ion mass spectrometry did not prove to be dependent on temperature. Thermal migration of samples on a surface was observed at high temperature. Secondary ion mass spectra obtained with a silver substrate and an aluminium substrate are compared.
Energy dependence of the fragmentation of some isomeric [C6H12]+˙ ions
Authors: Herman Jan A. , Li Yip‐Hoi , Harrison Alex. G. 
Published: May 2005

AbstractThe charge exchange mass spectra of 14 C6H12 isomers have been determined using [CS2]+˙, [COS]+˙, [Xe]+˙, [CO]+˙, [N2]+˙ and [Ar]+˙ as the major reactant ions covering the recombination energy range from ∼10.2 eV to ∼15.8 eV. From the charge exchange data breakdown graphs have been constructed expressing the energy dependence of the fragmentation of the isomeric [C6H12]+˙ molecular ions. The electron impact mass spectra are discussed in relation to these breakdown graphs and approximate internal energy distribution functions derived from photoelectron spectra.
A fast atom bombardment study of methionine in combination with deuterium labelling
Authors: van der Greef J. , de Brauw M. C. Ten Noever , Zwinselman J. J. , Nibbering N. M. M. 
Published: May 2005

AbstractThe mechanism of ion formation from methiomine under fast atom bombardment conditions shows similarities with those reported in secondary ion, laser desorption and field desorption mass spectrometry. Deuterium labelling has indicated that the mode of fragmentation of this compound upon fast atom bombardment closely resembles that observed under chemical ionization conditions using methane as reagent gas.
The formation, stability and decomposition of [RXH]+ (XNH2, SH, OH and Cl) ions during hydrogen chemical ionization mass spectrometry
Authors: Colosimo Marcello , Brancaleoni Enzo 
Published: May 2005

AbstractThe relevant peaks of the H2 chemical ionization mass spectra of C1C4 amines, thiols, alcohols and chloroalkanes are reported. The stability of alkylonium ions is discussed on the basis of the proton affinity of the starting neutrals, the substituent alkyl group, and the functional group. The main decomposition paths of [M+1]+ ions are described, and the formation of significant ions is discussed.
Mass spectrometry of nitroazoles: 4—ortho effects: The loss of CHO˙ and CH2O from methyl substituted nitrodiazoles
Authors: Luijten W. C. M. M. , van Thuijl J. 
Published: May 2005

AbstractThe interaction between methyl and nitro groups in some methyl substituted nitropyrazoles and ‐imidazoles causes the expulsion of CHO˙ and CH2O. This may occur when the two substituents are at adjacent positions in the ring. Labelling with deuterium and 13C shows that the loss of CHO˙ and CH2O originates exclusively from the substituents. The isotope effects observed in partially deuterated 3(5)‐methyl‐4‐nitropyrazole are consistent with a hydrogen transfer prior to fragmentation.
Mass spectrometry of 2,5‐dimercapto‐1,3,4‐thiadiazole methyl and aryl derivatives
Authors: Bottino Franscesco , Caccamese Salvatore , Pappalardo Sebastiano 
Published: May 2005

AbstractThe most significant mass spectral features of thirteen title compounds are discussed. Fissions occur across the thiadiazole ring, leading to the formation of [M‐RSCN]+˙ and \documentclass{article}\pagestyle{empty}\begin{document}${\rm R - }\mathop {\rm S}\limits^{\rm + } = {\rm C} = {\rm S}$\end{document} ions. In cases where the thiol‐thione equilibrium is present in the vapour state, expulsion of CS2 from the molecular ion is observed. The fragmentation pattern of the compounds having an ortho nitro group in the S‐aryl moiety is strongly affected by a prominent ‘ortho effect’.
The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study
Authors: Nobes Ross H. , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital calculations with moderately large polarization basis sets and including valence‐electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH3OH2]+. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH5O]+ potential surface. There is no evidence for a tightly‐bound complex, [HOCH2]+…︁H2, analogous to the preferred structure [CH3]+…︁H2 of [CH5]+. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol−1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol−1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol−1 but with a reverse activation barrier of 149 kJ mol−1). The results offer a possible explanation as to why production of [CH2OH]+ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol−1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol−1).
Diethanolamine assisted secondary ion mass spectrometry of naturally occurring complex oligosaccharides
Authors: Harada Ken‐ichi , Suzuki Makoto , Kambara Hideki 
Published: May 2005

