bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of cyclic acetals. XXIII—low resolution, electron impact mass spectra of some 6,8‐dioxa‐3‐thiabicyclo[3.2.1]octanes and related 2‐acetoxy, 3‐oxo and 3,3‐dioxo derivatives
Authors: Calinaud Pierre , Gelas Jacques , Horton Derek , Wander Joseph D. 
Published: May 2005

AbstractLow resolution, electron impact mass spectra of 6,8‐dioxa‐3‐thiabicyclo[3.2.1]octane and eight C‐methyl or ‐phenyl derivatives are, in the main, similar to those of the corresponding 3,6,8‐trioxa homologs. Oxygenation on C‐2 or on the sulfur atom decreases the number of prominent fragments in the scheme of decomposition and apparently affords greater opportunity for formation of small, stable, acylium ions, but the added oxygen atoms generally do not direct major new modes of fragmentation.
Labelling studies of hydrogen rearrangements in the chemical ionization mass spectra of cyclohexanone and its derivatives
Authors: Diakiw Vladimir , Goldsack Robert J. , Shannon James S. , Lacey Michael J. 
Published: May 2005

AbstractDeuterium labelling studies indicate that loss of water from the protonated molecular ion of cyclohexanone involves competitive site‐specific eliminations. Loss of alcohol from the protonated molecular ions of 4‐alkoxycyclohexanones involves competition between a direct cleavage, a 1,3‐hydrogen rearrangement and consecutive losses of alkene and water.
Ion–molecule reactions of methoxymethyl cations with some organic substrates studied by ion cyclotron resonance spectrometry
Authors: van Doorn R. , Nibbering N. M. M. 
Published: May 2005

AbstractThe reactions of methoxymethyl cations generated from dimethyl ether with propene, butene‐2, vinyl methyl ether, acetaldehyde and acetone have been studied. The collision complexes, generated with the olefines, may eliminate an olefine, a methanol and a formaldehyde molecule as shown by double resonance experiments. From deuterium labelling it is found, that in the cases of propene and butene‐2 the elimination of an olefine is accompanied by an extensive H/D interchange in the collision complexes, which has been shown not to occur in the long‐lived reactant methoxymethyl cations if the internal energy of the methoxymethyl cations is less than 2.3 eV. The H/D interchange in these collision complexes is reduced in the elimination of methanol and is almost completely suppressed in the elimination of formaldehyde. In reactions with vinyl methyl ether, however, the eliminations of methanol and formaldehyde from the corresponding collision complexes appear to proceed with extensive H/D interchange. These observations point to acyclic collision complexes rather than 4‐membered ring complexes. The collision complexes generated with acetaldehyde and acetone decompose by elimination of formaldehyde only. Deuterium labelling has shown that the formaldehyde molecule contains the original methylene group of the reactant methoxymethyl cations. In addition, 18O labelling in acetone has shown that the original oxygen atom of the methoxymethyl cations is retained completely in the eliminated formaldehyde. These observations exclude any formation of 4‐membered ring collision complexes and can only be explained by acyclic complexes. Possible mechanisms of all reactions mentioned are discussed in the light of these results.
Identification of amino acid thiohydantoin derivatives by chemical ionization mass spectrometry
Authors: Okada Kozo , Sakuno Akemi 
Published: May 2005

AbstractThe chemical ionization mass spectra of 16 amino acid thiohydantoins were examined using isobutane or ammonia as reagent gases. Except for a few cases, including some aromatic amino acids, the chemical ionization spectra were much simpler than the corresponding electron impact spectra. Therefore, the major component in the amino acid thiohydantoin mixture was easily detected by chemical ionization mass spectrometry. The combination of the chemical ionization method and thiohydantoin formation was applied successfully to the sequence analysis of model peptides.
The formation of [CH5O]+ and ions from the molecular ions of isobutyl alcohol
Authors: Tajima Susuma , van der Greef Jan , Nibbering Nico M. M. 
Published: May 2005

