bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen migrations in mass spectrometry. VI—the chemical ionization mass spectra of substituted benzoic acids and benzyl alcohols
Authors: Ichikawa Hiroshi , Harrison Alex. G.
Published: May 2005

The H2 and CH4 chemical ionization mass spectra of a series of series of substituted benzoic acids and substituted benzyl alcohols have been determined. For the benzoic acids the major fragmentation reactions of the protonated molecule involve elimination of H2O or elimination of CO2, the latter reaction involving migration of the carboxylic hydrogen to the aromatic ring. For the benzyl alcohols the major fragmentation reactions of [MH]+ involve loss of H2O or CH2O, analogous to the CO2 elimination reaction for the benzoic acids. It is shown that the CO2 and CH2O elimination reactions occur only when a conjugated aromatic ring system is present, and that for the carboxylic acid systems, methyl groups and, to a lesser extent, phenyl groups are capable of migrating. The only discernible effect of substituents on the fragmentation of [MH]+ is an enhancement of the H2O loss reaction in the benzoic acid system when an amino, hydroxyl, or halogen substituent is ortho to the carboxyl function. This ‘ortho’ effect, which differs in scope from that observed in electron impact mass spectra, is attributed to an intramolecular catalysis by the ortho substituent of the 1,3 hydrogen migration in the carbonyl protonated acid followed by H2O elimination. Apparently, this route is favoured over the direct elimination of H2O from the carbonyl protonated acid, since the latter has a high activation energy barrier because of unfavourable orbital symmetry restrictions.
The mass spectrometric fragmentation of n‐heptane
Authors: Lavanchy André , Houriet Raymond , Gäumann Tino
Published: May 2005

The electron impact fragmentation of n‐heptane has been investigated using 13C labelled derivatives. A mechanism is proposed for the loss of alkyl radicals where the cleavage of a CC bond is coupled with the rearrangement of a hydrogen atom, thus yielding a secondary alkyl ion that eventually fragments further by a subsequent loss of olefin. For alkyl ions with less than six carbon atoms this consecutive pathway is in competition with formation directly from the molecular ion. The consecutive pathway contributes about 15% to the intensity of the alkyl ions with four and five carbon atoms and 80% for smaller ions. The electron energy dependence was studied.
Collisional activation spectra at improved resolving power obtained by the use of a collision chamber and a linked scan of the electric and magnetic sector field strengths
Authors: Stradling R. S. , Jennings K. R. , Evans S.
Published: May 2005

A method for obtaining collisional activation spectra at much higher resolving power than before by use of a collision chamber and a B/E linked scan, is described.
Redox processes in the evaporation of N‐phenylpyridinium salts in the mass spectrometer
Authors: Ellingsen P. , Hvistendahl G. , Undheim K.
Published: May 2005

N‐Phenylpyridinium and 1,4‐diphenylpyridinium halides undergo both one and two electron reductions to the N‐phenyl‐ and 1,4‐diphenylpyridine free radicals and the corresponding 1,2‐ and 1,4‐dihydro derivatives respectively, prior to evaporation in the mass spectrometer. In addition, a third component is found in the gas phase, possibly due to dimerization of the free radical followed by dehydration.
Chemical ionization mass spectrometry of some crown ethers
Authors: Van Gaever F. , Van de Sande C. C. , Bucquoye M. , Goethals E. J.
Published: May 2005

Methane and isobutane chemical ionization mass spectrometry is superior to the classical electron impact technique for the analysis of aliphatic macrocyclic polyethers of the 4n‐crown‐n type. The latter reagent gas is particularly suited for molecular weight determinations.
Etude Structurale de Cations‐Radicaux
Authors: Maquestiau A. , Van Haverbeke Y. , Flammang R. , Menu A. , Wentrup C.
Published: May 2005

Les spectres d'énergie cinétique de cations‐radicaux issus de 26 précurseurs sont décrits. L'étude des caractéristiques d'ions métastables telles que les libérations d'énergie cinétique, les rapports d'abondances ioniques ou encore les distributions isotopiques pour des composés marqués, montre que tous les ions métastables sont isomérisés en une structure commune ou des mélanges semblables de structures avant fragmentation. Les dissociations induites par collisions et l'ionisation collisionnelle ont été utilisées pour l'étude des ions stables dont la durée de vie est supérieure au temps de vol entre la source et le collecteur. Les résultats sont interprétés sur la base de mélanges de structures initiales et isomérisées.
Spectrographie de Masse de Diazastéroïdes Possédant le Motif Tétrahydroisoquinoléique
Authors: Verchère Catherine , Hocquaux Michel , Viel Claude
Published: May 2005

Nous avons recherché les fragmentations caractéristiques dans la série de la dihydro‐3,4 isoquinoléine et de la diaza‐8,13 oestrone. La recherche des pics métastables, ľétude des spectres ‘simili’ MIKE et ľétude de dérivés deutériés ont été utilisées. En série diazastéroïdique, nous avons mis en évidence trois grands types de fragmentation, ainsi qu'un départ préférentiel de ľhydrogène porté par le carbone 14.
Spectrométrie de Masse d'Hétérocycles Azotés. VII—Phenyl‐1 Triazole‐1,2,3
Authors: Aubagnac J.‐L. , Campion P. , Guenot P.
Published: May 2005

La comparaison des spectres normaux et MIKE du phényl‐1 triazole‐1,2,3 et de ses dérivés deutériés et marqués au 13C indique que les ions peuvent se décomposer selon deux voies compétitives: une rupture simple sans réarrangement est préférentielle pour les ions de haute énergie (spectre normal). Au contraire, la perte de HCN domine pour les ions de basse énergie (métastables) et a lieu après mixage complet des atomes d'hydrogène.
The gas enhanced negative ion mass spectra of polychloroanisoles
Authors: Busch Kenneth L. , Hass J. Ronald , Bursey Maurice M.
Published: May 2005

