bluuebunny/crossref_metadata_2025 huggingface dataset:
Isomerization of hydrocarbon ions. VIII—The electron impact induced decomposition of n‐dodecane
Authors: Levsen Karsten , Heimbach Heinz , Shaw G. John , Milne G. W. A.
Published: May 2005

The literature on the mass spectrometry of 2H and 13C labelled higher alkanes is reviewed and the decomposition behaviour of both the molecular and the fragment ions of n‐dodecane, n‐dodecane‐1, 12‐[13C2] and n‐dodecane‐1,1,1,12,12,12‐[2H6] studied with special emphasis on metastable decompositions. It is shown that the elimination of alkane molecules and alkyl radicals from the n‐dodecane molecular ion occurs primarily by simple splitting of the CC bond. In addition, both small alkane molecule and alkyl radicals are eliminated with low probability from centreal parts of the molecular ion. The alkane elimination is less specific than the alkyl elimination. The methyl elimination shows an exceptionally high non‐specificity, but is of negligible abundance in the 70 e V electron impact spectrum. The metastable ion spectra suggest, but do not prove unambiguously, that those small alkyl ions (with up to four carbon atoms) originating directly from the molecular ion, may be formed both by direct cleavage of the terminal groups and from central parts of the molecular ion. However, the majority of the small alkyl fragment ions in the 70 eV spectrum are formed by secondary decomposition explaining their apparent non‐specific formation. The strikingly different fragmentation behaviour of even electron, [CnH2n+1]+, and odd electron magnified image fragment ions, results from differences in the product stabilities. Using collisional activation and metastable ion spectra it is shown that the odd electron fragments have the structure of the linear alkene (most probably the 1‐alkene) molecular ion. In contrast to the molecular ions, alkyl fragment ions decompose with complicated skeletal rearrangements, which lead to substantial, but not complete, carbon randomization. The terminal hydrogen atoms, however, show little scrambling.
Field desorption of electrolytic solutions using untreated wire emitters
Authors: Heinen H. J. , Giessmann U. , Röllgen F. W.
Published: May 2005

Simple untreated wire emitters can be used for field desorption of electrolytic solutions, e.g. acids or substances containing alkali salts. The ionization is achieved by the attachment of protons or alkali ions to molecules in the condensed phase which are subsequently desolvated by the action of high electric fields. This field desorption mode is demonstrated and discussed for a few characteristic examples. It is shown that the addition of substances of high viscosity and low vapour pressure in the liquid state favours the field desorption behaviour of many compunds. In general the mass spectra of untreated wires are less complicated than those of activated emitters since field ionization processes occurring at the tip of the field‐enhancing microneedles are avoided.
Massenspektrometrische Fragmentierung von Metallkomplexen des Tropolons
Authors: Grotjahn L. , Krüger P.
Published: May 2005

Die Fragmentierung der Metallkomplexe von Tropolonen ist entscheidend vom Metallatom beeinflußt. Im Unterschied zum freien Liganden wird die Eliminierung von Kohlenmonoxid stark zurückgedrängt. Die Bildung von metalltreien Fragmentionen sowie die außergewöhnliche Wasserabspaltung der Cu‐Verbindung werden beschrieben.
Dehydration reactions in the mass spectra of 13‐podocarpen‐12‐ols and 12‐podocarpen‐14‐ols
Authors: Wahlberg Inger , Enzell Curt R.
Published: May 2005

Electron impact induced dehydration of allylic cyclohexenols has been examined using 13‐podocarpen‐12‐ols and 12‐podocarpen‐14‐ols as model compounds. Deuterium labelling shows that ring cleavage prior to elimination of water is the principal dehydration route, whereas transannular 1,3 and 1,4 reactions account for only minor portions of the [M−18]+⋅ and [M−33]+ ion currents.
Mass spectra and energetic data for the formation of the [MCH3]+ ion of 10,10‐dimethylphenylthio‐silyn, ‐germyn and ‐stannyn derivatives, and of 9,9‐dimethyl‐thioxantene
Authors: Innorta G. , Torroni S. , Distefano G. , Pietropaolo D. , Ricci A.
Published: May 2005

The formation of the [M  CH3]+ ion from 10,10‐dimethylphenylthio‐silyn, ‐germyn and ‐stannyn derivatives as well as 9,9‐dimethylthioxantene with the aid of appearance and ionization potential measurements.
Effects of pressure on ion‐molecule reactions in the chemical ionization mass spectrometry of carboxylic acids
Authors: Grønneberg Truls
Published: May 2005

The water elimination caused by bifunctional interaction in protonated dicarboxylic acids diminishes as sample pressure increases. This appears to be the result of stabilization of the protonated dixarboxylic acid by reversible formation of a protonted dimmer. The effect reaches a minimum for dicarboxylic acid with interfunctional chain length of 6–9 carbons where the free energy of activation probably also reaches a minimum. Self‐acetylation by water elimination from protonated dimers was observed for the monocarboxylic acids only.
Mass spectra of trimethylsilyl Di‐O‐methyloximes of aldosuloses and dialdoses
Authors: Dizdaroglu Miral , Henneberg Dieter , Sonntag Clemens Von , Schuchmann Man Nien
Published: May 2005

Aldosuloses and dialdoses are readily converted to the corresponding acyclic methyloxime trimethylsilyl derivatives which give characteristic mass spectra. The gas chromatography mass spectrometry coupling technique also allows trace analysis since full information can be derived from the most intense fragment ions of the mass spectra which mainly arise from fragmentations β and δ to the O‐methyloxime group.
Mass spectrometry of steroid systems. XXIV–The origin of [M – 28]+ and [M – 43]+ ions in equilenin and its 14β‐isomer
Authors: Zaretskii Ze'ev V. I.
Published: May 2005

The formation of the [M43]+ ion in equilenin is due mainly to elimination of Me radical from the [MCO]+ ion and, to a lesser extent, to CO loss from the [MMe]+ ion. In 14β‐isoequilenin the [MCO]+ ion is absent, and the formation of [M43]+ occurs via the [MMe]+ ion. This makes the determination of the mode of junction of the rings C and D in the equilenin series possible, using high resolution mass spectra, even when only one stereoisomer is available.
Mass spectra of o‐aminobenzophenones
Authors: Nudelman N. Sbarbati , Waisbaum R. G.
Published: May 2005