AbstractOn the basis of field ionization kinetic and deuterium labelling experiments, it is shown that the molecular ions of isobutyl alcohol generate [CH5O]+ ions at 10−11 s via a 1,4‐shift of a hydrogen atom from one of the methyl groups to the oxygen atom, followed by a 1,2‐elimination of protonated methanol with a hydrogen atom of the other methyl group. At times > 10−11 s two distinct interchange processes between hydrogen atoms appear to compete with this reaction, as shown from field ionization kinetic experiments and metastable decompositions. Ion cyclotron resonance experiments on the long‐lived [CH5O]+ ions further demonstrate that they are protonated methanol ions. Arguments are put forward that the ions, generated by a specific 1,3‐elimination of a molecule of water from metastable decomposing molecular ions, have an isobutene structure.
Mass spectroscopy of natural products. II—allogibberic acid—A model for the skeletal fragmentation of the molecular ions of GA3 type gibberellins
Authors: Voigt D. , Adam G. , Schmidt J. , Franke P. 
Published: May 2005

AbstractThe positive ion mass spectrum of allogibberic acid was examined and fragmentation routes involving the carbon skeleton are proposed on the basis of mass measurements and metastable ion observations. The results are compared with the mass spectra of 3‐hydroxy‐epiallogibberic acid, as well as gibberellin A3 (GA3), 3‐epi‐GA3, 3‐dehydro‐GA3 and iso‐GA3, the latter compounds all being capable of undergoing aromatization of ring A giving a key ion corresponding to the molecular ions of the allogibberic acid and 3‐hydroxy‐epiallogibberic acid models, respectively. All the gibberellin derivatives investigated show the same fragmentation of the skeleton. Thus, the behaviour under electron impact of the GA3 type gibberellins follows a general pattern.
Ionization and appearance potentials in organic chemistry. II—Appearance potentials and enthalpy differences for the stereoisomers of methylbicyclo[4.4.0]decanes
Authors: Zaikin V. G. , Musaev I. A. , Kurashova E. Kh. 
Published: May 2005

AbstractThe ionization potentials for the stereoisomers of trans‐fused 2‐ and 3‐methylbicyclo[4.4.0]decanes and the appearance potentials for the ions at m/e 137 [M–CH3]+, 109, 96, 95 and 82 were measured by the electron impact method. The ionization potentials and appearance potentials of the [M–CH3]+ ions appeared to be equal for each of the epimers. Appearance potentials of the other ions were always lower for the less stable epimer. No quantitative correlation was observed between the difference in the appearance potentials for any ions and the differences in enthalpies of the ground states.
The Structures of the [2M–1]+ ions formed from benzene in a high pressure mass spectrometer source
Authors: Harris J. A. , Morgan R. P. , Beynon J. H. 
Published: May 2005

AbstractThe ionic species [C12H11]+ has been formed by ion‐molecule reactions in benzene at high pressure (˜0.5 Torr). This ion has been shown to be stable for at least 10−5 s and its structure has been inferred by a study of its unimolecular and collision induced fragmentations in both the first and second field free regions of the ZAB‐2F mass spectrometer.
Structure and fragmentations of [C3H7S]+ ions
Authors: Broer W. J. , Weringa W. D. 
Published: May 2005