Methane or a methane–oxygen mixture was used as an enhancement gas to obtain negative ion mass spectra of polychloroanisoles. Dichloroanisoles did not react with oxygen but the more highly chlorinated anisoles did. Compounds with hydrogen ortho to the methoxy group had [M1]− ions, while others gave . The fragment arose through loss of an ortho chlorine and amethyl hydrogen. The loss of HCl followed by oxygen displacement of a remaining ortho or para chlorine produced [M55]− ions; the para position was the preferred site of displacement. Another ion‐molecule reaction with oxygen leads to [MCH2Cl]−. The fragmentations resemble those of chlorinated aromatics such as the polychlorodibenzodioxins.
Electron impact mass spectra of some enols and their alkyl ethers
Authors: Nagraba Krzysztof , Moskal Janusz , Moskal Aleksandra
Published: May 2005

The mass spectra of α‐arylamino‐β‐hydroxycrotonic acid anilides and their O‐methyl and O‐ethyl ethers have been determined and the characteristic fragmentation pathways are discussed. The proposed fragmentation patterns are supported by the appropriate metastables and deuterium labelling.
EA‐Massenspektren Cyansubstituierter Heterocyclen
Authors: Holzmann G. , Rothkopf H. W.
Published: May 2005

Die EA‐Spektren cyansubstituierter Heterocyclen zeigen spezifische Fragmentierungen, die eine massenspektrometrische Unterscheidung isomerer Systeme gestatten. Die Strukturen der aus den Molekülanionen bzw. [(M – H)]− ‐Ionen direkt gebildeten ‐Ionen werden durch Vergleich der MI‐ bzw. CA‐spektren verschiedener Vorläuferionen untersucht. Das Fragmentierungsverhalten von Tetracyan‐substituierten Heterocyclen setzt Umlagerungen der Molekülanionen voraus.
In‐beam electron impact mass spectrometry of aliphatic alcohols
Authors: Ohashi Mamoru , Nakayama Noboru
Published: May 2005

The characteristics of the in‐beam electron impact mass spectra of six isomers of undecanol as well as several 1‐alkanols have been examined. In addition to the characteristic ions observed in the conventional electron impact spectra, the [2M+1]+, [2M+1‐H2O]+, [2M+1‐2H2O]+, [2M‐R or R′]+, [2M‐H2OR or R′]+, [2M2H2OR or R′]+ and [M+1H2O]+ peaks are common in the in‐beam electron impact mass spectra of the undecanol isomers of structure RCH(OH)R′. Deuterium labelling experiments have shown that the extra proton in the protonated dimer ions, [2M+1]+, originates from the hydroxy group. The processes which produce the important peaks in the high m/e regions are discussed.
Flophemesyl derivatives of alcohols, phenols, amines and carboxylic acids: Derivatives for mass spectrometric ion monitoring and structure determination
Authors: Francis Ainsley J. , Morgan E. D. , Poole C. F.
Published: May 2005

The flophemesyl (or pentafluorophenyldimethylsilyl) derivatives of representative alcohols, phenols, carboxylic acids and amines show rather simple spectra with a few abundant ions at high mass, characteristic of the parent compound and a few ions at low mass characteristic of the flophemesyl group. These derivatives are useful in the structure determination of simple compounds, and for the determination by single or multiple ion monitoring of known compounds at low levels.
N′,O,O′‐triacetyl‐N‐caffeoylputrescine: A new synthesis and mass spectrometry
Authors: Eagles John , Self Ron , Synge Richard L. M.
Published: May 2005

Some puzzling features of a published mass spectrum of the title compound have been clarified by mass spectrometric study of a specimen prepared by a new route, by coupling O,O′‐diacetylcaffeoyl chloride with N‐monoacetylputrescine.
The consecutive loss of two H2O molecules from protonated 1,2‐ and 1,3‐ cyclohexanediols in the gas phase: An example for the incidence of skeletal rearrangement in chemical ionization mass spectrometry
Authors: Wolfschütz Roland , Schwarz Helmut , Blum Wolfgang , Richter Wilhelm J.
Published: May 2005

The consecutive dehydration of protonated molecules [MH]+ of 1,2‐ and 1,3‐cyclohexanediols (cis and trans isomers) by loss of two H2O molecules has been investigated. Analysis of 2H labelled compounds showed that loss of the first H2O molecule represents a simple heterolysis, i.e. a dissociation without exchange of hydrogens between O—H and C—H bonds. Subsequent elimination of the second H2O molecule in the process [MH–H2O]+→[MH–2H2O]+ followed several competing paths. The two major ones corresponded formally (with reference to an intact 6‐ring skeleton) to 1,3‐ and 1,4‐eliminations; in comparison, the alternative 1,2‐elimination is only a minor route at most. At least for the 1,3‐elimination, water loss from the [MH–H2O]+ ions is not direct, but is associated with skeletal rearrangement, most probably of the Wagner‐Meerwein‐type, effecting contraction of the 6‐ to a 5‐membered ring.
The origin of the [M – 1]+ ion in the mass spectra of N,N‐dialkylbenzamides. A reinvestigation of the mechanism
Authors: Fong C. W. , Hameister C. R.
Published: May 2005

