bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

The 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

The 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

A 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

Several 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

The 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

The 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

The 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

Evolving 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

Multiphoton 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

The 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

The 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

The 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

Studies 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

The 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

The 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

The 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.
Differentiation of isomeric 5‐ and 7‐oxo derivatives of tetrahydrothiazolo[3,2‐a]pyrimidine by electron impact mass spectrometry
Authors: Jeanneau‐Nicolle Edwige , Bosso Claude , Benoit‐Guyod Martine , Leclerc Gérard
Published: May 2005

The electron impact mass spectra of two series of 5‐oxo‐tetrahydro‐5H‐thiazolo [3,2‐a]pyrimidine‐6‐ethylcarboxylates and 7‐oxo‐tetrahydro‐7H‐thiazolo [3,2‐a]pyrimidine‐6‐ethylcarboxylates were measured and fragmentation patterns examined. Structures were assigned from analysis of oxo molecular ion fragmentations. Compounds of the 5‐oxo series gave an [M – CO2C2H5]+ fragmentation whereas compounds of the 7‐oxo series gave three characteristic cleavages. This decomposition was confirmed for one pair of isomers by high‐resolution mass spectrometry and unimolecular mass‐analysed ion kinetic energy spectrometry. Electron impact mass spectrometry is a convenient method for assigning structures of 5‐ and 7‐oxo regioisomers of tetrahydrothiazolo[3,2‐a]pyrimidine‐6‐carboxylates.
Characterization of titanocenium and titanocene by tandem mass spectrometry
Authors: Zagorevskii Dmitri V. , Holmes John L.
Published: May 2005

Tandem mass spectrometric techniques were used for the characterization of gas‐phase titanocenium ions. Decomposition of metastable and collisionally activated C10H10Ti+˙ ions involved cyclopentadienyl–metal bond rupture, acetylene loss and dehydrogenation as the prominent processes. The intermediate formation of titanium (di)hydride complexes was proposed to explain the selective H2 molecule loss. The neutralization–reionization mass spectrum showed a very abundant recovery signal, indicating a high stability for the neutral gas‐phase C10H10Ti species.
Structural characterization of mono‐ and bisphosphonium salts by fast atom bombardment mass spectrometry and tandem mass spectrometry
Authors: Claereboudt J. , Baeten W. , Geise H. , Claeys M.
Published: May 2005

Positive‐ion fast atom bombardment (FAB) mass spectra are reported for a representative series of mono‐ and bisphosphonium halides derived from triphenylphosphine. The mass spectra of the monoalkyltriphenylphosphonium salts typically contain abundant intact cations that can be used to establish the cationic relative molecular mass and diagnostic fragment ions that allow the characterization of structural subgroups. Depending on the functional group substitution on the alkyl group, additional fragment ions are observed which are formed by loss of small neutral molecules from the intact cation and that can be used for the differentiation of isomeric phosphonium salts. Molecular dication are typically observed in the FAB mass spectra of the bisphosphonium salts when they are analysed in 3‐nitrobenzyl alcohol. In addition, production of singly charged ions by clustering with a counter ion, decomposition involving removal of one of the charge centres and one‐electron reduction are generally observed. Structurally diagnostic fragments are also obtained. The fragmentation pathways of the ions derived from the phosphonium salts were elucidated by precursor ion and product ion tandem mass spectrometric experiments. For the phosphonium salts containing a long‐chain hydrocarbon alkyl group, high‐energy collision‐induced decomposition of the intact cation is needed to obtain unambiguous structural information.
Mass spectrometry and pyrolytic decomposition of 2‐amino‐3′,4′,6‐trisubstituted isoflavones
Authors: Hu Peifeng , Li Yongfu , Lu Yongquan , Pihlaja Kalevi
Published: May 2005