AbstractA remarkable technique for identifying the molecular weight of involatile and/or thermally unstable compounds by molecular secondary ion mass spectrometry is described. This technique uses diethanolamine as a matrix material instead of glycerol which is at present considered to be the best medium. When this amine is used, adduct ions [M+DEAH]+ are formed from neutral saccharides, and these are very stable for reliable molecular weight determination.
The proton affinity of thioformaldehyde. Implications for the heat of formation of thioformaldehyde and thiolmethyl carbonium ion from ion cyclotron resonance investigations of the proton transfer reactions of [CH2SH]+
Authors: Roy M. , McMahon T. B. 
Published: May 2005

AbstractIons at m/z 47 have been generated from a variety of organosulfur compounds both at 70 eV and near threshold. From observations of the energetics of proton transfer from m/z 47 to reference bases of known proton affinity, the species obtained in all cases has been shown to be [CH2SH]+ rather than [CH3S]+. This result is shown to be consistent with recent ab initio calculations on these two isomers and collisional activation experiments.
Mass spectrometry of thio analogues of pyrimidine bases: 4‐alkoxycarbonyl‐alkylthiouracils
Authors: Wyrzykiewicz E. , Buczek J. 
Published: May 2005

AbstractThe mass spectral fragmentation of twelve new 4‐alkoxycarbonylakyithio substituted derivatives of uracils is discussed and fragmentation pathways. Elucidation of which assisted by accurate mass measurements and metastable transitions, are proposed. The comparison between the mass fragmentation of 2‐ and 4‐alkoxycarbonylakylthiouracils have shown that the position of uracil ring thiation may be deduced on the basis of mass special fragmentation patterns.
A mass spectral investigation of water and acetic acid elimination from 1‐ and 2‐indan derivatives
Authors: Groenewold G. S. , Gross M. L. , Zey R. 
Published: May 2005

AbstractWater and acetic acid eliminations from 1‐ and 2‐indan derivatives have been investigated. Deuterium labeling, high resolution peak matching and the metastable peak analysis capabilities of a high resolution triple analyzer (E B E) mass spectrometer were employed to examine the eliminations. These experiments showed that water was lost from 1‐indanol via 1,2 and 1,3 processes. These results contrast with those obtained for 1‐tetralol, which specifically eliminates water in a 1,4 process involving the benzylic hydrogens. Water elimination from 2‐indanol is preceded by a slow hydroxyl‐benzylic hydrogen exchange and proceeds specifically 1,2. Water losses from both 1‐ and 2‐indanol are characterized by large kinetic energy releases. Acetic acid elimination is shown to occur specifically 1,3 from 1‐acetoxyindan and 1,2 from 2‐acetoxyindan.
Unimolecular reactions of isolated organic ions: Some isomers of [C7H16]+˙
Authors: Wendelboe Jen S. F. , Bowen Richard D. 
Published: May 2005

AbstractThe slow unimolecular reactions of six isomers of [C7H16]+˙ are reported and discussed. These results are interpreted in terms of dissociation via complexes of incipient carbonium ions and the appropriate associated radical. In some cases, rearrangement of the incipient carbonium ion precedes or accompanies decomposition; such isomerization generally favours alkyl radical loss, relative to elimination of the corresponding alkane.
Electron impact mass spectrometry of 2‐hydroxymethyl‐3,4,5,6,7,8‐hexahydro‐2 H‐1‐benzopyran‐5‐ones. The unusual presence of [MH3O]+ species in the fragmentation pattern of 4‐phenyl derivatives
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of some 2‐hydroxymethyl‐3,4,5,6,7,8‐hexahydro‐2H‐1‐benzopyran‐5‐ones is described and discussed with the aid of exact mass measurements, linked scans, labelling experiments and low electron energy measurements. The unusual presence of abundant [MH3O]+ species in the mass spectra of 4‐phenyl substituted compounds is discussed in detail and a mechanism is proposed.
The question of tautomerism of alkylnitrile and isonitrile radical cations
Authors: Chess Edward K. , Lapp R. L. , Gross Michael L. 
Published: May 2005

