bluuebunny/crossref_metadata_2025 huggingface dataset:
On the formation of artefact peaks in linked scans of the magnet and electric sector fields in a mass spectrometer
Authors: Morgan R. P. , Porter C. J. , Beynon J. H.
Published: May 2005

The apperrance of peaks at non‐integral masses in linked scans, where the ratio B/E is kept constant, is shown to be caused by fragmentations of metastable ions occuring in the region between the magnetic and electric sectors. A formula is given for calculating the mass of the parent metastable ion and that of its daughter ion.
Studies in negative ion mass spectrometry. VIII—Electron capture by some monomeric and dimeric η5—cylcopentadienyl transition metal carbonyls
Authors: Blake M. R. , Garnett J. L. , Gregor I. K. , Wild S. B.
Published: May 2005

The negative ion mass spectra of a series of monomeric and dimeric η5‐cyclopentadienyl transition metal carbonyls have been examined. The base peak in the case of the monomeric compounds (η5‐C5H5)V(CO)4, (η5‐C5H5)Mn(CO)3 and (η5‐CH3C5H4)Mn(CO)3 arises from a reductive decarbonylation of the parent molecule—the resulting radical anion [M–CO]− is formally isoelectronic with the molecular cations [M]− observed in the positive ion mass spectra of these compounds and subsequently undergoes successive decarbonylations to the ‘aromatic’ cyclopentadienyl anions. For the compound (η5‐C5H5)Co(CO)2, however, a molecular anion was observed as the base peak which has been formulated as [(η3‐C5H5)Co(CO)2]− in the light of considerations based on the rare gas rule. As expected, the dimeric molecules [(η5‐C5H5)M(CO)3]2 (where M = Cr or Mo) and [(η5‐C5H5)Fe(CO)2]2 (and its methyl analogue) undergo reductive cleavage of their metal‐metal bonds to give the anions [(η5‐C5H5)M(CO)3]− and [(η5‐C5H5)Fe(CO)2]− as the base peaks in their negative ion mass spectra. The dimeric nickel compound [(η5‐C5H5)Ni(CO)]2, however, reductively decarbonylates to the [M‐CO]− radical anion as its predominant fragmentation in the gas phase. Very low abundances of [(η5‐C5H5)Fe(CO)2] and [(η5‐CH3C5H4)Fe(CO)2] were also observed.
Electron impact studies. CXX—The properties of positive ions produced by charge stripping from negative ions. The acetate and perfluoroacetate cations
Authors: Bowie John H. , Benbow John A.
Published: May 2005

The ions [CF3CO2]+ and [CH3CO2]+ give peaks of small abundance in conventional positive ion spectra. These ions can be produced by collision‐induced charge stripping of the corresponding stable negative ions. Six and ten fragment ions respectively are observed in the spectra of [CF3CO2]+ and [CH3CO2]+.
On the apparent ketonization of the [MC2H4]+ ion from o‐hydroxybutyrophenone
Authors: Molenaar‐Langeveld T. A. , Nibbering N. M. M. , Morgan R. P. , Beynon J. H.
Published: May 2005

Deuterium labelling and kinetic energy release measurements have shown that the initially enolic [MC2H4]+ ions from o‐hydroxybutyrophenone have rearranged to o‐hydroxyacetophenone ions, if they eliminate a methyl radical.
Etude en Spectrométrie de Masse. X—Fragmentation d'Ethanes Disubstitués par un Hétéroatome des Colonnes IV, V et VI, et par un Groupement Fonctionnel
Authors: Greiner Jacques , Rouvier Emile , Cambon Aimé
Published: May 2005

Nous comparons et discutons dans ce travail les résultats obtenus lors de la fragmentation d'éthers, sulfures, sélénoéthers, amines, germanes et stannanes fonctionalisés en β par un groupement méthoxycarbonyle, méthylcétone ou nitrile. Les divers composés possédant un élément de la colonne VB et VIB du tableau périodique sont relativement stables sous l'impact électronique, alors que ceux de la colonne IVB se fragmentent très facilement. Les ruptures en α de l'hétéroatome donnent des pics dont l'intensité augmente avec la taille de celui‐ci: [PhO]+<[PhS]+<[PhSe]+<[Ph3Ge]+<[Ph3Sn]+. La rupture en β conduit à des fragments d'autant plus intenses que le groupement fonctionnel a un potentiel d'ionisation plus faible ou un effet inductif plus fort (CN<CO2CH3<COCH3).
Dissociations Induites par Collisions d'Ions Générés par Echange de Charges
Authors: Maquestiau A. , Van Haverbeke Y. , De Meyer C. , Flammang R.
Published: May 2005

Les dissociations induites par collisions d'ions moléculaires créés par impact d'électrons et par échange de charges dans une source d'ionisation chimique (méthane) sont comparés.
A quality index for reference mass spectra
Authors: Speck David D. , Venkataraghavan Rengachari , McLafferty Fred W.
Published: May 2005

A numerical rating for evaluating the quality of reference mass spectra used for retrieval and interpretive applications is proposed. The overall quality index is the product of seven quality factors: (1) source of the spectrum; (2) ionization conditions; (3) higher molecular weight impurities; (4) illogical neutral losses; (5) isotopic abundance accuracy; (6) number of peaks; and (7) lower mass limit of peaks. For quality factor 6 the number of peaks of abundances ≥1% was found to correspond to 15 more than the number of atoms in the molecule with a correlation coefficient of 0.482. The program has been found useful in preparing a data base of 41429 mass spectra; for the majority of spectra judged to be unsatisfactory by the program this arose from a low quality factor 6 value (too few peaks).
The mass spectra of 1,2,5‐triazapentadienium salts
Authors: McNab Hamish
Published: May 2005

The mass spectra of some 1,2,5‐triazapentadienium salts are described. The major breakdown pathways involve loss of Ph· from the 1‐position of the azo form, and of PhNH· from the hydrazone tautomer of the conjugate base.
Mass spectra of some oxadiazole derivatives
Authors: Nakano Tatsuhiko , Márquez Víctor E. , Di Parsia María T. , Suárez Cecilia
Published: May 2005

