bluuebunny/crossref_metadata_2025_split huggingface dataset:
Internal energy deposition in doubly charged tungsten hexacarbonyl on low‐energy Charge exchange with organic targets
Authors: Dejarme Lindy E. , Cooks R. Graham , Ast Teodor 
Published: May 2005

AbstractEstimates are reported for the internal energy distribution and the average internal energy deposited in the molecular ion of tungsten hexacarbonyl, W(CO)˙, when it is generated by charge exchange of the corresponding doubly charged ion. Charge exchange was performed in the collision energy range from nominal zero to 40 eV using a triple quadrupole mass spectrometer with a variety of polyatomic targets including alkanes, aromatics and tungsten hexacarbonyl itself. At all energies, dissociative charge exchange was accompanied by collision‐induced dissociation and this meant that the energetics of charge exchange had to be measured by extrapolation to zero collision energy and zero pressure. Under these conditions, the average internal energy deposited into the charge‐exchanged product W(CO)˙ was 1.0, 0.9, 1.3 and 2.3 eV for the targets isobutane, n‐pentane, n‐heptane and toluene, respectively. Data for the symmetrical charge exchange reaction
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demonstrated that partitioning of internal energy between the two products occurred equally. Hence, assuming equipartitioning over all degrees of freedom (at threshold) in the other cases also, the total internal energies deposited in the target molecules were determined to be 1.1, 1.1, 2.3 and 2.7 eV, respectively. Comparison of these values with the reaction exothermicities revealed that ∼2 eV (1.2–2.6 eV) of additional energy is liberated on charge exchange in each case. This is suggested to appear as translational energy of separation of the two charged products. Charge exchange in this system is suggested to occur by a Landau‐Zener curve‐crossing mechanism and the estimated values of the coulombic energies correspond to electron transfer at internuclear distances of the order of 7 ± 2 Å.
Simplification and accuracy test for the collision cross‐section‐based quantification of isomeric ion mixtures
Authors: Oh Hyeon Ju , Kim Myung Soo 
Published: May 2005

AbstractA method was devised to determine the isomeric composition of an ionic mixture using collisionally activated decomposition mass spectrometry. Compared with the more rigorous approach based on collision cross‐sections reported previously, the main advantage of the proposed method is its experimental simplicity. Both the internal consistency and the accuracy of the method were tested for mixtures of isobaric ions, i.e. ions with the same nominal mass‐to‐charge ratios.
Mass spectral fragmentation pathways in some dinitroaromatic compounds studied by collision‐induced dissociation and tandem mass spectrometry
Authors: Yinon Jehuda 
Published: May 2005

AbstractA collision‐induced dissociation study of a series of dinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways were determined in the electron impact mode. Loss of NO2˙ from the molecular ion was observed In most of the investigated compounds. In some compounds loss of NO2˙ occurred only after loss of OH˙. In other compounds it was not observed at all because of competitive processes, such as loss of NO˙, CO2, CH2O, C2H4 or H2O. Loss of NO˙ was a major decomposition pathway, forming ‘dished peaks’ in some of the compounds having a nitro group ortho to a phenyl group, indicating a release of kinetic energy associated with the decomposition. Loss of OH˙ due to an ‘ortho effect’ occurred in compounds where a nitro group was ortho to a group containing a labile hydrogen, but was not observed when competitive processes such as loss of NO˙, NO2˙ or H2O occurred. ‘Nitro to nitrite’ isomerization was suggested to explain the decarboxylation process in 2,4‐ and 2,5‐dinitrobenzoic acid and the loss of COH2 in 2,4‐dinitroanisole.
Mass spectrometric studies on 17β‐estradiol‐17‐fatty acid esters: Evidence for the formation of anion‐dipole intermediates
Authors: Debrauwer Laurent , Paris Alain , Rao Dinesh , Fournier Françoise , Tabet Jean‐Claude 
Published: May 2005

