bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined gas chromatography‐mass spectrometry of the inositol trimethylsilyl ethers and acetate esters
Authors: Sherman William R. , Eilers Nancy C. , Goodwin Sally L.
Published: May 2005

Each of the inositol diastereomers have been subjected to low resolution gas chromatography‐mass spectrometry as their hexa‐O‐trimethylsilyl (TMSi) ethers and as their hexaacetyl esters. The TMSi ethers of the inositols each possess a unique spectrum consisting of the same ions occurring with remarkable variation in intensity. This variation, which is much greater with the inositol TMSi ethers than in the spectra of the inositol acetates, is presumably an expression of the stereochemistry of each isomer exaggerated by the bulky TMSi groups. Using TMSi‐d9, labeling as well as ring labeling with deuterium we identified several fragment ions which are characteristic of the cyclitols. The spectra of the TMSi inositols are compared with the spectra of other TMSi carbohydrates.

Two main series of fragmentation processes are observed in the inositol hexaacetates. With the aid of acetyl‐d3 labeling each of these series were found to divide into two more pathways consisting of ions of the same m/e values but of different structures. These pathways are compared with similar pathways observed in other acetyl carbohydrates.

A method is described for the direct conversion of TMSi ethers to acetate esters which has potential usefulness in natural product studies.
Reactions in the source of a mass spectrometer: The mass spectrum of 1‐chlorobenzotriazole
Authors: Thomas C. B.
Published: May 2005

The mass spectrum of 1‐chlorobenzotriazole contains ions derived from benzotriazole, a product of an exchange reaction with water in the source of the mass spectrometer. Relatively intense ions derived from iodine, iodine monobromide and other inter‐halogen compounds are also observed. These species are produced by oxidation of involatile halide coatings in the source region by 1‐chlorobenzotriazole. It is suggested that anomalous peaks produced by oxidation‐reduction reactions in the source may be expected in the spectrum of any organic oxidant.
Mass spectrometry of onium compounds—IV: Diazonium salts
Authors: Undheim Kjell , Thorstad Olav , Hvistendahl Georg
Published: May 2005

The zwitterions of diazotized ortho and para aminophenol are very volatile and give strong peaks in the mass spectra corresponding to the molecular ion. The m‐isomer, which cannot be stabilized through a simple quinonoid structure, gives rise to a complex spectrum through decomposition and coupling reactions. The zwitterions of diazotized anthranilic and sulphanilic acids did not give the molecular ion peak.
A small computer data system for low resolution magnetic deflection mass spectrometers
Authors: Plattner J. R. , Markey S. P.
Published: May 2005

A small on‐line computer system for complete processing of low resolution magnetic deflection mass spectrometric data has been demonstrated. An interpolated mass scale accuracy of 200ppm was achieved for both repetitive (five or ten second cycle times) and single scan modes. Identification of m/e values above 1000 is possible with an accuracy of 500 ppm to m/e 3600. Mass scale assignments are time based and externally calibrated (pfa).
Field desorption mass spectrometry of amino acids
Authors: Winkler H. U. , Beckey H. D.
Published: May 2005

The mass spectra of some amino acids have been studied using the field desorption method. All amino acids yield molecular or quasi‐molecular ions, even in the case of arginine and cystine, where these ions cannot be detected with the electron‐impact (EI) or chemical ionization (CI) methods. The fragmentation is reduced as compared to EI, CI and FI.
Mass spectral studies on mesoionic imidazo [1,2‐a] pyrid‐2 and ‐3‐one derivatives
Authors: Anderson Wayne K. , Friedman Alan E.
Published: May 2005

The mass spectral fragmentation patterns for 1‐substituted derivatives of anhydro (3‐chloroacetyl‐2‐hydroxyimidazo[1,2‐a]pyridinium hydroxide) (Ia to Ie) and 2‐acyl substituted derivatives of anhydro(1‐benzyl‐3‐hydroxyimidazo[1,2‐a]pyridinium hydroxide) (IIa and IIb) are reported. In all cases the mass spectra may be interpreted on the basis of initial cleavage of the ‘carbonyl‐heteroatom’ bond of the mesoionic system, followed by fragmentation.
Electron‐impact and thermal fragmentation patterns of some perfluoroalkylene‐linked aromatic and heteroaromatic compounds
Authors: Cotter J. L.
Published: May 2005

The pyrolysis of some perfluoroalkylene‐linked aromatic and heteroaromatic polymer precursors and a poly(1,3‐phenylenehexafluorotrimethylene) has been studied using a combined pyrolysis‐gas chromatographic‐mass spectrometric method. Whereas the electron‐impact induced fragmentations of the polymer precursors are almost exclusively controlled by cleavage β to the aromatic or heteroaromatic ring, thermolysis of these compounds yields products whose formation is consistent with the occurrence of primary cleavage processes that are not confined β to the ring.
High‐resolution mass spectra of two α,β‐unssaturated γ‐dilactones
Authors: Kolsaker Per
Published: May 2005

The fragmentations of two α,β‐unsaturated γ‐dilactones in a mass spectrometer are studied. The main feature is conecutive carbon monoxide expulsions. Strong indication of ejection of a fragment C2O2 is presented, however. Masses were determined by the high resolution rechnique and metastable transitions were detected by defocusing. Corresponding deuterated dilactones were also studied to verify the fragmentation mechanism.
Elimination reactions of ions in the gas phase–I: Elimination of water and acetic acid in epimeric borneols and bornylacetates
Authors: Robbiani R. , Seibl J.
Published: May 2005

Loss of water and acetic acid in the epimeric bornyl alcohols and acetates are shown to be analogous processes by specific 2H‐labelling. Among several competing mechanisms cis‐1,2‐elimination is the most important. Mctastable ion characteristics of this specific process exhibit some unusual features and its product is shown to have a different structure from that produced by the competing reactions.
Mass spectral studies on steroidal compounds—V: Rings B and A seco 5‐keto compounds in the cholestane series
Authors: Ahmad M. S. , Mushfiq M. , Ansari G. A. S. , Waris Miss F.
Published: May 2005