The electron impact induced fragmentation of chlorine substituted o‐aminobenzophenones has been examined. All the compounds show ions formed by α‐cleavage on either side of the carbonyl group. The relative intensity of the resulting ions is predictable from the quasi‐equilibrium theory. The most important features of the mass spectra of these compounds are, however, intense [MH]+ ions for the primary amines and [M – OH]+ ions for the N‐methylated compounds. These and other less intense peaks as well as some metastable ions allows structural elucidation.
Fragmentation sous l'Impact Electronique de Bitriazoles‐5(3),1′ et de Bitriazoles‐4,4′
Authors: Aouial Mohamed , Bernardini Antoine , Viallefont Philippe
Published: May 2005

Les spectres de masse d'un certain nombre de bitriazoles‐5(3),1′ et bitriazoles‐4,4′ sont décrits: les principales fragmentations sont données et leur utilité à la détermination des structures de composés isomères est montrée. Des dégradations spécifiques sont également observées à partir du groupement triazolyle en position 4.
Mass spectra of tetraselenafulvalenes, diselenadithiafulvalenes and tetrathiafulvalenes
Authors: Andersen Jan R. , Egsgaard Helge , Larsen Elfinn , Bechgaard Klaus , Engler Edward M.
Published: May 2005

The mass spectra of 13 heterofulvalenes are reported. The spectra show great similarities within the selenium and within the sulphur series. The main difference between the selenium and the sulphur compounds results from the more facile loss of selenium compared with sulphur, and from the first fragmentation of the molecular ion, as the selenium fulvalenes lose an alkyne molecule, whereas the sulphur fulvalenes first lose an (SĊR) radical. An important feature of the spectra of the simple heterofulvalenes is the formation of a rearrangement ion by migration of a heteroatom. The mechanism was elucidated by 13C labelling and is discussed in detail.
Fragmentation en Spectrométrie de Masse D'Imidazobenzodiazépines
Authors: Geneste Patrick , Kamenka Jean‐Marc , Vidal Yves
Published: May 2005

L'étude des benzodiazépines a fait apparaǐtre des modes de fragmentations différents pour les imidazo[4,5,1‐jk]benzodiazépines‐1,4 et les imidazo[1,5,4‐ef]benzodiazépines‐1,5. Les ruptures caractéristiques dans ces deux séries ont été identifiées. Elles mettent en évidence l'influence de la nature du cycle diazépine sur les processus caractéristiques de fragmentation et rendent possible l'identification et la différenciation des structures isomères.
On the fragmentation of stereoisomeric substituted cyclohexylamines under electron impact. Comparison with corresponding alcohols and ethers
Authors: Weissdorf Miriam , Sharvit Joseph , Mandelbaum Asher
Published: May 2005

The stereospecific elimination of H2O and CH3OH from substituted cyclohexanols and their methyl ethers upon electron impact is not reproduced in the corresponding amines. Ring cleavage α to the amino group is responsible for the non‐stereospecific formation of the most abundant fragments in the amines.
The elimination of metal(I) hydride in the mass spectra of some metal(II) compounds
Authors: Lacey Michael J. , Macdonald Colin G. , Shannon James S.
Published: May 2005

Metal(I) hydrides are eliminated as neutral species in the electron impact ionization mass spectra of copper(II) and palladium(II) complexes of ethylene‐N,N′‐3‐benzoylprop‐2‐en‐2‐amine. Deuterium labelling shows that the hydrogen atom of the metal(I) hydride is derived predominantly from the ethylene bridge both for ion source reactions and for metastable ion transitions. Evidence supporting the proposed rationalization for elimination of metal(I) hydride is provided by the observation of an analogous reaction in the mass spectrum of (ethylene‐N,N′‐salicylaldiminato)copper(II). The mass spectrum of ethylene‐d4‐N,N′‐3‐benzoylprop‐2‐en‐2‐amine shows an unusual rearrangement to give [C7H5D2]+ ions involving a formal phenyl‐to‐methylene transfer.
Etude en Spectrométrie de Masse. IX—Fragmentation de Cyclopropanes Dicarboxylate de Méthyle‐1,2 cis et trans Diversement Substitués, et des Homologues Cyclobutaniques, Cyclopentaniques et Cyclohexaniques non Substitués
Authors: Cambon Aimé , Rouvier Emile
Published: May 2005

L'étude des spectres de masse de divers cyclopropanes dicarboxylate de méthyle‐1,2 cis et trans, diversement substitués sur les carbones 1,2 et 3, a montré que tous ces composés avaient un comportement identique sous l'impact électronique. Dans tous les cas c'est la rupture du cycle qui conduit aux principaux fragments. Nous avons ensuite comparé les diesters cyclopropaniques non substitués aux homologues cyclobutaniques, cyclopentaniques et cyclohexaniques, afin d'analyser le degré de transmission des effets électroniques des différents cycles.
The mass spectra of some 2‐ and 4‐pyridylethylamines
Authors: Czuba W. , Rutkowski K. , Kowalski P.
Published: May 2005

The mass spectra of some N,N‐disubstituted 2‐aminoethylpyridines are reported and their principle fragmentation routes analysed.
Electron impact studies on α,β‐unsaturated carbonyl oximes
Authors: Kallury R. Krishna Mohan Rao , Loudon Alexander G. , Maccoll Allan
Published: May 2005

Electron impact studies on eight α,β‐unsaturated carbonyl oximes revealed many interesting hydrogen and skeletal rearrangements which were substantiated by deuterium labelling, exact mass measurements and metastable studies. Loss of H· and OH· as well as formation of the indenyl and fluorenyl cations and the [C9H6N]+ fragment proceed through cyclic intermediates. All the ionized oximes undergo a Beckmann rearrangement in the gaseous phase leading to intense aroyl cation peaks. Formation of the styrene radical ions and cleavage of the bond α to the oxime function have also been noticed.
Rearrangements and fragmentations of [C2H5S]+ ions
Authors: Broer W. J. , Weringa W. D.
Published: May 2005

