bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass spectrometry of hydroxy dicarboxylic acids as trimethylsilyl derivatives. Rearrangement fragmentations
Authors: Petersson G.
Published: May 2005

Gas chromatography—mass spectrometry offers a convenient method for the separation and identification of hydroxy dicarboxylic acids as open‐chain trimethylsilyl (TMS) derivatives. Mass spectra were studied of aldaric (tartronic, tartaric, pentaric and hexaric) acids and deoxyaldaric (malic, 2‐deoxypentaric, 2‐deoxyhexaric, 3‐deoxypentaric and 3‐deoxyhexaric) acids. The different structural types can be readily identified from their characteristic spectra.

The most prominent fragmentations involving the rupture of one bond are the loss of a siliconlinked methyl group and the formation of α‐cleavage ions by carbon chain cleavage. The further decay is characterized by a number of significant rearrangements specific of TMS derivatives. Several of these can be classified as involving migration of a TMS group to an oxygen atom or migration of an ester OTMS group to a silicon atom. Concomitant loss of a stable molecule often provides a driving force.

Prominent odd‐electron ions are formed by a McLafferty‐type rearrangement of a TMS group. The decomposition of several even‐electron ions can be regarded as analogous to that rearrangement.
A McLafferty‐type rearrangement of a trimethylsilyl group in silylated hydroxy carbonyl compounds
Authors: Petersson G.
Published: May 2005

A McLafferty‐type rearrangement of a trimethylsilyl group is demonstrated. Abundant rearrangement ions are formed for trimethylsilyl derivatives of α,β‐dihydroxy carbonyl compounds. Data are given for a large number of hydroxy acids and hydroxy ketones including aldonic acids, aldaric acids, acyclic ketoses and hydroxy keto acids. A few branched lactones are also shown to rearrange.

The positive charge and the unpaired electron are extensively delocalized in the odd‐electron rearrangement ions. Those substituents at the α‐carbon atom which offer a favourable delocalization promote the rearrangement. Spectra of specifically methylated species reveal that migration over larger than six‐membered rings occurs to some extent. An observed dependence of abundance on configuration is associated with steric strains in the transition state.

The rearrangement ions are of great diagnostic value in structural analysis. They are relatively more abundant at low electron energies and give rise to the base peak at 20 eV for many compounds. Ions produced by the competing conventional McLafferty rearrangement are less abundant.
The mass spectra of carbon‐13 labeled 2‐hydroxynaphthoquinones
Authors: Moore R. E. , Brennan M. R. , Todd J. S.
Published: May 2005

Carbon monoxide is lost from the molecular ion of 2‐hydroxy‐1,4‐naphthoquinone (I) almost exclusively from C‐2 as shown from carbon‐13 labeling studies. The fragmentation scheme originally proposed by Williams for I is not a major process.
Ion‐Molekül‐Reaktionen und Hammett‐Gleichung
Authors: Klotz H.‐D. , Drost H.
Published: May 2005

Im Rahmen der Untersuchungen über die Analogiebeziehungen zwischen elementaren Ion‐Molekül‐Reaktionen (IMR) in der Gasphase bestimmten Schritten chemischer Reationen in der Flüssigkeit wurde versucht, den Reaktionsschritt der σ‐Komplex‐Bildung bei der elektrophilen aromatischen Substitutionsreaktion durch eine Protonenübertragungsreaktion zu modellieren. Als Kriterium für die Modellierbarkeit die Hammett‐Gleichung.

Eine Gegenüberstellung von Hammett‐σ‐Kontanten und—Stellvertretend für die entsprechenden Geschwindigkeitskonstanten—dem Verhältnis der Wirkungsquerschnitte von unsubstituierten und substituierten Aromaten führte zu keiner die Gültigkeit der Hammett‐Gleicnung voraussetzenden linearen Beziehung. Charakterisiert man demgegenüber die elementare IMR durch die bei der Bildung des σ‐Komplexes frei werdende Energie, die Protonenaffinität PA, zeigt sich eine lineare bzw. allgemein eine gesetzmäßige Beziehung zwischen σ‐Konstante und PA, was auf eine Gültigkeit der Hammett‐Gleichung auch für den Bereich der IMR hindeutet.
Mass spectra of azetidines
Authors: Kostyanovsky R. G. , Markov V. I. , Gella I. M. , Khafizov Kh. , Plekhanov V. G.
Published: May 2005

The mass spectra of azetidine, 2‐methylazetidine, 2‐phenylazetidine, methylene‐bis‐azetidines, their N‐halo‐ and N‐tosyl derivatives, 2‐phenylazetine as well as N,N‐dimethylmethane sulphonamide, N,N‐dimethyl and N,N‐diethyl‐ p‐toluene sulphonamides have been investigated. The fragmentation of azetidine derivatives via the open form of the molecular ion is discussed.
Mass spectrometry of cycloheptatriene derivatives—II: Ring contraction of the molecular ion of 7‐cyanocycloheptatriene. Participation of ring carbon in the loss of HCN (or HNC)
Authors: Venema A. , Nibbering N. M. M. , De Boer Th. J.
Published: May 2005

At an electron energy of 70 eV (nominal) both the [M]+·‐ion and the [MH]+‐ion of the title compound expel hydrogen cyanide. 13C labelling in the cyano group shows that these ions lose—within experimental error—only H13CN when decomposing in the ion source, i.e. when possessing a relatively high internal energy. In the first and second field free region, however, as well as in the ion source at low ionizing energies (9 eV, nominal), H12CN is also eliminated. This phenomenon may be explained by ring contraction of the molecular ion to a six membered ring, possibly initiated by the formation of a norcaradiene structure, which may then rearrange further to a species of higher symmetry. This ring contraction is supported by the occurrence of peaks of low intensity at m/e 78 and m/e 77, due to fragments which are generated in one step from the molecular ion.
Studies in organic mass spectrometry—X: The fragmentation of substituted 1,3‐cyclo‐pentanediones and 1,2,4‐cyclopentanetriones, related to hop bitter acids
Authors: Cant E. , Vandewalle M.
Published: May 2005