The mass spectra of several structurally related ring B seco 5‐keto compounds (I to VII) have been examined. The mass spectra of I, II, III and IV are conspicuous by an intense peak at m/e112(C7H12O) and those of V (highest mass peak at [M  CH3COOH]), VI and VII by a prominent peak at m/e 100 (C7H10O), which apparently results from McLafferty rearrangement involving 5‐keto function and an appropriate γ‐hydrogen at C‐8 and C‐11. This rearrangement, leading to the aforementioned ions, is of diagnostic value in the characterisation of such compounds. The mass spectrum of VIII exhibits a prominent ion peak at m/e 332 (C23H40O) resulting from McLafferty rearrangement involving the 5‐keto function and C2H. This offers an excellent means of differentiating between the isomeric acids (III and VIII). The fragmentation pathways suggested are supported by accurate mass measurement of the salient fragment ions and in some cases by appropriate metastable peaks.
Spectres de Masse de Derives de l'Atractyloside. Determination du Nombre de Substituants par Combinaison d'Acetylation et de Silylation
Authors: Defaye G. , Ulrich J.
Published: May 2005

En créant des dérivés différents suivant la fonction que l'on transforme, il est possible de dénombrer rapidement chacune de ces fonctions sur une molécule complexe du type hétéroside. Silylation de toutes les fonctions dans un premier temps suivie de l'acétylation des fonctions alcools et de la silylation des sulfates et acides dans un second temps. Des molécules d'atractylate, d'apoa‐tractylate et de gummiférine ont été étudiées de cette façon.
Carbon‐oxygen bond formation in the mass spectra of aryl methyl sulphones
Authors: Pratanata Miss I. , Williams L. R. , Williams R. N.
Published: May 2005

Upon electron‐impact aryl methyl sulphones (I) rearranged to form aryl‐oxygen bonds. The mode of fragmentation of the intermediate ester (II) to give [aryl O]+ or [aryl OH]+ ions was found to be markedly influenced by the nature of the aryl substituent.
The mass spectra of substituted 2‐methylbenzophenones
Authors: Grimshaw James , Sell Charles S. , Haslett Reginald J.
Published: May 2005

The mass spectra of some methoxy and methyl derivatives of 2‐methylbenzophenone have been examined. Loss of a substituents from 3′‐and 4′‐positions as well as the previously known loss from 2′‐positions are important fragmentation processes. Thus, these fragmentations are of little use in locating substituents on benzophenones of unknown structure. Deuterium labelling shows the [M ‐ 1]+ ion from 3′,4,4′,5,5′‐pentamethoxy‐2‐methyl benzophenone to be due largely to loss of hydrogen from 2′‐ and 6′‐positions.
Mass spectrometry of antibiotic kikumycin A, B and related compounds
Authors: Takaishi Tetsuo , Suzuki Makoto , Tatematsu Akira
Published: May 2005

The structures of kikumycin A and B, antiviral amidine antibiotics, have been elucidated by means of low and high resolution mass spectrometry. Amino acid composition and their sequences were also clearly demonstrated by this technique. The evidence for the fragmentation of terminal amidines or amides of kikumycin derivatives and related synthetic compounds was represented by the elimination of ammonia or water from the molecular ions to give stable nitrile ions. Additionally, the participation of the iminol structure in the pyrrole‐2‐carboxamide portion of kikumycin A and B was confirmed by the fragment ions derived from their iminol tautomers.
The mass spectrometry of DT‐and monosubstituted biphenyls: Dependence of fragmentation patterns on position of substitution
Authors: Sheley Curtis F. , Patterson Robert T.
Published: May 2005

This paper describes the mass spectroscopy of a series of biphenyl derivatives substituted in the 2,2′, 4,4′ and 2 positions. The substitutent functional groups are carbomethoxy, carbothoxy, carboxylic acid and hydroxymethyl. In addition, some results are reported on the spectroscopy of the d5‐carboethoxy derivatives, the 2‐ and 2,2′‐αd2‐ hydroxymethyl derivatives and fluorene‐4‐methanol.

The molecular ions of the 4,4′‐disubstituted biphenyl derivatives are far more stable than those of the 2,2′ isomers. It is also observed that the fragmentation patterns of these two sets of isomers are sharply different. Paradoxically, the 2‐substituted biphenyl derivatives give relatively stable molecular ions and their fragmentation patterns are frequently different from those of the corresponding 2,2′‐disubstituted biphenyls. The bulk of the evidence presented in this paper suggests that the usual sort of ‘ortho effect’ is not a significant factor in the fragmentation mechanisms proposed for the 2,2′‐disubstituted biphenyl derivatives.
Massenspektroskopische Fragmentierungsreaktionen: VI –Produktstabilität oder ‘lokalisierte Ladung’ als Konzept zur Deutung der Bruchstückbildung?
Authors: Budzikiewicz H. , Pesch R.
Published: May 2005

An Hand von Alkylaminen, die ω‐ständig eine zweite funktionelle Gruppe (O, S, Se) tragen, wird gezeigt, daß bei Ionisierung unterhalb des Ionisierungspotentials primärer Amine Ladungswanderung zum N, die schließlich zur Bildung von CH2NH2+ führt, nicht generell über die σ‐Bindungen, sondern über spezielle Mechanismen erfolgen kann. Zusätzlich wird das Fragmentierungsverhalten einfacher Methyl‐alkyl‐selenide beschrieben.
The mass spectrometric fragmentation of n‐benzylacetamide
Authors: Gilbert J. R. , Potter E. , Stace A. J.
Published: May 2005