[C2H5S]+ ions (m/e 61) with different initial structures were generated in the mass spectrometer from twelve precursor ions. Abundance ratios of competing metastable ion decompositions were used to determine whether these ions decompose through the same or different reaction channels. It was concluded that all [C2H5S]+ ions isomerize to a common structure or mixture of structures prior to decomposition in the first field free region. From 13C labelling experiments it was concluded that [C2H5S]+ ions generated from the molecular ions of 2‐propanethiol‐2‐[13C], partially rearrange to a symmetrical structure before decomposition to [CHS]+ and CH4, whereas in [C2H5S]+ ions generated from the the molecular ions of 1,2‐bis‐(thiomethoxy‐[13C]) ethane, the two carbon atoms become fully equivalent before CH4 loss occurs.
Die massenspektrometrische Fragmentierung von Neopentylpolyolestern. 1—Pentaerythrittetrafettsäureester
Authors: Zeman Alfred , Bartl Peter , Schaaff Albert
Published: May 2005

Die Fragmentierung der homologen Fettsäuretetraester des Pentaerythrits (C‐2 bis C‐14) bei Elektronenbeschuß wurde untersucht. Hauptspaltfragmente entstehen durch [MRCOO]+ und [MRCOOH]+. Diese Ionen liegen vermutlich als cyclische Acetale vor. Der weitere Zerfall dieser lonen wird anhand von DADI‐Messungen und Massenfeinbestimmungen geklärt. Ester verzweigter Fettsäuren können anhand charakteristischer Ionen von solchen aus n‐Fettsäuren unterschieden werden. Die massenspektrometrische Identifizierung von isomeren n‐ Fettsäureestern, die gaschromatographisch nicht aufgetrennt werden können, ist ebenfalls möglich.
Negative ion mass spectra of salicylaldehydato and 2‐hydroxy‐1‐naphthylaldehydato complexes of Co(II), Ni(II) and Cu(II): Consecutive and competitive eliminations of CO and H2CO
Authors: Hirata Yukio , Matsumoto Kozo , Takeuchi Tsugio
Published: May 2005

The negative ion mass spectra of some divalent metal complexes, ML2, have been measured, where MCo, Ni and Cu, and LH = salicylaldehyde or 2‐hydroxy‐1‐naphthylaldehyde. All compounds yield intense molecular anions. The mass spectra of these compounds suggest that consecutive and competitive eliminations of CO and H2CO, and various types of hydrogen migrations are involved in the fragmentation of the molecular anions. The mechanism of the fragmentation process and metastable peaks observed are also discussed.
The mass spectra of some 1H‐imidazo[1,2‐a]pyrrolo[3,2‐e]pyridines
Authors: Bancroft Keith C. C. , Brown Kevan , Ward Terence J.
Published: May 2005

We report here the mass spectral fragmentations of some derivatives of a new heterocyclic system 1H‐imidazo[1,2‐a]pyrrolo[3,2‐e]pyridine. These compounds combine structural features of 1H‐pyrrolo[2,3‐b]pyridines and imidazo[1,2‐a]pyridines, but follow fragmentation pathways similar to the former.
Elimination reactions of ions in the gas phase. V—elimination of water in hydroxybornanes and related compounds
Authors: Robbiani R. , Bührer H. , Mändli H. , Kovačević D. , Fraefel A. , Seibl J.
Published: May 2005

Results of an investigation of deuterium labelled methylated norborneols and dihydrocarveols are presented to show that the 1,2 elimination of water in borneol and isoborneol is triggered by an initial ring cleavage reaction. Other eliminations of water in borneol and isoborneol are elucidated by specific and stereospecific deuterium labelling in different positions.
Stereospecific elimination of acetic acid in 3‐ and 4‐arylcyclohexyl acetates under electron impact
Authors: Sharvit Joseph , Mandelbaum Asher
Published: May 2005

The elimination of CH3COOH from the molecular ions of trans‐3‐ and 4‐arylcyclohexyl acetates takes place to a greater extent than in the cis isomers. Deuterium labelling shows that the elimination involves mainly the benzylic hydrogen in the trans‐acetates, but not in the cis isomers. This behaviour is similar qualitatively to that of the corresponding alcohols and methyl ethers, but entirely different from that of t‐butylcyclohexyl acetates, which do not exhibit any stereospecificity. Substituent effects on the elimination for both cis and trans isomers are discussed.
Mass spectra of some 4,5‐dihydroimidazole derivatives
Authors: Gioia Bruno , Citerio Luisa , Stradi Riccardo
Published: May 2005

The mass spectra of a series of 4,5‐dihydroimidazole derivatives were determined. Deuterium labelling and high resolution mass spectrometry were utilized in order to elucidate the mechanism of a number of fragmentations. The most significant ions arise from the following processes: (1) elimination of the C‐4 substituent; (2) cleavage of the 1,2‐NC and 4,5‐CC bonds with or without hydrogen migration; (3) cleavage of the 1,5‐NC and 2,3‐CN bonds with charge retention on the N‐1C‐2 moiety.

In this paper the standard numbering of the imidazole ring (see structures) is retained for the fragment ions.

Anomalous behaviour is shown by the t‐butoxy derivative; the reasons for this behaviour are discussed.
A predictive model for unimolecular reactions of organic ions
Authors: Bowen Richard D. , Stapleton B. Jane , Williams Dudley H.
Published: May 2005

The slow unimolecular dissociations of six members of the [CnH2n‐3]+ (n = 3‐8) series of unsaturated carbonium ions are explained in terms of a potential surface approach together with some concepts of mechanistic organic chemistry. The occurrence of some dissociations is shown to be precluded because either the reacting configurations or product combinations are inaccessible at energies appropriate to metastable transitions. The approach permits correct predictions to be made concerning the shapes of metastable peaks for dissociations which occur without σ‐bond formation in the final step. In particular, the observation of a composite peak, thus indicating two channels for reaction, for C2H4 loss from [C7H11]+ is naturally accommodated.
Complete isomerization of the molecular ion of 1,3,5‐trimethyl‐2,4,6‐trithian to that of 3,5,6‐trimethyl‐1,2,4‐trithian before decomposition in the gas phase
Authors: Wolkoff Peder , Holmes John L.
Published: May 2005