The 2‐aminoisoflavones studied exhibited some familiar fragmentation pathways, such as the formation of the retro‐Diels–Alder ions. However, substitutions at C(2), C(3′), C(4′) and C(6) induced some specific decompositions of both mass spectrometric and pyrolytic origin. Pyrolytic decompositions reverse to the Mannich reaction occurred with all compounds to variable extents. The three compounds with the (Me)2NSO2 substitution at C(6) exhibited another type of pyrolytic reaction, namely the formation of products corresponding to ions of m/z 272, 300 and 314, depending on the type of substitution at C(3′). The occurrence of an interesting ‘ortho effect’, the elimination of the elements of CH3O from C(3′) and C(4′), was also established.
Novel proximity effects and Ortho interactions in 2,2′‐disubstituted diphenylamines on electron impact
Authors: Ramana D. V. , Mahalakshi P.
Published: May 2005

Unexpected ejections of CH3NO2/[˙CH3 + ˙NO2], N2O4/[˙NO2 + ˙NO2] and CH3OCH3/[˙CH3 + ˙OCH3] were observed from the molecular ions of 2‐methoxy‐2′‐nitrodiphenylamine, 2,2′‐dinitrodiphenylamine and 2,2′‐dimethoxydiphenylamine, respectively, under electron impact conditions owing to proximity effects. In other competing fragmentation pathways, novel proximity effects triggered by the ortho interactions leading to the unusual eliminations of [˙CH3 + H2O] from M+˙ of 2‐methoxy‐2′‐nitrodiphenylamine and HNO3/[˙NO2 + ˙OH] from M+˙ of 2,2′‐dinitrodiphenylamine were observed. Evidence for the interpretation of the main fragmentation pathways was obtained from the metastable ion spectra and high‐resolution mass spectrometry. Confirmation of the structures assigned to the ions was provided by collision‐activated dissociation mass‐analysed ion kinetic energy spectra.
Energy dependence of rearrangements of an N‐terminal protecting group in tandem mass spectrometry of protonated tripeptides containing C‐terminal arginine
Authors: Schwartz Brenda L. , Erickson Bruce W. , Bursey Maurice M. , Marbury G. Dean
Published: May 2005

The types and intensities of tandem mass spectrometric products of side‐chain interactions were investigated with a hybrid tandem instrument. Positive‐ion unimolecular decomposition and collisionally activated decomposition studies were conducted on the [M + H]+ ions of two N‐benzyloxycarbonyl (Cbz or Z)‐protected tripeptides, Cbz‐Gly‐Leu‐Arg‐NH2 and Cbz‐Gly‐Pro‐Arg‐NH2. The loss of benzyl alcohol (108 u) and the formation of other significant product ions and their dependence on collision energy and gas pressure suggest reaction between both ends of the molecule. Replacement of leucine with proline at the second position in the tripeptide produces a very intense [M + H − 108]+ ion and fewer lower mass fragment ions in the tandem mass spectra for Cbz‐Gly‐Pro‐Arg‐NH2 than in those for Cbz‐Gly‐Leu‐Arg‐NH2.
Addition of alkenes to phenyl‐substituted enol radical cations, C6H5C(OH)CHR+˙
Authors: Mourgues P. , Denhez J. P. , Audier H. E. , Hammerum S.
Published: May 2005

The addition‐fragmentation reactions of phenyl‐substituted enol radical cations, C6H5C(OH)CHR+˙ (R = H, CH3), with alkenes were studied by Fourier transform ion cyclotron resonance spectroscopy. These reactions (involving both labelled and unlabelled reactants) were compared with the unimolecular reactions of aromatic ketone molecular ions and related species that give rise to C6H5C(OH)CHR+˙ and alkene products. It is shown that the phenyl‐substituted enol ions react with alkenes by CC bond formation leading to an intermediate γ‐distonic ion; the reactions are not accompanied by cyclization to cyclobutanol intermediates.
Gas‐phase bimolecular chemistry of isomeric cyclic ethylenehalonium and α‐haloethyl cations
Authors: Heck Albert J. R. , de Koning Leo J. , Nibbering Nico M. M.
Published: May 2005