AbstractThe isomeric pairs [CH3CN]+˙ and [CH2CNH]+˙ and [CH3NC]+˙ and [CH2NCH]+˙ have been established as stable, noninterconverting structures. The conclusion derives from studies of collision induced decomposition spectra. The same conclusion pertains for the ions [CH3CH2CN]+˙ and [CH3CHCNH]+˙, and for [NCCH2CH2CN]+˙, [HNCCHCH2CN]+˙ and [HNCCHCHCNH]+˙. The energy barrier of a [1,3]‐hydrogen shift, a possible isomerization mechanism, is determined to be at least 163 kJ mol−1 for the [CH3CN]+˙ and [CH2CNH]+˙ pair, and the barrier may be as high as 318 kJ mol−1. The C3H5N and C4H4N2 radical cations decompose before they can be activated with 318 kJ mol−1 of internal energy.
Doubly charged ion mass spectra: V—Oxygen containing hydrocarbons
Authors: Teleshefsky L. A. , Jones B. E. , Abbey L. E. , Bostwick D. E. , Burgess E. M. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra were obtained for 46 low molecular weight oxygen containing compounds. A double focusing Hitachi RMU‐7L mass spectrometer, operated at 3.2 kV accelerating voltage, was used to measure spectra for aliphatic alcohol, ketone, ether, aldehyde, ester and acid molecules, as well as several aromatic oxygen containing compounds. In general, the spectra were dominated by fragment ions which resulted from extensive H loss and CC bond rupture as well as O elimination from the doubly charged molecular ions. Total product ion intensities from doubly charged ion spectra of aliphatic oxygen containing compounds were approximately 1% of the corresponding total ion intensity in the benzene doubly charged ion spectrum. Appearance energies for forming prominent doubly charged molecular and fragment ions were determined. Measured values ranged from 26 to 45 eV. A geometry optimized quantum mechanical SCF treatment was used to compute the energies, charge densities and structures for several of these oxygen containing doubly charged ions.
Dimer formation in methane chemical ionization mass spectrometry of organic functionalities, including 2‐azaadamantane derivatives
Authors: Bezoari Massimo D. , Kovacic Peter , Gagneux André R. 
Published: May 2005

AbstractThe methane chemical ionization mass spectra of 1‐hydroxy‐2‐azaadamantane, its lactolactam, and 1‐chloro‐2‐azaadamantanes exhibit high intensity dimeric species. These correspond to [2M+H]+ or stable fragments formed via gas phase chemical reactions, such as dehydration (aminol case) or dehydrohalogenation (chloroazaadamantanes). The tert‐amino chloroazaadamantane forms a stable [2M+C2H5]+ ion with much higher intensity than the [2M+H]+ ion. Similar dimeric species were observed with simple functionalities, including amide, amine, alcohol and alkene. Pressure, temperature and, apparently, steric effects play important roles. Structures are proposed for the various dimeric ions.
Fast atom bombardment mass spectra of involatile sulphonated azo dyestuffs
Authors: Monaghan John J. , Barber Michael , Bordoli Robert S. , Sedgwick R. Donald , Tyler Andrew N. 
Published: May 2005

AbstractFast atom bombardment mass spectra of a range of involatile mono and disazo sulphonated dyestuffs are presented. Excellent spectra are obtained for dyestuffs containing up to five sulphonate groups. The fragmentations are discussed with special reference to the ions formed by cleavage of the azo linkage. The negative ion spectra are shown to be superior to those obtained in the positive ion mode.
Gas phase electron attachment reactions and negative ion mass spectra of tris‐ and bis(N,N‐diethyldithiocarbamato) metal complexes
Authors: Gregor I. K. , Guilhaus M. 
Published: May 2005

AbstractResults are presented for the gas phase thermalized electron attachment reactions of transition metal dithiocarbamates Metal·[S2CN·Et2]n, with n = 3 for the trivalent metals Cr, Mn, Fe, Co and n = 2 for the divalent metals Fe, Co, Ni, Pd and Cu. Details of negative ion mass spectra are given, and these were obtained by use of the complementary methods of in‐beam direct insertion and desorption chemical ionization of samples into temperature and pressure controlled ion source methane gas plasmas. For the tris‐complexes, only small abundances of [M]− were observed, being consistent with the electron entering a metal‐based orbital to give a reduced [MetalII·L3]*− species—the precursor of the observed [MetalII·L2]− or [L]− product ions. For the bis‐complexes, a much higher proportion of the total ion current was carried by [M]−, with [L]− being the next most abundant species in all cases and the principal product in the reaction sequence \documentclass{article}\pagestyle{empty}\begin{document}${[{\rm Metal}^{{\rm II}} \cdot {\rm L}_{\rm 2}] + {\rm e} \to [{\rm Metal}^{\rm I} \cdot {\rm L}_{\rm 2}]^{*-} \mathop {\rightarrow}\limits^* [{\rm L]}^{\rm - } + [{\rm Metal}^{\rm I} \cdot {\rm L}].}$\end{document}. Rearrangement ions [L·MetalI·X]− with X=SH, SCN, NEt2 were also identified for this series which can be accounted for by rearrangement reactions occurring in ligands not fulfilling a bidentate function towards the relevant metal.
Detection of C‐nitroso dimer formation by field desorption mass spectrometry
Authors: Johnson R. L. , Lever O. W. , Brent D. A. 
Published: May 2005