The mass spectra of some substituted oxadiazoles have been determined and analysed with the aid of high resolution mass spectrometry. Some characteristic and major differences between their spectra have been noted, and possible rationalizations have been advanced. The main fragmentation patterns of the 1,3,4‐oxadiazole derivatives have been interpreted in terms of diazirine intermediates. Specific skeletal rearrangement processes have been observed in the spectra of the 1,3,4‐ and 1,2,4‐oxadiazoles, and possible mechanisms are proposed.
Collisional activation mass spectra of [C6H8]+ ions
Authors: Smith Trudy E. , Smith S. Ruven , McLafferty Fred W.
Published: May 2005

Collisional activation spectra and isotopic labeling indicate that for [C6H8]+ ions at least six stable isomers can be formed from a variety of precursors.
Characterization by three‐dimensional representation of sequential transitions of metastable ions in a double focusing mass spectrometer
Authors: Lacey M. J. , Macdonald C. G.
Published: May 2005

The ion currents due to products of selected ion reactions of toluene and 3‐chlorophenol, occurring in the source or flight tube of a double focusing mass spectrometer for which the electric sector precedes the magnetic sector, have been represented by plotting them against two variables that reflect independently the effects of the sectors. The daughter ion produced from the molecular ion of 3‐chlorophenol that decays by sequential losses of CO in the field free region preceding the electric sector and Cl˙ in the field free region preceding the magnetic sector gives rise to a peak with a distinctive shape on the resultant three‐dimensional surface. A peak due to the daughter ion arising from the corresponding sequential losses of H˙ and C2H2 from the molecular ion of toluene could not be detected. A portion of the ion kinetic energy spectrum which would be recorded by a detector at the energy resolving slit is derived from the surface for 3‐chlorophenol and is in satisfactory agreement with a published spectrum.
Mass spectra of germacranolide type sesquiterpene dilactones and derivatives
Authors: Perry Donald L. , Desiderio Dominic M. , Fischer Nikolaus H.
Published: May 2005

The low and high resolution mass spectra of five germacranolide sesquiterpene dilactones together with the d0‐, d3‐acetates, d0‐, d9‐TMSi derivatives and deuterium exchange products were obtained. The mass spectra of the five dilactones revealed several kinds of common fragment ions. The germacranolides containing a 4,5 double bond exhibit characteristic ions at m/e 274, 256, 228, 165 and 147, while the 4,5‐dihydro compound exhibits fragment ions at m/e 276, 258, 230 and 162.
A mass spectrometric investigation of the reduction product of 3H‐1,2‐benzodithiole‐3‐thione
Authors: Parfitt Robert T. , Games David E. , Cookson Ronald F. , Richards Alan C. , Lynaugh Norman
Published: May 2005

A combination of electron impact, chemical ionization, field desorption and field ionization mass spectrometry has been employed to demonstrate that the LAH reduction product of 3H‐1,2‐benzodithiole‐3‐thione is the dimer, dibenzo[c,h]‐3H,10H‐dihydro‐1,2,8,9‐tetrathiecine.
Laser assisted field desorption mass spectrometry
Authors: Schulten H.‐R. , Lehmann W. D. , Haaks D.
Published: May 2005

The method of indirectly heating the emitter wire with a laser is introduced into field desorption mass spectrometry. Use of this method results in improved sensitivity, more reliable high resolution performance, and extension of field desorption mass spectrometry to the area of high temperature chemistry.
Ionen‐Cyclotron‐Resonanzuntersuchungen an Ionen–Molekül‐Komplexen von Anisol und Anisolhomologen
Authors: Szabo A. , Suhr H. , Miller L. L.
Published: May 2005

Die ICR‐Spektren von Anisol, 3‐Methylanisol, Phenetol, 3‐Methylphenetol und Thioanisol, die bei 10−6Torr weitgehend mit den normalen Massenspektren übereinstimmen, zeigen oberhalb von 10−5Torr zahlreiche Signale von Produktionen. Doppelresonanzmessungen ergaben, daß die meisten Produktionen durch Reaktion eines Fragmentions mit einem Äthermolekül unter Abspaltung eines Alkyl‐, Alkoxy‐ oder Thioalkylradikals bzw. von Äthylen entstanden sind. Daneben finden sich einzelene Produktionen (möglicher‐weise Ion‐Molekül‐Komplexe), die durch Zusammentreten von Ionen mit Äthermolekülen ohne Eliminierung entstanden sind. Radikalionen, mit Ausnahme des Molekular ions, nehmen nicht an den Ionen‐Molekül‐Reaktionen teil.
Zur Lokalisierung funktioneller Gruppen mit Hilfe der Massenspektrometrie. XVII—Massenspektren von 3,6,20β‐Trihydroxy‐pregnanen
Authors: Grupe Albrecht , Spiteller Gerhard
Published: May 2005

Die Massenspektren von 3,6,20β‐Trihydroxy‐pregnanen unterscheiden sich je nach Stellung der Hydroxy‐gruppen und der Ringverknüpfung teilweise beträchtlich voneinander. So wird von allen Isomeren nur das 3α,6β,20β‐Trihydroxy‐5β‐pregnan unter Bildung eines intensiven Schlüsselions der Masse 263 gespalten. Für das 3β,6α,20β‐Trihydroxy‐5α‐pregnan ist die Bildung eines Schlüsselions der Masse 141 charakteristisch.
Beiträge zum Studium einiger Heterocyclen. L—Massenspektrometrische Untersuchungen von 2‐Aryl‐4‐r‐5‐acetylthiazolen
Authors: Demian H. , Coman Mioara , Muresan Ana , Iovanov I. , Simiti I.
Published: May 2005

