bluuebunny/crossref_metadata_2025_split huggingface dataset:
The [MOH]+ ions of m‐ and p‐ethylnitrobenzene: A common structure?
Authors: Baldwin Michael A. , Bowley Heather J. 
Published: May 2005

AbstractThe structures of the [MOH]+ ions of m‐ and pethylnitrobenzene have been compared by measurements of metastable ion spectra, collisional activation spectra, kinetic energy releases and critical energies for the formation of these ions and their subsequent decomposition. Normalized rates of fragmentation of metastable molecular ions and metastable [MOH]+ ions have been compared for ion lifetimes up to 30 μs. The energy measurements fail to distinguish between the structures of the [MOH]+ ions, but the normalized fragmentation rates and the collisional activation spectra show their structures to be different.
Electron impact induced hydrogen rearrangements in (Z)‐ and (E)‐styryl alkyl sulfoxides
Authors: Liu Lilian Kao , Luo Fen‐Tair 
Published: May 2005

AbstractAlkene elimination, alkyl loss, styryl and alkyl migrations to oxygen are the major fragmentations of (Z)‐ and (E)‐alkane‐sulfinyl‐2‐phenylethenes (cis‐ and trans‐styryl alkyl sulfoxides) under electron impact. Alkene elimination has been found to go through a McLafferty‐type hydrogen rearrangement to yield the benzylic carbon and the sulfinyl oxygen, respectively. This is the most facile and interesting process for compounds with longer alkyl chains (R⩾C3H7), and is a unique feature for styryl sulfoxides. Product ion analyses show the migrating aptitude to carbon and to oxygen to be qualitatively similar.
Pyrolysis reaction of carpronium chloride and its structurally related compounds. 1—electronic and steric effects on the orientation of the pyrolysis reaction
Authors: Ohya Kazumi , Yotsui Yasuhiko , Yamazaki Kenichi , Sano Mitsuji 
Published: May 2005

AbstractThe pyrolysis reaction of carpronium chloride and its structurally related compounds, which were trimethyl‐aminoalkyl acid alkyl esters involving two, three or four skeletal methylene groups, have been investigated by pyrolysis gas chromatography mass spectrometry. The results indicated that the reaction modes of these ammonium compounds were essentially dependent on the number of skeletal methylene groups, and secondarily on the length of the carbon chain of the ester group. These phenomena have been interpreted in terms of electronic and steric contributions for the ionic elimination reaction. The electronic and steric effects on the orientation of the reaction are discussed on the basis of the atomic population calculated by the CNDO/2 method.
Competing oxygen migrations in ortho nitro aromatic thioamides on electron impact
Authors: Ramana D. V. , Viswanadham S. K. 
Published: May 2005

AbstractInteresting competitive oxygen migrations from the nitro group to the nitrogen and to the sulfur have been noticed during the mass spectral decomposition of ortho nitro aromatic thioamides on electron impact. The migration of the oxygen to the nitrogen of the thioamide function results in the formation of stable o‐nitrosothiobenzoyl cation. The other novel ortho effect noticed in the ortho isomers is the transfer of an oxygen from the nitro group to the sulfur followed by the ejection of SO from the molecular ions. A mechanism involving the initial oxygen migration to the sulfur through a favourable 6‐membered transition state followed by cyclization with the concomitant expulsion of SO is proposed for this process. Other interesting decomposition processes occurring as a consequence of this ortho effect have also been noticed. The proposed mechanisms for these processes are supported by mass analysed ion kinetic energy spectra and high voltage scans.
Quantitation of isomeric ion mixtures using collisional activation mass spectra
Authors: Proctor Christopher J. , McLafferty Fred W. 
Published: May 2005