The low energy mass spectra of N‐benzylacetamide have been recorded. The major fragmentations of the molecular ion are similar to those observed in the acetanilide spectrum. In addition, the secondary dissociation of the [C6H5CH2NH]+ ion by loss of HCN is shown to occur with transfer of the ‐N–H hydrogen to the ring.
Computer‐aided interpretation of mass spectra. Information on substructural probabilities form stirs
Authors: Dayringer Henry E. , Pesyna Gail M. , Venkataraghavan Rengachari , McLafferty F. W.
Published: May 2005

The capability of the ‘Self‐Training Interpretive and Retrieval System’ has been extended so that the compounds selected as providing the best match in each data class to the unknown mass spectrum are examined by the computer for the presence of each of 179 common substructural fragments. Stastical methods were used to evaluate the selectivity for identification of each substructure by each data class using a reference file of 18 806 spectra of different compounds. In tests using at least 373 unknown spectra for each of the substructures, with criteria that gave a mean reliability of 98.1%, the method averaged 49% recall, which corresponds to the identification of 2.55 substructures per unknown spectrum, as well as the normal “Self‐Training Interpretative and Retrieval System” match‐factor results, requires 68 s on a laboratory computer. The method is also available to outside users on an international computer network.
Computer‐aided interpretation of mass spectra. Increased information form characteristic ion
Authors: Dayringer H. E. , McLafferty F. W.
Published: May 2005

The characteristic ion data classes of the ‘Self‐Training Interpretive and Retrieval System’ have been modified to test the effect of number of ions, even‐and odd‐electron ion requirement, over‐lapping mass ranges and arithmetic combinations of the rankings found by several data classes. Statistical methods were applied to evaluate the performance achieved for 202 substructures using a reference file of 18 806 spectra of different compounds and testing at least 373 compounds for each substructure. A Linear combination of the new characteristic ion data classes gave 47% recall with 98% prediction reliability, a substantial improvement over the performance of the previous system. The use of overlapping mass ranges was the most important factor in the improved performance, increasing the recall for 42 of the substructures. Three examples illustrate the utility of the improved system.
Gas phase isomerization of \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm C}_{{\rm 10}} {\rm H}_{{\rm 14}} } \right]_{}^{_.^ + } $\end{document} ions generated from adamantanoid compounds
Authors: Majerski Zdenko , Karlović Gordana , Ðigaš Stjepan , Stefanović Duško
Published: May 2005

\documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm C}_{{\rm 10}} {\rm H}_{{\rm 14}} } \right]_{}^{_.^ + } $\end{document} ions have been generated from a number of adamantanoid compounds, both by ionization and ionization followed‐by fragmentation. Metastable ion abundance ratios of competitive reactions indicate the decomposition of these ions from common structures in all cases.
Etude de la Fragmentation en Spectrographie de Masse de Spiropyrannes Benzodithioliques. Influence de la Position et de la Nature des Substituants
Authors: Derocque Jean Luc , Appriou Pierre , Guglielmetti Robert , Dürr Heinz
Published: May 2005

Nous reportons les spectres de 12 spiropyrannes benzodithioliques. Leurs cartes de fragmentation on été déterminées par étude des transitions métastables et par mesure à haute résolution. La fragmentation on de ces composés dépend de la nature et de la position des substituents et nos résultats sont comparés à ceux observés par action de la lumière et de la chaleur sur ces composés.
Hydrogen rearrangements of ionized propanoic acid and isomeric ions
Authors: McAdoo David J. , Witiak Dennis N.
Published: May 2005

Ionized propanoic acid and its enol isomer lose H˙ in both normal and metastable decompositions. These C3H6O2 ions lose their distinctness prior to undergoing metastable decomposition in the mass spectrometer. Deuterium labeling indicated that this results from the transfer of a β‐hydrogen to oxygen in the propanoic acid ion followed by rapid exchange of hydrogen and deuteriums between the α‐ and β‐carbons and slower exchange between the carbons and the oxygens. 3‐ and 5‐Membered ring hydrogen rearrangements are preferred over 4‐membered ring transfers. It is concluded that 1,2‐hydrogen shifts following removal of hydrogen from alkyl chains may sometimes cause site‐specific hydrogen rearrangements to appear non‐site specific.
Anchimeric assistance in the fragmentation of protonated glycol derivatives in a flowing afterglow
Authors: Schmitt Robert J. , Shapiro Robert H.
Published: May 2005

A series of monomethyl, monoacyl glycols was protonated in a flowing afterglow system. In the subsequent fragmentation reactions acetic acid was found to be a better leaving group than methanol, but the acetoxy group was shown to participate in methanol expulsion under certain conditions. The effects of leaving group ability, anchimeric assistance, stereochemistry and steric hindrance on the fragmentation patterns of the protonated molecular ions are discussed.
The mass spectrometry of polychlorinated dibenzo‐p‐dioxins
Authors: Hass J. Ronald , Friesen Marlin D. , Hoffman Michael K.
Published: May 2005

The negative ion chemical ionization mass spectra of polychlorinated dibenzo‐p‐dioxins using oxygen, methane and methane/oxygen are reported together with their methane positive ion chemical ionization mass spectra and conventional electron impact spectra. The methane/oxygen negative ion chemical ionization mass spectra proved to be the most useful of the negative ion spectra for structure determination.
Aktivierungsenergie und Mechanismus der intramolekularen Wasserstoff‐Wanderung bei Radikal‐Kationen von Keto/Enol‐Tautomeren in der Gasphase
Authors: Schwarz Helmut , Wesdemiotis Chrysostomos
Published: May 2005