The gas‐phase bimolecular chemistry of C2H4X+ (X = F, Cl, Br) cations was studied using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). The results support earlier suggestions that at least two isomers of the halonium ions C2H4X+ (X = Cl, Br) exist, but no experimental evidence was found for the possibility of more than one stable isomer for C2H4F+. It is shown that the cyclic ethylenehalonium and α‐haloethyl cations react differently with various substrates. The probe reactions used to characterize the two isomers were hydrogen–deuterium exchange with deuterium oxide and reactions with benzene, alkenes and vinyl ethers. It was found that the α‐haloethyl cations react as proton donors and/or electrophiles, whereas the cyclic ethylene‐chloronium and ethylenebromonium ions react as electrophile and/or as haloganyl cation donors in reactions with alkenes and vinyl ethers.
Cyclization of α‐substituted α,ω‐diphenylalkyl carbenium ions: Reactivity of α‐trifluoromethylbenzyl cations vs. α‐methylbenzyl cations
Authors: Sürig T. , Grützmacher H.‐Fr. , Bégué J.‐P. , Bonnet‐Delpon D.
Published: May 2005

1‐(n‐Phenylalkyl)‐1‐trifluoromethylbenzyl cations and the α‐CH3‐substituted analogues were generated from the corresponding protonated benzyl alcohols by loss of H2O during chemical ionization (CI). The unimolecular reactions of these ions and of their derivatives specifically deuterated at the 1‐phenyl group were studied using the CI (methane) and CI (isobutane) mass spectra and the mass‐analysed ion kinetic energy spectra. The characteristic reaction giving rise to abundant ions in all the spectra is the elimination of C6H6 initiated by an electrophilic attack of the benzyl cation on the remote phenyl group. The α‐CH3‐ and α‐CF3‐substituted benzyl cations respond differently to the effect of internal excess energy on the intensity of the benzene elimination process and on the H–D exchange accompanying this process of the deuterated ions. This different reactivity of both series of ions demonstrates unambiguously that the α‐CF3‐substituted benzyl cations correspond to destabilized benzyl cations exhibiting the particular reactivity of ‘hot’ carbenium ions in the gas phase.
Electron impact fragmentation of binuclear crown ethers
Authors: Gren A. I. , Mazepa A. V. , Timofeev O. S.
Published: May 2005

It is shown that fragmentation under electron impact of binuclear crown ethers is similar to those for crown ethers with the general formula 3n‐crown‐n‐n except for the formation of fragment ions with mass numbers reflecting the ring sizes in binuclear crown ether molecules. The formation of these ions occurs with hydrogen atom migrations in CH…︁O interactions between atoms from different rings determined in the crystal state.
Study of transition‐state methods in the calculation of vertical ionization potentials by local density approximation
Authors: Duffy Patrick , Chong Delano P.
Published: May 2005

The vertical ionization potentials of nine small molecules were computed by the deMon density functional program and different versions of the transition‐state method and the results were compared with earlier calculations and with experiment. The average absolute deviation of the 38 computed ionization potentials of the valence electrons of nine small molecules from experiment is 0.4 eV, which compares well with previous ab initio post‐Hartree–Fock and semi‐empirical HAM/3 calculations. The efficient methods were then used to calculate 68 ionization potentials of sixteen 22‐electron molecules, with results of similar quality.
Molecular fragmentation patterns of carbon dioxide at very high internal energies
Authors: Svensson A. , Bordas J. , Hughes E. A. , Mant G.
Published: May 2005

Ion–ion coincidence measurements following K‐shell absorption in the carbon dioxide molecule were performed by applying time‐of‐flight mass spectrometry in conjunction with monochromatic synchrotron radiation and electron impact. Identification of particularly sensitive electronic transitions and the consecutive molecular fragmentation in real time was performed. Analysis of coincidence recordings from decomposition of carbon dioxide reveals one distinct pathway in which three cations are formed following excitation of oxygen Is electrons.
Multi‐electron‐capture processes by C4+ from CH4, C2H6, C3H8 and n‐C4H10 in the energy range 0.7–400 eV u−1
Authors: Soejima K. , Okuno K. , Kaneko Y.
Published: May 2005