Es werden die Massenspektren von 5‐Acetylthiazolen untersucht und Unterschiede im Vergleich zu den in einer vorhergegangenen Arbeit veröffentlichten Spektren von entsprechenden 4‐Acetylderivaten, auf Grund deren man beide Verbindungsgruppen indentifizieren könnte, aufgezeigt. Die Natur der Substituenten vom C‐4 beeinflusst das Fragmentierungsschema des Thiazolringes. Bei 4‐Hydroxymethylderivaten findet eine Skelettneuanordnung vor der Fragmentierung statt.
Studies in negative ion mass spectrometry. IX—electron capture by a series of tris‐ and bis‐(dipivaloylmethanato) metal chelates
Authors: Garnett J. L. , Gregor I. K. , Guilhaus M.
Published: May 2005

Electron capture data and negative ion mass spectra are reported for a series of tris‐ and bis‐chelates of the types Metal·L3, Metal·L2, where L (or dpm) refers to the ligand or enolate ion of the β‐diketone 2,2,6,6‐tetramethyl‐3,5‐heptanedione (dipivaloylmethane) and the metals are: Sc(III), Cr(III), Mn(III), Fe(III), Co(III), Al(III), Ga(III), In(III), Co(II), Ni(II), Cu(II), Zn(II). The spectra were all very simple and the principal ions observed in all cases were the molecular anions and ligand ions. Reaction schemes have been established to account for the formation of ligand and other fragment ions, many of which carried less than 0.1% of the total ion currents. Variations in the negative ion mass spectra are attributed to the influence of the metal atom and its 3d electron configuration on the electron capture process. The simplicity of the negative ion mass spectra, together with the fact that many of these metal chelates gave relatively high total ion currents of c. 10−9–10−10 A, indicates the potential value of negative ion mass spectrometry in the area of ultra‐trace metal analysis, and some estimates of detection limits for some of the metals considered in this study have been made.
On the CO elimination from [M – CH3]+ ions in substituted phenyl methyl ethers
Authors: Florêncio Helena , Heerma Wigger , Vijfhuizen Peter C.
Published: May 2005

It was inferred from the collisional activation spectra that CO loss from [M – CH3]+ ions generated from o‐,m‐ and p‐cyanoanisole yields a common ion, presumably the cyanocyclopentadienyl cation. A similar product ion is found to be generated in the three dimethoxybenzene isomers. In case of o‐dimethoxybenzene loss of CO was also found to occur via an important additional route, which leads to the formation of protonated phenol.
Mass spectrometry of π‐complexes of transition metals. XIII—The dehydration process and genesis of ions [M–O]+⋅ in the mass spectra of cymantrenyl‐, ferrocenyl‐and benchrotrenylcarbinols
Authors: Nekrasov Yu. S. , Sizoi V. F. , Zagorevskii D. V. , Vasyukova N. I.
Published: May 2005

The mass spectra of a number of cymantrenyl‐, ferrocenyl‐ and benchrotrenylcarbinols have been studied. The elimination of water molecules from the molecular ions proceeds by the 1,2‐elimination mechanism involving hydroxyl transfer to the metal. The [M–16]+ ions originate from thermal decomposition of the compounds studied in the inlet system.
Skeletal rearrangements of protonated molecular ions of some ethers
Authors: Diakiw Vladimir , Shannon James S. , Lacey Michael J. , MacDonald Colin G.
Published: May 2005

Skeletal rearrangements are reported of protonated molecular ions in the chemical ionization mass spectra of allyl cyclohexyl ether, benzyl cyclohexyl ether, t‐butyl cyclohexyl ether and dibenzyl ether.
The activation energy of the skeletal isomerization in the radical cations of toluene and cycloheptatriene by mass spectrometry of their 2‐phenylethyl derivatives
Authors: Kuck Dietmar , Grützmacher Hans‐Fr.
Published: May 2005

The Unimolecular mass spectrometric fragmentations of the molecular ions of 1,3‐diphenylpropane, 1‐(7‐cycloheptatrienyl)‐2‐phenylethane and the 1‐phenyl‐2‐tolylethanes and their [d5]phenyl analogues have been investigated by metastable ion techniques and measurements of ionization and appearance energies. By comparing the formation of [C7H7]+, [C7H8]+⋅, [C8H8]+⋅ and [C8H9]+ it is shown that the molecular ions of the four diaryl isomers do not undergo ring expansion reactions of the aromatic nuclei prior to these fragmentations. Conversely, the molecular ions of the cycloheptatrienyl isomer suffer in part a contraction of the 7‐membered ring. From these results and from the measured ionization and appearance energies lower limits to the activation energies of these skeletal isomerizations have been estimated yielding E > 33±5 kcal mol−1 formonoalkylbenzene, E > 20 2±5 kc mol−1 for 7‐alkylcycloheptatriene and E > 40±5 kcal mol−1 for dialkylvbenzene positive radical ions. Upper limits can be deduced from literature evidence yielding E < 45 kcal mol−1 for monoalkylbenzene and E < 53 kcal 4mol−1 for dialkylbenzene positive radical ions. The activation energy thus estimated for monoalkylbenzene is in excellent agreement with the recently calculated value(s) for the toluene ion.
Electron impact induced fragmentations of 2‐(2‐nitroanilino)thiophens and Di(2‐nitrophenyl)sulphides
Authors: Mallen David N. B. , Smith Julie M.
Published: May 2005

A prominentorthointeraction occurs during the mass spectral fragmentation of di(2‐nitrophenyl)sulphides. No such effects are observed for the corresponding ethers or 2‐(2‐nitroanilino)thiophens. Variation of aromatic substituents can dramatically alter the effect. Examination of analogous sulphone, sulphoxide, and disulphide molecules, implicates the involvement of theorthonitro substituent and the sulphur atom in this rearrangement.
Distinction between glycosylamines and amadori products by mass spectrometry of their trimethylsilyl derivatives
Authors: Funcke Werner , Henneberg Dieter , Von Sonntag Clemens , Klemer Almuth
Published: May 2005