The Mass spectra of some 1,3‐cyclopentanediones and 1,2,4‐cyclopentanetriones, related to compounds encountered in the chemistry of hops bitter constituents have been determined. Methyl substituted compounds mostly show ring degradation, while for longer alkyl groups and acyl groups, fragmentations in the side chain carry most of the total ionization. When both alkyl (> 2C) and acyl substituents are present, fragmentations in the alkyl group always occur before those in the acyl side chain. The observed degradation processes are useful for the interpretation of the spectra of hop bitter acids and derived products.
Etude d'un Couple de Diastereoisomeres en Spectrometrie de Masse: Les 2,3‐Diphenyl‐butanes Thréo et Erythro
Authors: Pechine J. M.
Published: May 2005

Les spectres de masse de 2,3‐diphénylbutanes érythro et thréo sont attribués à un réarrangement et à une rupture simple; leur calcul est proposé. II est suggéré que les différences entre les spectres des deux isoméres proviennent essentiellement de al différence d'enthalpie entre les ions moléculaires et non de la différence d'enthalpie entre les états de transition du réarrangement; il en est déduit qu'à l'état gazeux le 2,3‐diphénylbutane thréo est plus stable que l'érythro.
Elektronenstossinduzierte Fragmentierung von Trimethyl‐Benzaldehyden
Authors: Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Das ungewöhnliche Fragmentierungsverhalten von Trimethylbenzaldehyden wurde durch 2H‐ und 13C‐markkierte Verbindungen aufgeklärt. Statistischen Berechnungen Zeigen, dass in diesem Fall die C‐Atome nicht gleichwertig sind, es für die H‐Atome bezüglich der C2H4‐Eliminierung beobachtet wird.
Specific and random fragmentations in the mass spectra of some neopentyl compounds
Authors: Holmes J. L. , Tong D. C. M. , Rye R. T. B.
Published: May 2005

The mass spectra of neopentyl alcohol, bromide and chloride and some 13C and 2H labelled analogues have been studied. Most fragmentations of the molecular ions of these compounds occur by simple bond cleavages and do not involve rearrangement before fragmentation. We propose that in the [M  CH3]+ fragment ions, seven of the eight hydrogen atoms and all four carbon atoms are involved in randomisation when an ethylene molecule is ejected. The eighth hydrogen atom (which comes from a methyl group) is probably associated with the heteroatom. The neopentylcation, observed only in the mass spectrum of the bromide, fragments mainly by loss of an ethylene molecule, also containing randomly selected hydrogen and carbon atoms. The [C4H7]+ ion also was observed to undergo complete atom scrambling.
Chemical ionization mass spectrometry using ammonia reagent gas. Selective protonation of conjugated ketones
Authors: Dzidic I. , McCloskey James A.
Published: May 2005

Studies using ammonia as a selective reagent gas in chemical ionization mass spectrometry were extended to conjugated ketones. Their proton affinities were in the range of most nitrogen‐containing compounds (> 207 ± 3 kcal/mole), thereby permitting proton transfer from [NH4]+‐, leading to well stabilized protonated molecular ions as the most abundant ion products.
Factors influencing the formation of some characteristic fragment ions in the mass spectra of 16‐trimethylsilyloxy androstanes
Authors: Vouros Paul , Harvey D. J.
Published: May 2005

The mass spectra of the trimethylsilyl derivatives of several steroids containing a 16‐hydroxy function are presented. The mechanisms giving rise to various characteristic fragment ions were investigated with the aid of deuterium and 18O‐labeling.
Energetic data as a guide to the interpretation of mass spectral features of dicarbonyl diketonates of Rh and Ir
Authors: Bonati F. , Distefano G. , Pignataro S. , Torroni S.
Published: May 2005

The relative intensities and appearance potentials of the principal ions formed from a series of rhodium and iridium dicarbonyl diketonates were measured by mass spectrometry. These compounds show the usual CO losses generally found in the fragmentation of metal carbonyls. Additionally several fragmentation peculiarities characteristic of metal acetylacetonates were found. Energetic data were used to interpret some aspects of the cracking patterns.
Etude de la fragmentation de semi‐carbazones terpeniques
Authors: Cassan J. , Azarro M. , Reed R. I.
Published: May 2005

Dans le cadre d'une étude générale des dérivés des carbonylés des terpénes, nous étudions dans le présent travail, une série de semicarbazones terpéniques en spectrométrie de masse à l'aide de la haute résolution. Nous comparons en fonction des différents squelettes hydrocarbonés, les fragmentations induites par le groupement fonctionnel semicarbazone. Les spectres de masse sont beaucoup plus complexes que ceux des oximes, methyloximes, hydrazones correspondantes. Nous nous sommes basés sur des mécanismes classiques pour rendre compte de la quasi‐totalité des pics obtenus. Nous avons constaté que la fragmentation du squelette des semicarbazones a une importance moins grande que celle des oximes. Le groupement fonctionnel semicarbazone se décompose suivant différentes voies. Les ions obtenus sont à l'origine de dégradations secondaires. Malgré la prépondérance de la localisations de la charge sur l'azote imino, les autres centres jouent un rôle dans la dégradation de ces dérivés terpéniques.
Mass spectral studies of some fructose containing oligosaccharide permethyl ethers
Authors: Das K. G. , Thayumanavan B.
Published: May 2005

Mass spectrometry can be used to characterise fructofuranose units connected via C2 to another sugar. The intensity of the m/e 101 and m/e 88 ions cannot be used to differentiate between furanose and pyranose ring forms in disaccharide permethyl ethers. The type of glycosidic linkage has considerable influence on the formation of these ions.
Electron‐impact studies—LXXIV: A survey of rearrangement processes in the ‘doubly‐charged ion’ mass spectra of aromatic compounds
Authors: Blumenthal T. , Bowie J. H.
Published: May 2005

The technique of Beynon2 has been used to determine the ‘doubly‐charged ion’ mass spectra of a variety of aromatic compounds which contain pronounced rearrangement peaks in their conventional mass spectra. Many, but not all, of the ‘doubly‐charged ion’ spectra contain similar rearrangement peaks to those observed in conventional spectra.
Specific isotopic labeling of sugars: Applications in mass‐spectral analysis. The mass spectrum of 1,6‐anhydro‐2,3‐O‐iso‐Propylidene‐β‐D‐talopyranose
Authors: Horton Derek , Just Ernst K. , Wander Joseph D.
Published: May 2005