Die nicht zerfallenden Radikalkationen des Methylacetates [CH3COOCH3]+. und seiner Enolform [CH2C(OH)OCH3]+⋅ liegen aufgrund ihrer Stoßaktivierungsspektren in Potentialminima vor. Für zerfallende [C3H6O2]+ ‐Ionen wird belegt, daß der CH3O⋅ ‐Eliminierung aus [CH2C(OH)OCH3]+⋅ eine geschwindigkeitsbestimmende, symmetrieverbotene [1,3]‐Wasserstoffumlagerung vorgelagert ist. Der Alternativweg von zwei konsekutiven, formal symmetrieerlaubten [1.2]‐Wasserstoffverschiebungen spielt bei dieser Isomerisierung mit Sicherheit keine Rolle. In Abhängigkeit von der elektronischen Natur der Kationen (“open” “order” “closed” shell‐Systeme) liegt die Aktivierungsenergie solcher Umlagerungen im Bereich von 41–83 kcal · Mol−1.
Substituent effects in the mass spectra of benzoyl hetarenes
Authors: Grützmacher Hans‐Fr. , Schubert Ralf
Published: May 2005

The mass spectra of several benzoyl hetarenes, of 2‐benzoyl pyridines substituted at the phenyl and pyridyl group, respectively, and of phenyl substituted 2‐benzoyl pyrroles, have been studied with respect to the formation of benzoyl and hetaroyl ions. A correlation between the intensity of benzoyl ions, relative to molecular ion intensity, and the π‐electron density at the substituted carbon atom of the hetarene has been observed for benzoyl hetarenes. The relative intensities of (substituted) benzoyl ions of substituted 2‐benzoyl pyridines and 2‐benzoyl pyrroles are not easily related to substituent constants of Hammett equations. The relative ionization energies of phenyl substituted 2‐benzoyl pyridines, however, and the relative appearance energies of substituted benzoyl ions derived therefrom follow the σIP+‐constant of Bentley and Johnstone and the σ+‐constants of Brown, respectively.
Mass spectrometry of organic compounds of the group V Elements: VI—A new type of amine fragmentation under electron impact
Authors: Kostyanovsky R. G. , Voznesensky V. N. , Kadorkina G. K. , El'natanov Yu. I.
Published: May 2005

A new type of amine fragmentation under electron impact is elucidated for proline, sarcosine and aspartic acid derivatives and aminomethylphosphines of the general formula R2NCH2X. Ordinary α‐cleavage affording the \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_2 \mathop {\rm N}\limits^{\rm + } {\rm = CH}_{\rm 2} $\end{document} ion is suppressed by elimination of a neutral HX particle and [M ‐ HX]+ ion formation, or M‐HX neutral particle ejection and generation of an [HX]+ ion from [M]+˙. Such fragmentation is ensured by the presence of an α‐heteroatom (N, O, P, S) in one substituent (X) and a CO2R type delocalizing group in the α‐position of the other substituent (R2N).
Anionization of volatile molecules on the surface of electrolytic solutions exposed to high electric fields
Authors: Ott K. H. , Röllgen F. W. , Dähling P. , Zwinselman J. J. , Fokkens R. H. , Nibbering N. M. M.
Published: May 2005

The anionization of molecules supplied from the gas phase onto a negatively charged [Cl]− or [NO3]− ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO3) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]− and [NO3]− attachment and of some acids by proton abstraction is reported.
Metastable ion studies: XIII—the measurement of appearance energies of metastable peaks
Authors: Burgers Peter C. , Holmes John L.
Published: May 2005

A simple, accurate and reproducible method is described for measuring the appearance energy of a metastable peak. The method involves the comparison of the metastable peak intensity with that of a ‘standard’ metastable peak, over a small range of ionizing electron energies above their onsets. Six fragmentation processes whose reaction energetics are well established were selected to provide suitable calibrant metastable peaks. Results are also presented for fragmentations having large kinetic shifts and for some primary and secondary ion decomposition of current interest.
Stereochemistry of HOH and HOAc elimination from 1‐tetralol and 1‐acetoxytetralin radical cations
Authors: Groenewold G. S. , Gross M. L.
Published: May 2005

Water and acetic acid eliminations from 1‐tetralin radical cations have been shown previously to be highly regiospecific 1,4 processes. Utilizing deuterium labeling, high resolution peak ratio measurements and metastable ion defocusing techniques, the stereochemistry of these processes has been investigated. cis‐4‐d1‐ and trans‐4‐d1‐1‐Tetralol both lose HOH and DOH in appreciable amounts; similarly, both acetoxy derivatives lose HOAc and DOAc. These results are interpreted in terms of an ionic epimerization which operates in competition with a stereospecific 1,4 elimination mechanism. A hydrogen exchange process which occurs between the 4‐carbon and the oxygen atom situated on the 1‐carbon of 1‐tetralol has also been observed. This process accounts for observed H/D ratios in the ethene elimination reaction of various deuterium labeled 1‐tetralols.
Quality control and evaluation of mass spectra
Authors: Milne G. W. A. , Budde W. L. , Heller S. R. , Martinsen D. P. , Oldham R. G.
Published: May 2005

Over 1400 electron ionization mass spectra of selected organic compounds have been measured under carefully defined conditions. In this paper, the variables such as sample purity and spectrometer calibration that are controlled are described. The quality of the resulting spectra as well as the cost of the measurements is reported.
Fast atom bombardment mass spectrometry of butyloxycarbonyl protected (BOC) amino acids
Authors: Garner George V. , Gordon Derek B. , Tetler Lee W. , Sedgwick R. Donald
Published: May 2005

The positive and negative ion mass spectra of a series of BOC‐protected amino acids have been obtained using an FAB source. The spectra show characteristic features including a McLafferty type of rearrangement.
The structure of [C3H4N2]+· and [C5H5N2]+ ions formed from vinylimidazoles, studied by collisionally activated dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Houte J. J. , Van Thuijl J.
Published: May 2005