The complete isomerization of the molecular ion of r‐2‐deuterio‐2, cis‐4,cis‐6‐trimethyl‐1,3,5‐trithian into equal proportions of 3, 5‐ and 6‐d1‐3,5,6‐trimethyl‐1,2,4‐trithian molecular ions adequately accounts for all major fragmentations of the former. These fragmentations are losses of C4H8, C2H4S, S2H˙, C4H8S and C2H4S2. Similar rearrangements are proposed for other 1,3,5‐trithans and 1,3‐dithians.
On the interconversion of o‐methoxybenzaldehyde and 2,3‐ dihydrobenzofuran‐3‐ol molecular ions
Authors: Florêncio Helena , Heerma Wigger
Published: May 2005

Kinetic energy release measurements show that the similar primary fragmentation reactions in o‐methoxybenzaldehyde and 2,3 dihydrobenzofuran‐3‐ol occur from common ion structures.
Umlagerungen Schiffscher Basen
Authors: Holzmann G. , Rothkopf H. W. , Wöhrle D.
Published: May 2005

Die elektronenstoßinduzierten Zerfälle Schiffscher Basen des DMD (Diaminomaleinsäuredinitril) werden durch Cyclisierungsreaktionen der Aminogruppe des DMD‐Restes mit der Azomethingruppierung beherrscht. Die innerhalb der Zerfallsprozesse gebildeten Imidazolsysteme werden durch MI‐ und CA‐ Spektren unter positiven und negativen Ionisierungsbedingungen sowie durch Vergleich des kinetic energy release unter Hinzuziehung von Modellionen bewiesen. Deuterierungsexperimente zeigen, daß die für Anile charakteristische HCN‐Eliminierung nicht unter Angriff der Azomethingruppierung sondern ausschließlich über den DMD‐ Rest ablaüft.
Mass spectra of a series of 2‐p‐substituted phenyl‐1,3,2‐dioxaborolanes
Authors: Kaminski James J. , Lyle Robert E.
Published: May 2005

The mass spectra of a series of 2‐p‐substituted phenyl‐1,3,2‐dioxaborolanes have been examined and compared with the mass spectrum of 2‐phenyl‐1,3,2‐dioxaborolane. Formation of the substituted ion [C7H6X]+ by electron impact induced rearrangement has been found to be influenced significantly by the presence and nature of the substituent at the para position of the phenyl ring.
Collisional activation spectra of [M + Li]+, [M + Na]+ and [M + K]+ ions formed by field desorption of some monosaccharides
Authors: Röllgen F. W. , Giessmann U. , Borchers F. , Levsen K.
Published: May 2005

The collisional activation spectra of monosaccharide ions formed by [Li]+, [Na]+ and [K]+ ion attachment under field desorption conditions are reported. It is shown that the elimination of the alkali ions is determined by the alkali ion affinities of the molecules (M) and competes with a fragmentation of M which is almost independent of the alkali ion attached. Correspondingly the alkali ion is predominantly retained in the fragment ions. The usefulness of this method for the differentiation of underivatized isomers is demonstrated.
A photoionization study of the [C7H8]\documentclass{article}\pagestyle{empty}\begin{document}$\mathop +\limits_.$\end{document} ion formed from some monosubstituted alkyl benzenes
Authors: McLoughlin R. G. , Morrison J. D. , Traeger J. C.
Published: May 2005

Appearance potentials for the [C7H8]\documentclass{article}\pagestyle{empty}\begin{document}$\mathop +\limits_.$\end{document}ion produced in the fragmentation of n‐butyl benzene, iso‐butyl benzene and n‐pentyl benzene have been measured by photon impact. The results indicate that, at threshold, the fragment ion has the toluene molecular ion structure.
Artifact peaks in linked electrostatic and magnetic field scans of double focusing mass spectrometers of conventional Nier–Johnson geometry
Authors: Bilton J. N. , Kyriakidis N. , Waight E. S.
Published: May 2005

Broad peaks of non‐integral mass in daughter ion spectra obtained by linked scans of double focusing mass spectrometers of conventional Nier‐Johnson geometry are shown to arise from transitions of higher mass ions in the first field free region.
The behaviour of beryllium μ4‐oxo‐μ‐carboxylates under electron impact
Authors: Nekrasov Yurii S. , Sil'vestrova Svetlana Yu. , Grigo'ev Aleksandr I. , Reshetova Lyudmila N. , Sipachev Viktor A.
Published: May 2005

The electron impact mass spectra of eight polynuclear beryllium complexes Be4O(RCO2)6 (RH, CH3, C2H5) and Be4O(RCO2)5OR′ (RCH3, R′H, CH3, C2H5, C3H7; RC2H5, R′C2H5) are reported. The major fragmentations involve the elimination of (RCO)2O (RCOOR′) or Be(RCO2)2 (Be(RCO2)OR′) from the ions [ML]+ and of {(RH)CO}, (R′H), H2O and BeO from the lighter ions. The fragmentation patterns are practically independent of the organic groups present and can be rationalized by stereochemical considerations.
Computerunterstützte Identifizierung von Isotopenmustern in niederaufgelösten Massenspektren
Authors: Kwiatkowski J.
Published: May 2005

Zur Identifizierung von Isotopenmustern in niederaufgelösten Massenspektren wird ein Computerprogramm beschrieben. Die mit dern Isotopenmusten übereinstimmenden Massen des Massenspektrums werden erkannt und ausgedruckt. Eine Ziffer gibt den Grad der Übereinstimmung des berechneten mit dem gemessenen Isotopenmuster an. Das Programm ist in FORTRAN IV geschrieben und kann auch auf kleineren Rechenanlagen ausgeführt werden.
Nitrile elimination and hydrogen rearrangement upon electron impact in schiff base peptide esters
Authors: Jayasimhulu K. , Day R. A.
Published: May 2005

A series of Schiff base peptide esters were examined by gas chromatography mass spectrometry. Electron impact induced elimination of aryl nitriles (ArCN) from Schiff bases magnified image, where R, R′ …are amino acid sidechains formed from aromatic aldehydes and peptide esters was shown to be associated with formation of C‐terminal peptide fragments. Schiff base derivatives prepared from benzaldehyde and α‐deuterobenzaldehyde with several peptide esters indicated that aryl nitrile elimination was accompanied by H(D) transfer to the α‐C of the N‐terminal amino acid residue. Of the many Schiff base peptide esters of different aldehydes studied, HCN elimination of the type observed in some nonpeptide Schiff bases could only be found among N‐methyl pyrrolemethylidene derivatives.
Competing ring cleavages in substituted 4‐arylcyclohexanols and their methyl ethers under electron impact
Authors: Sharvit Joseph , Mandelbaum Asher
Published: May 2005