Charge‐changing cross‐sections σ43, σ42 and σ41 of C4+ injected into CH4, C2H6, C3H8 and n‐C4H10 were measured in the energy range 0.7–400 eV u−1. A tandem mass spectrometer system with an ion source of the EBIS type (Mini‐EBIS) and a collision cell consisting of an octupole ion beam guide was used. It is a significant feature that both the magnitude and energy dependence of the cross‐sections obtained showed very little target dependence for all the hydrocarbon targets studied. Another feature is that σ41 is very close to σ42, and they become flat at low energy, in contrast to the case with an argon target which was studied as a reference. This implies that multi‐electron‐capture processes become dominant in low‐energy collisions with hydrocarbon molecules.
The reaction of germyl ions with ethylene
Authors: Lim K. P. , Lampe F. W.
Published: May 2005

The reactions of [GeH3]+ ions with C2H4 and C2D4 have been studied in a tandem mass spectrometer over a pressure range of 1–20 millitorr and over an energy range of 1–9 eV (LAB). The predominant reaction of an initial [GeC2H7]+ collision complex is back‐reaction to reactants. However, stabilized adduct ions [GeC2H7]+ and their daughter decomposition products [GeC2H5]+ are observed in increasing amounts as the pressure of C2H4 is increased. It is proposed that the structures of these product ions are [CH3CH2GeH2]+ and [CH2CHGeH2]+, respectively. The hydrocarbon ions [C2H5]+ and [C2H3]+ are observed as products of endothermic reactions of ground electronic state [GeH3]+ ions with C2H4; these same ions along with [C2H4]+ and [C2H2]+ are observed as products of exothermic reactions of an electronically excited state of [GeH3]+ present in the ion beam.
Time‐dependent mass spectra and breakdown graphs. 16–The methylnaphthalenes
Authors: Gotkis I. , Lifshitz C.
Published: May 2005

Time‐resolved photoionization efficiency (PIE) curves were measured for [C11H10]+ and [C11H9]+ for 1‐ and 2‐methylnaphthalene and for the ion–molecule reaction product [C12H11]+. PIE curves were modelled by k(E) dependences via RRKM/QET calculations based on a model by Huang and Dunbar, with a critical energy E0 = 2.41 eV and a 1000 K activation entropy ΔS‡ = −13.3 eu. Kinetic shifts are much higher than for the analogous H˙ loss reaction in toluene. The crossover shift in the breakdown graphs between 24 μs and 40 ms is 1.45 eV; the conventional shift is 2.05 eV and the intrinsic shift, due to radiative decay in the infrared, is 1.1 eV. The heat of formation of [C11H9]+ is deduced to be ΔHf298(C11H9+) ≤ 890 ± 20 kJ mol−1. The [C11H9]+ population contains at least 20% of methylnaphthylium, the rest being benzotropylium.
Application of B–E time‐of‐flight mass spectrometry to the detection of high‐energy neutral atoms following the photoexcitation of Ar
Authors: Smith J. A. , Winkel J. F. , Stace A. J. , Whitaker B. J.
Published: May 2005

A novel instrument which combines high‐resolution double‐focusing mass spectrometry with time‐of‐flight detection was applied to the study of cluster ion photofragmentation. Using this apparatus, kinetic energy measurements were made on neutral photofragments following the excitation of Ar at 532 nm. The results show that one and possibly two argon atoms with high centre of mass kinetic energies emerge from the cluster within a few picoseconds of the photon being absorbed.
Formation and reactivity of metal carbonyl anions in the gas phase
Authors: van den Berg Klaas Jan , Ingemann Steen , Nibbering Nico M. M.
Published: May 2005