Mass spectra of the three isomeric vinylimidazoles have been compared and the structures of the fragment ions [C3H4N2]+· and [C5H5N2]+ have been investigated by collisionally activated dissociation mass spectrometry. The greater part of the non‐decomposing ions m/z 68 from 2‐vinylimidazole and from 2‐imidazolecarboxylic acid methyl ester, and a minor part of this ion formed from the free acid, all have the same structure: the imidazole ring system, with hydrogens at both nitrogen atoms but none at C(2). An analogous structure, with an ethyl group at C(2), is proposed for the m/z 93 ion from 2‐vinylimidazole.
Mass spectra of chlorinated aromatics formed in pulp bleaching 2—Chlorinated guaiacols
Authors: Knuutinen Juha , Korhonen Ilpo O. O.
Published: May 2005

The fragmentation of chlorinated guaiacols (2‐methoxyphenols) on electron impact has been studied. The most common fragmentation processes are interpreted and in some cases the small differences between spectra of positional isomers are explained. In addition to the well‐known alkyl‐oxygen fission (loss of methyl radical), metastable ion studies and deuterium labelling have indicated several new fragmentation pathways. The most characteristic are the formation of [MCH3HCl]+ and [MCH3Cl]+· ions. In general, however, the spectra of positional isomers are shown to be very similar.
Mass spectrometry of 7,7′,8,8′‐tetracyanoquinodimethane and of some of its radical anion salts
Authors: Mermilliod N. , Sellier N.
Published: May 2005

We present mass spectrometry experiments on tetracyanoquinodimethane (TCNQ), deuteriated TCNQ and on some TCNQ salts. Apart from the usual nitrile fragmentation, at least two original features appear in the spectra. The first is the formation of TCNQ dimers, as evidenced by their molecular peaks and their fragmentation. The second aspect concerns the spectra of the ammonium salts, which show that hydrogen or alkyl groups add to TCNQ before its decomposition, leading to new fragments (as m/z 141).
Gas phase protonation and subsequent dissociations in β‐amino alcohols as a function of exoergicity and interfunctional distance
Authors: Houriet Raymond , Rufenacht Hermann , Stahl Daniel , Tichy Milos , Longevialle Pierre
Published: May 2005

The gas phase protonation of β‐amino alcohols and subsequent water loss is investigated in an ion cyclotron resonance spectrometer. It is found that the loss of water is correlated with the formation of oxonium ions (OH protonation). A relationship is found between the extent of internal stabilization at short interfunctional distance in protonated amono alcohols and the exoergicity of protonation required to induce the loss of a water molecule.
Stereochemical effects in mass spectrometry: 2—Chemical ionization mass spectra of some cyclic glycols and mono‐ and di‐saccharides using trimethyl borate as reagent gas
Authors: Suming Hua , Yaozu Chen , Longfei Jiang , Shuman Xue
Published: May 2005

The chemical ionization mass spectra of cyclic glycols and mono‐ and di‐saccharides using trimethyl borate as reagent gas have been studied. In the gas phase, the trimethyl borate ions react stereospecifically with molecules of cis‐cyclic glycols to form characteristic ions, from which the stereochemical isomers of 1,2‐cyclopentanediols, 1,2‐cyclohexanediols and mono‐ and di‐saccharides can be definitely distinguished.
A combined time‐resolved and stereospecific deuterium labelling study of the elimination of methanol from the molecular ion of methoxycyclohexane
Authors: Molenaar‐Langeveld Tineke A. , Nibbering Nico M. M.
Published: May 2005

It is shown by field ionization kinetics in combination with both site‐specific and stereospecific D‐labelling that the loss of a molecule of methanol from the molecular ion of methoxycyclohexane can occur via 1,4‐ and 1,3‐eliminations. The 1,4‐elimination predominates at molecular ion lifetimes of ≥10−10.1 s. It is found that ∼19% of this reaction channel corresponds to a stereospecific cis‐elimination, whereas the remaining 81% is only site‐specific. At molecular ion lifetimes of between 10−10 and 10−9 s, a very sudden increase of the 1,3‐elimination is observed at the expense of the 1,4‐elimination. A stereospecific loss of methanol, however, is not observed at all for the 1,3‐elimination within the limits of error. Possible intermediates and reaction pathways, which can account for the observations made, are discussed.
Charge reversal of the conjugate base of formamide
Authors: Kiplinger Jeffrey P. , Maynard Andrew T. , Bursey Maurice M.
Published: May 2005

Charge reversal collisional activation mass spectremetry of negative ions has been used in conjunction with positive ion collisional activation to investigate several isomeric [H2, C, N, O]+ ions. Generation of m/z 44 ions from formamide, acetamide, JV‐methylformamide, acetaldoxime and by charge reversal of the [M–1]− ion formed from formamide yields several different isomeric structures. Charge reversal of the conjugate base of formamide appears to yield a mixture of singlet and triplet H2NCO+ ions; experiments with deuterium‐labeled compounds have been used to support this. Ab initio molecular orbital calculations indicate that the triplet ion is a stable structure, existing in a potential minimum 390.6 kJ mol−1 above the ground state singlet.
The ethyl halides: Stable neutral and radical cation isomers [C2, H2, X] where X = F, Cl, Br, I
Authors: Blanchette Marcia C. , Holmes John L. , Lossing F. P.
Published: May 2005

The following isomers of the ethyl halide molecular ions have all been shown to be stable species in the gas phase: [CH2CH2FH]+˙; [CH3ClCH2]+˙ (ΔHf° = 1012 kJ mol−1); [CH3CHClH]+˙ (ΔHf° = 971 kJ mol−1); [CH2CH2ClH]+˙; [CH3BrCH2]+˙ (ΔHf° = 1058 KJ mol−1); [CH3CHBrH]+˙ (ΔHf° = 995 kJ mol−1) and [CH2CH2BrH]+˙.