A reinvestigation of the mechanism of formation of the [M – 1]+ ion in a series of N,N‐dialkylbenzamides suggests that previous mechanisms put forward to account for the formation of the [M – 1]+ ion are deficient. A new mechanism is proposed which accounts for the data observed previously, as well as our results for a series of N,N‐dialkyl‐2‐chlorobenzamides, 4‐substituted N,N‐dimethylbenzamides and some related compounds. For the N,N‐dialkyl‐2‐chlorobenzamides, comparison of the abundances of the [M – 1]+ ion with the [M – 35]+ ion suggests that a concurrent reaction is occurring, besides loss of the ortho aromatic hydrogen atom. A study of substituent effects on the intensity ratio [M – 1]+/[M]+ shows an upward concave plot of this against σ+, suggesting that two competing mechanisms occur for the formation of the [M – 1]+ ion.
Structure and formation of gaseous [C4H5O]+ ions. I—isomeric ions of the type C3H5\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O
Authors: Hommes Henk , Terlouw Johan K.
Published: May 2005

Characterization of [C4H5O]+ ions in the gas phase using their collisional activation spectra shows that the four C3H5\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O isomers CH2C(CH3)\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O, CH2CHCH2\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O, CH3CHCH\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O and ▹\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O are stable for ≥ 10−5 s. It is concluded further from the characteristic shapes for the unimolecular loss of CO from C3H5\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O ions generated from a series of precursor molecules that the CH2CH(CH3)\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O‐ and CH2CHCH2\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O‐type ions dissociate over different potential surfaces to yield [allyl]+ and [2‐propenyl]+ [C3H5]+ product ions respectively. Cyclopropyl carbonyl‐type ions lose CO with a large kinetic energy release, which points to ring opening in the transition state, whereas this loss from CH3CHCH\documentclass{article}\pagestyle{empty}\begin{document} $\mathop {\rm C}\limits^ + =\!= $\end{document}O‐type ions is proposed to occur via a rate determining 1,2‐H shift to yield 2‐propenyl cations.
The fragmentation of 5‐phenyl‐1,4‐benzodiazepin‐2‐ones. Mechanism for the formation of [M  H]+
Authors: Benz Wolfgang , Vane Floie M. , Rapp Uwe
Published: May 2005

The fragmentations under electron impact of 5‐phenyl‐1,4‐benzodiazepin‐2‐ones are investigated with the aid of high resolution, metastable decompositions and deuterium labeling. Based on our data a mechanism for the formation of the [M – H]+ ion is proposed. It is shown that the [M – CHO]+ ion is probably formed by two different pathways. Data on two minor fragment ions give support to the structure proposed for the [M – CHO]+ ion.
Elimination sous Impact Electronique de HCN et H· a partir de l'Indole. Comparaison avec l'Indolizine
Authors: Corval Madeleine
Published: May 2005

Les deux fragmentations primaries de l'indole sous l'impact d'électrons, perte de HCN et perte de H⋅, sont étudiées au moyen de onze variétées marquées au deutérium. Tous les hydrogènes sont impliqués dans le processus de perte de HCN, avec une prédominance des hydrogènes du cycle pentagonal, plus marquée dans le spectre à 70 eV que dans la gamme d'éenergie des ions métastables, où les trois sommets du cycle pentagonal sont équivalents. Les résultats d'ordre qualitatif relatifs à la perte de H⋅ mettent en évidence l'existence d'un effet d'isotopie et sont également compatibles avec une prédominance des hydrogènes du cycle pentagonal, qui d'une élimination très préférentielle de l'hydrogène lié à l'azote. Ce comportement est comparé à celui de l'indolizine, et les niveaux d'énergie des états de transition menant à la perte de HCN sont discutés pour les deux composeés.
Isomerisierung von Methoxy‐ und Carbomethoxysubstituierten Cycloalkyl‐ und Alken‐radikalkationen
Authors: Schwarz H. , Wesdemiotis C. , Levsen K. , Heimbach H. , Wagner W.
Published: May 2005

Unter Benutzung mehrerer Techniken, wie Stoßaktivierung, Charakteristik metastabiler Ionen und Feldionisationskinetik, wird das äußerst komplexe Isomerisierungsverhalten von methoxy‐ und caarbomethoxysubstituierten Cycloalkanen (drei‐bis siebengliedrege Ringe) analysiert. Das Ausmaß der Isomerisierung hängt sowohl von der Ringgröße als auch vom Substituenten ab, während die Ringöffnung unabhängig von den elektronischen Eigenschaften der Substituenten immer die C‐1C‐2‐Bindung betrifft. Hierbei werden ausschließlich lineare Alken‐Radikalkationen erzeugt. Bei OCH3‐ und COOCH3‐Substituenten wird die Lage der resultierenden Doppelbindung terminal oder α,β‐ungesättigt hauptsächlich durch die Ringgröße des Cycloalkan‐Molekülions und weniger durch den Substituenten beeinfluß. Alkylsubstituierte Cycloalkane (drei‐ bis fünfgliedrige Ringe) lagern sich allerdings nur zu terminalen Alken‐Radikalkationen um. Die Barriere der Doppelbindungswanderung scheint vom Substituenten abhängig zsu sein.
Fragmentation of even electron ions. Protonated ketones and ethers
Authors: Sigsby M. L. , Day R. J. , Cooks R. G.
Published: May 2005