The TMS‐ethers of four glycosylamines and seven Amadori compounds have been investigated by electron impact mass spectrometry. The mass spectra of glycosylamine‐TMS derivatives and of their isomeric Amadori rearrangement products are quite characteristic. The two types of compounds can be distinguished by a few characteristic peaks.
Massenspektrometrie kondensierter N‐Heterocyclen. 1–Elektronenstoßinduzierte Bildung von Cyclaziniumionen aus 5‐Aryl(Hetaryl)‐9‐methyl‐s‐triazolo[4,3‐c]tetrazolo‐[1,5‐a]pyrimidinen
Authors: Könnecke Anderas , Lepom Peter , Dörre Ronald , Lippmann Eberhard
Published: May 2005

Die Elektronenstoß‐Massenspektren von 5‐aryl(hetaryl)‐9‐methyl‐s‐triazolo[4,3‐c]tetrazolo[1,5‐ a]‐pyrimidinen wurden untersucht. Die Fragmentierung gehorcht einem allegmeinen Mechanismus und durch Cyclisierung werden stabile Cyclaziniumionen gebildet. Bei 5‐Hetarylderivaten konnte die postulierte Struktur durch Vergleich der MIKE‐Spektren mit geeigneten Modellverbindungen gesichert werden.
Struktur des [C3H5]+‐Ions im Cl(CH4)‐Plasma
Authors: Wesdemiotis Chrysostomos , Wolfschütz Roland , Höhne Gerhard , Schwarz Helmut
Published: May 2005

Die Analyse von CA‐Spektren belegt, daß dem im Methan‐Plasma (Chemische Ionisation) vorliegenden [C3H5]+ Ion die Struktur enies Allylkations zukommt.
The m/z 91 rearrangement ion in the mass spectra of some 1,4‐benzodiazepines
Authors: Vane Floie M. , Benz Wolfgang
Published: May 2005

With the aid of isotope labeling and by substituent shifts, the relatively strong m/z 91 ion in the mass spectra of 7‐chloro‐2‐methoxy‐5‐phenyl‐3H‐1,4‐benzodiazepine and related compounds was shown to contain the 5‐phenyl ring and the 3‐CH2 group. Mechanisms involving the opening of the 7‐membered ring and the migration of the phenyl ring from C‐5 to C‐3 are postulated for the formation of this ion. This rearrangement ion was also observed in the mass spectra of some 1‐alkyl‐7‐chloro‐1,3‐dhydro‐5‐phenyl‐2H‐1,4‐benzodiazepin‐2‐ones.
The fragmentation of doubly charged ions of halogenated benzenes
Authors: Medved Miran , Kralj Bogdan , Marsel Jože , Kramer V. , Ast Teodor , Beynon John H.
Published: May 2005

The unimolecular charge separation fragmentations of doubly charged benzene and 18 derivatives containing various numbers of fluorine, chlorine and bromine atoms have been studied. In the majority of cases two distinct kinds of transition state can be characterized, in one of which the ring system remains intact and in the other of which a linear transition state ion is formed. There is evidence for rearrangement of halogens both around the ring and along the linear chain.
Interference peaks in mass analysed ion kinetic energy spectra
Authors: Ast T. , Bozorgzadeh M. H. , Wiebers J. L. , Beynon J. H. , Brenton A. G.
Published: May 2005

When mass analysed ion kinetic energy spectroscopy is performed on ions of low abundance and low mass compared with the rest of the ions present in the ion chamber, severe interference may be observed. The major form taken by the interference is of narrow peaks at non‐integral mass numbers. Many such peaks can be observed in mass analysed ion kinetic energy spectra and they are mainly attributed to decompositions of metastable ions occurring in the first field free region of the reversed geometry double focusing mass spectrometer.
Electron impact and chemical ionization mass spectra of aryl ureas
Authors: Brophy Joseph J. , Nelson Derek , Shannon James S. , Middleton Sydney
Published: May 2005

The electron impact and chemical ionization mass spectra of a series of N,N′, ‐diaryl ureas have been compared. The electron impact mass spectra indicate rearrangements leading to two pairs of aromatic amines and isocyanates, either as ions or molecules. The chemical ionization mass spectra showed the formation of protonated amines and isocyanates via rearrangement.
Mass spectrometry of thio analogues of pyrimidine bases: n‐butylthiouracils and i‐propylthiouracils
Authors: Wyrzykiewicz E. , Stobiecki M. , Golankiewicz K.
Published: May 2005

The mass fragmentation of twelve new 2‐ and 4‐alkylthio substituted derivatives of uracils is discussed and fragmentation pathways, elucidation of which was assisted by accurate mass measurements and metastable transitions, are proposed. It has been found that the position of uracil ring thiation may be deduced on the basis of mass spectral fragmentation patterns.
Mass spectroscopy of natural products. V—Mass spectroscopic studies of ring a substituted allobetulane derivatives
Authors: Schmidt J. , Huneck S.
Published: May 2005

The mass spectrometric behaviour of ring A substituted allobetulane derivatives is discussed. The position and nature of a substituent both influence the mass spectral decomposition remarkably. In the case of the epimeric 1‐hydroxy‐ and acetoxy allobetulanes, the mass spectral differences are great enough to distinguish these from each other. The results should yield a general rationalization for other saturated triterpenes having the same A, B, C ring system.
[C3H3O]+ ions; reacting and non‐reacting configurations
Authors: Holmes John L. , Terlouw Johan K. , Burgers Peter C.
Published: May 2005

Three [C3H3O]+ ion structures have been characterized. The most stable of these is \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm CH} - \mathop {\rm C}\limits^ + = {\rm O} $\end{document} its heat of formation ΔHf was measured as 749±5 kJ mol−1. In the μs time frame this ion fragments exclusively by loss of CO, a process which also dominates its collisional activation mass spectrum. The other stable [C3H3O]+ structures, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}\equiv \mathop {\rm C}\limits^ + - {\rm CHOH} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 2} = {\rm C} = \mathop {\rm C}\limits^{\rm + } - {\rm OH}, $\end{document}, were generated from some acetylenic and allenic precursor ions; their heats of formation were estimated to be 830 and 880 kJ mol−1 respectively. The former ion was also produced by the gas phase protonation of propynal. These ions show loss of C2H2 and CO in both their metastable ion and collisional activation mass spectra. The broad Gaussian‐type metastable peak for the loss of CO was shown to consist of two components corresponding to gragmentations having different activation energies.
Evidence suggesting the occurrence of [2+3] cycloaddition products in the ion/molecule reactions of suitably substituted allyl cations and olefins
Authors: van Tilborg M. W. E. M. , van Doorn R. , Nibbering N. M. M.
Published: May 2005