Ring cleavage α to the oxygen function leads to [C3H5O]+ and [C4H7O]+ ions in the mass spectra of 4‐arylcyclohexanols and their methyl ethers, respectively. Cleavage α to the aryl group gives rise to [C3H7O]+ (from the alcohols), [C4H9O]+ (from the ethers) and [ArC3H4]+ (from both) ions. The competition between the two ring cleavages explains the effect of the substituents of the aryl groups on the relative abundances of the resulting ions.
Mass spectrometry of transition–metal π‐complexes. V—fragmentation and structure of chromium‐coordinated ions
Authors: Davis R. , Ojo I. A. , Webb M. L.
Published: May 2005

Mass spectrometric studies have been made of the [(C7H8)Cr]+ ions generated from (η6‐PhCH3)Cr(CO)3 and (η6‐c‐C7H8)Cr(CO)3. Fragmentation behaviour and appearance potential measurements have been used to show that the ions from the two precursors do not achieve a common structure. [(C8H10)Cr]+ generated from (η6‐PhEt)Cr(CO)3 and (η6‐c‐C7H7Me)Cr(CO)3 behave similarly. A study of the α‐d3 toluene complex suggests the structure [CH3C6H4–CrH]+ is appropriate for [C7H8Cr]+ ions generated from (η6‐PhMe)Cr(CO)3 and decomposing to [CrH]+.
Kinetic shift in some para‐substituted acetophenones
Authors: Helal A. I. , Zahran Nagwa F.
Published: May 2005

An Atlas CH4 mass spectrometer has been used in conjunction with the electron ‘Energy Distribution Difference’ technique to investigate the kinetic shift associated with the process of elimination of CH3 from acetophenone, p‐methylacetophenone, p‐chloroacetophenone, p‐fluoroacetophenone and p‐methoxy‐acetophenone. The heats of formation of the ions investigated have been calculated.
Spectrométrie de Masse d'Hétérocycles Azotés. VIII–Comportement sous l'Impact Electronique de Nitroarylazoles
Authors: Atmani Aziz , Aubagnac Jean‐Louis
Published: May 2005

Les spectres de masse des nitrophénylimidazoles et des nitrophénylpyrazoles sont étudiés afin d'apprécier l'influence de l'effet de voisinage ortho‐ortho′ sur la fragmentation. Cet effet conduit à des processus spécifiques pour les composés qui ont un groupement nitro en ortho de l'hétérocycle. L'examen des dérivés deutériés permet de confirmer ces processus par la mise en évidence d'un effet isotopique et d'établir dans le cas des o‐nitroimidazoles que le proton H‐2 adjacent aux deux atomes d'azote est concerné dans le départ de OH. La fragmentation de chaque composé est spécifique et son étude peut éventuellement constituer un moyen adéquat pour connaître la structure.
1,3‐Dioxolanylium‐ und 1,3‐Dioxanylium‐Derivate via Protonenkatalysierte SNi‐Reaktionen in der Gasphase
Authors: Respondek J. , Schwarz H. , Van Gaever F. , Van de Sande C. C.
Published: May 2005

1,3‐Dioxolanylium‐ und 1,3‐Dioxanylium‐Ionen sind in der Gasphase durch protonenkatalysierte, SNi‐assistierte Heterolysen unter den Bedingungen der Chemischen Ionisation zugänglich. Konstitutionelle und konfigurative Effekte werden diskutiert und mit den Ergebnissen der Heterolyse in kondensierter Phase verglichen. Es wird ferner gezeigt, daß die unimolekulare Eliminierung von HX (X = Br, OAc) aus vicinal disubstituierten [MH]+‐Ionen nicht durch die Protonenaffinität der eliminierten Neutralteile bestimmt wird, so wie es bei monofunktionellen Verbindungen der Fall ist.
Identifikation der Partialstrukturen von unbekannten Steroiden mit einer Schlüsselionenkartei und einem rechnerunterstützten Retrieval‐System
Authors: Spiteller G. , Spiteller Margot , Ende M. , Hoyer G.‐A.
Published: May 2005

Die Anwesenheit eines Strukturelementes verursacht oft die Bildung einer Folge von Schlüsselionen, die in threr Gesamtheit von hoher struktureller Spezifität sind. Auf dieser Basis wurde für Steroide ein rechnerunterstütztes Suchsystem geschaffen, das die Bestimmung von Teilstrukturen in unbekannten Verbindungen ermöglicht.
Hydrogen transfer in the retro Diels‐Alder fragmentation of oxygen‐containing heterocyclic Compounds. I—chromanones and 4‐hydroxychromans
Authors: Eguchi Shizuko
Published: May 2005

The mass spectra of 2,2‐dimethylchromanones and 2,2‐dimethyl‐4‐hydroxychromans show peaks corresponding to the ions formed by the retro Diels‐Alder reaction with or without hydrogen transfer to the ion. The hydroxychromans also show peaks corresponding to an ion formed by the loss of hydrogen from the ion formed by the retro Diels‐Alder reaction. Deuterium labelling showed that the hydrogen transferred in the chromanones arises from the gem‐dimethyl groups on C‐2, and the hydrogen atom lost in the case of the hydroxychromans is from C‐4, the carbinyl carbon.
On the mechanism of isomerization in the esters of some α,β‐unsaturated carboxylic acids—II
Authors: Burgers Peter C. , Terlouw Johan K. , Vijfhuizen Peter C.
Published: May 2005

The effect of a phenyl group on the mechanisms of isomerization in the ionized methyl esters of simple α,β‐unsaturated acids (methyl acrylate and related compounds) has been investigated with the aid of deuterium labelling as well as information from mass analysed ion kinetic energy spectra and first field free region metastable peak shapes. Substitution of a hydrogen atom of the OCH3 group by a phenyl group (benzyl acrylate and homologues) greatly enhances the rate of [ester] → [acid] isomerizations (loss of H2O and COOH˙). It is inferred that this is due to an accelerating effect of the phenyl group on the first and the third steps (ring opening of the key intermediate ion which has the structure of the ionized enol form of γ‐butyrolactone) of the reaction whose mechanism is basically the same as that in methyl acrylate. A phenyl group present at the α‐ or β‐position of the vinylic double bond appears to suppress the [ester] → [acid] isomerization in some compounds by promoting other reactions or opening up a new reaction pathway, i.e. the loss of CH2O from ionized methyl atropate for which mechanisms are proposed.
Effects of annulation on the mass spectral behaviour of bicyclo[4.3.0]‐3‐nonene derivatives: Keto esters and ketones
Authors: Tureček F. , Hanuš V.
Published: May 2005