Derivatives of 1,6‐anhydro‐2,3‐O‐isopropylidene‐β‐D‐talopyranose (I) specifically deuterated at C‐3 (II), at C‐4 (III), at C‐3 and C‐4 (IV), and in the isopropylidene group (V) have been examined by high‐resolution, electron‐impact mass spectrometry. From the elemental compositions of the fragment ions, the mass‐number shifts upon deuterium incorporation, and analysis of metastable transitions, it was possible to identify the origin of the hydrogen atoms in all fragments formed from I and to present a complete scheme of fragmentation pathways undergone by this molecule.
Fragmentation du 1,2,4‐triazole sous L'impact electronique
Authors: Maquestiau A. , Van Haverbeke Y. , Flammang R.
Published: May 2005

Ce travail décrit le comportement sous l'impact életronique du 1,2,4‐triazole et de 1,2,4‐triazole et de quelques dérivés substitués. Les résultats obtenus à l'aide de dérivés deutériés démontrent: 1. L' absence de scrambling (NH‐CH) avant la dégradation. 2. La spécificité du clivage principal (élimination de HCN ou RCN au départ de l'ion moléculaire). 3. La présence en phase gazeuse des deux tautoméres non‐symétriques. La possibilité d'une isomérisation rapide de l'ion moléculaire avant dégradation est également envisagée.
Spectres de masse de derives de l'aza‐6 bicyclo[3, 2, 1]octane
Authors: Furstoss R. , Heumann A. , Waegell B. , Gore J.
Published: May 2005

Les spectres de masse d'une série de dérivés aza‐bicycliques pontés sont examinés Dans la totalité des cas, la fragmentation est à la fois simple et caractéristique. De plus, sur deux couples d'épimères, on observe un effet stéréochimique, se traduisant par des fragmentations nettement différenciées.
Spectrometrie de Masse du Dimethoxy‐2,6 Naphtalene et de Certains de ses Derives
Authors: Castonguay J. , Rossi A. , Richer J. C. , Rousseau Y.
Published: May 2005

On rapporte les spectres de masse du diméthoxy‐2,6 naphtaléne et de 14 de ses dérivés. La rationalisation du mode de decomposition par impact électronique qui est proposée, est confirmée la plupart du temps par des pics dûs aux transitions métastables appropriées. L'ion moléculaire, qui est le plus intense des ions dans chacun des spectres enregistrés ne semble pas subir d'élimination directe d'un group méthoxy ou de tout autre substituant directement relié au noyau naphtalénique. La dégradation semble plutot amorcée par l'élimination d'un radical méthyle à partir de l'ion moléculaire. Pour les dérivés nitrés, on a pu mettre en évidence la perte d'une molécule d'oxyde nitrique de l'ion moléculaire. Ce processus est confirmé par une mesure précise de masse du fragment résultant.
The mass spectra of some 2,1,3‐benzothiadiazoline and 2,1,3‐benzothiadiazine 2,2‐dioxides
Authors: Bancroft K. C. C. , Guindi L. H. Morcos , Temple A. F. , Millard B. J.
Published: May 2005

Although the behaviour of 1H, 2H‐2,1,3‐benzothiadiazoline 2,2‐dioxide is similar to that of sulphoxides in the mass spectrometer in losing a molecule of SO2, the 1,3‐dimethyl derivative loses the radical SO2H. In addition the radical CH3SO2 is lost in a one step process that must involve a methyl migration. The radical SO2H is also lost from 2,1,3‐benzothiadiazine 2,2‐dioxides methylated in the 3‐position and the hydrogen involved is shown to originate from this methyl group by deuterium labelling. The mass spectra of other 2,1,3‐benzothiadiazine 2,2‐dioxides are also discussed.
Studies in organic mass spectrometry—XII: Mass spectra of chalcones and flavanones. The isomerisation of 2′‐hydroxy‐chalcone and flavanone
Authors: Van De Sande C. , Serum J. W. , Vandewalle M.
Published: May 2005

The mass spectra of isomeric 2′‐hydroxy‐chalcones and flavanones (i.e. 2‐phenyl‐chroman‐4‐ones) are essentially identical. Thermal isomerisation prior to ionisation was ruled out. A study of metastable transitions (first and second field free region of a double focusing instrument), as well as low energy spectra of both isomers, pointed towards completely identical fragmentation pathways for the two compounds. Five deuterated compounds were then investigated. The heats of formation of the most important ions were determined. It was concluded that an intramolecular equilibrium exists between a chalcone type and a flavanone type molecular ion.
Substituent effects in mass spectrometry—II. The effect of substituents on the dissociation of para and meta disubstituted benzenes
Authors: Benoit F.
Published: May 2005

The effect of substituents on the activation energy for primary dissociation processes in the molecular ions of mono‐ and para and meta di‐substituted benzenes has been examined. Where the daughter ion retains the substituent group, variation of the energy of activation derives from a combination of the effects of substituents on the ionisation potential of the molecular ion and the appearance potential of the daughter ion. An equation relating the energy of activation for the fragmentation of the molecular ion of a mono‐substituted benzene to that of related para and meta di‐substituted benzenes is presented.
Alloxazines and isoalloxazines. Mass spectrometric analysis of riboflavin and related compounds
Authors: Brown Peter , Hornbeck Cecil L. , Cronin John R.
Published: May 2005

The positive ion electron‐impact mass spectra of a series of alloxazines, iso‐alloxazines and some derivatives have been examined. The compounds employed were lumichrome (7,8‐dimethylalloxazine), 1,3‐dimethyllumichrome, lumiflavin (7,8,10‐trimethyl‐iso‐alloxazine), 3‐methyllumiflavin, riboflavin [7,8‐dimethyl‐10‐(D‐1′‐ribityl)‐iso‐alloxazine], riboflavin tetraacetate, 3‐methylriboflavin tetraacetate and riboflavin tetrapropionate. By using exact mass measurements, metastable ion defocusing and the mass/composition shifts occurring with derivatives, it has been possible to arrive at detailed interpretations of the mass spectra of all compounds. With lumichrome and lumiflavin, fragmentation commences by elimination of HNCO from the pyrimidine ring. With riboflavin and its derivatives the ribityl chain cleaves off first, followed by decomposition of the iso‐alloxazine ring. Application of these methods and findings to the structural analysis of chemically interesting modified flavins is predicted to be rewarding.
On the mass spectra of thallium(III) porphyrin chelates
Authors: Smith K. M.
Published: May 2005