The ion/molecule reactions of allyl cations and 2‐methoxyallyl cations with vinyl methyl ether, 1‐chloro‐2‐ethoxyethene and 1,2‐dimethoxyethene are discussed in terms of [2+3] cycloaddition reactions. Deuterium labelling of the cations has been used for the study of the reaction mechanisms. The appearance of various product ions in these ion/molecule reactions lead to the suggestion that in reactions of allyl cations with alkenes non‐cyclic [C5H5]+ product ions are formed preferentially, but that in reactions of 2‐methoxyallyl cations with alkenes a significant part of the product ions are methoxycyclopentadienyl cations. These observations are ascribed to the stabilizing effect of the methoxy group with regard to the positive charge in the product ions.
Stereochemical effects in the mass spectra of 2‐hydroxy‐, 5‐hydroxy‐ and 2,5‐dihydroxyprotoadamantanes
Authors: Munson Burnaby , Jelus Barbara L. , Hatch Frank , Morgan Thomas K. , Murray Roger K.
Published: May 2005

Electron ionization and methane and isobutane chemical ionization mass spectra have been obtained for the four configurationally isomeric 2,5‐protoadamantanediols and the corresponding model monoalcohols. Although the electron impact (both 70 and 15 eV) and methane chemical ionization mass spectra of the 2,5‐protoadamantanediols are distinct, the variations are not large and in general they are difficult to rationalize in terms of specific structural features. In contrast, the isobutane chemical ionization mass spectra of these diols show significant differences which can easily be correlated with sterochemical orientations of the substituents.
Field desorption mass spectral fragmentation of monosaccharide isomers
Authors: Deutsch Joseph
Published: May 2005

Field desorption ionization of selected monosaccharide isomers by potassium ion attachment in high fields is described. The ionization is obtained with a tungsten wire activated with carbon needles and covered with KH2PO4 salt. In addition to the potassium cationized molecular ions, reproducible fragmentation was obtained at 10 mA and 20 mA typical of the various monosaccharides. For instance, D‐glucose tends to lose a water molecule, whereas D‐fructose loses primarily methanol under similar conditions. Methanol elimination is suggested to be characteristic of furanoidal ketoses and water elimination for pyranoidal aldoses, whereas glycol elimination occurs for furanoidal aldoses.
Stereochemical applications of mass spectrometry: 1—The utility of electron impact and chemical ionization mass spectrometry in the differentiation of stereoisomeric benzoin oximes and phenylhydrazones
Authors: Harrison Alex. G. , Kallury R. Krishna Mohan Rao
Published: May 2005

A study of the electron impact and chemical ionization (H2, CH4, and iso‐C4H10) mass spectra of stereoisomeric benzoin oximes and phenylhydrazones indicates that while the former can be distinguished only by their chemical ionization mass spectra the latter are readily distinguishable by both their electron impact and chemical ionization mass spectra. The electron impact mass spectra of the isomeric oximes are practically identical; however, the chemical ionization spectra show that the E isomer forms more stable [MH]+ and [MHH2O]+ ions than the Z isomer for which both the [MH]+ and [MHH2O]+ ions are relatively unstable. In electron impact the Z‐phenylhydrazone shows a lower [M]+˙ ion abundance and more facile loss of H2O than does the E isomer. This more facile H2O loss also is observed for the [MH]+ ion of the Z isomer under chemical ionization conditions.
Aziridinone intermediates in electron impact induced fragmentation of some new hydantoins
Authors: Moskal Janusz , Nagraba Krzysztof , Moskal Alexandra
Published: May 2005

Mass spectra of some 5‐substituted 1,3,5‐triarylimidazolidin‐2,4‐diones have been determined and the chief fragmentation pathways considered. The fragmentation sequences and ion structures are discussed with the help of the appropriate metastables, precursor ion measurements and high resolution measurements.
Chemical ionization mass spectra of mononitroarenes
Authors: Harrison Alex. G. , Kallury R. Krishna Mohan Rao
Published: May 2005

The H2 and CH4 chemical ionization mass spectra of a selection of substituted nitrobenzenes have been determined. It is shown that reduction of the nitro group to the amine is favoured by high source temperatures and the presence of water in the ion source. The H2 chemical ionization mass spectra are much more useful for distinguishing between isomeric compounds than the CH4 CI mass spectra because of the more extensive fragmentation. For ortho substituents bearing a labile hydrogen abundant [MH  H2O]+ fragments are observed. When the substituent is electron‐releasing both ortho and para substituted nitrobenzenes show abundant [MHOH]+ fragment ions while meta substituted compounds show abundant loss of NO and NO2 from [MH]+. The latter fragmentation is interpreted in terms of protonation para to the substituent or ortho to the vitro function, while the first two fragmentation routes arise from protonation at the nitro group. When the substituent is electron‐attracting the chemical ionization mass spectra of isomers are very similar except for the H2O loss reaction for ortho compounds.
Negative ion field desorption mass spectra of some inorganic and organic compounds
Authors: Ott K. H. , Röllgen F. W. , Zwinselman J. J. , Fokkens R. H. , Nibbering N. M. M.
Published: May 2005

Field desorption of negative ions can be achieved below the threshold of field electron emission. To this end a mixture of the sample with polyethylene oxide and water was applied to smooth wire cathodes. The mass spectra of some inorganic and organic compounds are reported. Anionization by [CI]− ion attachment is demonstrated with the examples of 20‐hydroxycholesterol and sucrose.
Mass spectrometry of hydroxystilbazoles
Authors: Wyrzykiewicz E. , Łapucha A. , Golankiewicz K.
Published: May 2005