AbstractThe principal fragmentation reactions of metastable [C3H7S]+ ions are loss of H2S and C2H4. These reactions and the preceding isomerizations of [C3H7S]+ ions with six different initial structures were studied by means of labelling with 13C or D. From the results it is concluded that the loss of H2S and C2H4 both occur at least mainly from ions with the structure [CH3CH2CHSH]+ or from ions with the same carbon sulfur skeleton, with the exception of the ions with the initial structure [CH3CH2SCH2]+, which partly lose C2H4 without a preceding isomerization. For all ions, more than one reaction route leads to [CH3CH2CHSH]+. It is concluded that the loss of H2S is at least mainly a 1,3‐elimination from the [CH3CH2CHSH]+ ions. Both decomposition reactions are preceded by extensive but incomplete hydrogen exchange.
Origin of the [C4H9O]+ ions in the mass spectrum of n‐butyl ethyl ether
Authors: Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractThe mechanisms of formation of m/z 73 ions in the mass spectrum of the ionized title compound were investigated by deuterium substitution and by examining the decompositions of metastable ions. Two routes to the [C4H9O]+ ions were found in the normal spectrum. The ethyl lost by the major pathway contains the α‐ and β‐hydrogens and a γ‐hydrogen from the butyl group. The minor route involves the loss of ethylene from the [MH]+ ion. There were metastable peaks for losses of ethyl, ethanol and methyl from the molecular ion. The ethyl contains the α‐ and β‐methylenes and a γ‐hydrogen, while the methyl is the δ‐methyl of the butyl group. The labeling data rule out a previous mechanistic proposal for the loss of ethyl and support a mechanism involving stepwise isomerization to the sec‐butyl ethyl ether molecular ion. However, the metastable ion chemistries of the molecular ions from the n‐ and sec‐butyl ethyl ethers are highly dissimilar, perhaps due to decompositions from different electronic states. The n‐pentyl methyl ether ions loses both ethyl and propyl, apparently following rearrangements to the 3‐pentyl and 2‐pentyl ether ions. Di n‐butyl and n‐butyl methyl ethers also give metastable peaks for loss of methyl, ethyl and the shorter chain alcohol.
Profil de Pics Métastables (Pertes de NO·) en Série Nitroindazolique
Authors: Maquestiau A. , Van Haverbeke Y. , Vanovervelt N. , Flammang R. , Elguero J. 
Published: May 2005

AbstractLes libérations d'énergie cinétique associées aux fragmentations (pertes de NO·) des ions moléculaires de nitroindazoles ont été mesurées. Les résultats montrent que le profil des pics métastables correspondants permettent de différencier les cinq isomères.
The mechanism for elimination of acetic acid from 1‐acetoxy‐ and 2‐acetoxytetralin
Authors: Wojinski Stanley F. , Gross Michael L. 
Published: May 2005

AbstractBy employing deuterium substitution and metastable ion defocusing methods, it has been determined that 1‐acetoxytetralin undergoes a highly regiospecific (>98%) 1,4‐elimenation of acetic acid. The mechanism closely parallels that for loss of water from 1‐tetralol in terms of specificity. However, unlike the water loss, which shows a significant kinetic isotope effect (KH/KD = 2.0) and a large release of translational energy (270 meV), the expulsion of acetic acid occurs without an isotope effect and with release of only 10 meV of kinetic energy. Competitive with acetic acid loss is the elimination of ketene which has been shown to occur by a 4‐centered transition state. The 2‐acetoxytetralin exhibits the more traditional 1,2‐elimination of acetic acid which contrasts with a 1,3‐elemination of water for the corresponding alcohol.
The isobutane chemical ionization mass spectra of 2‐methyl substituted 1,3‐cycloalkanediol diacetates and dimethyl ethers
Authors: Dhaenens L. , Van De Sande C. C. , Vangaever F. 
Published: May 2005

AbstractThe isobutane chemical ionization mass spectra of 2‐methyl‐1,3‐cyclopentane and 1,3‐cyclohexanediol diacetates and dimethyl ethers reveal that the proton bridge in the protonated cis diol derivatives is sensitive to conformational and steric effects. The latter dominate in the case of the methyl ethers on account of the smaller ring created by the proton bridge in the ethers in comparison with the diacetates. Finally, the spectra of the trideuterocetates and trideuteromethyl ethers reveal the occurrence of protolysis in the ionizing plasma.
Massenspektrometrische Untersuchungen an Organophosphorverbindungen. II—Elektronenstoßinduzierte Fragmentierungen von Tetraorganodiphosphandisulfiden
Authors: Keck Helmut , Kuchen Wilhelm 
Published: May 2005