Neutralization–reionization mass spectrometry, employing Xe as the electron transfer target gas and O2 as the target gas for reionization, indicated that the ylides CH3ClCH2 and CH3BrCH2 could not be generated by such means. However, the species CH3CHClH, CH2CH2ClH and CH2CH2BrH (and possibly CH3CHBrH) were unambiguously identified.
Internal reactions of ion–neutral complexes from some disubstituted protonated benzaldehydes and acetophenones
Authors: Grützmacher Hans‐Fr. , Thielking Gerhard
Published: May 2005

Protonated benzaldehydes ‘a’ and protonated acetophenones ‘b’, substituted by a methoxymethyl group, a hydroxy‐methyl group and a mercaptomethyl group, respectively, in position 3, in addition to a methoxymethyl side chain at position 5, have been prepared by electron impact induced dissociation from the corresponding benzylic alcohols. The spontaneous fragmentations of metastable ions of ‘a’ and ‘b’ have been investigated with the aid of specifically deuterated derivatives. Large signals arc observed for the loss of methanol induced by a proton migration across the aromatic ring. The competing loss of H2O and H2S, respectively, from the second side chain is less abundant, in agreement with the smaller PA's of HO and HS groups. The elimination of HCOX and CH3COX (X = OCH3, OH, SH), respectively, from ‘a’ and ‘b’ is also observed. The label distributions for these reactions are in agreement with a mechanism corresponding to an internal reaction of [CHO] + and [CH3CO] +, respectively, with the functional group of the side chains in an intermediary ion–neutral complex. In addition, fragmentations are observed arising from reactions between the two side chains at positions 3 and 5. The D labelling proves specific reactions without any H/D exchange and thus reaction channels separated from the methanol loss. The results are explained by internal ion‐molecule reactions in an intermediary ion‐neutral complex of a methoxymethyl cation, a hydroxymethyl cation and a mercaptomethyl cation, respectively, formed by a protolytic bond cleavage of the side chains.
A reinvestigation of the collisional activation mass spectra of [C7H7]+ ion mixtures
Authors: Buschek J. M. , Ridal J. J. , Holmes J. L.
Published: May 2005

The collisional activation (CA) mass spectra of the two isomeric [C7H7]+ ions, benzyl and tropyl, have been reassessed. The structure‐characteristic feature of their CA mass spectra, the m/z 77:74 abundance ratio, has been confirmed as 3.15 ± 0.2 for benzyl cations and lowered to 035 ± 03 for tropyl ions. Benzyl–tropyl cation mixture analyses were made and were in general agreement with earlier CA results, but still disagree with the results of ion cyclotron resonance experiments. The behavior of toluene molecular ions close to their dissociation threshold to [C7H7]+ + H˙ was examined; for metastable [C7H8]+˙ ions an approximately 55:45 benzyl:tropyl ratio was found. Observations are discussed in relation to photoionization and photoelecrron‐photoionization coincidence studies, both of which predict high tropyl ion contents at low energies. However, at the lowest energies attainable in this study the benzyl content failed to fall below 50% and it is concluded that toluene molecular ions do not generate tropyl cations at their dissociation limit.
Energetics of retro‐Diels–Alder fragmentation in limonene as characterized by surface‐induced dissociation, and energy‐ and angle‐resolved mass spectrometry
Authors: Vincenti Marco , Horning Stevan R. , Cooks R. Graham
Published: May 2005

Ionized limonene and related isomeric compounds have been examined by collisional activation at both gaseous and solid targets. The gas‐phase collision‐induced dissociation (CID) experiments were performed as a function of collision energy and scattering angle and the surface‐induced dissociation (SID) experiments as a function of collision energy, in order to vary systematically the internal energy deposited in the molecular ion. The virtual absence of retro‐Diels–Alder (RDA) fragmentation upon conventional CID, as compared to its importance in the electron impact (EI) mass spectrum, the subject of a study by Boyd and coworkers, was confirmed. However, as the ion internal energy was increased by raising the collision energy or the scattering angle, RDA fragmentation was observed and it became a dominant mode of fragmentation for SID at collision energies in the range of 25–50 eV. The energy deposited into the colliding ion in the SID technique is compared with that deposited upon CID in the eV and keV energy ranges and upon EI. The order obtained is: SID > EI > low‐energy, multiple‐collision CID > high‐energy, single‐collision CID > low‐energy, single‐collision CID. The distribution of energies in SID is narrower than in the other techniques. High internal energies are accessible by increasing the scattering angle in CID; however, this is accompanied by an increase in the width of the internal energy distribution, and it is therefore not possible to channel fragmentation predominantly into RDA by this method. It is concluded that RDA fragmentation of limonene is a high‐energy process and that this is the explanation for its behavior. Isomerization, occurring through 1,3‐hydrogen migrations of the molecular ions of limonene, isolimonene, terpinolene and α‐terpinene, was investigated and long‐lived molecular ions of the first three compounds were found to maintain distinct structures.
Fragmentation characteristics of trialkylphosphane oxides, R3P(O)
Authors: Keck Helmut , Kuchen Wilhelm , Kühlborn Sabine
Published: May 2005

Fragmentation characteristics of trialkylphosphane oxides, R3P(O) (R: Et, n Pr, n Bu) are given and discussed. For phosphane oxides with substitutents R > Et fragmentations within the alkyl groups and ‘conventional’ McLafferty rearrangements are observed. The results of a structure determination for radical cations [C2H7PO]+˙ (m/z 78) and [C4H11PO]+˙ (m/z 106) obtained by collisional activation mass spectrometry are reported.
Triterpenoids. Part IV. Mass spectrometry of pentacyclic triterpenoids: 18β‐ and 18α‐11‐oxooleanolic acid derivatives
Authors: Wyrzykiewicz E. , Wrzeciono U. , Zaprutko L.
Published: May 2005