The mass spectral fragmentation of the six 2′‐, 3′‐ and 4′ ‐hydroxy substituted 4‐ and 2‐azastilbenes is discussed and fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed. It has been found that the position of the hydroxystyryl group in the pyridine ring may be deduced on the basis of mass spectral fragmentation patterns.
The location of olefinic bonds in mono‐ and di‐unsaturated compounds
Authors: Greathead Roger J. , Jennings Keith R.
Published: May 2005

The use of vinyl methyl ether as a chemical ionization reagent gas for the location of olefinic bonds is limited by reactions of various ion with vinyl methyl ether molecules. A 75: 20: 5 mixture of nitrogen/carbon disulphide/vinyl methyl ether suggested by Harrison and Chai gives much cleaner spectra and has been used to study octenes and octadienes. Evidence is presented to indicate the formation of two reaction complexes with octenes and four reaction complexes with unconjugated octadienes. Elimination of olefins from these complexes allows one to infer the positions of the carbon‐carbon double bonds in each type of molecule.
Mass spectrometric decomposition processes of 2‐methyl‐1‐hexene
Authors: Falick A. M. , Gäumann T. , Heusler A. , Hirota H. , Stahl D. , Tecon P.
Published: May 2005

Unimolecular decompositions of 2‐methyl‐1‐hexene and several labelled analogues were studied following 70 eV electron impact (normal and metastable spectra) and field ionization (field ionization kinetic measurements). Molecules labelled with 13C in the 1‐position and the methyl position were found to behave essentially identically. This is attributed to rapid transfer of a hydrogen atom mainly from C‐5 to C‐1 (γ‐hydrogen shift). Loss of ethene, propene or propenyl do not involve loss of the methyl carbon or C‐1. All three reactions are better than 90% specific in this respect under all conditions studied. At shorter times, C3H6 loss is the dominant reaction, while at longer times C2H6 loss accounts for >90% of the ion current. It is proposed that at least two distinct pathways for C2H4 loss operate in linear 1‐alkenes, one of which (loss of carbons 1 and 2) is blocked by a 2‐methyl substituent. The [C6H11]+˙ and [C5H10]+˙ ions formed from 13C labelled 2‐methyl‐1‐hexenes fragment in an essentially statistical fashion.
Field ionization mass spectrometry as a facile method for the study of the thermal formation of radicals
Authors: Møller Jørgen , Pedersen Carl Th. , Egsgaard Helge , Larsen Elfinn
Published: May 2005

Electron impact spectra of thermolysis products of organic salts heated in the ion source of a mass spectrometer may give rise to organic ions corresponding to the cation of the salt. Field ionization mass spectrometry has been used as a facile method for detemining whether such an ion is due to ionization of the corresponding radical present in the gas phase, or to an electron impact induced fragmentation of a reaction product of higher mass. By comparison of the electron impact and field ionization spectra of a series of N‐methyl pyridinium, tropylium and 1,2‐dithiolylium salts it has been found possible to identify the radicals formed thermolytically, when present.
Photodissociation of protonated β‐diketones in the gas phase
Authors: Reents W. D. , Murray K. J. , Freiser B. S.
Published: May 2005

The gas phase photodissociation spectra of four protonated β‐diketones were obtained and compared with the absorption spectra of the corresponding ions in solution. Protonated 2,4‐pentanedione was observed to undergo the photodissociation process [C5H9O2]+ +hν → [CH3CO]+ +C3H6O with a λmax at 276±10 nm compared with a solution absorption maximum at 286 nm. Protonated 2,4‐hexanedione was observed to undergo the photodissociation processes [C6H11O2]+ +hν → [CH3CO]+ +C4H8O and [C6H11O2]+ +hν → [C2H5CO]+ +C3H6O with a λmax at 279±10 nm compared with a solution absorption maximum at 288 nm. Protonated 3‐methyl‐2,4‐pentanedione was observed to undergo the photodissociation process [C6H11O2]+ +hν → [CH3CO]+ +C4H8O with a λmax at 295±10 nm compared with a solution absorption maximum at 305 nm. Protonated 1,1,1‐trifluoro‐2,4‐pentanedione was observed to undergo the photodissociation process [C5H6F3O2]+ +hν → CF3H+[C4H5O2]+ with a λmax at 273±10 nm compared with a solution absorption maximum at 288 nm. The [CH3CO]+ and [C2H5CO]+ produced photochemically with the first three ions react to regenerate the protonated β‐diketone leading to a photostationary state. Photodissociation of the protonated alkyl β‐diketones is believed to occur from the protonated keto form, whereas photodissociation of protonated 1,1,1‐trifluoro‐2,4‐pentanedione is believed to occur from the protonated enol form. Mechanisms for the observed photodissociation processes are proposed and comparisons with results from related techniques are presented.
The fragmentation of isotetronic acids under electron impact
Authors: Bonini C. C. , Iavarone C. , Trogolo C. , Poulton Gerald A.
Published: May 2005

The mass spectral fragmentation of eleven α‐hydroxybutenolide compounds (isotetronic acids) are reported. The main features are carboxyl and consecutive carbon monoxide expulsions. Masses were determined using high resolution techniques, metastable transitions were detected by defocusing experiments, and pathways were further documented by isotopic labelling experiments.
The electron impact and chemical ionization mass spectra of some glycidyl ethers
Authors: Brown Roger M. , Creaser Colin S.
Published: May 2005

The electron impact and chemical ionization mass spectra of a number of aliphatic and aromatic glycidyl ethers are reported. For electron impact spectra, partial fragmentation pathways have been determined by metastable linked scan techniques.
Mass spectrometry of natural products: VIII—Mass spectrometric studies of ring a saturated gibberellins
Authors: Voigt D. , Adam G. , Franke P.
Published: May 2005