The reactions of metal carbonyl anions (M(CO)n−; M = Cr, Mn and Fe; n = 1–3) with n‐heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer equipped with an external ion source. The M(CO)n− ions were formed in the FT‐ICR cell by collision‐induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)n− ions were allowed subsequently to undergo non‐reactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)3−, Mn(CO)3− and Fe(CO)2− ions react with n‐heptane. This reaction proceeds by loss of H2 from the collision complex and the Cr(CO)3− and Fe(CO)2− ions react about three times more efficiently than the Mn(CO)3− ion. With water, Mn(CO)− and Fe(CO)3− are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)3−, Fe(CO)2−, Cr(CO)2−, Fe(CO)−, Mn(CO)3− and Mn(CO)2−. With methanol, the Cr(CO)2− ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H2 occur in the reaction with Cr(CO)3−. Competing loss of CO and one or two H2 molecules occurs in the reactions of Mn(CO)3− and Fe(CO)2− with methanol. The rate of the reaction with methanol decreases in the order Cr(CO)3−, Fe(CO)2−, Cr(CO)2− and Mn(CO)3−.
Behaviour of methyl red under fast atom bombardment conditions
Authors: Florêncio M. Helena , Heerma Wigger
Published: May 2005

The influence of the pH, the nature of the matrix and the presence of a surfactant on the positive‐ and negative‐ion abundances in the molecular mass region in the fast atom bombardment (FAB) mass spectra of methyl red was investigated. A small but significant pH effect was observed which was attributed to the non‐ or at the most low surface‐active character of the intact methyl red molecule. As expected, the more basic the solution, the less protonated molecules with respect to M+˙ are observed and in the negative‐ion mode less [M + H]− and more [M – H]− ions with respect to M−˙ were found. In contrast to neutral solutions, both acidic and basic solutions give a long‐lasting stable response of all methyl red ions. For dyes with a moderately negative redox potential such as methyl red, beam‐induced redox reactions seem to play a role in the ionization process, the neutral medium offering the best conditions for reduction processes. The ion intensities in the molecular mass region depend on the nature of the matrix. Protonation of the molecule has been found to be more effective in glycerol than in 3‐nitrobenzyl alcohol; the former also appears to offer the best conditions for reduction processes. Anionic and cationic surfactants effectively suppress the contribution of ions from glycerol in both positive‐ and negative‐ion spectra and generally promote the formation of analyte ions at the surface. The most important effect of the surfactant in a neutral medium seems to be the promotion of a regular transport of ions and molecules to the surface, which permits the creation of stable ion currents, instead of an unstable ion beam if the surfactant is absent. Moreover, when the surfactant is present an increase of the sample ion abundances is observed. Redox reactions involving molecules and molecular ions and also molecules and preformed ions in the solution, brought to the surface by micelles, have been proposed to give some contribution for the small but significant enhanced abundance of [M + nH]+ (n > 1) ions with respect to [M + H]+ ions, in the presence of a surfactant. The results have been rationalized in terms of the surface phenomena while the important role of surfactants for obtaining better FAB mass spectra is emphasized.
Mechanism for dehalogenation reactions in fast atom bombardment mass spectrometry
Authors: Musser Steven M. , Kelley James A.
Published: May 2005

The mechanism of a dehalogenation reaction that occurs during fast atom bombardment (FAB) mass spectrometry was examined using halogenated nucleosides as model compounds. For aglycone‐halogenated nucleosides, an inverse linear relationship exists between the extent of FAB dehalogenation and the calculated electron affinity of an individual nucleoside. The degree of dehalogenation for a given nucleoside also varies inversely with the calculated electron affinity of most FAB matrices. The observed dehalogenation reaction can be completely inhibited when matrices with positive electron affinities, such as 3‐nitrobenzyl alcohol and 2‐hydroxyethyl disulfide, are used. High‐performance liquid chromatographic analysis of the bulk glycerol matrix following exposure to the FAB beam indicates measurable amounts of dehalogenated product, suggesting that this reaction occurs in the condensed phase prior to gas‐phase ion formation. A dehalogenation mechanism involving thermal electron capture and subsequent negative charge stabilization is consistent with these observations.
Concerted chain isomerization in protonated alkylbenzenes
Authors: Denhez J. P. , Audier H. E. , Berthomieu D.
Published: May 2005