AbstractThe behaviour towards low collision energy processes (eV range) of [M  H]− prepared under negative ion chemical ionization (NICI) ammonia conditions from 17β‐estradiol‐17‐fatty acid esters has been investigated. From such bifunctional compounds containing two acidic sites (i.e. phenol and ester groups), two isomeric forms (i.e. phenoxide and enolate forms) characterize the [M  H]− ion structures, whose distribution depends on the ion preparation mode. Here NICI (ammonia) provides both phenoxide and enolate forms as the [M  H]− species. This behaviour contrasts with the regioselectivity observed for proton abstraction from phenol under NICI (N2O) and fast atom bombardment conditions. Production of both phenoxide and enolate forms in NICI (ammonia) is demonstrated under NICI (ND3) conditions in which DO‐labelled [Md  H]− enolate ions are produced in a similar yield to unlabelled [Md  D]− phenoxide ions. Collisionally activated dissociation (CAD) spectra of both isomeric deprotonated molecules differ strongly by the presence of two different pairs of complementary daughter ions, suggesting that these ionic species are unconvertible. This is due to a steric hindrance effect on the long‐distance proton transfer. A mechanistic investigation on the formation of fragment ion pairs produced under CAD was performed with various deuterium‐labelled molecules. From these experiments, evidence is provided for molecular isomerizations into ion‐dipole complexes (prior to dissociation) which are structurally dependent on the initial charge location. Direct dissociation of these intermediates competes with the occurrence of exothermic proton transfer(s) yielding the formation of other isomeric intermediate forms. The orientation of these proton transfers is dictated by the relative acidities of both moieties of the complex.
Electron impact mass spectra of some tertiary aliphatic nitro compounds. Nitrocarbonyl compounds and some analogues
Authors: Konopski Leszek , Grela Karol 
Published: May 2005

AbstractThe mass spectra of some tertiary aliphatic nitroaldehydes, nitroketones, nitroesters, nitronitriles and related nitrocarbonyl compounds are discussed and compared with those of some analogous nitro compounds lacking the carbonyl function. The M+˙  NO2˙ and in several cases M+˙  HNO2 fragmentation seem to be the most characteristic features of all tertiary aliphatic nitro compounds. In the presence of the primary nitro group, the loss of NHO2 is always observed.
Electron impact‐induced decomposition of some substituted 7‐ethoxycarbonylpyridopyrrolidenequinolines
Authors: Plaziak Adam S. , Girek Tomasz , Śliwa Wanda 
Published: May 2005

AbstractThe electron impact ionization mass spectrometric behaviour of three cycloadducts of 4,6‐benzo[h]naphthyridinum ethoxycarbonylmethylide with acrylonitrile, ethyl acrylate and diethyl maleate was studied with the aid of exact mass measurements and metastable transitions. The study showed that the electron impact‐induced decomposition of substituted pyridopyrrolidenequinolines occurs exclusively on the aliphatic five‐membered ring.
Relative metal ion affinities of organic nitriles in the gas phase
Authors: Chen Lin‐Zhi , Miller Jack M. 
Published: May 2005

AbstractThe relative metal ion (Ni+ and Co+) affinities of 14 alkanenitriles, alkenenitriles and benzonitrile were estimated using Cooks' kinetic method in a fast atom bombardment mass spectrometer. The results are compared with proton affinities, affinities for other metal ions, two‐ligand dissociation enthalpies and the dipole moments of the nitriles. The RCNCo+ bond is found to be close to the RCNNi+ bond but weaker than the RCNAl+ bond. The effective temperature (T) of the metal‐bound dimer ions falls in the range 298 K < T < 400 K.
Mass spectra of some 2‐(o‐and p‐R1‐phenyl)‐indole‐3‐carboxaldehyde derivatives. III
Authors: Cortés C. Eduardo , Cortés R. Eduardo , Arreguín B. Hortensia 
Published: May 2005

AbstractThe mass spectra of sixteen substituted 2‐(o‐ and p‐R1‐phenyl)indole‐3‐carboxaldehydes which have potentially useful pharmacological properties are presented.
Mass spectra of some 2‐methyl‐3‐(o‐ and p;‐R‐phenyl)‐3,3a,4,5,6,7‐hexahydro‐2H‐indazoles
Authors: Cortés C. Eduardo , Cortés R. Eduardo , Fuentes B. María P. A. 
Published: May 2005

AbstractThe mass spectra of twelve 2‐methyl‐3‐(o‐ and p‐R‐phenyl)‐3,3a,4,5,6,7‐hexahydro‐2H‐indazoles which have potentially useful pharmacological properties are presented.
Unimolecular reactions of ionized methyl allyl ether
Authors: Bowen Richard D. , Wright Andrew D. , Derrick Peter J. 
Published: May 2005