AbstractRecently Bass and Bowers have criticized methods for calculation of isomeric composition of gaseous ions based on mass spectra from collisionally activated dissociations (CAD). They fault values from this laboratory on the proportion of benzyl and tropylium ions calculated by two methods from product ion abundances. However, a careful remeasurement of the relevant yields of CAD product ions shows that neither calculation method affected the result outside experimental error, as the ion yields for at least 14 higher energy dissociations are insensitive to both isomeric identity and internal energy. Reducing the [C7H7]+ internal energy by 1.5 eV does give a 25% reduction in the ion yield for the lowest energy process, supporting the accepted recommendation that these be omitted for quantitative spectral comparisons. A calculation error was made in one of our previous reports on [C7H7]+, and corrected isomeric composition values are presented. The disparate values from recalculation by Bass and Bowers of other data from this laboratory on [C2H4O]+˙ ions are shown here to be consistent with the large experimental error of those measurements; the medians of their values are actually near the values originally reported. In direct contrast to their assertions, we find no evidence that previous calculation methods have produced misleading conclusions, or that the assumption of linear superposition of CAD spectra in ion mixtures has yielded unreliable results.
Stable C2H5X+˙ (X=Cl, Br) radical cations of structure [CH3CHXH+˙]: Their energetics and dissociation characteristics
Authors: Holmes John L. , Burgers Peter C. , Terlouw Johan K. , Schwarz Helmut , Ciommer Bernhard , Halim Herman 
Published: May 2005

AbstractA new radical cation having the methyl carbene type structure [CH3CHClH]+˙ has been characterized in the gas phase. It is readily generated by the dissociative ionization [CH3CHCICO2H]+˙ → CO2+[CH3CHCIH]+˙. Its enthalpy of formation has been estimated to be 951 kJ mol−1, close to that of [CH3CH2CI]+˙. The principal fragmentation characteristics (loss of HCl and Cl˙) of the ion are discussed. A brief description of the bromo analogue [CH3CHBrH]+˙ is also given.
Further examples of skeletal rearrangements of the Wagner‐Meerwein type in chemical ionization mass spectrometry: The case of [C6H9]+ ions
Authors: Gäumann Tino , Houriet Raymond , Stahl Daniel , Tabet Jean‐Claude , Heinrich Nikolaus , Schwarz Helmut 
Published: May 2005

AbstractThe [C6H9]+ ions produced either via unimolecular H2O loss from 13 [C6H11O]+ precursors or direct protonation of 1,3‐ and 1,4‐cyclohexadiene have identical collisional activation mass spectra. The kinetic energy release data for the process [C6H11O]+→[C6H9]++H2O are also very similar (on average T0.5=24 meV) irrespective of the constitution of the precursor. From the proton affinities of 1,3‐cyclohexadiene (PA=837.2 kJ mol−1) using ion cyclotron resonance mass spectrometry the heat of formation of the [C6H9]+ ion is determined to 804.6 kJ mol−1. This value taken together with the results of molecular orbital calculations (MNDO) and the structure indicative losses of CH3. and C2H4 upon collisional activation suggest that the [C6H9]+ ion has the structure of the 1‐methylcyclopentenylium ion f and not that of the slightly less stable cyclohexenylium ion g. The generator of an easily interconverting system of isomeric [C6H9]+ ions is unlikely to be due to the high barrier separating the various isomers.
A photo‐ionization study of organosulfur ring compounds: Thiirane, thietane and tetrahydrothiophene
Authors: Butler James J. , Baer Tomas 
Published: May 2005

AbstractThe gas phase heats of formation of several organosulfur cations were determined from thiirane, thietane and tetrahydrothiophene precursor molecules by photoionization mass spectrometry. Heats of formation at 0 K and 298 K are reported for the following ions: [H2CS]+˙, [H3CS]+, [C2H3S]+, [C2H4S]+˙, [C3H5S]+, [C3H6S]+˙, [C4H7S]+ and [C4H8S]+˙. The [C4H7S]+ (m/z 87), [C2H4S]+˙ (m/z 60), [C2H3S]+ (m/z 59), [C4H7]+ (m/z 55), [C4H6]+˙ (m/z 54) and [CH2S]+˙ (m/z 46) ions are produced from metastable tetrahydrothiophene ions at photon energies between 10.2 and 10.7 eV. Decay rates of internal energy selected parent ions to the m/z 60, 59, 55 and 54 fragments were measured by threshold photoelectron‐photoion coincidence, the results of which are compared to statistical theory (RRKM/QET) calculations. The [C2H4S]+˙ ion from tetrahydrothiophene is found to have the thioacetaldehyde structure. From the measured [C2H4S]+˙ onset a ΔH = 50±8 kJ mol−1 was calculated for the thioacetaldehyde molecule.
Characterization of isomeric [CH5P]+˙ and [C2H7P]+˙ radical cations and some [C2H6P]+ phosphonium ions in the gas phase by their collisional activation spectra
Authors: Weger E. , Levsen K. , Ruppert I. , Burgers P. C. , Terlouw J. K. 
Published: May 2005