The first step in the unimolecular reaction of metastable protonated alkylbenzenes is the stretching of the C(benzene)—C(α) bond. Therefore, the intermediacy of a π‐complex [C6H6, alkyl+] has often been proposed. In this work, the kinetic energy releases associated with the [tert‐alkyl]+ product were measured for a large number of [C6H6–CnH] (n > 3) ions. At least for β‐branched alkylbenzenes, it is shown that the chain isomerization which occurs prior to dissociation involves neither the [C6H6, CnH] π‐complex nor a [C6H7+, alkene] ion–neutral complex. The data are explained by a concerted process in which the stretching of the C(benzene)—C(α) bond is accompanied by the migration of the tertiary β‐hydrogen from C(β) to C(α).
Studies on the complexation of polyols and carbohydrates with excess borate using thermospray mass spectrometry
Authors: Lipták Miklós , Dinya Zoltán , Herczegh Pál , Jekő József
Published: May 2005

Complex formation between different polyols, carbohydrates and borate was studied by thermospray mass spectrometry. The analytes were dissolved in 0.1 M ammonium borate buffer and introduced through a standard thermospray interface into a quadrupole mass spectrometer. The formation of various complexes which gave rise to relatively abundant ions in the thermospray spectra was observed. A correlation has been found between the relative intensities of these ions and the orientation of the hydroxyl groups involved in the complexation.
Mass spectrometric investigation of polyfluorinated C60. Evidence for the existence of C60F2n (n = 0–30)
Authors: Chowdhury Swapan K. , Cameron Stephen D. , Cox Donald M. , Kniaz Krzysztof , Strongin Robert A. , Cichy Maria A. , Fischer John E. , Smith Amos B.
Published: May 2005

Electron‐capture negative ion chemical ionization (EC‐NICI) and field desorption (FD) mass spectrometric techniques were utilized to examine polyfluorinated C60. Two different samples from the same preparation, one prior to sublimation and the other sublimed material, were investigated. From the raw non‐sublimed product in EC‐NCI six series of ions corresponding to different numbers of attached oxygen atoms were obtained, which are represented by the formula [C60F2nOm]−, where n ranged from 0 to 30 and m from 0 to 5. The sublimed material in EC‐NICI produced the same six series of ions with up to 48 fluorine atoms attached to C60. The field desorption of the same sample produced similar results, but the signal‐to‐noise ratios of the spectra were low. Both samples, in the two different techniques examined, yielded C60F60 ions with only an even number of fluorine atoms attached. The present investigation, for the first time, provides direct experimental evidence for the existence of higher fluorinated C60 up to C60F60 and multiple oxides of polyfluoro‐C60 with up to five oxygen atoms attached.
Fragmentation pathways of isomeric dodecenols studied by electron impact mass spectrometry
Authors: Yuan Gu , He Meiyu , He Xiaoran
Published: May 2005

Electron impact‐induced fragmentations of isomeric dodecen‐1‐ols were investigated using mass‐analysed ion kinetic energy (MIKE) spectrometry and high‐resolution data. The principal fragmentation pathways of the positional isomers studied are dominated by the CC double bond and involve migration and radical‐site rearrangements along the carbon chain with the aid of consecutive rearrangements of hydrogen atoms.
Electron impact ionization tandem mass spectrometry of glycosphingolipids. Part III. Study of the fragmentation modes of selected glycosphingolipids
Authors: Curtis Jonathan M. , Holgersson Jan , Derrick Peter J. , Samuelsson Bo E.
Published: May 2005