AbstractThe fragmentation of CH2CHCH2OCH3+· cation‐radicals has been investigated by means of 2H‐ and 13C‐labelling experiments and by analysis of collision‐induced dissociation spectra. Metastable C4H8O+· species decompose via one of three main channels which involve loss of (a) a hydrogen atom, (b) a methyl radical or (c) a formaldehyde molecule. Extensive, but not complete, exchange of the hydrogen and deuterium atoms in specifically labelled C4H8‐nDnO+· analogues precedes each of the three fragmentation pathways. The role of distonic ions in the rearrangement steps which bring about hydrogen exchange is discussed. The influence of isotope effects on the relative rates of the major reactions and the associated kinetic energy releases is examined. Only loss of a hydrogen atom is subject to a substantial isotope effect. Elimination of a methyl radical releases a large amount of kinetic energy, as is shown by the broad and dish‐topped appearance of the corresponding metastable peak (T1/2 ≈ 42 kJ mol−1). The carbon atom of the original methoxy group is specifically expelled in this process. Both the large T1/2 value and the unusual site selectivity are atypical of methyl and other alkyl radical losses from ionized alkenyl methyl ethers. The carbon atom of the methoxy group also participates specifically in formaldehyde elimination, but the two hydrogen atoms are not always selected from the three contained in the initial methoxy group. The implications of these labelling results for the synchronicity of concert of formaldehyde loss, which can be formu lated as a pericyclic process, is analysed.
Analysis of tetrabenzyl N‐giucosidic, N‐mannosidic and N‐galactosidic Isomers using fast atom bombardment/mass‐analysed ion kinetic energy spectrometry
Authors: Yan Lin , Peng Jiarou , Jiao Xianyun , Cai Mengshen 
Published: May 2005

AbstractA series of new synthetic tetrabenzyl N‐glucosidic, N‐mannosidic and N‐galactosidic isomers were investigated by fast atom bombardment (FAB)/mass‐analysed ion kinetic energy (MIKE) spectrometry. The [M + H]+ ions were obtained with high abundance in the FAB spectra when using 3‐nitrobenzyl alcohol as the matrix. The FAB/MIKE spectra provide characteristic daughter ions fragmented from selected molecular parent ions, allowing these isomers to be differentiated. In addition, an interesting rearrangement was found from the MIKE spectra, indicating that the benzyl (Bzl) group on the sugar ring is rearranged on to the N atom of the base (R) group to form [R + Bzl + H]+ and [R+ 2Bzl]+ ions.
Quantitative analysis of isomeric ion mixtures
Authors: Zhang Mei‐Yi , McLafferty Fred W. 
Published: May 2005

AbstractSeveral approaches have been proposed for the use of mass spectra from collisionally activated dissociation (CAD) to determine the isomeric composition of mass analyzed ions. As originally proposed, measurement at collision gas pressures (≈︁ 30% transmittance) yielding maximum CAD cross‐sections provides improved precision, whereas differential isomeric scattering should not be an appreciable problem, despite earlier warnings. For the C2H4O+˙ ions from butan‐1,3‐diol, this CAD method found [CH3CHO+˙] = 50 ± 4%, in agreement with values of 44 ± 6 and 45 ± 6% from two methods of neutralization‐reionization mass spectrometry, but in contrast with 66 ± 5% from a proposed CAD methodology using high transmittance measurements. The agreement of the three methods also shows that the principle of linear superposition of spectra is applicable to CAD as well as to electron ionization mass spectra.
The gas‐phase Smiles rearrangement the effect of ring substitution. An 18O labelling study
Authors: Eichinger Peter C. H. , Bowie John H. 
Published: May 2005

AbstractThe gas‐phase Smiles reaction of RC6H4O(CH2)nO−(n = 2 or 3) is an ipso rearrangement which is strongly influenced by the nature of the substituent R. Electron‐withdrawing groups enhance the rearrangement. When the substituent R is halogen or MeO, and occupies the ortho position, ortho cyclization competes with the Smiles rearrangement.
Field desorption mass spectra of the cyclic depsipeptide valinomycin: Energy deficits in ion formation
Authors: Sheil Margaret M. , Derrick Peter J. 
Published: May 2005

AbstractThe formation of ions of the cyclic depsipeptide valinomycin by field desorption has been investigated in detail. The ratio of molecular ions M+˙ to protonated molecules [M + H]+ has been found to be independent of emitter heating current and the nature of particular additives to the solution. In contrast, the abundance of sodiated [M + Na]+ ions compared with the molecular ions and protonated molecules was strongly dependent on the heating current. The energy deficits for M+˙ and [M + H]+ ions were similar, but were significantly larger than the energy deficits for [M + Na]+ ions. There appeared to be no relationship between the abundance of cationized species generated by field desorption and the selectivity of valinomycin for monovalent cations in solution. The implications of these observations for the mechanism of field desorption are discussed.
Mass spectrometric studies of the path of carbon in photosynthesis: Positional isotopic analysis of 13C‐labelled 2‐octulose phosphates
Authors: Irvine Robert W. , Flanigan Ian L. , MacLeod John K. , Collins J. Grant , Williams John F. 
Published: May 2005