The fragmentation patterns of the title compounds are shown to depend on the nature of the ring annulation. On ionization the cis‐annulated isomers lose a molecule of benzene in contrast to the corresponding trans isomers which do not. A mechanism involving a participation of the π‐electron system in the cleavage of the 5‐membered ring is suggested to explain the observed differences.
Electrohydrodynamic ionization mass spectrometry of sulfonates
Authors: Lai Shook‐T. F. , Evans Charles A.
Published: May 2005

Electrohydrodynamic ionization mass spectrometry has been applied to the analysis of 2‐naphthol‐3,6‐disulfonic acid, disodium salt and 4,5‐dihydroxy‐2,7‐naphthalenedisulfonic acid, disodium salt. The negative ion mass spectra indicate ions characteristic of the sample and no fragment ions are observed. Degrees of dissociation of the sulfonates and the ion‐solvent interactions are reflected in the negative ion spectra.
Das Verhalten disubstituierter Benzole RC6H4Si(CH3)2F bei Elektronenstoß
Authors: Dube Gunther , Gey Erhard
Published: May 2005

Der elektronenstoßinduzierte Abbau von disubstituierten Benzolen RC6H4Si(CH3)2F (R  p‐N(CH3)2, p‐OCH3, p‐, m‐CH3, H, p‐, m‐Cl, p‐, m‐Br und p‐NO2) besteht hauptsächlich in der Abspaltung eines Methylradikals vom Molekülion. Die Aktivierungsenergien für diese Fragmentierung wurden bestimmt. Sowohl die Intensitäten von Molekül‐ und Fragmentpeak in den Massenspektren als auch die Aktivierungsenergien hängen vom Substituenten R ab. Die änderung der Aktivierungsenergie wird mit der Einwirkung des Substituenten auf die Ladungsverteilung in den Molekülionen erklärt. Die Aktivierungsenergien werden näherungsweise quantenchemisch nach dem Pariser‐Parr‐Pople‐Verfahren berechnet. Die erhaltenen Daten stimmen mit den experimentell ermittelten Energiewerten größenordnungsmäßig überein, und die Tendenz wird richtig wiedergegeben. Durch Intensitätsberechnungen auf der Grundlage der QET wird der Zusammenhang zwischen Aktivierungsenergie und den Peakintensitäten in den Massenspektren bestätigt.
INDO calculations on the [Be3O(HCO2)3]+ ion configuration
Authors: Sipachev Viktor A. , Gloriozov Igor' P.
Published: May 2005

SCF–MO–LCAO–INDO calculations show that the total energy of the [Be3O(HCO2)3]+ ion, which is the base peak in the mass spectra of the beryllium μ4‐oxoformato complex, depends on the deviation of the ion configuration from planarity. The planar form is shown to have the lowest energy. The results obtained confirm the suggestion that steric interactions are the major factor governing fragmentations of beryllium μ4‐oxocarboxylato complexes under electron impact.
Wasserstoffumlagerungen bei der elektronenstoßinduzierten Fragmentierung von Aminoäthern
Authors: Eckhardt Gert
Published: May 2005

Auf Grund von Wechselwirkungen der funktionellen Gruppen ist das massenspektrometrische Verhalten vieler Aminoäther des Typs RO(CH2)nNR1R2 deutlich verschieden von dem einfacher äther und Amine. Zusätzlich zu α‐Spaltungen werden häufig zwei weitere Primärfragmentierungen beobachtet, eine, die zu [M–Aldehyd]+. bzw. [M–Keton]+.‐Ionen, eine andere (bei n≥3), die zu [M–R]+‐Ionen führt. Beide Prozesse sind mit Wasserstoffumlagerungen verbunden, die mit Hilfe deuterierter Verbindungen untersucht wurden, und ihre Bedeutung ist stark abhängig von den Substituenten R, R1, R2 und der Länge der Kohlenstoffkette n zwischen den Heteroatomen. Diese Abhängigkeit kann durch die zugrundeliegenden Zerfallsmechanismen gut erklärt werden.
Spectrométrie de Masse d'Hétérocycles Azotés. IX—Structure des Ions [MCH2CO]+⋅ Formés à Partir des Ions Moléculaires d'Acétamido‐2 Benzazoles et mixage d'Hydrogěnes avant leur Fragmentation
Authors: Aubagnac Jean‐Louis , Campion Philippe
Published: May 2005

II est établi que le départ de cétěne à partir des ions molécularies de l'acétamido‐2 benzothiazole et de l'acétamido‐2 benzimidazole s'effectue suivant un mécanisme γ quatre centres pour donner l'ion amino‐2 benzazole correspondant. Pour les ions métastables γ faible énergie et é longue durée de vie, un mixage des hydrogěnes intervient avant fragmentation par départ de HNC au niveau de l'ion amino‐2 benzazole. Un mécanisme est proposé pour ce mixage.
Über quantitative Beziehungen zwischen Fragmenten und ihren relativen Intensitäten im Massenspektrometer. V—Untersuchungen an N‐t‐Alkylaminen und ‐acetamiden
Authors: Záhorszky U. I.
Published: May 2005

Die Ionenintensitätsverhältnisse aus α‐Spaltungen von N‐t‐Alkyl‐ethylaminen sind oberhalb 18 eV unabhängig von der Elektronenenergie und gehorchen in diesem Bereich dem ‘Ionenmasseneffekt’. Der Verlauf der Intensitätsverhältnisse über den gesamten Energiebereich kann durch Zusammenwirken von Auftritts‐energie‐Differenzen und Ionenmasseneffekt erklärt werden. Anhand der N‐t‐Alkyl‐acetamide wird gezeight, daß der übliche Anstieg der Intensitätsverhältnisse I(MRgroß): I(MRklein) mit zunehmender Elektronenenergie im oberen Energiebereich hauptsächlich durch den Weiterzerfall der Ionen verursacht wird. Für die Bildungstendenz der Sekundärionen wird ein Zusammenhang mit den Massen sowie offenbar mit der inneren Energie der Primärionen festgestellt. Der ‘Ionenmasseneffekt’ ist kein direkter Effekt der Ionenmassen.
Ionisation Chimique de Composés Aromatiques Nitrés
Authors: Maquestiau A. , Van Haverbeke Y. , Flammang R. , Mispreuve H. , Elguero J.
Published: May 2005