Results are presented from a systematic study of the high‐energy tandem mass spectra (fragment ion spectra) of derivitized (permethylation followed by LiAlH4 reduction) porcine glycosphingolipids (GSLs) using a four‐sector mass spectrometer. The ions studied were the ammonium ions of the GSLs formed on loss of the sphingosine side‐chain following electron impact ionization. Fragment ion spectra are shown to provide structural data useful in identifying carbohydrate sequence, the location of hexosamine residues and the identification of fatty acid chain length. Differences between the fragment ion spectra of isomers differing in carbohydrate linkage position and stereochemistry were observed, but not easily predicted.
Calculation of ion composition in organic high‐resolution mass spectrometry
Authors: Ioffe B. V. , Vitenberg D. A. , Zenkevich I. G.
Published: May 2005

The theory of a method for the calculation of organic ion compositions is described. It is based on concepts of homologous groups and homologous increments of ‘mass defect.’ Unlike the common algorithms usually used for this purpose, the proposed method excludes the analysis and outcome of chemically unreal combinations of atoms. Reduction of the number of alternative compositions is discussed. The possibility of a single (non‐alternative) solution is considered in the case of additional information on the presence of functional groups containing nitrogen and/or oxygen and also aromatic fragments easily identified by their infrared spectra. The efficiency of the method is demonstrated with the help of new software for DEC‐ and IBM‐compatible computers.
Unprecedented double‐electron transfer to a triply charged cation: Reactions of C with anthracene, corannulene, benzo[rst]pentaphene and pyrene
Authors: Jahavery Gholamreza , Becker Hansjürgen , Petrie Simon , Cheng Pei‐Chao , Schwarz Helmut , Scott Lawrence T. , Bohme Diethard K.
Published: May 2005

An unprecented double‐electron transfer reaction has been observed between triply charged buckminsterfullerene, C, and the PAH molecules anthracene, corannulene, benzo[rst] pentaphene and pyrene at 294 ± 2 K in helium at 0.35 ± 0.01 Torr. The measurements were made with a selected‐ion flow tube (SIFT) apparatus. With anthracene, corannulene and pyrene double‐electron transfer was a minor channel (<5%): single‐electron transfer was the predominant channel. With benzo [rst] pentaphene, which requires the lowest energy for double ionization, single and double‐electron transfer proceeded in almost equal amounts.
Ion–neutral reorientation and unimolecular loss of alkanes from organic ions in the gas phase
Authors: Longevialle P. , Lefèvre O.
Published: May 2005

The loss of alkanes from ionized aliphatic alkanes, alcohols, ketones, ethers or amines takes place by a 1,2‐elimination involving a CC bond cleavage and the specific rearrangement of a hydrogen atom to the incipient radical. This reaction should normally occur within a limited distance between the reactant sites. This condition is accomplished with most probability during a concerted (or quasi‐concerted) mechanism, before the completion of the CC bond cleavage. The same reaction may also occur, however, in ion–neutral complexes, i.e. by a non‐concerted mechanism, after the CC bond cleavage is completed, provided that the probability is large enough for ion–neutral complexes to adopt suitable reactant configurations. This depends essentially on the proportion of possible reacting sites in the whole molecular ion.
Bimolecular reactions of distonic ions: Proton transfer and hydrogen atom abstraction with ˙CH2OH2+
Authors: Mourgues Philippe , Audier Henri Edouard , Leblanc Danielle , Hammerum Steen
Published: May 2005

The bimolecular reaction of ˙CH2OH2+ with a variety of neutral molecules in the gas phase were studied by Fourier transform ion cyclotron resonance experiments. The distonic ion is found to be considerably more acidic than protonated methanol; bracketing experiments provide a value of 695 ± 8 kJ mol−1 for the proton affinity of the conjugate base, the hydroxymethyl radical, Efficient hydrogen atom abstraction is only observed from neutral species less basic than ˙CH2OH. Transfer of CH to CS2, CH3I and C6H2F4 is observed.
H–D exchange at low energy in a collision cell between protonated aromatic hydrocarbons and D2O, CD3OD and C6D6
Authors: Stone John A.
Published: May 2005