A systematic study of the types of fragmentation undergone by internally excited protonated molecules is presented. Two representative functional groups, ethers and ketones, are selected, and both aliphatic and aromatic substituents are examined. The ions are formed by protonation or alkylation in a chemical ionization source, and caused to fragment by collision at high relative kinetic energy. The prevalence of 1,3‐rearrangements and the breakdown of the even electron fragmentation rule highlight the ion chemistry uncovered here. Specific findings include: (i) electron unpairing reactions associated with alkyl radical loss are common. These are probably energetically less favorable simple bond cleavages and are observed in competition with entropically less favorable elimination reactions. (ii) Alkane elimination is a characteristic reaction, which often occurs by a four‐centered mechanism. Several variations on this reaction type are encountered. (iii) Alkene elimination is another ubiquitous reaction which occurs by a four‐centered mechanism in the systems studied here. Competition between alkene and alkane loss is extremely sensitive to the particular system in hand.
Mass spectra of flavonoids. Electron impact mass spectra of flavan‐4‐ols
Authors: Radford Terence , Sweeny James G. , Iacobucci Guillermo A. , Hribar Jeremy D. , Weibel Leo A.
Published: May 2005

The electron impact mass spectra of seven flavan‐4‐ols are reported. Fragmentation pathways were investigated using deuterium labeling and high resolution measurements. The results are consistent with previously proposed ion structures for these compounds, but indicate that the mechanisms suggested for certain hydrogen rearrangements should be revised.
Structural correlations with kinetic energy release during loss of chlorine from nineteen selected chlorinated biphenyls
Authors: Hass J. Ronald , Bursey Maurice M. , Levy Louis A. , Harvan Donald J.
Published: May 2005

Unimolecular and collision induced decompositions of the major ions of selected polychlorinated biphenyls in the field free region between the magnetic and electric sectors of a reversed Nier‐Johnson instrument were studied. Loss of a single chlorine atom is associated with a wide range of kinetic energy releases but still can be correlated by a single reaction mechanism. Loss of two chlorines is interpreted as a rapid sequential loss from isomerized molecular ions for all but one compound. The decompositions which metastable ions undergo are not always the same as those of high energy ions in the source. Correlations between substituent positions and kinetic energy release can be made for the [M]+·→[MCl]+ and [MCl2]+· processes.
Kinetic energy release in unimolecular decompositions of ions. hydrogen rearrangements
Authors: Cole Neil W. , Rickard Gregory J. , Christie John R. , Derrick Peter J.
Published: May 2005

The partition of reverse activation energy in hydrogen rearrangements is considered in terms of atomic motions composing the transition state reaction coordinate. It is shown how this approach predicts that, in general, elimination of H2 from any small ion (as defined in the paper) is likely to be characterized by partition of significant proportions of any reverse activation energy as translational energy of the products. Hydrogen rearrangements in large ions leading to fragments of comparable mass are much less likely to partition reverse activation energy into product translation.
The mass spectral fragmentation of phenyl ω‐dialkoxyethyl tellurides
Authors: Knapp Furn F.
Published: May 2005

The 70 eV mass spectrum of phenyl ω‐dimethoxyethyl telluride [C6H5TeCH2CH(OR)2, RCH3]contains an intense peak at m/z 238 which corresponds to a rearrangement ion [C6H5TeOR]+. The formation of this species is further illustrated by the presence of a peak at m/z 241 in the spectrum of the hexadeuterated analog (RCD3) and a peak at m/z 252 in the spectrum of the ethyl analog (RCH2CH3). These combined results illustrate the presence of only one of the alkoxyl groups in the rearrangement ion. Several other abundant ions that contain oxygen but not tellurium are present in the spectra of these compounds. High resolution analyses have aided in the determination of the origin and composition of several of the characteristic ions formed upon electron impact fragmentation of phenyl ω‐dimethoxyethyl telluride.
Fragmentation sous l'Impact Electronique d'Amino‐4 triazole‐1,2,4 ones‐5
Authors: Bernardini Antoine , Viallefont Philippe , Milcent René
Published: May 2005

Les spectres de masse d'un certain nombre d'amino‐4 triazole‐1,2,4 ones‐5 différemment substituées en position 1 sont rapportés; ils mettent en évidence de nouveaux réarrangements et des migrations d'hydrogène. La comparaison des spectres normaux et des spectres d'énergie cinétique obtenus selon la technique simili MIKE a permis de déterminerla structure des ions moléculaires et des ions fragments et de décrirela formation de ces derniers. Ces résultats montrent que ľion moléculaire des amino‐4 triazolones‐5 non substituées en position 1 existe probablement en phase gazeuse sous deux formes tautomères (N‐1‐H et OH).
Mass spectrometry of transition metal π‐complexes. XV—The effect of substituents on the fragmentation of benchrotrenyls under electron impact
Authors: Nekrasov Yu. S. , Vasyukova N. I.
Published: May 2005

Mass spectra of substituted benchrotrenyls RC6H5Cr(CO)3 where RH, F, CI, I, CH3, OCH3, COOCH3, C2H5, N(CH3)2, NH2, C6H5, C(CH3)3, p‐C6H4NH2, CH2C6H5, CH2CH2C6H5), 1,3,5‐(CH3)3C6H3Cr(CO)3 and 1,2,3,5‐(CH3)4C6H2Cr(CO)3 have been studied. It has been found that for monosubstituted benchrotrenyls there is a linear dependence of the parameter log [Cr]+/[RC6H5Cr]+) on the number of degrees of freedom of the [RC6H5Cr]+ ion. Decarbonylation of the molecular ions is not affected by the nature of the substituent R. The results are interpreted in terms of the quasi‐equilibrium theory of mass spectra.
A Photoionization study of some benzoyl compounds—Thermochemistry of [C7H5O]+ formation
Authors: McLoughlin R. G. , Traeger J. C.
Published: May 2005