AbstractField desorption mass spectrometry is shown to be a useful technique for observing dimer formation in C‐nitroso compounds. Mixed dimer formation (RN2O2R′) is shown to be readily observed by field desorption mass spectrometry.
Electron impact mass spectrometry of 2‐(2‐pyridyl)‐2,3‐dihydroxy‐5‐phenyl‐4‐pentene
Authors: Clerici Angelo , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of 2‐(2‐pyridyl)‐2,3‐dihydroxy‐5‐phenyl‐4‐pentene has been studied with the aid of B/E, B2/E linked scans, exact mass measurements, collisionally activated dissociation mass‐analysed ion kinetic energy spectra, and labelling experiments. The primary loss of water is proved to involve both hydroxylic hydrogens, thus suggesting the formation of an epoxidic radical ion and the presence of extensive skeletal rearrangements.
Unexpected structural integrity of gas phase isoquinoline cations that eliminate HCN
Authors: Baldwin Michael A. , Gilmore Jeremy , Mruzek Margaret N. 
Published: May 2005

Abstract13C labelling has been used to study isoquinoline molecular ions undergoing breakdown by HCN elimination in a mass spectrometer. For otherwise stable ions caused to fragment by collisional activation, there is no skeletal rearrangement prior to HCN loss. Of the ions formed by 70 eV electron impact, 69% of those which fragment in the ion source by HCN loss retain their structural integrity, as do 44% of the metastable ions. Of the ions that eliminate HCN without prior arrangement, approximately two‐thirds eliminate C‐1 and one‐third eliminate C‐3. Critical energies are reported for the elimination of HCN from pyridine and isoquinoline molecular ions.
Ionization and dissociation of diethylamine by field ionization mass spectrometry
Authors: Zahran N. F. , Helal A. I. 
Published: May 2005

AbstractThe field ionization mass spectrum of diethylamine on a 5 μm activated wire at 300 K yields surface product ions like protonated molecular ions and doubly charged ions as well as gas phase ions like parent minus CH3 group. Variations of the reaction rate as a function of the decomposition times in the range 10−11‐10−6 s for the elimination of a CH3 group are studied. The reaction rates are evaluated with the help of the retarding potential technique.
The mechanism of the loss of H2 and H2O from 1,4‐cyclohexanediol anion and related compounds
Authors: Gäumann T. , Stahl D. , Tabet J. C. 
Published: May 2005

AbstractLosses of H2 and H2O from the [M‐H]− alkoxide anions of 1,4‐cyclohexanediol formed in OH− negative chemical ionization were studied using synthetic deuterated analogues and labelling by hydrogen‐deuterium exchange between neutrals in the ion source prior to ionization. Simple 1,2‐H2 elimination leading to an enolate ion does not occur, but stereospecific mechanisms are shown to give a ketolate intermediate daughter ion. Collisionally activated dissociation spectra of the resulting daughter ions are the same as those of the corresponding ions generated directly from ketols.
Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids
Authors: Korhonen Ilpo O. O. 
Published: May 2005

AbstractMetastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α‐Cleavage, [MOCH3]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H2O, CH3. and COOH. indicate the isomerization of some ionized chloro esters to the chlorinated 2‐butenoic acid molecular ions. An intense loss of H2O observed for methyl 2‐chloropropenoate indicates its most facile isomerization, [ester]+˙ → [acid]+˙, whereas the isomerization in methyl trichloropropenoate could not be observed. The molecular ion of chloromethyl propenoate, however, also seems to partly rearrange to the chlorinated 3‐butenoic acid ion, since the first field free region metastable peak shows a weak loss of CO. The new reaction pathways, i.e. the losses of CHO˙, CH2O and CH2CO from ionized chloromethyl propenoate, were detected.
Structure determination of some C4H5N+˙Ions from substituted pyridines by collisionally activated dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Thuijl J. 
Published: May 2005

AbstractA standard procedure for recording and correcting collisionally activated dissociation mass spectra is proposed, and used to distinguish between the C4H5N+˙ions formed from hydroxy‐ and amino‐pyridines after loss of CO and HCN, respectively. It is concluded that these ions are cyclic. From the 4‐isomers the 3H‐pyrrole ion is formed whereas from 2‐hydroxypyridine the 1H‐pyrrole ion is formed. In the other cases, mixtures of 2H‐ and either 1H‐ or 3H‐pyrrole ions are generated, depending on the nature of the precursor.