AbstractCollisional activation spectra were used to characterize isomeric ion structures for [CH5P]+˙ and [C2H7P]+˙ radical cations and [C2H6P]+ even‐electron ions. Apart from ionized methylphosphane, [CH3PH2]+˙, ions of structure [CH2PH3]+˙ appear to be stable in the gas phase. Among the isomeric [C2H7P]+˙ ions stable ion structures [CH2PH2CH3]+˙ and [CH2CH2PH3]+˙/[CH3CHPH3]+˙ are proposed as being generated by appropriate dissociative ionization reactions of alkyl phosphanes. At least three isomeric [C2H6]+ ions appear to exist, of which \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} - \mathop {\rm P}\limits^{\rm + } {\rm H = CH}_{\rm 2} $\end{document} could be identified positively.
Positive and negative ion mass spectrometric studies of dioximes of α‐diketones and their nickel complexes
Authors: Charalambous J. , Soobramanien G. , Stylianou A. D. , Manini G. , Operti L. , Vaglio G. A. 
Published: May 2005

AbstractThe positive and negative ion mass spectra of glyoxime, methylglyoxime, dimethylglyoxime, diphenyl glyoxime and of their nickel(II) complexes are reported. Both the positive and negative ion mass spectra of the dioximes show loss of OH˙ and H2O from the molecular ion to give fragment ions which probably have cyclic furazan type structures. The positive ion spectra of the complexes fragment mainly by loss of ligand radicals whereas the negative ion spectra show mainly loss of OH˙ and H2O.
Cyclic ions in the mass spectra of trimethylsilyl derivatives of substituted o‐dihydroxybenzenes
Authors: Horvat Robert J. , Senter Samuel D. 
Published: May 2005

AbstractThe mass spectra of trimethylsilyl (TMS) ethers/methyl esters of phenolic acids containing o‐dihydroxybenzene groups have base peaks at [M−119]+ instead of the usual [M−15]+ and [M−31]+ that are characteristic of TMS/methyl esters of monohydroxyphenolic acids. These ions, formed by the loss of 31+88 u from the parent ion, possess a cyclic moiety as proven by substitution of deuterium atoms for hydrogen atoms in the TMS groups of the methyl esters of 3,4,5‐trihydroxybenzoic (gallic), 3,4‐dihydroxybenzoic (protocatechuic) and β‐(3,4‐dihydroxyphenyl)propenoic (caffeic) acids. Although these cyclic ions are the base peaks in TMS‐derivatized o‐dihydroxyphenolic acid esters, similar ions represent intense peaks but not necessarily the base peak in other derivatized compounds such as 1,2‐dihydroxybenzene, 1,2‐dihydroxy‐3‐methyl‐ and 1,2‐dihydroxy‐4‐methyl‐benzenes and flavan‐3‐ols that possess o‐dihydroxybenzene groups. Compounds possession m‐ or p‐dihydroxybenzene groups do not form these cyclic ions; therefore, this procedure for derivatization and interpretation of mass spectra is valuable for the identification of compounds containing o‐dihydroxybenzene groups in complex mixtures of isomeric compounds.
Electron impact mass spectra of 3,5,7‐triaryl‐and ‐trialkyl‐4H‐1,2‐diazepines
Authors: Balaban Alexandru T. , Gheorghiu Mircea D. , Balaban Teodor Silviu 
Published: May 2005