Appearance energies for [C7H5O]+ fragment ions, formed from a variety of benzoyl compounds, have been measured by photon impact. The mean heat of formation calculated for [C7H5O]+ is 705 ± 6 kJ mol−1, which can be correlated with either a single threshold structure or a mixture of structures with similar heats of formation. Previously observed variations of ΔHf([C7H5O]+) with precursor molecule are shown to be consistent with a structure dependent kinetic shift, rather than the presence of isolated electronic states.
Loss of hydrogen cyanide from monocyanopyridines upon electron impact: Dewar pyridine structures and ring opening—Ring closure reactions revealed by 13C and 15N Labelling
Authors: Molenaar‐Langeveld T. A. , Vermeulen N. P. E. , Nibbering N. M. M. , Morgan R. P. , Brenton A. G. , Beynon J. H. , Sharma D. K. Sen , Jennings K. R.
Published: May 2005

Extensive 13C and 15N labelling has shown that the molecular ions of 2‐, 3‐ and 4‐cyanopyridine with lifetimes up to 10−6 s eliminate hydrogen cyanide originating predominantly from the ring (˜65%). Moreover, this hydrogen cyanide loss occurs after an equilibrated positional interchange of the ring carbon atoms at positions interchange of the ring carbon atoms at positions 2, 4 and 6 via Dewar pyridine structures. In molecular ions with lifetimes of 10−6–10−5 s skeletal rearrangements have taken place in such a way that both nitrogen atoms have become equivalent prior to the loss of hydrogen cyanide. Arguments are put forward that this equivalence of nitrogen atoms is caused by the intermediacy of ions with a 1,4‐dicyanobuta‐1,3‐diene structure. About 60% of these intermediate ions eliminate hydrogen cyanide in a fast process. The remaining 40% of these ions undergo ring closure again to a pyridine ring in which the carbon atoms of positions 2, 4 and 6 are positionally interchanged rapidly via Dewar pyridine structures followed by ring opening again and eventual loss of hydrogen cyanide. This interpretation of the 13C and 15N labelling results is further corroborated by a study of the loss of hydrogen cyanide from molecular ions of 1,4‐dicyanobuta‐1,3‐diene labelled with 13C in both cyano groups.
Identification of some isomeric [C8H6O]+˙ ions generated from phenyl substituted cyclic ketones using collisional activation
Authors: Van Den Heuvel C. G. , Nibbering N. M. M. , Heimbach H. , Levsen K.
Published: May 2005

[C8H6O]+˙ ions with o‐quinonoid ketene, benzocyclobutenone, phenyl ketene and benzofuran structures have been generated from various precursors. Their collisionally induced decompositions in both field free regions of a double focusing mass spectrometer with so‐called reversed geometry have been studied using mass analysed ion kinetic energy scans and B/E linked scans. In both cases the abovementioned [C8H6O]+˙ structures can be distinguished–except the benzocyclobutenone ion which gives very similar spectra to the o‐quinonoid ion–on the basis of the intensity ratios [m/z 77]/[m/z 76] and [m/z 104]/[m/z 102]. The stable [C8H6O]+˙ ions generated from the molecular ions of 7 ‐phenylbicyclo[3.1.1]heptan‐6‐one appear to have the phenyl ketene structure, as was suspected from previous kinetic energy release measurements.
Structure and formation of gaseous [C4H5O]+ Ions. II–Ions of the type HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}(OH)(CH3)
Authors: Burgers Peter C. , Hommes Henk , Terlouw Johan K.
Published: May 2005

Loss of an alkyl group X⋅ from acetylenic alcohols HCCCX(OH)(CH3) and gas phase protonation of HCCCOCH3 are both shown to yield stable HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}(OH)(CH3) ions. Ions of this structure are unique among all other [C4H5O]+ isomers by having m/z 43 [C2H3O]+ as base peak in both the metastable ion and collisional activation spectra. It is concluded that the composite metastable peak for formation of m/z 43 corresponds to two distinct reaction profiles which lead to the same product ion, CH3\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}O, and neutral, HCCH. It is further shown that the [C4H5O]+ ions from related alcohols (like HCCCH(OH)(CH3)) which have an α‐H atom available for isomerization into energy rich allenyl type molecular ions, consist of a second stable structure, H2C\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}C(OH)CH2.
Structure and formation of gaseous [C4H5O]+ ions. IV—Ions derived from the cyclopropenium ion [C3H3]+
Authors: Terlouw Johan K. , Burgers Peter C. , Hommes Henk
Published: May 2005

Characterization of [C4H5O]+ ions in the gas phase using their metastable ion and collisional activation spectra shows that the three isomeric ions HCC\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}HOCH3, CH3O\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}CCH2 and OCH3 related to the two stable [C3H3]+ cations [HCCCH2]+ and are stable for ≥ 10−5s. In contrast to the formation of cyclopropenium ions, it is found that the methoxy cyclopropenium ion is not generated from acyclic precursor molecules. The small but significant intensity differences found in the collisional activation spectra of [C3H3]+ ions generated from HCCCH2I and HCCCH2Cl possibly indicate the presence of [C3H3]+ ions of different structures.
Mass spectral fragmentation of thioesters. 1—Identification of low energy, slow processes
Authors: Wood Gordon Walter , Kiremire Bernard T.
Published: May 2005

A variety of thiol and thion esters, including acetates and benzoates with n‐butyl and β‐phenethyl alkyl groups, have been studied by electron impact mass spectrometry. Several rearrangement ions were documented and their persistence in low voltage and field ion spectra demonstrated. Among the significant ions found in the rich thion spectra, the most general requires O to S rearrangement of the alkyl group and subsequent cleavage to yield acyl ions (CH3CO or PhCO). This process is more important in longer chain compounds than in the methyl and ethyl homologues studied previously.
Effects of annulation on the mass spectral behavior of bicyclo[4.3.0]‐3‐nonene derivatives: Aldehydes
Authors: Tureček F. , Hanuš V.
Published: May 2005