AbstractThe electron impact mass spectrometric fragmentation patterns of the per‐O‐trimethylsilyl (TMS) and alkoxime‐TMS derivatives of D‐glycerol‐D‐altro and D‐glycerol‐D‐ido‐octuloses were fully analysed using seven specifically labelled 13C analogues. Many of the more intense‐ ions in the spectra of the per‐O‐TMS furanose and pyranose derivatives have more than one origin. On the other hand, the mass spectra of the straight‐chain methoxime and ethoxime hepta‐O‐TMS derivatives contain ions each of which in general originares from a single cleavage process. This makes gas chromatography/mass spectrometry of the aikoxime‐TMS derivatives a suitable method for monitoring 13C incorporations at individual carbon atoms in the corresponding octulose phosphates during photosynthesis experiments with 13CO2.
Evolving factor analysis in gas chromatography/mass spectrometry—a feasibility study
Authors: Roach Lisa , Guilhaus Michael 
Published: May 2005

AbstractEvolving factor analysis (EFA) is a promising multivariate technique for model‐free computational resolution of overlapping chromatographic peaks when a multi‐channel detector is available. Most applications of EFA in chromatography have involved simultaneous UV–visible detection at several wavelengths. This study examines the feasibility of EFA applied to data from gas chromatography/mass spectrometry (GC/MS) where there is a very large number of detection channels (nominal masses) and, importantly, where there is a high degree of specificity in the spectra, even for related compounds which most multi‐channel spectroscopic techniques cannot effectively distinguish. Potential problems caused by noise and spectral distortion from scanning analysers are addressed and finally the potential applications of GC/MS/EFA are discussed.
Multiphoton and electron impact ionization of azirines. Part II: 2,3‐diphenyl‐1‐azirine at 248 nm and 193 nm
Authors: Opitz Joachim , Bruch Detlev , Banert Klaus , von Bünau Günther 
Published: May 2005

AbstractMultiphoton ionization of 2,3‐diphenyl‐1‐azirine Is reported for nanosecond laser excitation at 248 and 193 nm and compared with electron impact ionization. The dependence of the ion intensity on the laser intensity shows that the formation of the parent ion and some of the more prominent fragment ions require the absorption of two photons per molecule. Other fragment ions are produced after the absorption of three photons. The results of the absorbed photon energy are corroborated by ionization and appearance energies obtained on calibrated electron impact ionization. Pure metastable ion spectra were obtained both by the defocusing method and by direct analysis of daughter ions produced by electron impact ionization and also by multiphoton ionization. The multiphoton absorption is shown to proceed via two different excitation pathways. A complete ionic decay scheme is given.
Negative‐ion mass spectra of avermectins
Authors: Havlíček Vladimír 
Published: May 2005

AbstractThe fragmentation behaviour of a series of six avermectins and two of their derivatives has been studied in the negative‐ion mode in the presence of ammonia. In contrast with positive‐ion mass spectra the negative‐ion spectra show abundant ions in the high mass region. Molecular mass determination and rapid structural differentiation between all types of avermectins are possible.
Structure and reactivity of molecular ions of isomeric pyrrolquinolinones and benzoquinolizinones
Authors: Fontana S. , Curcuruto O. , Traldi P. , Castellin A. , Chilin A. , Rodighiero P. , Guiotto A. 
Published: May 2005

AbstractThe structure and mass spectrometric behaviour of molecular species of two benzo[ij]quinolizin‐5‐ones and one pyrrol [3,2,1‐ij] quinolin‐4‐one were studied in detail with the aid of mass‐analysed ion kinetic energy spectrometry and ion trapping experiments. Whereas in the usual electron impact spectra obtained with a double‐focusing instrument clear differences are present among the three isomeric com ponds, the unimolecular fragmentation processes of the related M+· indicate the occurrence of isomerization processes to give a common structure. Significantly, under ion trap conditions nearly identical electron impact spectra are obtained; such unexpected behaviour was explained by either the presence of the buffer gas or the occurrence of different ionizing phenomena, leading to lower energy deposition in the molecular species. Under fast atom bombardment conditions, an acid‐catalysed isomerization process occurs.
Tetramethylsilane chemical ionization mass spectrometry of some isomeric unsaturated dicarboxylic acids and esterst
Authors: Srinivas R. , Vairamani M. , Kumar K. V. Siva , Rajeev M. S. , Rao G. K. Viswanadha 
Published: May 2005