AbstractElectron impact mass spectra of 3,5,7‐trisubstituted 4H‐1,2‐diazepines indicate that aryl substituents lead to N2expulsion while alkyl substitutents do not. A common fragmentation pattern is observed and discussed for all alkyldiazepines, most of which are newly reported compounds. Assignments are based on electron impact mass spectra of deuteriated substrates and high resolution mass spectra. A previous interpretation of N2expulsion is corrected.
The decompositions of metastable [C4H8O]+˙ ions and the [C4H8O]+˙ potential surface
Authors: McAdoo David J. , Hudson Charles E. 
Published: May 2005

AbstractCollisionally activated decomposition (CA) spectra of [C4H8O]+˙ ions and the products of their metastable decompositions are used to refine a previously presented picture of the reactions of [C4H8O]+˙ ions. Metastable [C4H8O]+˙ isomers predominantly rearrange to the 2‐butanone ion and decompose by loss of methyl and ethyl, although up to 38% of the methyl losses take place by other pathways to form \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = {\rm{CHCH = }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H}}{\rm{.}} $\end{document}
. The CA spectra of many of the [C4H8O]+˙ ions with the oxygen on the first carbon are very similar, consistent with those ions isomerizing largely to common structures before or after collision. However, several of these ions have unique CA spectra, so they must remain structurally distinct from the majority of the [C4H8O]+˙ ions below energies required for decomposition. The CA spectra of ions with the oxygen on the second carbon are distinct from those of ions with the oxygen on the first carbon, so there is limited interconversion of the non‐decomposing forms of the two types of ions. A potential energy diagram for the reactions of metastable [C4H8O]+˙ ions is constructed from appearance energy measurements. As would be expected, the relative importances of most of the [C4H8O]+˙ isomerizations seem to be inversely related to the activation energies for those processes. Some parallels between the isomerizations of [C4H8O]+˙ ions and those of related ions are pointed out.
A fast atom bombardment and field ionization/field desorption study of some isomeric unsaturated dicarboxylic acids
Authors: Dallinga J. W. , Nibbering N. M. M. , Van Der Greef J. , Ten Noever De Brauw M. C. 
Published: May 2005

AbstractGeometrically isomeric dicarboxylic acids, such as maleic and fumaric acid and their methyl homologues, and the isomeric phthalic acids, have been investigated using fast atom bombardment, field ionization and field desorption mass spectrometry. The most intense peak in the positive ion fast atom bombardment spectra corresponds with the [M + H]+ ion. This ion, when derived from the E‐acids, tragments either by successive loss of water and carbon monoxide or by elimination of carbon dioxide. In the case of the Z‐acids only elimination of water from the [M + H]+ ions is observed to occur to a significant extent. The same is true for the [M + H]+ ions of the isomeric phthalic acids, that is the [M + H] ions derived from iso‐ and terephthalic acid exhibit more fragmentation than those of phthalic acid. All these acids undergo much less fragmentation upon field ionization, where not only abundant [M + H]+ ions, but also abundant [M]+· ions, are observed. Upon field desorption only the [M + H]+ and [M + Na]+ ions are observed under the measuring conditions. Negative ion fast atom bombardment spectra of the acids mentioned have also been recorded. In addition to the most abundant [MH]− ions relatively intense peaks are observed, which correspond with the [M]−˙ ions. The fragmentations observed for these ions appear to be quite different from those reported in an earlier electron impact study and in a recent atmospheric pressure ionization investigation.
Conjugated Schiff's bases 16—Substituent effect on electron impact fragmentation of some 1‐oxa‐4‐azabutadienes1
Authors: Moskal Janusz , Moskal Alexandra , Nagraba Krzysztof 
Published: May 2005