The mass spectral fragmentation of five pairs of 18β‐ and 18α‐11‐oxooleanolic acid derivatives 1a, 1b–5a, 5b are investigated and discussed. Fragmentation pathways, elucidation of which were assisted by accurate mass measurements and metastable transitions, are proposed, The obtained data create a safe basis for distinguishing the above‐mentioned 18 diastereomers.
Sulphonylium ions in the gas phase
Authors: Chatgilialoglu C. , Guerra M. , Pelli B. , Traldi P.
Published: May 2005

Electron impact mass spectrometry was used to investigate the fragmentation of a series of arenesulphonyl chlorides. Sequential losses of a chlorine atom and sulphur dioxide from the molecular ions occurred and the reverse of these reactions had small critical energies that were generally unaffected by the ring substituent. However, an interesting intramolecular cyclization reaction occurring on the ortho‐nitro derivative is discussed with the aid of kinetic energy release measurements on this derivative and on a model compound. Appearance energy measure ments combined with multiple scattering Xα calculations led to an estimate of the sulphur‐chlorine bond strength in benzenesulphonyl chloride.
Analyzer scan modes for hybrid mass spectrometers
Authors: Glish Gary L. , McLuckey Scott A.
Published: May 2005

The scan modes that can be used to obtain daughter ion, parent ion, and constant neutral‐loss spectra on hybrid mass spectrometers are derived for instruments with a quadrupole combined with a magnetic and/or electric sector. All combinations of sector/quadrupole and quadrupole/sector instruments are discussed. The advantages or lack thereof of the various scans are presented with respect to operation, resolution and potential artifacts.
Gas‐phase chemistry of electron deficient organometallic anions: the reactions of [Cr(CO)3]− ˙ and [Cr(CO)4]− ˙ with aldehydes, ketones, esters and ethers
Authors: Gregor I. K.
Published: May 2005

Reactions in the gas phase of the 13‐ and 15‐electron radical anions [Cr(CO)3]− ˙ and [Cr(CO)4]− ˙ with a series of 27 aldehydes, ketones, esters and ethers have been examined. Sequential alkane eliminations and metal‐bonded CO ligand displacements were the principal reactions identified for the RCHO/[Cr(CO)3]− ˙ systems with the latter reaction also common to the RCHO/[Cr(CO)4]− ˙ systems. While [Cr(CO)4]− ˙ was generally unreactive towards ketones R · R'CO, the principal products identified for [Cr(CO)3]− ˙/ketone reactions were the metal‐decarbonylated species, respectively [R · R'CO · Cr(CO)x]− ˙ with x = 0–3, and [R · (R' ‐ H2)CO · Cr(CO)2]− ˙. The reaction of [Cr(CO)3]− ˙ with esters RCOOR' proceeds via metal insertion into the alkoxy CO bond to give end products of the type [R'O · Cr · R(CO)2]− and [R'OCr(CO)3]− while the sole ionic products of dialkyl ether/[Cr(CO)3]− ˙ reactions were identified as the alkoxytricarbonylchromium species [RO · Cr(CO)3]−.
Fragmentation and rearrangement patterns of phospho‐ureas. Possible consequences for biotin activation
Authors: Belghith Hachemi , Blonski Casimir , Klaébé Alain , Périé Jacques , Roussel Jean
Published: May 2005

Analysis by electron impact and metastable ions (MIKE technique) of the fragmentation patterns for one acyclic and two cyclic N‐phosphorylated ureas reveals for the first case an isomerization from nitrogen to the ureido oxygen atom of the phosphoryl group and subsequent fragmentation. For the other two cases, fragments result from PN bond breaking and ring‐opening. Possible involvement in the biotin‐ATP activation process is discussed.
Mass spectra of substituted pyrrolidine‐N‐oxyl radicals
Authors: Jerkovich Gyula , Hankovszky H. Olga , Hideg Kálmán
Published: May 2005

Electron impact mass spectra of 65 pyrrolidine‐N‐oxyl derivatives have been assigned on a ‘peak‐to‐subgraph’ basis. On average, 50% of the total ion current is represented by structurally significant fragments associated with the nitroxide group. Secondary fragmentation is, as a rule, of a minor importance (30%), and fragments due to functional groups other than NO· seldom contribute more than 10% of the total ion current An enhanced specificity of fragmentation is observed when one or more of the 2,2, 5,5‐methyl groups is replaced by a longer aliphatic chain or an aromatic group.
Gas‐phase ion–molecule reactions in dilute mixtures of dimethyl ether in krypton. Bimolecular and clustering reactions
Authors: Illies Andreas J.
Published: May 2005

The results of high‐pressure variable‐temperature and variable ionizing electron energy studies of gas‐phase ion‐molecule reactions of dimethyl ether in krypton are presented. Near the ionization threshold a series of peaks corresponding to (CH3OCH3)nH+ (n = 1‐4) clusters are observed. At higher ionizing electron energies, two new series of peaks appear, corresponding to [CH3OCH2]+(CH3OCH3)n and [(CH3)3O]+ (CH3OCH3)n clusters. The onium ion, [(CH3)3O]+, has been previously reported at elevated temperatures under methane chemical ionization conditions. It was suggested that the onium ion is formed by reaction of (CH3)2OH+ with CH3OCH3 with subsequent elimination of methanel, i.e. by fragmentation of an adduct ion. The present results strongly suggest that, under our conditions, [CH3OCH2]+ rather than thermal (CH3)3OH+, is the precursor to [(CH3)3O]+.
Mass spectrometric behaviour of cyclopentane‐and cyclohexane‐condensed pyrimidinediones under electron impact
Authors: Himottu Marja , Pihlaja Kalevi , Bernáth Gábor , Stájer Géza , Vainiotalo Pirjo
Published: May 2005