Thallium(III) porphyrins show anomalous features in their mass spectra compared with other metalloporphyrins. The base peak in all of the spectra arises by loss of the thallium atom and its axial ligands with transfer of two hydrogens to the macrocycle; the liberated thallium undergoes ion‐molecule interaction with the thallium porphyrin, resulting in the observation of ions containing two thallium atoms per porphyrin ligand.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen—IV: Mechanistische Betrachtungen zur Bildung des Benztropyliumkations aus den Chlormethyl‐Naphthalinen und 1‐Chlor‐Phenyl‐(5)‐Penten‐(2)‐in‐(4)
Authors: Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Massenspektrometrische Untersuchungen von 2H‐ und 13C‐markierten Derivaten des 1‐ bzw. 2‐Chlormenthyl‐naphthallins und des 1‐Chlor‐Phenyl‐(5)‐penten‐(2)‐in‐(4)s zeigen, dass das Ion [C11H9]+ das unter Acetylen‐Eliminierung [C9H7]+ ergibt, eine Benztropyliumkationstruktur besitzt. Modellbetrachtungen zeigen, dass die Bildung diese Kations über einen gemeinasmen Übergangszustand mit einem Dreiring sehr wahrscheinlich ist.
Geminale Spaltung Beim Massenspektrometrischen Zerfall von Benzodioxasilolen
Authors: Liehr J. G. , Richter W. J.
Published: May 2005

Ein stufenweiser Verlust von zwei Substituenten (CHC3/CH3 bzw. H/CH3 Radikale) dessenlben Zentralatoms (silicium), ein ungweöhnlicher Vorfall in der Massenspektrometrischen Fragmentierung, wird für 1,3,2‐Benzodioxasilole berichtet. Da naheliegende Möglichkeiten für Skelettumlagerungen fehlen, wird eine durch die niedrigeren Si‐C und Si‐H Bindungsenergien erleichterte geminale spaltung vorgeschlagen.
The mass spectrometry of some aromatic azides
Authors: Fraser R. T. M. , Paul N. C. , Bagley M. J.
Published: May 2005

Bromophenyl azides provide the only exceptions to the observation that nitrogen (N2) is eliminated from the molecular ions. Splitting out of HCN, C2H2 and (in the case of acyl or o‐nitroaryl azides) CO are important processes.
Mass spectrometric studies of some 4‐acyl substituted 1‐phenyl‐3‐methyl‐5‐pyrazolones
Authors: Larsen Elfinn , Qureshi Iqbal H. , Møller Jørgen
Published: May 2005

The electron‐impact‐induced fragmentation of 1‐phenyl‐3‐methyl‐5‐pyrazolone and six 4‐acyl substituted derivatives, have been studied with the aid of deuterium labelling, high resolution mass measurements and the metastable defocusing technique. The mass spectra of the pure keto and the pure enol forms do not show any significant differences. The predominant decomposition of the 4‐acyl substituted pyrazolones is the α‐cleavage with respect to the carbonyl group leading to intense peaks at m/e 201 by loss of the alkyl group. In the case of benzoyl and ethoxycarbonyl derivatives the α‐cleavage is associated with a specific hydrogen rearrangement causing the loss of a benzene and an ethyl alcohol molecule, respectively.
Spectrometrie de Masse de Produits Naturels Aromatiques Polychlores
Authors: Butruille Daniel , Dominguez Xorge A. , Teller Gérard
Published: May 2005

On discute les spectres de masse de trois produits naturels aromatiques: le diméthoxy‐1,4 tétrachloro‐2,3,5,6 benzén (I), le méthoxy‐4 tétrachloro‐2,3,5,6 phénol (II) et le diméthoxy‐1,4 nitro‐2 trichloro‐3,5,6 benzéne (III). Les principlaes fragmentations sont expliqués en fonction de la formation de la structure quinoide (a), qui conduit sous l'impact électronique à la formation de l'ion chlorocyclopropénone (c). On propose également des voies secondaires conduisant à la formation d'ions [Cx]+. On relevé les variations introduites dans la fragmentation par la présence du groupement nitro.
Mass spectra of some partially fluorinated aliphatic compounds
Authors: Santoro E. , Piccardi P.
Published: May 2005

The mass spectra of several fluorohydrocarbons are shown and discussed. The fragmentation of these compounds displays a close correlation with the molecular structure and points to the importance of the charge‐stabilisation concept for the ion intensities. The iodo‐derivatives show a large abundant molecular ion.
Etude de Steroides Fluores par Spectrometrie de Masse—IV. Fluoro‐3 Epoxy‐5,6 Steroides
Authors: Borgna J. L. , Guida A. , Fonzes L.
Published: May 2005

L'étude d'époxydes 5,6 de stéroïdes flourés en 3 ne nous a pas permis de mettre en évidence l'influence de l'atome de flour sur la fragmentation. Par contre, nous avons montré que la stéréochimie de l'époxyde joue un rôle prépondérant.
Mass spectrometry of the trimethylsilyl derivatives of some cardiac aglycones and monoglycosides
Authors: Falkner Fred C. , Frölich Jürgen , Watson J. Throck
Published: May 2005

Mass spectra of the trimethylsilyl (TMS) ethers of digitoxigenin, digoxigenin, digitoxigenin monodigitoxoside, digoxigenin monodigitoxoside and peruvoside were obtained. Ions appearing at m/e 170 and m/e 183 are proposed to be indicative of the enol TMS ether moiety as confirmed by appropriate shifts in the mass spectrum of digitoxigenin derivatized with perdeuterotrimethylsilylating reagent. The TMS ether derivatives of the monoglycosides produced abundant molecular ions and the base peaks in the spectra represent fragments of the sugar portion of the molecule.
The ion kinetic energy spectra of isomeric chlorobenzenes and polychlorinated biphenyls (PCB'S)
Authors: Safe S. , Hutzinger O. , Jamieson W. D.
Published: May 2005