Les dissociation induites par collisions d'ions [MH‐30]+ observés lors de l'ionization chimique (méthane) de composés aromatiques nitrés indiquent que ces ions sont formés par réduction suivie de protonation et non par perte de NO⋅ des ions moléculaires protonés.
Metastable peaks of exponential shape
Authors: Hijazi Nasrat H. , Holmes John L. , Terlouw Johan K.
Published: May 2005

It is shown that a monotonically decreasing translational kinetic energy distribution predicted from the quasi‐equilibrium theory for the unimolecular fragmentation ([CH2CO]+˙→[CH2]+˙ +CO) is reflected in an exponential shape for the metastable peak in contrast to the commonly observed Gaussian type profile.
Réactions de Transposition Ionique et de Rétrocycloaddition de Dihydro‐3a, 8a Pyrazolo (3,4‐b) Indoles Sous l'Impact Electronique
Authors: Daunis Jacques , Soufiaoui Mohamed , Laude Bernard
Published: May 2005

Trois composés isomères de structures dihydro‐3a, 8a pyrazolo (3,4‐b) indole, hydrazone D'aryl indolyl cétone et triaryl‐1,3,4 pyrazole possèdent le měme spectre de masse; il est montré que celui‐ci résulte de la superposition des spectres des deux premiers composés en équilibre après ionisation. Les dihydro‐3a, 8a pyrazolo (4,3‐b) indoles résultant de la deuxième possibilité de cycloaddition, ont aussi les měmes fragmentations. Ces résultats rendent impossible le détermination par spectrométrie de masse, de la structure des produits formés lors de la réaction de cycloaddition.
The application of a new sampling technique using an atomizer for chemical ionization mass spectrometry to free amino acids, drug components, higher phthalates and oligomers of styrene and ethyleneglycol
Authors: Hirata Yukio , Takeuchi Tsugio , Tsuge Shin , Yoshida Yu
Published: May 2005

A new vacuum atomizing sample introduction device was developed and applied to take stable and reproducible chemical ionization mass spectra of various involatile compounds. As examples, chemical ionization spectra of some free amino acids, drug components in a cold medicine, higher phthalates, oligomers of styrene and ethyleneglycol, etc., are presented.
Mass spectra of some naturally occurring stictane triterpenoids and their trimethylsilyl derivatives
Authors: Holland Patrick T. , Wilkins Alistair L.
Published: May 2005

The mass spectra of ten di‐ and tri‐oxygenated stictane triterpenoids and their trimethylsilyl derivatives have been studied in detail. Gas chromatography mass spectrometry of the TMS derivatives on OV‐17 and OV‐101 columns provided useful separations and identifications of mixtures of stictanes triterpenoids in lichen extracts. The major fragmentations involve ring C, but specific cleavages in rings A, B and E are also observed which allow the substitution pattern of the skeleton to be readily determined. The formation of an intense [M – C5H11⋅]+ ion for 22α‐OTMS stictanes appears specific to their ring E configuration.
α‐Silyl ketones: A high resolution mass spectrometric study
Authors: Ho Benedict Y. K. , Dexheimer Edward M. , Spialter Leonard , Smithson Lee D.
Published: May 2005

The mass spectrometric fragmentation modes of a series of α‐silyl phenyl ketones are reported. For comparison, the fragmentation modes of the analogous silanol and α,β‐epoxysilane are also reported. Migration of phenyl moieties to silicon is common throughout the ketone series.
Metastable ion studies. XII—Molecular and fragment ion structures for isomeric C4H6O2 acids
Authors: Holmes John L. , Terlouw John K. , Vijfhuizen Peter C. , A'Campo Cor
Published: May 2005

Metastable peak characteristics, ionization and appearance energy data and isotopic labelling experiments have been applied to a study of the fragmentation behaviour of the molecular ions of the isomeric C4H6O2C acids, cis and trans‐crotonic acids, methacrylic acid, butenoic acid and cyclopropane carboxylic acid. Prior to the losses of H2O and CH3, all the metastable molecular ions rearrange to [cis‐crotonic acid]+⋅ ions. Loss of H2O, which generates a composite metastable peak, is proposed to yield vinylketene and/or cyclobutenone molecular ions. Detailed mechanisms are presented for the isomerizations of the various molecular ions and for the above fragmentations. Ionized 3‐butenoic and cyclopropane carboxylic acids display a major loss of CO from their metastable ions, a minor process in the other isomers. The metastable peaks consist of two components and these are ascribed to the formation of propen‐1‐ol and allyl alcohol as daughter ions. Some comparative data are presented for the isomeric C5H8O2 acids, tiglic acid, angelic acid and senecioic acid.
Studies in chemical ionization mass spectrometry. 2–i‐C4H10 and NO spectra of alkynes
Authors: Busker E. , Budzikiewicz H.
Published: May 2005

The position of the triple bond of n‐alkynes can be determined by the analysis of the relative abundance of the CnH2n−1 ions in the chemical ionization (i‐butane) spectra. However, chemical ionization (NO) spectra where both hydrocarbon and NO‐containing ions are formed in a characteristic manner are more reliable for this purpose. The limitations of the fragmentation rules established earlier for electron impact spectra of alkynes were investigated by examination of additional examples.
Electron impact fragmentation of 2‐arylhydrazonopropandioic acid derivatives
Authors: Kallury R. Krishna Mohan Rao , Loudon Alexander G.
Published: May 2005

Examination of the mass spectra of eleven 2‐arylhydrazonopropandioic acid derivatives reveals that a radical ion which is tentatively formulated as a 1H‐diazirine species is produced in each case (except for the diphenyl este) by more than one process. Formation of what is formally the aryl amine radical ion occurs by a novel hydrogen rearrangement. Simple cleavage of the bonds β to either the aromatic ring or the CN moiety also produces abundant ions. The diphenyl ester behaves anomalously yielding the phenol ion instead of the amine. The proposed mechanisms were confirmed by metastable studies, deuterium labelling and exact mass measurements.
The origins of the base peak in the electron impact spectrum of limonene
Authors: Harris Debi , McKinnon Stewart , Boyd Robert K.
Published: May 2005