Mass spectral fragmentations of four cyclopentane‐condensed cis‐pyrimidinediones and of six cyclohexane‐condensed cis‐ or trans‐pyrimidinediones were examined using metastable ion analyses and exact mass measurements. The fragmentation patterns of all of these compounds were clearly different and also cis‐ and trans‐fused isomers were easy to distinguish from each other by their mass spectra. In spite of the differences in their mass spectral fragmentations, all compounds formed phenylisocyanates (m/z 119 and 153) and anilines (m/z 93 and m/z 127), the structures of which were verified by collision‐induced dissociation experiments.
Differentiation of stereoisomers with electron impact mass spectrometry: (E)‐ and (Z)‐α‐hydroxyoximes
Authors: Łożyński Marek , Rusińska‐Roszak Danuta
Published: May 2005

The electron impact mass spectra of 5,8‐diethyl‐7‐hydroxydodecan‐6‐one (Z)‐oxime and (E)‐oxime provide a basis for distinguishing these stereoisomers.
Comparison of mass spectrometric methods for studying thermally labile compounds: Rifapentine
Authors: Vékey Kàroly , Edwards Duncan M. F. , Zerilli Luigi F. , Màk Marianna , Tamàs Jòzsef , Raverdino Vittorio , Selva Antonio
Published: May 2005

Results of 16 different mass spectrometric ionization and sample‐introduction methods are compared for the case of a thermally very labile antibiotic, rifapentine. These suggest that extensive thermal decomposition occurs during evaporation when the sample can come into contact with hot metal parts, usually the source housing. The intensity of the molecular ion and the extent of fragmentation depend on various parameters, such as the ionization process, positive or negative‐ion detection and the type of sample introduction. The most informative methods for rifapentine seem to be ‘in‐beam’ electron impact, negative ionization with particle beam and direct liquid introduction interfaces and positive‐ and negative‐ion fast atom bombardment.
Positive‐ion mass spectra and collision‐induced dissociation of some 2,3‐didehydro amino acids
Authors: Hamdan Mahmoud , Tarzia Giorgio , Balsamini Cesarino , Spadoni Gilberto , Curcuruto Ornella , Traldi Pietro
Published: May 2005

The positive‐ion mass spectra of a number of didehydro amino acids, ionized by electron impact and/or thermospray, and collision‐induced dissociation spectra taken at collision energies of a few electron volts and keV have been performed on multiple quadrupole and reversed geometry sector instruments. Observed differences in the mass spectra and in the fragmentation patterns are explained in terms of different isomeric structures, different internal excitation energies and different ion transit times between the ion source and the collision cell. Molecular ions of unhydrated amino acids are efficiently formed both by electron impact and thermospray, whilst molecular ions of the hydrated compounds are formed more efficiently by the latter technique. The present investigation demonstrates that the use of different ionization techniques combined with mass spectrometry/mass spectrometry measurements at different collision energies yields a wealth of information relevant to structural characterization of this important class of molecules.
Nature of methyl cation bonding to dihydroxybenzenes elucidated using an ion trap mass spectrometer
Authors: Nourse B. D. , Brodbelt J. S. , Cooks R. G.
Published: May 2005

Methylation of the isomeric dihydroxybenzeres using the dimethylfluoronium ion ([CH3FCH3]+) was studied in a quadrupole ion trap mass spectrometer. The products were characterized by tandem mass spectrometry using collision‐activated dissociation. A comparison of the daughter ion spectra of the methylated products with those of model ions, generated by protonation of substituent‐ and ring‐methylated analogs, demonstrates that a mixture of methylated products is generated. Included are structures in which the methyl is σ‐bonded to the ring and others with σ‐bonds to the heteroatom, the latter being favored in catechol and hydroquinone. The energy‐resolved daughter ion spectra for the methylated isomers, acquired by varying the amplitude of the a.c. voltage used to excite resonantly the mass‐selected ions, support these conclusions regarding the site of methylation.
Ion‐neutral complexes and the proton‐bound dimer of acetone
Authors: Hunter John A. , Johnson Chris. A. F. , Parker John E. , Smith Gerry P.
Published: May 2005

High‐ and low‐energy collision‐induced dissociation, and multi‐photon infrared dissociation spectra of the proton‐bound dimer of acetone all show the formation of protonated‐acetone and an acetone molecule as the only dissociation products. In the present paper evidence is presented that the proton‐bound dimer of acetone can exist as three isomeric ion‐neutral complexes, two of which may interconvert. The dissociation channels and energetics of these three complexes are modelled using the MINDO/3 quantum chemical method.
Influence of experimental conditions on the liquid secondary ion mass spectra of sulfonated azo dyes
Authors: Richardson Susan D. , Thruston Alfred D. , McGuire John M. , Baughman George L.
Published: May 2005

Two monosulfonated and eight disulfonated azo dyes of varying relative molecular mass were examined by liquid secondary ion mass spectrometry (LSIMS). The effects of matrix, concentration, primary beam energy, and mode of operation were addressed in order to optimize sample ionization, whilst minimizing interference from matrix ions. Seven matrices were investigated: glycerol, thioglycerol, 3‐nitrobenzyl alcohol, diethanolamine, 2‐hydroxyethyl disulfide, a 1:1 (v/v) mixture of 2‐hydroxyethyl disulfide and thioglycerol, and a 1 : 3 (v/v) mixture of dithioerythritol and dithiothreitol. Of these matrices, 3‐nitrobenzyl alcohol produced LSIMS spectra that exhibited the most intense sample ions and the least inteiference from matrix ions. Minimum concentrations of 0.4 μg/μl and 4 μg/μl (dye in matrix) were necessary to produce useful full‐scan spectra for monosulfonated azo dyes and disulfonated azo dyes, respectively; maximum sample ion intensities were obtained with concentrations ranging from 20 μg/μl to 60 μg/μl. A primary ion beam (cesium) of 10 to 15 kV produced the greatest secondary ionization efficiency, and a negative‐ion analysis mode produced more useful spectra than those obtained in the positive‐ion mode.