The ion kinetic energy (IKE) spectra of the isomeric di‐and trichlorobenzenes have been examined and the data for the latter compounds suggested that there was incomplete chlorine randomization in their molecular ions in the first field‐free region of the mass spectrometer. Previous studies on the mass spectra and [metastable ion]/[daughter ion] ratios of the di‐, tetra‐ and hexachlorobiphenyls (PCB's) indicated chlorine randomization in the molecular ions of those isomers containing less than two chlorine groups ortho to the Ph‐Ph ring junction. In contrast the IKE spectra of the isomers are different and the results indicate incomplete chlorine randomization in the first field‐free region of the mass spectrometer. These spectral differences may be of some use in PCB analysis.
Multiply charged ions in the mass spectra of aromatics
Authors: Engel Robert , Halpern Donald , Funk Betty‐Anne
Published: May 2005

The prominence of multiply charged molecular and fragment ions upon electron‐impact in the mass spectrometer is proposed as an experimental, empirical indication of aromatic character. The effects of electron withdrawing and donating substituents on the production of multiply charged ions are considered and appearance potentials are noted for several species.
Mesoionic compounds—XIX: Mass spectral fragmentation patterns for some five‐membered systems containing oxygen, nitrogen and sulfur
Authors: Potts K. T. , Armbruster R. , Houghton E. , Kane J.
Published: May 2005

Mesoionic compounds of the s‐triazole, 1,3,4‐oxadiazole, 1,3,4‐thiadiazole, 1,2,3‐thiadiazole, 1,3‐thiazole and 1,3‐dithiole systems all underwent deep‐seated decomposition on electron‐impact to small stable ions, determined to a large extent by the nature of the peripheral heteroatoms and the exocyclic substituent. In some instances fragmentation most probably involved an open‐chain isomer of the cyclic system.
Heterocyclic studies—XXIX: Mass spectra of some 1,2‐dihydro‐5‐trifluoromethyl‐pyrimido(5,4‐E)AS‐triazines
Authors: Clark Jim
Published: May 2005

Mass spectra of five 7‐substituted‐1,2‐dihydro‐5‐trifluoromethylpyrimido(5,4‐e)as‐triazine derivatives are recorded. Fragmentation pathways, elucidation of which was assisted by deuterium labelling and accurate mass measurements, are compared with those of corresponding heteroaromatic compounds. Loss of HF initiated the major breakdown pathways, unless a large 7‐substituent was present, which then fragmented preferentially.
Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen—IXSterische Effekte in den Massenspekten der Stereoisomeren von Decalin‐2,3‐diolen, Decalin‐2,4‐Diolen und Ihen Dimethyläthern
Authors: Grützmacher Hans‐Friedrich , Fechner Karl‐Heinz
Published: May 2005

Die Massenspektren aller Stereoisomeren des Decalin‐2,3‐diols und des Decalin‐1,4‐diols sowie ihrer Dimethyläther und einiger spezifisch deuterierter Dervae dieser Verbindungen werden diskutiert. Bei den Decallin‐2,3 diolen weden nur geringe quantitative Unterschiede in den Ionenintensitätten gefunden. Die Massenspektren der stereoisomeren 2,3‐Dimethoxy‐decaline sind innerhalb der cis‐ und trans‐Reihe nahezu glech, so daß eine massenspektrometrische Identifizierung der Stereoisomeren schwerfällt. Stereoselektive Eliminierungsreaktionen in den Molek¨︁l‐Ionen können nicht nachgewiesen werden.

In den Massenspektren der Decalin‐1,4‐diole treten charakteristische Unterschiede in den Intensitäten der Ionen [M  H2O]+˙ auf, die in übersichtlicher Weise wie bei de Cyclohexan‐1,4‐diolen mit der Molekülgeometrie der einzelnen Stereoisomeren in Beziehung gesetzt werden können. Die sterischen Kontrolle der H2O‐Abspaltung aus den Molekül‐Ionen wird durch Deuterium‐Markierungen bewisen. Die Massenspektren der Stereoisomeren der 1,4‐Dimethoxydecaline zeigen ebenfalls deutliche Unterschiede in den Intensitäten der [M  CH3OH]+˙‐Ionen. Weiterhin treten Peaks von [M  CH2O]+˙‐Ionen nur in den Massenspektren derjenigen Isomeren auf, bei denen in irgendeiner der Moleküklonformationen ein kurzer Abstand zwischen den Methoxygruppen errricht werden kann. Die Stereoseletivität der CH3OH‐ und CH2O‐Eliminierungen wird gleichfalls druch Deuterium‐Markierungen bewiesen.
The computation of some molecular weights
Authors: Jardine A. , Reed R. I. , Silva M. E. S. F.
Published: May 2005

A method is described for deducing the molecular weight of a compound, the mass spectrom of which does not extend as far as the molecular weight, It is based upon the combination of fragment ions and restricted to limits determined by an approximate estimate of that weight.
Substituent effects on retro‐Diels‐Alder reactions in some 3,6‐diphenyl‐5‐aryl‐4‐amino‐Δ′cyclohexenes
Authors: Das K. G. , Madhusudanan K. P.
Published: May 2005

The variation in the ratio of the relative abundances of the diene and ene ions formed by competing retro‐Diels‐Alder reactions with electron energy and subtituents has been studied. This ratio represents the ratio of the rate constants of the processes and depends on the internal energy distribution within the decomposing molecular ions.
Mass spectral studies of stereoisomers: The photoionisation of some substituted cyclohexanols
Authors: Akhtar Zinat M. , Brion C. E. , Hall L. D.
Published: May 2005

The fragmentation of the stereoisomers of 4‐t‐butylcyclohexanol, and 3‐methylcyclohexanol has been studied by photoionisation mass spectrometry at 1216 Å and 584 Å. Deuterium substitution and high resolution mass spectrometry have been used to gain further insight into the fragmentation pathways.
The mass‐spectral fragmentation of bicyclo[3.3.1]nonanes
Authors: Nicoletti R. , Gambacorta A.
Published: May 2005

The mass spectra of twelve bicyclo[3.3.1]nonanes have been recorded. The high number of metastables observed, exact mass measurements of the ions and low ionising voltage spectra, permitted the rationalisation of most of the fragmentation pathways. The 1‐phenyl substituent triggers the major fragmentation in the hydrocarbon, whereas it has minor influence in the oxygenated compounds. Significant differences in the abundance of [M  H2O]+ ions for stereoisomeric alcohols of this series have been observed.
Heterocyclic studies—XXX: Application of mass spectrometry to the study of covalent hydration
Authors: Clark Jim , Cunliffe A. E.
Published: May 2005

Comparison of the mass spectra of 3,4‐hydrated 4‐trifluoromethylpteridine derivatives with those of corresponding anhydrous compounds shows that this technique can be used to deduce the position of covalent hydration in heterocyclic compounds.