The mass spectra of the title compounds depend markedly on ring annulation. On ionization, the cis‐annulated isomers lose alcohol and benzene regardless of the configuration of the alkoxyl. In the trans‐annulated isomers, the fragmentation is governed by the configuration of both the aldehyde and the alkoxyl groups. The role of non‐bonding interactions is discussed.
On the evaluation of ion source conditions for optimum sensitivity of chemical ionization
Authors: Morgan R. P. , Hayward E. J. , Steel G.
Published: May 2005

The best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS‐25 mass spectrometer. The best reagent gas pressure is shown to be different for each gas and is significantly lower than is usually reported in the literature.
Laser desorption mass spectrometry of thermally labile compounds using a continuous wave CO2 laser
Authors: Stoll R. , Röllgen F. W.
Published: May 2005

A continuous wave CO2 laser has been used for the production of gaseous ions from organic sample layers. The long desorption times of a few seconds enabled a quadrupole mass spectrometer to be used for recording the mass spectra by signal accumulation. The laser desorption spectra of several thermally labile compounds are reported and discussed. The level of fragmentation is rather low. Molecular and fragment ions are formed almost exclusively by alkali ion attachment, even with acids. A particularly long desorption time of more than one minute has been observed with quarternary ammonium salts.
Mass spectroscopy of natural products. VI—Localization of functional groups in the hopane skeleton
Authors: Schmidt J. , Huneck S.
Published: May 2005

The mass spectral fragmentation of hopane derivatives with oxygenated substituents at C‐3, C‐6, C‐7, C‐15, C‐16 and C‐22 is discussed. It is shown, that the positions of functional groups in rings A and B or D and E respectively can be distinguished using several derivatives and deuterated analogues.
Mass spectrometric study of conjugated bifunctional acetylenes: 2—Ynals and ynones
Authors: Bachiri M. , Perros P. , Verneuil B. , Mouvier G. , Carlier P.
Published: May 2005

This study is based on results obtained by new techniques for observing metastable ions which make it possible to determine the fragmentation paths of conjugated ynals and ynones. For the ynals, the most interesting fragment is the [M–28]+˙ ion. For the ynones, when a McLafferty rearrangement is feasible, the ion arising therefrom is more abundant than the [MCO]+. ion. However, this elimination of a neutral CO molecule is quite important for the true acetylene ketones.
Chemical ionization mass spectrometry: Oligomerization reactions in tight ion sources
Authors: Hancock Richard A. , Thyagarajan B. S. , Walder Raymond
Published: May 2005

Association of carbonyl compounds with protons to give cluster ions can be observed in conventional chemical ionization mass spectrometry. The variation of the relative ion currents of proton bound ‘dimers’ formed with acetone and methylethyl ketone have been examined as a function of ion source partial pressures. Multiple ion/molecule reactions with N‐methylol derivatives of amides and carbamates and repetitive losses of water give protonated oligomeric species. Ions having m/z values as large as 625 [M6H5H2O]+ have been detected in the chemical ionization spectrum of N‐hydroxymethylurethane (M).
The fragmentations of substituted cinnamic acids after electron impact
Authors: Schaldach Bernd , Grützmacher H.‐Fr.
Published: May 2005

The fragmentations of a number of cinnamic acids substituted at the phenyl ring have been studied with the aid of 70 eV mass spectra and mass analysed ion kinetic energy spectra. Evidence is presented that the formation of [C9H7O2]+ ions occurs by intramolecular aromatic substitution reactions. A mechanism is proposed for the energetically favourable loss of the substituents from meta and para positions of the phenyl ring. The analytical use of intramolecular aromatic substitution reactions is briefly discussed.
Further interference peaks in mass analysed ion kinetic energy spectra
Authors: Schaldach Bernd , Grützmacher Hans‐Friedrich
Published: May 2005

It is shown that interference peaks in mass analysed ion kinetic energy spectra can also occur from ions decomposing in the accelerating region of the ion source.
Mass spectral characteristics of the sulfur‐containing ketoxime carbamates thiofanox and metabolites
Authors: Corkins H. G. , Mannion J. J. , Storace L.
Published: May 2005

Deuterium labeling and high resolution mass spectroscopy have been used to determine the modes of electron impact fragmentation of 3,3‐dimethyl‐1‐methylthio‐2‐butanone O‐[(methylamino)carbonyl]oxime, thiofanox and its metabolites, the sulfoxide and sulfone. The mass spectra of the corresponding oximes were also examined. The carbamates fragmented chiefly by two competing pathways—the loss of CH3NCO or the sulfur‐containing moiety. The favored process was dependent on the oxidation state at sulfur. Several unusual rearrangements were noted.
Mass spectrometric study of μ4‐oxohexa‐μ‐acetatotetrazinc, Zn4O(CH3CO2)6
Authors: Sipachev Viktor A. , Reshetova Lyudmila N. , Nekrasov Yurii S. , Sil'vestrova Svetlana Yu.
Published: May 2005

The electron impact mass spectrum of Zn4O(CH3CO2)6 isostructural to Be4O(CH3CO2)6 studied earlier is reported. The principal fragmentation paths of both compounds involve the elimination of M(CH3CO2)2 where M is Zn, Be, or (CH3CO)2O. Further fragmentations proceed by the losses of CH2CO and H2O. The spectrum of Zn4O(CH3CO2)6 contains intense doubly charged ions. The results obtained are interpreted in terms of stereochemical considerations.
Direct mass spectrometric analysis of the 18O/16O ratio in sulfur‐containing organophosphorus compounds
Authors: Reimschüssel Wladyslaw , Paneth Piotr
Published: May 2005