The fragmentation behaviour of gibberellin A1 methyl ester and gibberellin C methyl ester has been studied by means of positive and negative ion mass spectrometry, high resolution techniques and metastable ion transitions. The results obtained allow a mass spectrometric distinction to be made between both structural types.
A flowing afterglow study of [C3H3]− ions generated from the reactions of [OH]− with allene and propyne
Authors: Mackay Gervase I. , Bohme Diethard K.
Published: May 2005

Flowing afterglow studies are reported for the rates and modes of reaction of [C3H3]− ions produced from allene and propyne by reaction with [OH]− or by electron impact. Studies with methyl formate provide further evidence for the formation from propyne of two distinct stable species.
Multimetalated carboxylates in a filament in‐beam electron impact mass spectrometer
Authors: Matsumoto Kozo , Kosugi Yoshio , Yanagisawa Masaaki , Fujishima Iwao
Published: May 2005

An in‐beam electron impact mass spectrometer has been modified using a tungsten or platinum filament as an in‐beam probe. With this simple device, metalated organic molecular ion peaks of strong intensities are observed under electron impact conditions. New cluster ions, [(CH3CO2)mLin]+ are detected, where m=3‐6 and n=3, 4. Sodium and potassium acetates give stable dimetalated carboxylate ions, and less stable carboxylate ions are formed from benzoates.
Fragmentation mechanism for the loss of XCY (X and Y = O, OR, S) from 2‐phenyl‐1,3,4‐oxadiazole‐5‐one and related sulfur‐containing compounds
Authors: Bouchoux G. , Hoppilliard Y. , Golfier M. , Guillerez M. G.
Published: May 2005

The fragmentation mechanism for loss of XCY (X and Y = O or S) from 2‐phenyl‐1‐3‐4‐oxadiazole‐5‐one and related sulfur‐containing compounds begins with the breaking of the CN bond of the heterocyclic ring. Then a XCY molecule is ejected with the initial formation of a non‐rearranged ion. The major part of ΔHR0 is associated with the stabilization of this neutral fragment. The initial fragment ion is further rearranged before it decomposes.
Fragmentation of the protonated stereoisomers of 5,7‐Undecanediol and its bis(trimethylsilyl) ether under conditions of isobutane chemical ionization
Authors: Wolfschütz Roland , Schwarz Helmut , Blum Wolfgang , Richter Wilhelm J.
Published: May 2005

The chemical ionization induced fragmentation behaviour of an open chain model compound, 5,7‐undecanediol (meso and d,l stereoisomers), is studied and compared with that of previously studied alicyclic models, e.g. cyclohexanediols (cis and trans isomers). In close analogy to the latter, the major fragmentation processes are the one‐ and twofold loss of H2O from the protonated molecules [MH]+. As borne out by appropriately deuterium labelled analogues, the first loss of H2O is invariably a ‘clean’ heterolysis. The second loss is considerably more complex in that 1,3‐ and 1,4‐elimination processes occur concurrently. While the 1,4‐mode may be a direct elimination process in both types of compounds, the 1,3‐mode is rearrangement induced in both. Whereas skeletal rearrangement (ring contraction) precedes this 1,3‐elimination in the alicyclic models, hydrogen rearrangement (1,2‐hydride shift) precedes it in the open chain model. No pronounced stereochemical effect is observed on the mechanistic course of the elimination processes, but is observed in their relative ease. The trimethylsilyl ethers of the stereoisomers of 5,7‐undecanediol are also studied for analogous reactions, and are discussed in this context.
Reaction of cyclohexanone with [NH4]+ under chemical ionization conditions. 1—formation of protonated unsubstituted imines
Authors: Tabet J. C. , Fraisse D.
Published: May 2005

High resolution and metastable decomposition spectra of the ions [M + NH4]+ (and [M + ND4]+) formed by reaction of [NH4]+ (and [ND4]+) with cyclohexanone have been measured. The results provide evidence that the m/z 98 ion, which is abundant in the chemical ionization (NH3) spectrum of cyclohexanone, is in fact composed of two isobaric ions: a protonated imine ion and the molecular ion of cyclohexanone. The former is formed by a mechanism analogous to that occurring in solution.
The modern mass spectrometer—a complete chemical laboratory
Authors: Porter C. J. , Beynon J. H. , Ast T.
Published: May 2005

Using nitrobenzene as an example, various ways in which a contemporary mass spectrometer can be utilized to yield a wealth of information about the compound studied are reviewed. Applying a variety of different techniques and procedures, in addition to the conventional low resolution mass spectrum, the following nitrobenzene spectra have been obtained: collision induced dissociation mass spectrum, mass analysed ion kinetic energy spectra, collision induced dissociation mass analysed ion kinetic energy spectra, spectra obtained at constant B/E, spectra obtained at constant B2/E, high voltage scans of metastable ion fragmentation processes, consecutive fragmentations in different field free regions, charge exchange mass spectra, charge stripping mass spectra, doubly charged ion mass spectra, chemical ionization mass spectra, negative ion mass spectra, negative ion mass analysed ion kinetic energy spectra, negative ion mass analysed ion kinetic energy collision induced dissociation spectra, charge inversion spectra, etc. The complementary types of information available from the above studies are discussed to show the unique versatility of mass spectrometry as a technique for the examination of organic compounds.
The mass spectrum of isopropyl o‐toluate
Authors: Tajima Susumu , Yanagisawa Tamae , Azami Tadashige , Niwa Yoshio , Tsuchiya Toshikazu
Published: May 2005

The formation of an [M + 1]+ ion and the fragmentation of isopropyl o‐toluate have been investigated by the deuterium labelling technique and kinetic energy release measurements. The hydrogen atom involved in the [M + 1]+ ion formation does not originate from a specific part of the molecule, but from all parts. A small amount of hydrogen exchange between the secondary carbon atom in the isopropyl group and the carbon atoms in the tolyl group takes place prior to decomposition of the molecular ion into the m/z 136 ion by a McLafferty rearrangement. Either almost complete scrambling of the hydroxyl hydrogen atom and the methyl hydrogen atoms in tolyl group or an almost equilibrated exchange of the hydroxyl hydrogen atom with one of the remaining hydrogen atoms in tolyl group also takes place prior to the elimination of a water molecule from the intermediate m/z 136 ion.
Mass spectrometry of trialkylsilyl and acyl derivatives of 2′‐deoxynucleosides
Authors: Quilliam Michael A. , Ogilvie Kelvin K. , Westmore John B.
Published: May 2005