It is less easy to demonstrate the presence of added water molecules in 5,6,7,8‐dihydrated derivatives of ethyl pteridine‐4‐carboxylates, but spectra run at low ionising voltages give the required information.

Two hydrates (3,4‐hydrates of 4‐ethoxycarbonyl‐ and 4‐trifluoromethyl‐pteridine‐2(1H)‐thione) which are very much more thermally stable than usual are also discussed.

Metastable peaks and accurate mass measurements support many of the postulated fragmentation pathways.
Mass spectrometry in structural and stereo‐chemical problems—CCXXIV: Fragmentation of cyclopropanes
Authors: Dias Jerry R. , Djerassi Carl
Published: May 2005

Generalizations for interpreting the mass spectra of cyclopropanes are enumerated and are based on the examination of many deuterium labeled substrates. Most cyclopropyl fragmentations can be visualized as resulting from ionization of the most substituted cyclopropyl bond in which the positive charge is localized on the most substituted carbon atom. Subsequent hydrogen shifts and/or simple scissions produce an array of predictable fragment ions.
Mass spectrometry in structural and stereochemical problems—CCXXV: Sulfur migration in the [MC2H4]+˙ ion of s‐ethyl thiobenzoate
Authors: Tomer Kenneth B. , Djerassi Carl
Published: May 2005

Sulfur migration to an ortho position is observed in the fragmentation of S‐ethyl thio‐benzoate.
The mass spectra of cyclo‐tripeptides of B‐alanine and 3‐amino‐3‐methyl butanoic acid
Authors: Drey C. N. C. , Lowbridge J.
Published: May 2005

The cyclo‐tripeptides of B‐alanine and of 3‐amino‐3‐methyl butanoic acid have been synthesised, the latter for the first time, and structures were confirmed by elemental analysis and mass spectrometry; accurate mass measurements showed that carbon monoxide was lost from the molecular ions; prominent peaks in the mass spectrum of both cyclic peptides are otherwise consistent with those reported for α‐peptides.
The mass spectra of methoxycycloalkanes and methoxymethoxycycloalkanes
Authors: Jones R. B. , Waight E. S. , Herz J. E.
Published: May 2005

Mass spectra of methoxycycloalkanes (CH3OR, R  C5 to C8) and of methoxymethoxycycloalkanes (CH3OCH2OR, R  C5 to C8, C12) have been compared with each other and with spectra of some steroidal analogues. It is concluded that the different fragmentation occurring in dimethoxymethane indicates decomposition before randomisation of excess energy.
Use of metastable peak shapes in determining ring size in cyclic rearrangements in the mass spectrometer
Authors: Beynon J. H. , Bertrand M. , Cooks R. G.
Published: May 2005

A general method is described in which the mechanism of a reaction occurring in the ion source is inferred from the kinetic energy release accompanying further fragmentation of metastable product ions. In several cases the probe reaction occurred competitively by two mechanisms, and if high energy resolution is available this allows the detailed metastable peak shapes and not merely the average kinetic energy released, to be used to characterize the product ion formed in the fast (ion source) reaction. It is found that most substituted benzaldoxime O‐methyl ethers undergo HCN elimination via a five‐centered methoxyl transfer in the ion source, but that the p‐methoxy substituted compound reacts through both a four‐ and a five‐membered cyclic intermediate. The slow reactions of the corresponding metastable ions occur predominantly through a four‐centered transition state in the p‐methoxy compound and probably through both four‐ and five‐membered intermediates for the less strongly electron donating substituents. The fraction of the excess energy of the products is higher than expected from a consideration of energy partitioning data for other systems involving activated complexes of comparable tightness.
Elektronenstossinduzierte CH4‐Abspaltung aus dem Fragment [C7H9]+ von p‐Methyl‐1‐phenyläthanol‐1
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Hochauflösende Massenspektrometrie von 2H‐markierten Verbindung zeigt, dass das Ion [C7H9]+, das aus p‐Methyl‐(1)‐Phenyläthanol‐(1) durch Verlust von CH3· und CO gebildet wird, Methan bevorzugt aus einer Dreiringstruktur verliert. Andere Reaktionswege haben nur einen geringen Anteil an dieser Abspaltung.
A field ionization study of octan‐2‐one
Authors: Derrick P. J. , Falick A. M. , Lewis S. , Burlingame A. L.
Published: May 2005

H/D randomization is not observed within the octan‐2‐one‐1,1,1,3,3‐d5 molecular ion at times less than 7 × 10−10 sec following field ionization. Partial H/D randomization is observbed at 10−6 to 10−5 sec. It is deduced that the curves of microscopic rate constant k against internal excitation energy E for the reactions effecting randomization and for the McLafferty rearrangement intersect. The field ionization kinetics (FIK) for the McLafferty rearrangement in octan‐2‐one‐1,1,1,3,3‐d5 are investigated over a time range extending from 10−11 to 10−6 sec. The maximum microscopic rate constant k for the reaction is estimated as 5 × 1010 sec−1. It is suggested that FIK measurements with a double focusing mass spectrometer be made by sweeping the blade potential rather than by the alternative technique of sweeping the electric sector analyzer potential. The ‘normnal’ FI mass spectra of octan‐2 one and octan‐2‐one and octan‐2‐one‐1,1,1,3,3‐d5 are presented and discussed. It is proposed that the m/e 56 species in the ‘normal’ FI mass spectrum of octan‐2‐one represents a doubly charged ion formed by loss of oxygen in a surface process.
Mass spectra of substituted 4,6‐bis‐aryl‐2‐pyrimidoles
Authors: Ivanovskaya L. Yu. , Gorfinkel M. I. , Sedova V. F. , Dubovenko Z. D.
Published: May 2005