High precision measurements of the 18O/16O ratio in bis‐(5,5‐dimethyl‐2‐oxo‐1,3,2‐P‐dioxaphosphorinanyl)‐sulfide and P1‐oxo‐P2‐thiono(5,5‐dimethl‐1,3,2‐dioxaphosphorinanyl)oxidee have been carrid out using a Finnigan 4000 mass spectrometer.
Program for elemental analysis using low or medium resolution mass spectra
Authors: Kavanagh Peter E.
Published: May 2005

A program, called ELANAL, has been written in basic which computes all possible empirical formulae for a molecular ion or a fragment ion containing up to eleven common elements. The program then calculates the expected intensities of the peaks following the molecular or fragment ion due to heavier isotopes in the formulae. These calculated intensities are compared with the intensities in an experimentally determined mass spectrum.
A study of some cations formed in the ammonia chemical ionization of ketones using mass analysed ion kinetic energy spectrometry
Authors: Maquestiau André , Flammang Robert , Nielsen Lawrence
Published: May 2005

The structures of the major adduct ions formed in ammonia chemical ionization of thirteen aliphatic and aromatic ketones have been studied by mass analysed ion kinetic energy spectrometry. The [M+NH3+H]+ ion is shown to have a protonated carbinolamine structure, [M+2NH3+H]+ to be a protonated carbinolamine with hydrogen‐bonded ammonia and [2M+NH3+H]+ to be, at least in part, a protonated carbinolamine with hydrogen‐bonded ketone. These structures may imply a nucleophilic addition of ammonia at the carbonyl of the ketone‐ammonium ion complex. An unusual hydroxy migration is seen in the internal rearrangement of the [2M+NH3+H]+ ion leading to the formation of a protonated imine.
Bond breaking energy in collision induced dissociation: A study of carbon cage fragmentation in cubane, kepone and mirex
Authors: Lehman Thomas A. , Harvan Donald J. , Hass J. Ronald
Published: May 2005

Collision induced dissociation of the carbon cage compounds cubane, kepone and mirex breaks the cage structures. The energy available for bond breaking is thus not less than about 9 eV, and the time between energy acquisition and subsequent unimolecular fragmentation is long enough that the available energy can be concentrated in three bonds to the same carbon atom. Collision induced dissociation mass‐analyzed ion kinetic energy spectra of [C5Cl6]+˙ from mirex and from hexachlorocyclopentadiene are virtually identical, and similar for [C6H6]+˙ ions from cubane and benzene.
Chemical ionization and electron impact mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes
Authors: Shaw Charles J. , Kane Vinayak V.
Published: May 2005

The methane and isobutane chemical ionization mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.
The constant neutral linked magnetic field electric sector scan
Authors: Haddon William F.
Published: May 2005

A linked magnetic field‐electric sector scan for which (B/E)\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {1 - E} $\end{document} is constant selectively records first field free region metastable peaks representing loss of the same neutral fragment. The constant neutral metastable ion spectra produced by this scan should provide information about the presence and location of particular functional groups beyond that which is available from focused mass spectra. Constant neutral linked scans can be obtained consecutively with focused spectra and with B/E and B 2/E linked scans by simple extension of a computerized B‐E scanning method developed previously.
Some PhCNO‐containing molecules; mass spectral similarity and molecular diversity
Authors: Deem M. L.
Published: May 2005

Some diverse compounds possessing a PhCNO unit cleave the NO link upon electron impact to give [PhCN]+˙. Different and especially significant modes of NO scission occur in metastable processes when the oxygen atom of the PhCNO group is exocyclic to a heterocyclic nitrogen atom. Upon electron impact, rupture of the NO bond in PhCNO‐containing molecules generally dominates over 1,3‐dipolar cycloreversion, which generates the radical cation of benzonitrile oxide. Stable PhCNO‐containing molecules survive competing fragmentations in the ion source to produce [M+H]+ ions of moderate relative intensity. Other ions, which are larger than [M]+ are implicated where M is PhCHNOR. Several values of m/z for metastable ions are common to compounds which have a PhCNO moiety. These m/z values generally derive both from a parent ion with m/z⩽105 and from a PhCNO moiety.
Mass spectrometric studies of organophosphorus compounds: III—Remarkable migration of chalcogen on electron impact of organophosphorus compounds
Authors: Keck Helmut , Kuchen Wilhelm , Mahler Hans F.
Published: May 2005

The mass spectra of several dibenzo (d.f)‐1,3,2,‐dioxaphosphorepines of the type magnified image where X=0, S, Se and R=2,2′‐biphenylylene, have been studied. Dibenzochalcogen ions [RX]+˙ stemming directly from [M]+˙ were observed with high intensities, indicating specific migration of X from phosphorus to carbon with simultaneous destruction of the dioxaphosphorepine ring. Simple cleavage of PY as usually observed in similar organophosphorus compounds is not a common process here.
Mass spectrometry of diaziridines: 1—Rearrangements of the molecular ion of 1‐benzyl‐3,3‐dimethyldiaziridine and identification of some daughter ions using collisional activation
Authors: Mintas Mladen , Mayer Klaus K.
Published: May 2005