The origins and nature of the [C5H8]+⋅ ions which form the base peak in the electron impact spectrum of limonene, at nominal electron energies greater than 11 eV, have been investigated. Linked scan techniques were used to study unimolecular and collision induced fragmentation reactions. No fragmentation pathway leading to [C5H8]+⋅ could be found. Measurement of ionization efficiency curves indicated that the threshold for formation of C5H8[+⋅] lies above the range of internal energies deposited in incident ions by collisional activation. By a combination of comparisons of collisionally activated spectra and energetic considerations, the [C5H8]+⋅ ions formed from limonene were shown to resemble those of the molecular ion of isoprene, while the neutral fragment is most likely isoprene also. Deuterium labelling experiments yielded evidence of extensive scrambling prior to fragmentation. The most probable mechanism of formation of [C5H8]+⋅ appears to involve a retro Diels–Alder reaction of a structurally intact molecular ion of limonene.
The determination of steric purity of amines and amino acids by gas chromatography and mass spectrometry
Authors: Wiecek C. , Halpern B. , Sargeson A. M. , Duffield A. M.
Published: May 2005

Amines and amino acids have been condensed with a mixture of N‐TFA‐R‐prolyl chloride and n‐TFA‐S‐[1‐2H]‐prolyl chloride and the resulting four diastereoisomers have been separated by gas chromatography into two peaks. The amount of each diastereoisomer formed was then determined by chemical ionization mass spectrometry. The steric purity of the enantiomeric mixture can be calculated from these values. The method is not dependent on the diastereoisomer formation going to completion.
Molecular ion rearrangements of benzenesulfonylhydrazides
Authors: Kascheres Concetta , Bravo Ruiess Van Fossen
Published: May 2005

The mass spectra of a series of substituted benzenesulfonylhydrazides are discussed. The main fragmentation mode of these compounds corresponds to rearrangement of the molecular ion with subsequent loss of N2H˙ and/or N2H2. These fragmentations are confirmed by mass analysed ion kinetic energy spectra. Simple cleavage of the SN bond with retention of the charge on nitrogen is observed for all the hydrazides studied but is favoured by electron withdrawing substituents. This latter fragmentation could not be confirmed by mass analysed ion kinetic energy spectra as it is probably very rapid and occurs mainly in the source.
Hydrogen transfer in the retro diels–alder fragmentation of oxygen‐containing heterocyclic compounds. II—Chromones
Authors: Eguchi Shizuko
Published: May 2005

Mass Spectra of unsubstituted, 2‐methyl‐, 3‐methyl and 2,3‐dimethylchromones were examined. These compounds showed [RDA]+˙ and [RDA + H]+ ions as characteristc ions, together with [MH]+,[MCO]+˙,[MCHO]+ and [RDACO]+˙ ions. Based on deuterium labelling experiments and measurement of metastable peaks by the ion kinetic energy defocusing technique, the origin of transferred hydrogen in the [RDA + H]+ ion was clarified. The mechanism of the [RDA + H]+ ion formation is discussed.
Metastable [C4H8O]+˙ ions: Additional decompositions via the [2‐butanone]+˙ ion
Authors: McAdoo David J. , Hudson Charles E. , Witiak Dennis N.
Published: May 2005

The losses of methyl and ethyl through the intermediacy of the [2‐butanone]+˙ ion are shown to be the dominant metastable decomposition of 14 of 19 [C4H8O]+˙ ions examined. The ions that decompose via the [2‐butanone]+˙ structure include ionized aldehydes, unsaturated and cyclic alcohols and enolic ions. [Cyclic ether]+˙ [cyclopropylmethanol]+˙ and [2‐methyl‐1‐propen‐1‐ol]+˙ ions do not decompose through ionized 2‐butanone. The rearrangements of various [C4H8O]+˙ ions the the 2‐butanone ion were investigated by means of deuterium labeling. Those pathways involve up to eight steps. Ions with the oxygen on the end carbon rearrange to a common structure or mixture of structures. Those ions which ultimately rearrange to the [2‐butanone]+˙ ion then undergo oxygen shifts from the terminal to the second and third carbons at about equal rates. However, this oxygen shift does not precede the losses of water and ethylene. Losses of water and ethylene were unimportant for ions with the oxygen initially on the second carbon. Ionized n‐butanal and cyclobutanol, but not other [C4H8O]+˙ ions, undergo reversible hydrogen exchange between the oxygen and the terminal carbon. Rearrangement of ionized n‐butanal to the [cyclobutanol]+˙ ion is postulated.
A mass spectral study of 1‐(aryldimethylsilyl)‐2‐propanones and their isomeric 2‐(aryldimethylsiloxy)‐1‐propenes
Authors: Tsai Robert S.‐C. , Larson Gerald L. , Oliva Alfonso
Published: May 2005

The mass spectra of a series of β‐ketosilanes, p‐YC6H4Me2SiCH2C(O)Me and their isomeric silyl enol ethers, p‐YC6H4Me2SiOC(CH3)CH2, where Y = H, Me, MeO, Cl, F and CF3, have been recorded. The fragmentation patterns for the β‐ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [MMe·]+, [MC6H4Y·]+, [MMe2SiO]+˙, [MC3H4]+˙, [MHCCCF3]+˙, [Me2SiOH]+˙ and [C3H6O]+˙ Apparently, upon electron bombardment the β‐ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [MMe2SiO]+˙ and [Me2SiOH]+˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.
Effects of annulation on the mass spectral behaviour of bicyclo[4.3.0]‐3‐nonene derivatives: Alkoxy esters
Authors: Tureček F. , Hanuš V.
Published: May 2005

Fragmentation of ethyl(18‐alkoxybicyclo[4.3.0]‐3‐nonene‐7‐carboxylates) was found to depend on the annulation of the rings. Following ionization, the cis‐annulated isomers lose alcohol and benzene, while the trans‐isomers fragment by other reaction paths. The regiospecificity of alcohol elimination from both the ester and the ether groups was determined by using deuterium‐labelled analogues. A mechanism is discussed which rationalizes the differences observed in the spectra of the annulation isomers.