AbstractDas massenspektrometrische Fragmentierungsverhalten sowie einige Umlagerungsprozesse in den durch Elektronenstoß induzierten 70 eV Massenspektren von Tetraorganodiphosphandisulfiden R2P(S)‐P(S)R2 (R  CH3, C2H5, n‐C3H7, n‐C4H9, C3H5, C6H5) und CH3RP(S)–P(S)CH3R (R  C2H5, n‐C3H7, n‐C4H9, C6H5, C6H5, C6H5,CH2) werden aufgeführt und diskutiert. Fragmentierungsschemata, die in übereinstimmug mit der Messung metastabiler übergänge nach der Methode DADI und Defokussing stehen, werden angegeben. Die Elementarzusammensetzung der meisten Ionen wurde durch Massenfeinbestimmung ermittelt. Im Gegensatz zu Organophosphansulfiden R3P(S) wird hier praktisch keine Schwefelabspaltung beobachtet. Erster Fragmentierungsschritt bei diesen Verbindungen ist die Spaltung einer P–C‐Bindung unter Abspaltung von R⋅. Folgeschritt ist dann die Eliminierung von RPS unter Bildung von [R2PS]+, aus dem in fast allen Spektren der Basispeak resultiert. Die phenylsubstituierten Verbindungen ergeben Spektren, in denen mit hoher Intensität [(C6H5)3P]+. bzw. [(C6H5)2CH3P]+. auftreten, die aus [M]+. durch Wanderung von C6H5 entstanden sind. Es wird angenommen, daß sich das Molekülion vor seiner Fragmentierung in einen P–S‐Vierring umlagert.
Electron impact mass spectra of 2‐[acyl(alkyl)amino]oxazoles
Authors: Mallen D. N. B. , Cort L. A. , Cockerill A. F. 
Published: May 2005

AbstractThe mass spectral behaviour of 2‐methyl‐N‐butyl‐N‐(4‐methyloxazol‐2‐yl)propanamide is characterized by cleavage of the acylamino substituents and the elimination of a hydroxyl radical. An understanding of this elimination has been obtained from the analysis of further 2‐[acyl(alkyl)amino]oxazoles and the use of deuterium labelled compounds.
Field desorption of non‐electrolytes using simply activated wire emitters
Authors: Giessmann U. , Heinen H. J. , Röllgen F. W. 
Published: May 2005

AbstractThe high field strengths obtained with activated emitters are necessary to accomplish field desorption of non‐electrolytes, i.e. samples containing neither salts nor acids. A simple procedure to produce activated emitters in a few seconds for this mode of field desorption is described. The method was applied to W and Pt wires, as well as carbon fibres.
Formation and stability of gaseous tolyl ions
Authors: McLafferty Fred W. , Bockhoff Frank M. 
Published: May 2005

AbstractCollisional activation mass spectra confirm that tolyl ions can be produced from a variety of CH3C6H4Y compounds. High purity o‐, m‐ and p‐tolyl ions are prepared by chemical ionization of the corresponding fluorides (Y=F) as proposed by Harrison. In electron ionization of CH3C6H4Y formation of the more stable tropylium and benzyl ionic isomers usually accompanies that of the o‐, m‐ and p‐tolyl ions. Isomerization of low energy [CH3C6H4Y]+⋅ to [Y–methylenecyclohexadiene]+⋅ is proposed to account for most [benzyl]+ formation, while the tropylium ion appears to arise from the isomerization of tolyl ions formed with higher internal energies, [o‐, m‐, p‐tolyl]+→ [benzyl]+→ [tropylium]+, consistent with Dewar's predictions from MINDO/3 calculations.
Chemical ionization induced fragmentations of 2‐phenyl‐1,3,2‐dioxaborolanes and 2‐phenyl‐1,3,2‐dioxaborinanes
Authors: Hancock Richard A. , Weigel Helmut 
Published: May 2005