AbstractThe electron impact fragmentation patterns of some 1‐oxa‐4‐azabutadienes have been determined and supported by the corresponding metastables. The effect of substituents on this fragmentation has been investigated. Satisfactory correlation of intensity ratios of the peaks characterizing the primary fragmentation versus the Brown and Okamoto σ+ substituent parameters has been found. The relationship between the substituent parameters and the dissociation energy ED,C(3)‐C(5), estimated with the help of appearance energies has been considered.
Further investigation of the mass fragmentation of dinucleotide analogues containing the 6‐azauracil moiety
Authors: Jankowska Jadwiga , Golankiewicz BożEnna , Golankiewicz Krzysztof 
Published: May 2005

AbstractThe mass fragmentation of four dinucleotide analogues in which uracil and 6‐azauracil derivatives are connected by a trimethylene bridge is discussed. The fragmentation pathways have been proposed on the basis of high resolution data and metastable transitions. The distinct influence of alkyl substituents in the 5‐position of the uracil moiety on the fragmentation pathway has been observed and a novel fragmentation of 6‐azapyrimidine ring noted.
The isomerization of 1,4‐cyclohexadiene ions to the 1,3‐cyclohexadiene structure as studied by photodissociation
Authors: Van Velzen P. N. T. , Van Der Hart W. J. 
Published: May 2005

AbstractPhotodissociation experiments in a trapped ICR cell show that at low ionizing energies about two‐thirds of the molecular ions of 1,4‐cyclohexadiene have isomerized to the 1,3‐cyclohexadiene structure. The major fraction of the remaining ions isomerizes by a reaction with the parent neutral.
Secondary ion mass spectrometry of some promazines and photochemistry of chlorpromazine in glycerol
Authors: Dung Dao Viet , Marien J. , De Pauw E. , Decuyper J. 
Published: May 2005

AbstractSIMS using 6 keV Cs+ ions has been performed on glycerol solutions of various promazines. Fragmentation patterns are compared to those obtained by other ionization methods. The photochemical degradation of chlorpromazine has been observed directly in the glycerol droplet, showing the potentiality of SIMS for the direct study of photochemical reactions in solution.
The elimination of masses 27 and 28 from the [MOH]+ ion of 2‐nitrotoluene
Authors: Herbert C. G. , Larka E. A. , Beynon J. H. 
Published: May 2005

AbstractThe expulsion of neutral fragments of masses 27 and 28 from metastable [M  OH]+ ions derived from 2‐nitrotoluene has been observed. The relative abundances of the resulting fragment ions, together with the kinetic energy released in each process, has been compared with similar fragmentation of [C7H6NO]+ ions derived from other precursor molecules. In this way, the nature of the neutral fragments and the structure of the [M  OH]+ ions from 2‐nitrotoluene has been investigated. The most likely structure is the 1,2‐benzisoxazolenium cation although the coexistence of other structures cannot be ruled out on the present evidence.
Investigation of the relative stability of positive alkali halide cluster ions generated by fast atom bombardment
Authors: Morgan T. G. , Rabrenović M. , Harris F. M. , Beynon J. H. 
Published: May 2005

AbstractThe stabilities of alkali halide cluster ions [M(MX)n]+ (M  Li, Na, K, Rb, Cs; X  F, Cl, Br, I) have been studied by measuring the fragment ion yields following dissociation of the ions in the second field free region of a ZAB‐2F mass spectrometer. Extractable cluster ions were observed for certain values of n. It was found that the stabilities of the neutral fragment species formed are also of importance in determining the fragmentation rates. Possible configurations of M and X in the stable ions are discussed.
Structures and relative energies of gas phase [C3H7O]+ ions
Authors: Nobes Ross H. , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital calculations have been carried out for 17 possible isomeric [C3H7O]+ structures. Optimized geometries have been obtained with a split‐valence basis set and improved relative energies determined with polarization basis sets and with incorporation of electron correlation. The results agree well with available experimental data. In particular, (CH3)2COH+, CH3CH2CHOH+, CH3CHOCH3+, CH3CH2OCH2+,
equation image
and
equation image
have been confirmed as low‐energy isomers. Six additional structures appear to be energetically accessible and to offer a reasonable prospect for experimental observation. These are CH2CHCH2OH2+, CH2C(CH3)OH2+, CH3CHCHOH2+, CH2CHOHCH3+,
equation image
and
equation image
.
The heats of formation of some protonated olefinic carbonyl compounds: [C5H9O]+ and [C4H7O2]+ ions
Authors: Bouchoux G. , Hoppilliard Y. , Jaudon P. , Houriet R. 
Published: May 2005