The electron impact mass spectra of monosilyl and mixed acyl‐silyl derivatives of 2′‐deoxynucleosides are described in detail. (Silyl = tert‐butyldimethylsilyl, cyclo‐tetramethylene‐isopropylsilyl, or cyclo‐tetramethylene‐tert‐butylsilyl; acyl = acetyl or trifluoroacetyl.) The interpretation of the fragmentation pathways was aided by metastable ion decomposition studies, precise mass and deuterium labelling measurements. Mass spectrally, the acyl substituents are mostly ‘passive’ and have (with possibly one exception) little fragmentation directing capability. In contrast, the silyl groups have powerful fragmentation directing properties. Elimination of the bulky alkyl radical R˙ (tert‐butyl or isopropyl) from the molecular ion produces the siliconium ion, [M–R]+, which is the precursor for most of the other prominent ions in the spectra. These arise from ‘siliconium ion rearrangements’ resulting from the interaction of the positively charged siliconium ion centre with the electron dense regions (i.e. oxygens) in the molecule, to form cyclic silyloxonium ions which subsequently decompose. Since the interacting oxygen and silicon must be sterically accessible, the fragment ion types and their abundances are very dependent upon structure. Consequently, [M–R]+ ions formed from 3′‐ or 5′‐O‐silyl groups give rise to different sets of daughter ions which, for the most part, are not found, or have very low abundances, in the mass spectra of underivatized or trimethylsilylated nucleosides. Detailed information on sugar and base moieties and isomeric substitution is readily obtained.
The mass spectrum of glycine
Authors: Majer J. R. , Al‐Ali B. I. , Azzouz A. S. P.
Published: May 2005

Irreproducibilities in the measurements of isotopic abundance in 15N labelled glycine have been related to the complex nature of chemical processes occurring during the evaporation of glycine prior to ionization.
Loss of methyl radical from some small immonium ions: Unusual violation of the even‐electron rule
Authors: Bowen Richard D. , Harrison Alex G.
Published: May 2005

Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R1, R2, R3 = H or alkyl) eliminate .CH3; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even‐electron rule, which states that closed‐shell cations usually decompose to give closed‐shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH3)2CNH]+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH3. and CD3., via different mechanisms, but very little CH2D. or CHD2. loss occurs.
Photoionization studies of substituted trimethylamines
Authors: Loguinov Yuri , Takhistov Vyatcheslav V. , Vatlina Lidya P.
Published: May 2005

Ionization energies of substituted trimethylamines (CH3)2NCH2X, together with appearance energies of [M − X]+ ions, have been measured by the photoionization technique. The heats of formation for the following radicals have been derived (in kJ mol−1): C2H3˙ (+ 314), Ph. (+ 347), p‐CH3C6H4˙ (+ 326), HC2˙ (+ 494), (CH3)2NĊH2 (+ 134), NC˙ (+ 452), CF3. (− 435), (CH3)3Si˙ (+ 54.5). The heats of formation obtained for [(CH3)2NCH2]+ (+ 649) and (CH3)3Si+ (+ 610) lead to ionization energies of 5.35 eV for (CH3)2NĊH2 and 5.75 eV for (CH3)3Si˙.
On the heat of formation of [C6H4]+˙
Authors: Maccoll Allan , Mathur Deepak
Published: May 2005

The appearance energy of the [C6H4]+˙ ion from benzonitrile has been measured, using an electron monochromator. The value observed at onset, 12.54±0.03 eV, leads to a heat of formation of 1304±3 kJ mol−1. Possible reasons for widely divergent values reported previously are proposed.
The relative abundances of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{R}}_{\rm{1}} \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{O}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{R}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{O}} $\end{document} from R1R2CO, and the low voltage mass spectra of some methyl ketones
Authors: Maccoll Allan
Published: May 2005

The relative abundances of the ions formed by the loss of the larger and the smaller radical from RCOCH3 are interpreted in terms of the appearance energies of these fragments, calculated from the heats of formation of the relevant species. The appearance energies for the McLafferty rearrangement are also reported, as are the low voltage, low temperature mass spectra of propanone, butanone, pentan‐2‐one, pentan‐3‐one, 3‐methylbutan‐2‐one and 3,3′dimethylbutan‐2‐one.
Negative chemical ionization mass spectrometry of explosives
Authors: Bouma Willem J. , Jennings Keith R.
Published: May 2005

The negative chemical ionization mass spectra of nitrobenzene, ethylene glycol dinitrate and nitroglycerine have been obtained using various reagent ions. For nitrobenzene, [OH]− gives the [M − H]−, together with [M]−˙ ions formed by electron capture, but other reagent ions gave relatively low intensity adduct peaks. Ethylene glycol dinitrate and nitroglycerine gave abundant [M + X]− ions (X = NO2, NO3, Cl, Br, I), together with ions arising from the thermal decomposition of the samples in the heated inlet system. The rate of anion attachment to these compounds is much greater than that to related compounds having only one functional group, and it is suggested that this is due to the participation of the adjacent groups in the bonding between the substrate and anion.
Stereochemical effects in electron impact mass spectra of cis‐trans isomeric 1,2,4,5‐tetramethylcyclohexanes
Authors: Herzschuh R. , Mann G. , Werner H. , Mende Elke
Published: May 2005

The mass spectrometric fragmentation of the five cis‐trans isomeric 1,2,4,5‐tetramethylcyclohexanes is influenced by their configuration. The thermochemically stable isomers show a higher abundance of the [MCH3]+ ions and a lower abundance of the [MC2H5]+ ions than the strained isomers. The [MCH3]+/[MC2H5]+ intensity ratio correlates with the enthalpy difference ΔHisom and with the mean number of gauche arrangements ZgI of the stereoisomers.