AbstractChemical ionization induced fragmentations (with 2‐methylpropane as reagent gas) of 4‐methyl‐ and 4,5‐dimethyl‐2‐phenyl‐1,3,2‐dioxaborolane and 4‐methyl‐2‐phenyl‐1,3,2‐dioxaborinane gave in each case two fragments, a hydrocarbon ion and metaboric acid. Propeae and thence metaboric acid are eliminated from 4,6‐dimethyl‐2‐phenyl‐1,3,2‐dioxaborinane. The mechanisms of the fragmentations are discussed. Under the conditions used 2‐phenyl‐1,3,2‐dioxaborolane and 2‐phenyl‐1,3,2‐dioxaborinane do not fragment.
Effect of substituents on the kinetic energy release in unimolecular decompositions of substituted anisoles
Authors: Florêncio Helena , Vijfhuizen Peter C. , Heerma Wigger , Dijkstra Geo 
Published: May 2005

AbstractThe kinetic energy relased on the loss of a CH3 ⋅ radical from para substituted anisoles appears to depend on the nature of the substituent. The application of the dual parameter equation of Yukawa and Tsuno yields a linear correlation with the T0.5‐values. The mesomeric effect predominates strongly over the inductive effect.
Hydrogen migration in the electron impact induced retro diels‐alder fragmentation of N‐aryl‐4H‐5,7a‐epoxyisoindolines
Authors: Mintas M. , Klepo Ž. , Jakopčić K. , Klasinc L. 
Published: May 2005

AbstractThe electron impact induced fragmentations of the C‐5 unsubstituted and 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines (where aryl is pheny, p‐tolyl, p‐methoxyphenyl, o‐methoxyphenyl and p‐chlorophenyl) were investigated. The fragmentation patterns deduced were supported by exact mass measurements of prominent ions and by deuterium labelling. The retro Diels‐Alder fragmentation turned out to be a predominant process in all the compounds investigated. In the mass spectra of the 5‐methyl N‐aryl‐4H‐5,7a‐epoxyisoindolines hydrogen migration preceding fragmentation occurred. From the mass spectrum of the specifically deuterated compound it was concluded that the transferred hydrogen originates exclusively from the 5‐methyl group.
Chemical ionization and electron impact mass spectrometry of some organophosphonate compounds
Authors: Sass Samuel , Fisher Timothy L. 
Published: May 2005

AbstractThe application of gas chromatography chemical ionization mass spectrometry to the determination of a variety of alkyl alkylphosphonates, phosphonofluoridates, phosphonothiolates and an amidophosphorocyanidate is described. Comparison is made between the electron ionization and chemical ionization mass spectrometry of these compounds. Chemical ionization mass spectrometry is shown to enhance the capability for identification, especially when a limited sample is available. Results indicate that methane is highly useful for obtaining protonated molecular ions and association ions (formed by the transfer of a reactant ion to a sample molecule) as well as meaningful fragment ions. Ionizing ethylene and isobutane gives protonated molecular ions as base peaks for all of the compounds studied, including those where a lower abundance of the [MH]+ ion is found via methane chemical ionization mass spectrometry. Ethylene is superior to isobutane on the basis of its effectiveness for serving as both a carrier and a reagent gas and gives better sensitivity. Although not an intrinsic part of this present study, analytical sensitivities in the subnanogram range were found.
Water loss from ester molecular ions upon electron impact
Authors: Folk Theodore L. , Wideman Lawson G. , Cottman Kirkwood S. 
Published: May 2005

AbstractTo date, in mass spectral studies of esters, a single reference to loss of water from the molecular ions has been noted. A series of aromatic esters which exhibit that sparsely observed phenomenon are reported herein. Through a combination of synthetic and deuterium labeling studies, support for a unique fragmentation route for the loss of water from these ester molecular ions has been obtained.
Studies in negative ion mass spectrometry. X—Electron capture by a series of tris(hexafluoroacetylacetonato) metal chelates
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K. 
Published: May 2005