AbstractThe proton transfer equilibrium reactions involving 3‐penten‐2‐one, 3‐methyl‐3‐buten‐2‐one, crotonic acid and methacrylic acid were carried out in an ion cyclotron resonance (ICR) spectrometer. The semiempirical method MNDO, used to estimate the heats of formation for 14 protonated [C5H9O]+ and [C4H7O2]+ ions and the energetic aspect of the fragmentations of metastable [C6H12O]+. and [C6H12O2]+. ions, leads to the conclusion that the ions corresponding to protonation at the carbonyl oxygen are the most stable. Thus the experimentally determined heats of formation of protonated olefinic carbonyl compounds can be attributed to the following structures: [CH3COHCHCHCH3]+ (δHf = 490 KJ mol−1), [CH3COHC(CH3)CH2]+ (δHf = 502 KJ mol−1), [HOCOHCHCHCH3]+ (δHf = 330 KJ mol−1) and [HOCOHC(CH3)CH2]+ (δHf = 336 KJ mol−1).
Mechanism for the formation of [M–1]+ in flavones
Authors: Guidugli F. H. , Pestchanker M. J. , Kavka J. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe electron impact induced fragmentations of flavone have been studied with the aid of high resolution measurements, metastable decompositions and deuterium labelling. Based on the obtained data a mechanism for the formation of the [MH]+ ion is proposed and further substantiated from the study of substituted flavones.
Effects of stereoisomerism on the electron impact fragmentation of some compounds with an eburnane skeleton1
Authors: Czira Gábor , Tamás József , Kalaus György 
Published: May 2005

AbstractThe mass spectra of five sets of stereoisomers possessing an eburnane basic skeleton (vincamine, vincaminic acid ethyl ester, deoxyvincamine, deoxyvincaminic acid ethyl ester, apovincaminic acid ethyl ester and all their possible epimers) have been compared. All of the epimers, among them the 3H‐β isomers, not studied formerly, have characteristically different electron impact spectra. For vincamine and its epimers similar differences were also found in the argon charge exchange ionization, mass‐analysed ion kinetic energy and collisionally activated mass‐analysed ion kinetic energy spectra. The main effects of stereoisomers on the abundance ratios clearly indicated the occurrence of some highly stereospecific or stereoselective decomposition processes. Conclusions concerning the mechanism of these reactions, based on the normal and metastable ion spectra as well as on some energetic data for the epimers, have also been drawn. For several fragment ions the observed unexpected abundance differences seem to be rationalized in terms of the competing effects of other decomposition processes of higher stereoselectivity.
An energy‐resolved study of the fragmentation of ionized 1‐Penten‐3‐ol
Authors: Zwinselman Jan J. , Harrison Ale X. G. 
Published: May 2005

AbstractA detailed energy‐resolved study of the fragmentation of CH2CHCH(OH)CD2CD3 (1‐d5) has been carried out using metastable ion studies and charge exchange techniques, combined with collision‐induced dissociation studies to establish the structures of fragment ions. At low internal energies (metastable ions) the molecular ion of 1‐d5 rearranges to the 3‐pentanone structure and fragments by loss of C2H5 or C2D5 leading to the acyl structure, [CH3CH2CO]+ or [CD3CD2CO]+, for the fragment ion. However, with increasing internal energy of the molecular ion this rearrangement process decreases rapidly in importance and loss of C2D5 by direct cleavage, leading to [CH2CHCHOH]+, becomes the dominant fragmentation reaction. As a result the [C3H5O]+ ion seen in the electron impact mass spectrum of 1‐penten‐3‐ol has predominantly the protonated acrolein structure.