Intense rearrangement processes involving migrations of hydrogen atoms and the phenyl group were observed in the electron impact induced fragmentation of 1‐benzyl‐3,3‐dimethyldiaziridine. The following ions are observed: (i) m/z 146: a two‐step fragmentation involving hydrogen transfer followed by loss of NH2; (ii) m/z 119: C—N1 bond fission followed by a 1–4 phenyl shift and loss of CH3N2; (iii) m/z 106: a process involving reciprocal hydrogen migration between the methyl and benzylic methylene groups; (iv) m/z 58: hydrogen transfer from benzylic methylene and subsequent loss of PhCHN. The origin of these ions has been confirmed by measurements of metastable transitions in 1‐benzyl‐3,3‐dimethyldiaziridine, and on specifically deuterated and substituted diaziridines. The structure of the ions at m/z 119 and m/z 106 has been deduced by means of collisional activation spectrometry.
Structure and formation of some [C4H5O2]+ ions generated by radical losses in pseudo simple cleavage reactions
Authors: Terlouw Johan K. , Burgers Peter C. , Schwarz Helmut
Published: May 2005

Characterization of some [C4H5O2]+ ions in the gas phase using their collisional activation mass spectra shows that the isomeric ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O,} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HC} \equiv {\rm C} - \mathop {{\rm C}({\rm OH}){\rm OCH}_3 }\limits^ + $\end{document} are stable for t⩾10−5 s. Of these, ions of structure were generated by the site specific gas phase protonation of γ‐crotonolactone with isobutane or methanol as chemical ionization reagent gases. These results and those derived from measurements on some 2H, 13C and 18O labelled [C4H5O2]+ product ions, were used to study the mechanisms of unimolecular radical elimination reactions, viz. (1) loss of CH3˙ from [trans‐methyl crotonate], (2) loss of H˙ from [methyl acrylate]+˙, (3) loss of H˙ from [cyclopropane carboxylic acid]+˙ and (4) loss of CH3˙ from [1,3‐dimethoxypropyne]+˙. It is concluded that none of these losses occur by simple bond cleavage. Mechanisms are presented which account for the observation that the first three reactions yield product ions of structure whereas the ions generated by reaction (4) have structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}. It is further proposed that a minor fraction of the [M‐CH3]+ ions from ionized trans‐methyl crotonate is generated via a rearrangement process which yields ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}.
The computer processing and interpretation of mass spectral information. VII—identification of ions in terms of structural symbols
Authors: Sukharev Yu. N. , Sizoi V. F. , Molgachova N. S. , Nekrasov Yu. S.
Published: May 2005

A new version of the AELITA‐F program for computation of a monoisotopic spectrum and identification of the ion composition as a collection of elements or as structural fragments is described. A technique is proposed for specifying a priori information on the compound in a ‘hybrid’ form which combines structural fragments of the molecule and individual chemical elements. This version permits the elimination of redundant information and reduces the requirements of computer resources. The program effectiveness is increased by reducing the number of ions to be generated. The format in which the mass spectral information is read out is more comprehensible to a chemist.
Cyclization of dimethyl oxalate upon electron impact
Authors: Liehr J. G. , Larka E. A. , Beynon J. H.
Published: May 2005

Isotope labelling experiments and also consecutive fragmentation investigations of metastable ions, a novel technique in mechanistic studies, have been carried out to elucidate structure and genesis of the m/z 45 ions from dimethyl oxalate as well as dimethyl carbonate. It is shown that the formation of the m/z 45 ions, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{O}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document}, in the mass spectra of these compounds arises via single step processes. Mechanisms involving hydrogen transfer and subsequent formation of cyclic intermediates which then collapse to give \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{O}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} directly from molecular ions are suggested. No evidence was found for a two‐step fragmentation route to m/z 45 from the molecular ions of either dimethyl oxalate or dimethyl carbonate.
The fragmentation of the ions of nonan‐4‐one: A study by triple quadrupole mass spectrometry
Authors: Yost R. A. , Enke C. G.
Published: May 2005

The fragmentation pathways for the ions generated by electron impact from nonan‐4‐one have been studied using low energy collision induced dissociation in a triple quadrupole mass spectrometer. Over 400 fragmentation pathways have been identified. These results are compared with data from earlier ion kinetic energy spectrometry studies of nonan‐4‐one which employed metastable decompositions.
Mass spectrometry of thio analogues of pyrimidine bases: 2‐alkoxycarbonylalkyl‐thiouracils
Authors: Wyrzykiewicz E. , Buczek J. , Golankiewicz K.
Published: May 2005

The mass spectral fragmentation of twelve new 2‐alkoxycarbonylalkylthio substituted derivatives of uracils 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 basic mass spectral fragmentation of these compounds is due to cleavage of SC, OC and CC bonds of the alkoxycarbonylalkylthio group.
Mechanisms of formation of [MHCO]+ and [MC6H5CO]+ ions from isomers of 1,4‐benzodioxin derivatives
Authors: Bouchoux Guy , Dagaut Jacques
Published: May 2005

It is demonstrated that phenyl and benzocyclobutenyl derivatives of 1,4‐benzodioxin interconvert before fragmentation at low internal energy. The mechanisms of the two major fragmentations (HCO and C6H5CO losses) are investigated by means of kinetic energy release determination and appearance energy measurements. From these experiments it is concluded that the fragment ions possess a dibenzopyran structure.
Reduction of trinitroaromatic compounds in water by chemical ionization mass spectrometry
Authors: Yinon Jehuda , Laschever Miriam
Published: May 2005

A reduction process was found to occur in the ion source when observing the chemical ionization mass spectra of a series of trinitroaromatic compounds, using water as reagent. The [MH–30]+ ions in the CI mass spectra were due mainly to the reduction of the compounds to their corresponding amines. This was proved by using D2O as reagent: the [MH–30]+ ions were shifted to [MD–28]+ ions. The trinitroaromatic compounds investigated included 1,3,5‐trinitrobenzene, 2,4,6‐trinitrotoluene, 2,4,6‐trinitro‐m‐cresol, 2,4,6‐trinitroaniline (picramide) and 2,4,6‐trinitrophenol (picric acid).