AbstractThe tetramethylsilane (TMS) chemical ionization (CI) mass spectra of some geometrical isomers of unsaturated dicarboxylic acids, esters and isomeric phthalic acids reveal explicit differences. The (E)‐acids show an abundant [M + 73 − CH4]+Ion whereas the (Z)‐acids exhibit a strong [M + 73 − H2O]+ ion in their TMS CI spectra. The loss of CH4 from the adduct of fumaric acid has been confirmed by the study of fumaric acid‐d2 and B/E linked scan studies. In the case of esters, the TMS CI spectra of (E)‐isomers contain abundant [M + 73]+ adduct ions, whereas these are weakly abundant in the TMS CI of the (Z)‐isomers.
Origin of the [M − H]+ ion in flavanone
Authors: Guidugli Federico H. , Kakva Juan , Santillan Rosa L. , Garibay Maria E. , Joseph‐Nathan Pedro 
Published: May 2005

AbstractStudies of the genesis of the [M − H]+ ion in flavanone and 2′‐hydroxychalcone, performed with the aid of metastable decompositions and deuterium labelling, allow new structural notations to be postulated for the [M − H]+ ions, which in turn provide evidence for the pathways in the [M − H – ketene]+ fragmentation routes for these compounds.
Mechanistic study of the decomposition reactions of azobenzene
Authors: Srzic Dunja , Žinić Mladen , Meić Zlatko , Czira Gábor , Tainás József 
Published: May 2005

AbstractThe electron impact‐induced fragmentation of azobenzenes and itsd1,d2,d5,d10, and15N analogues was studied by mass Spectrometry and ion kinetic energy spectroscopy. The main fragment ions found in the mass spectrum of azobenzene are due to two parallel stepwise processes from the molecular ion: the expulsion of N2and two hydrogen radicals producing an ion atm/z152 having possibly a biphenylene radical cation structure and loss of C6H5⋅ and N2. Except in the elimination of two hydrogen atoms from [M − N2]+·ions, hydrogen scrambling between the phenyl rings does not feature in azobenzene upon electron impact.
New fragmentation pathways in the electron impact mass spectrometry of derivatized pyrano‐1,3‐diphenylprop‐2‐enones
Authors: Parmar Virinder S. , Sharma Sunil K. , Vardhan Anand , Sharma Rakesh K. , Møller Jørgen , Boll Per M. 
Published: May 2005

AbstractThe fragmentation patterns of closely related chalcones, cinnamoylchromans and cinnamoylchromenes, are reported to be strikingly different. The mass spectra of the first group show peaks typical of the fragmentation of simple chalcones balanced by additional fragmentation routes competing effectively with the typical chalcone fragmentation. For the other group with the introduced double bond the fragmentation is considerably changed. Initial loss of a methyl group gives rise to formation of the base peak in three of four examples. The [M – CH3]+ ion decomposes further, eliminating a styrene yielding the m/z 187 ion. This process may be rationalized as a retro‐Diels–Alder fragmentation of a flavanone formed on intramolecular rearrangement of the molecular ion.
Methylene radical cation transfer from ionized oxirane to CH3SCH3 and C6H5SCH3 in the gas phase: Formation of sulphur distonic ions and/or insertion in a carbon–sulphur bond
Authors: van Amsterdam Margot W. , Zappey Herman W. , Ingemann Steen , Nibbering Nico M. M. 
Published: May 2005

AbstractThe α‐distonic sulphur‐containing ion \documentclass{article}\pagestyle{empty}\begin{document}$ {}^ \cdot {\rm CH}_2 \mathop {\rm S}\limits^ + \left({{\rm CH}_3 } \right)_2 $\end{document} has been generated by transfer of CH from ionized oxirane to dimethyl thioether and distinguished from the molecular ion of ethyl methyl thioether by collision induced dissociation (CID) experiments. In particular, the α‐distonic ion expels CH2 to a minor extent following collision, whereas the molecular ion of ethyl methyl thioether does not undergo this reaction. The metastable C3H8S+˙ ions formed by CH transfer to dimethyl thioether and ionization of ethyl methyl thioether decompose by competing losses of CH3R˙, CH4 and C2H4. The elimination of ethene is taken as evidence for isomerization of the α‐distonic ion to the molecular ion of ethyl methyl thioether prior to spontaneous dissociation. Evidence for the formation of stable α‐distonic sulphur‐containing ions by transfer of CH from ionized oxirane to methyl phenyl thioether has not been obtained. The collision‐induced and spontaneous reactions of the ions formed by CH transfer to methyl phenyl thioether indicate that a mixture of the radical cations of CH3C6H4SCH3, C6H5SCH2CH3 and C6H5CH2SCH3 is generated implying that attack on the phenyl group occurs in addition to a formal insertion of a methylene entity in a CS bond.