H–D exchange reations which occur between protonated molecules (mainly aromatic hydrocarbons) and deuterated neutrals (D2O, CD3OD and benzene‐d6) were studied using a hexapole collision cell. The efficiency of exchange is dependent on the proton affinity difference between aromatic and target molecules but the pattern of deuteration in the exchanged ions does not change as might be expected with collision gas pressure. The incident ion energy also has only a small effect on the pattern up to a certain value, but above that value no exchange occurs. It is suggested that ions which shows multiple exchange have the same distribution of transit times, independent of collision gas pressure and, within the above limits, of initial energy. The rate‐determining step is then exchange in an ion–molecule complex rather than collision rate.
O−˙ chemical ionization mass spectra of fluoroaromatic compounds
Authors: Merrett Kim , Young Alex. B. , Harrison Alex. G.
Published: May 2005

The O−˙ chemical ionization (CI) mass spectra of the mono‐ to pentafluorobenzenes, fluorotoluenes and fluoroanisoles were measured. For comparison, the O−˙ CI mass spectra of toluene (including deuterium‐labelled variants) and anisole were also measured. The major reaction channels of O−˙ with fluorobenzene involve H‐atom displacement and H abstraction. With increasing fluoring substitution H+ abstraction increases in importance. For the tri‐ and tetrafluorobenzenes H abstractions is important only when there are two hydrogen ortho to each other. Reaction channels which are unique to the fluoroaromatic molecules involve the formation of [M + O – HF]−˙, which, for polyfluoro compounds, fragments further by elimination of HF or CO. For the fluoroanisoles, formation of FC6H4O− and elimination of CH2O from [M – H]− and [M – 2H]−˙ are important reaction channels. The formation of [M + O – H]− by reaction of O−. with toluene is shown to involve specific displacement of a ring hydrogen, whereas the formation of [M – H]− involves primarily abstraction of a proton from the methyl group. By contrast, H abstraction is non‐specific and proceeds by three pathways: (i) abstraction of two hydrogens from the aromatic ring, (ii) abstraction of two hydrogens from the methyl group and (iii) abstraction of one hydrogen from each position; however, the resuls are not in accord with a random selection of hydrogens.
Measured and calculated double‐ionization energies of 2‐haloethanols
Authors: Seakins M. , Griffiths W. J. , Harris F. M. , Andrews S. R. , Parry D. E.
Published: May 2005

Double‐charge‐transfer spectroscopy was used to measure the double‐ionization energies of the 2‐haloethanols FCH2CH2OH, ClCH2CH2OH, BrCH2CH2OH and ICH2CH2OH; the values obtained were 30.1 ± 0.5, 28.1 ± 0.5, 27.6 ± 0.5 and 26.9 ± 0.5 eV, respectively. In addition, the energies were calculated using ab initio methods and the GAUSSIAN 90 program package. The measured and calculated values for FCH2CH2OH are in agreement, but for the three other molecules the calculated values are significantly lower than those measured. The discrepancies in the calculations are due mainly to the underestimation of correlation energies by the appropriate MP2 method, which becomes progressively worse with increasing number of electrons in the system.
The fast atom bombardment mass spectra of furyl and thienyl silanes and germanes in comparison with their electron impact mass spectra
Authors: Mažeika I. , Grīnberga S. , Gavars M. , Gaukhman A. P. , Erchak N. P. , Lukevics E.
Published: May 2005

The interaction of the π electron system of furyl and thienyl substituents with the silicon (or germanium) atom is less significant in fragmentation under fast atom bombardment than under electron impact. Under fast atom bombardment the primary fragmentation of the title compounds is determined by steric influence of the heteroaromatic substituents.