An analysis of the mass spectra of 18 4,6‐bis‐aryl‐2‐pyrimidoles was performed. Regularities allowing structure determination, in particular for isomers, are discussed.
Mass spectra of trimethylsilyl ethers of some Δ5‐3β‐hydroxy C 19 steroids
Authors: Brooks C. J. W. , Harvey D. J. , Middleditch B. S. , Vouros P.
Published: May 2005

The mass spectra (20 eV electron energy) of a wide range of %Δ5‐3β‐hydroxy C19 steroid TMS ethers have been examined with the aid of high‐resolution mass measurements, together with deuterium and oxygen‐18 labelling data. The validity of many previously proposed fragmentation modes has been confirmed. A number of ions regarded as diagnostic have been shown to be less specific than had been formerly supposed. Several novel fragmentations have been observed and investigated.
Elektronenstossinduzierte fragmentierung von polymethylbenzaldehyden—II: Mechanismus der Methyl‐Abspaltung aus dem Molekül‐Ion von Tri‐ und Pentamethylbenzaldehyden
Authors: Schwarz Helmut , Bohlmann Ferdinand , Russ Barbara
Published: May 2005

Die elektronenstossinduzierte Methyl‐Abspaltung aus Tri‐und Pentamethylbenzaldehyden kann durch eine vinyloge α‐Spaltung erklärt werden. Umlagerungen können ausgeschlossen werden.
The high resolution mass spectra of α,β‐unsaturated and α‐chloromercuri‐α,β‐unsaturated steroidal ketones
Authors: Smith Howard E. , Smith Roy G.
Published: May 2005

The high resolution mass spectra (500 eV) of some α,β‐unsaturated steroidal ketones have been studied and compared with the spectra of the corresponding α‐chloromercuri ketones. In the latter, the carbon‐mercury bond frequently remains intact at the expense of the fission of two carbon‐carbon bonds. The abundance of mercury‐containing ions allows the use of the mercury atom fingerprint in confirming ring B fragmentation of the steroid nucleus at C(6)–C(7) and C(9)–C(10) for 5α‐androst‐1‐ene‐3,17‐dione, 1,4‐androstadiene‐3,17‐dione and their 2‐chloromercuri derivatives; and at C(7)–C(8) and C(9)–C(10) for 1,4,6‐androstatriene‐3,17‐dione, 1,4,6‐androstarien‐17 β‐ol‐3‐one and their 2‐chloromercuri derivatives. 2‐Chloromercuri‐1,4,6‐androstatriene‐3,17‐dione and 2‐chloromercuri‐1,4,6‐androstatrien‐17 β‐ol‐3‐one also give an abundant ion as the result of ring C fragmentation at C(8)–C(14) and C(11)–C(12), the chloromercuri group being replaced by a hydrogen atom. This ring C cleavage gives the only recognizable distinctive fragmentation ion for 1,4,6‐pregnatriene‐3,20‐dione and 2‐chloromercuri‐1,4,6‐pregnatriene‐3,20‐dione. For most of the mercurated steroids, the low resolution mass spectra (70 eV) are reported. In these spectra, the fragmentation patterns are similar to those obtained using the higher ionization energy employed for the high resolution spectra.
Studies in organic mass spectrometry‐XIII: Investigation of electron‐induced isomerisation of αβ‐ and βγ‐unsaturated esters
Authors: Lauwers W. , Serum J. W. , Vandewalle M.
Published: May 2005

The mass spectral fragmentation of methyl esters of α,β‐ and β,γ‐unsaturated carboxylic acids has been studied. Deuterium labelling, metastable ion analysis and high resolution mass spectrometry have been utilised to elucidate the mechanism of a number of fragmentations and to check possible double bond migration prior to fragmentation. Some breakdown modes were found to occur through double bond migration. Additional support was provided by application of the ‘Metastable Ion Characteristics’ method. Partial isomerisation of molecular ions must therefore be accepted.
Octahedral metal carbonyls‐XXIX: Mass spectra of cis‐disubstituted derivatives of the group VI‐B metal carbonyls
Authors: Brown Richard A. , Paxson John R. , Dobson Gerard R.
Published: May 2005

The mass spectra of a number of cis‐disubstituted derivatives of the Group VI‐B metal carbonyls (M = Cr, Mo, W), in which the substituents are bidentate ligands bonding to the metal through As, S or N donor atoms, have been obtained. The spectra for derivatives of o‐phenylenebis‐(dimethylarsine) (diars) have been examined in greatest detail. For these latter complexes, competitive loss of carbonyls and diars methyl groups was observed. The proposed use of such competition in the evaluation of metal‐carbonyl bond strengths is examined. For complexes containing ethylene‐bridged bidentate ligands, ions indicative of the loss of five fragments of 28 mass units from the parent ion, corresponding to loss of four carbonyls and the ethylene bridge, are observed. The question of whether ethylene loss occurs prior to, competitively with or after carbonyl loss is considered.
Mass spectrometry of pyridine compounds–IV: The formation and decomposition of the [M – methyl]+ ion [C8H10N]+ from 4‐t‐butylpyridine in comparison with that of the [M – methyl]+ ion [C9H11]+ from t‐butylbenzene, as studied by D‐ and 13C‐labelling
Authors: Neeter R. , Nibbering N. M. M.
Published: May 2005

A strong secondary isotope effect is observed in the preferred loss of methyl vs. trideutero‐methyl from the molecular ions of appropriately labelled 4‐t‐butylpyridine and t‐butylbenzene decomposing in the first and second field free regions of a double focusing mass spectrometer. This has been rationalised by invoking the theory of radiationless transitions2, which can account for the higher population of activated states responsible for loss of methyl vs. that for trideuteromethyl.

13C‐Labelling at the central carbon atom of the t‐butyl group indicates that the [M – methyl]+ ions, decomposing further by elimination of ethylene, cannot be represented exclusively by a pyridylated (or phenylated) cyclopropane ion if present at all. It is concluded that ions with structures generated by 1,2‐hydrogen‐, 1,2‐pyridyl‐ (or 1,2‐phenyl‐) and 1,2‐methyl shifts must also play a role.