AbstractResults of electron capture and negative ion mass spectrometric studies are reported for a series of tris‐chelates of the type Metal. L3, where L refers to the ligand or enolate ion of the β‐diketone 1,1,1,5,5,5‐hexafluoro‐2,4‐pentanedione (hexafluoracetylacetone), and the metals are: Sc(III), Ti(III), V(III), Cr(III), Mn(III), Fe(III), Co(III), A1(III), Ga(III), In(III). The negative ion mass spectra were all relatively simple; the most abundant ions being the molecular and ligand ions for all the metals studied. Reaction schemes have been established to account for the appearance of all significant fragment ions, many of which have been formed as a result of fluorine atom transfer processes. For the transition metal complexes, evidence for elimination of neutral divalent metal fluorides comes from the ion decomposition reactions [Metal.L.F2]−→[L]−, and for the Group III metal complexes, [Metal.L3]−→[Metal.L2]− as well as [Metal.L2]−→[L]− processes indicate that the metals have been reduced as a consequence of the initial electron capture and subsequent fragmentations of metal‐containing ions. The influence of the metal atom and its 3d‐electron configuration has been shown not to affect significantly the electron capture processes. However, the relative instabilities of molecular anions of the transition metal tris‐complexes show an approximately linear dependence on the increasing 3d‐electron populations of the metal ions from Ti(III) to Co(III).
Structure and formation of gaseous [C4H5O]+ ions. III—Ions derived from unsaturated ethers
Authors: Terlouw Johan K. , Burgers Peter C. , Hommes Henk 
Published: May 2005

AbstractThe abundant [C4H5O]+ (m/z 69) ions found in the 70 eV mass spectra of a series of acetylenic, allenylic and unsaturated cyclic ethers are shown to have the following structures: HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HOCH3 (e), H2CC—OCH3 (f), (g) and HCCCH2—O\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H2 (h). Of these, the cyclic ion g is the most stable: its ion enthalpy (≥ 165 kcal mol−1) is close to that found for the acyclic C3H5\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O isomers identified in a previous study. Evidence that these four isomeric [C4H5O]+ ions are stable species with lifetimes ≥ 10−5 s is obtained from their collisional activation spectra, the shape of the metastable peaks and the associated kinetic energy release values for the common loss of CO, thermochemical information and analysis of deuterium and carbon‐13 labelled precursor molecules. It is further shown that loss of X⋅ from ethers of the type XCCCH2OCH3 involves isomerization into energy rich allenyl type ions [(X)HCCCHOCH3]+˙ . These ions undergo loss of X⋅ by simple bond cleavage, yielding, e type product ions, when the CX bond strength is relatively low (XI, Br). When XCl and especially CH3 or H, X⋅ is only lost after rearrangement yielding the cyclic product ion g. The mechanism for this cyclization reaction is related to that proposed in a previous study for the ester→ acid isomerization in the molecular ions of the esters of α, β‐unsaturated carboxylic acids.
Fragmentation of even electron ions: Protonated amines and esters
Authors: Sigsby M. L. , Day R. J. , Cooks R. G. 
Published: May 2005

AbstractThe fragmentation of protonated amines and esters is examined by collision induced dissociation of mass selected ions generated by chemical ionization. Four fragmentation types are observed: (i) loss of an alkane moiety, explicable in terms of a four‐centered reaction, (ii) loss of alkene, also explicable as a four‐centered process, (iii) loss of an alkyl radical, requiring electron unpairing, (iv) losses of other neutral molecules, viz. acids and alcohols from protonated esters, or amines and ammonia from protonated amines. Proposed mechanisms were checked by characterizing selected product ions through their collision induced dissociation spectra. The usefulness of these generalizations is substantiated by the successful prediction of the fragmentation patterns and the order of relative abundances of daughter ions for eight unknowns including some containing functional groups not studied previously.