D‐labelling further shows an extensive randomisation of side‐chain hydrogen atoms in the [M‐methyl]+ ions of 4‐t‐butylbenzene; in this case, however, the expelled ethylene also contains ring hydrogen atoms (≤2). Presumably this is caused by exchange between the side‐chain and ortho‐hydrogen atoms in the initially generated phenyldimethylcarbinyl carbenium ion.
Field desorption mass spectra of stereoisomeric glycosides
Authors: Lehmann W. D. , Schulten H.‐R. , Beckey H. D.
Published: May 2005

Field desorption mass spectrometry (FD‐MS) yields differentiated spectra for unshielded α‐ and β‐stereoisomeric glycosides. The small but characteristic differences enable a distinction to be made between the two isomers. Valuable structural information can be deduced from the simple cleavage between the sugar moiety of the molecule and the aglycon. A short comparison with electron‐impact (EI) and field ionisation (FI) spectra is given.
Liquid chromatography‐mass spectrometry interface–I: The direct introduction of liquid solutions into a chemical ionization mass spectrometer
Authors: Baldwin M. A. , McLafferty F. W.
Published: May 2005

Mass spectra of solutes can be obtained by direct introduction of the solution into a chemical ionization source. This should facilitate direct monitoring of the effluent from liquid chromatography columns with nanogram sensitivity.
An experimental and indo molecular orbital study of variable response of the p‐phenyl substituent to electron demand. Relative conformations of two p‐arylacetophenones as neutral molecules and +1 molecular ions
Authors: Twine Charles E. , Parker Carol E. , Bursey Maurice M.
Published: May 2005

The INDO molecular orbital method suggests that the rings of p‐phenylacetophenone and 2‐fluoro‐4′‐acetylbiphenyl are more nearly coplanar in the +1 molecular ion than in the neutral molecule. This is indicated by old experimental data for the former and new data for the latter, based on the cleavage to [CH3CO]+.
The ortho effect in mass spectra. Insight into the tightening of activated complexes for the loss of ketene from phenyl acetates and ethylene from phenetoles from INDO molecular orbital calculations
Authors: Parker Carol E. , Hass J. Ronald , Bursey Maurice M. , Pedersen Lee G.
Published: May 2005

INDO Molecular orbital calculations of the energetically most favourable conformation of the molecular ions of phenyl acetate and its o‐fluoro‐ and o‐chloro‐analogs indicate bond formation between carbonyl oxygen and ortho halogen. For the molecular ions of phenetole and its o‐fluoro and o‐chloro‐analogs, no ring formation is observed. These results are in accord with the frequency factor changes found for the ortho substitution in these systems by halogens.
Mass spectral studies of some complexes of niobium(V) and tantalum(V) with chloro, alkoxy, acetylacetonato or salicylaldehydato ligands
Authors: Stefanović D. , Stambolija Lj. , Katović V.
Published: May 2005

Mass spectra of complex compounds of niobium (V) and tantalum (V) of the type MCl2(OR)2L have been measured, where M = Nb and Ta; HL = 2,4‐pentanedione, R = CH3, C2H5 and HL = Salicyladehyde, R = CH3. The fragmentation upon electron‐impact depends on the nature of the ligands and to a minor extent on the central metal atom. A fragmentation scheme has been constructed on the basis of measurements of metastable transitions and accurate masses of important fragment ions. Rearrangement reactions involving hydrogen migration among ligands have been observed.
Internal energy effects on metastable characteristics. The structure of [C3H7O]+ ions
Authors: Tsang C. W. , Harrison A. G.
Published: May 2005

The effect of changes in the internal energy distribution of the fragmenting ion on the ratio of metastable ion intensities for two competing fragmentation reactions has been investigated both theoretically and experimentally. Model calculations have shown that if the competing reactions have significantly different activation energies the metastable intensity ratio does depend on the internal energy distribution although large changes are necessary before the ratio changes by more than a factor of two. Experimentally the metastable characteristics of [C3H7O]+ ions of nominal structures [CH3CH2O+CH2] (I), [(CH3)2CO+H] (II), [CH3CH2CHO+H] (III) and [CH3O+CHCH3] (IV) have been examined. For each structure the metastable characteristics are found to be distinctive and independent of changes in the internal energy distribution of the fragmenting ion where these changes result from altering the precursor of the [C3H7O]+ ions. It is suggested that these internal energy changes can be estimated from the fraction of [C3H7O]+ ions which fragment in the ion‐source. It is concluded that structures I to IV represent stable and distinct ionic structures.
Silylgruppenwanderung und CO2‐Eliminierung beim massenspektrometrischen Zerfall von N‐Trifluoracetyl‐α‐aminosäretrimethylsilylestern
Authors: Birkoffer L. , Schmidtberg G.
Published: May 2005

Die Molekü‐Ionen der N‐Trifluoracetyl‐α‐amminosäuretrimethylsilyester zeigen im Gegensatz zu anderen Aminosäurederivaten eine charakteristische Abspaltung von CO2, offensichtlich als Folge einer Wanderung der Ester‐trimethylsilylgruppe zum Sauerstoff der N‐Trifluoracetylfunktion. Durch die weitere Fragmentierung der so gebildeten [M‐CO2]+˙‐Ionen entstehen besonders bei Derivaten der aliphatischen Aminosäuren intensive Bruchstü ke. Bei den Isomeren leucin und Isoleucin führt sie sogar zu unterschiedlichen basispeaks für die 20 eV‐Spektren. Aminosäuren mit leicht abspaltbarer gruppe in β‐Position scheinen Co2 synochron mit dieser Gruppe zu eliminieren, so daß bei ihnen das [M‐CO2]+˙‐Ion selbst nicht zu beobachten ist. Als Konkurrenzreaktion zur Wanserung der estersilylgruppe zum N‐Triffuoracetyl‐sauerstoff tritt bei Serin, Threonin und Cystein eine Si‐Umlagerung zur β‐ständigen funktionellen Gruppe auf. Auch sie verläuft unter gleichzeitiger Abspaltung von CO2.