bluuebunny/crossref_metadata_2025 huggingface dataset:
The mass spectral fragmentation of some substituted 3‐Amino‐2‐salicylideneamino‐benzofurans
Authors: Blythin D. J. , Kyriakidis N. , Waight E. S.
Published: May 2005

Electron impact mass spectra of eight of the title compounds are discussed. The important fragment ions are shown by high resolution and deuterium labelling to contain the benzofuran nucleus and to involve extensive rearrangement processes. Fragmentation pathways have been confirmed by measurement of daughter ion spectra (B/E linked scans).
Gas chromatography mass spectrometry of some steroidal spirolactones
Authors: Boreham D. R. , Vose C. W. , Balasubramanian V. , Brooks C. J. W.
Published: May 2005

Gas chromatography mass spectrometry of a number of steroidal spirolactones and their TMS ethers is reported. Open tubular column gas chromatography provides useful structural information for these compounds as shown by shifts in retention index values. The electron impact fragmentation pathways have been established for a number of the compounds. The results of the study indicate that open tubular column gas chromatography mass spectrometry will be of value in studies of the metabolism of this class of steroids in animals and man.
The Loss of a hydroxyl group from the molecular ions of alkylnitrobenzenes
Authors: Butcher A. R. , Thomas C. B.
Published: May 2005

It is confirmed that the loss of HO˙ from the molecular ion of o‐nitrotoluene involves exclusively a hydrogen from the methyl group. However, in higher homologues hydrogen atoms from non‐benzylic sites are also implicated. With such compounds this fragmentation mode is shown not only by the ortho but, to a lesser extent, by the meta and para isomers as well. The proportion of the total ion current borne by the [M – 17]+ ion follows the order ortho > meta > para, which is attributed to substituent migration around the ring with a hydroxyl radical only being lost when the groups are on adjacent ring atoms. Other ions present in the spectra point to interaction between substituents to form a new heterocyclic ring.
Zum massenspektrometrischen Fragmentierungsverhalten von Thiophen‐Benzologen
Authors: Riepe W. , Zander M.
Published: May 2005

Das Fragmentierungsverhalten bei den untersuchten Thiophen‐Benzologen ist sehr ähnlich. Unterschiede treten nur in der Häufigkeit der Brushstück‐Ionen auf, die durch Abspaltung von S bzw. CS und deren wasserstoffhaltigen Varianten entsteren. Die Bildungsmöglichkeiten der resultierenden Fragment‐Ionen werden diskutiert.
The effect of a phosphorus bridgehead atom on the loss of neutral species in the mass spectra of bicyclooctanes
Authors: Voorhees Kent J. , Hileman Fred D. , Smith David L.
Published: May 2005

The effect of a bridgehead phosphorus atom, as both the three (phosphate)and five (phosphate) oxidation states, to influence unique mass spectral neutral losses from a 1‐phosphabicyclo[2.2.2]octane system has been investigated. A conventional neutral loss of formaldehyde was found for the phosphites while a unique loss of ethylene was observed for the phosphate. These losses are discussed in terms of the substituent effects from the 4‐position.
Acetylenic ketones. VII—Structural analyses by mass spectrometry of the products obtained from the reaction of acetylenic ketones with nucleophilic sulphur compounds
Authors: Baddar Fawzi G. , Al‐Hajjar Farouk H. , El‐Rayyes Nizar R.
Published: May 2005

The mass spectra of β‐hydroxy‐α‐thiobenzoylstyrene derivatives and (E, Z)‐ or (E, E)‐β,β‐di(α‐aroylstyryl)sulphides as well as β,β′di(α‐aroylstyryl)disulphides are discussed. The fragmentation patterns support their proposed structure and configuration.
Rearrangements and fragmentations of [C2H5S]+ ions
Authors: Broer W. J. , Weringa W. D. , Nieuwpoort W. C.
Published: May 2005

From deuterium labelling experiments it was concluded that metastable molecular ions of ethyl methyl sulfide lose a methyl radical with the formation of both [CH3SCH2]+ amd [CH3CHSH]+˙ The fragmentation reactions of metastable ions generated with these structure are losses of C2H2, H2S and CH4. These reactoins and the preceding isomerizations have also been studied by means of deuterium labelling. From the results it is concluded that the three fragmentation reactions most probably occur from ions with a CCS skeleton. Appearance energy measurements for ions generated with the two structures above and all give rise to the same ΔHf value for these three isomeric forms. Ab initio molecular orbitals calculations confirm that these three ions fortuitously have very similar heats of formation. A potential energy diagram rationalizing the isomerizations and the principal fragmentation reaction is presented.
Mass spectrometric study of conjugated bifunctional acetylenes. 1—Enynes
Authors: Bachiri M. , Perros P. , Verneuil B. , Mouvier G. , Carlier P.
Published: May 2005

This study on the fragmentation of conjugated enynes demonstrates the relationships between the mass spectra and the structures of these compounds. The rearrangements of the molecular ions and the fragment ions are characterized; the mechanisms by which the most important peaks are formed have been established and detailed analysis of the metastable transitions reveals all the fragmentation steps. A complete scheme is presented for 2‐methyl‐1‐nonene‐3‐yne since it includes all the transitions which can be detected for the lower homologues. The ion kinetic energy spectra for this family of compounds are distinct (even though the conventional spectra are similar) and could very well be used for identification purposes.
The fragmentation of 2‐aminooxazoles under electron impact
Authors: Selva A. , Traldi P. , Rapi G. , Ginanneschi M. , Chelli M.
Published: May 2005

The 70 eV electron impact mass spectra of six 2‐aminooxazoles are discussed in detail with the aid of exact mass measurements, metastable ion detection in the defocused mode and labelling experiments. The fragmentation is markedly influenced by strong electron donating substituents at the 2‐position. Some 2‐acetylamino and 2‐diacetylamino derivatives have also been considered, which lose ketene from [M]+⋅ giving the corresponding aminooxazole molecular ions. The mass spectral behaviour is peculiar and the most important differences between the fragmentation pathways of these compounds and those reported in the literature for oxazole (alkyl and aryl) derivatives are outlined. The mass spectrum of 4‐methyl‐5‐phenylimidazol‐2‐one is compared with that of the isomeric 4‐methyl‐5‐phenyl‐2‐aminooxazole.
Positive and negative ion mass spectra of Aryl‐ONN‐azoxy compounds containing electron withdrawing groups
Authors: Vaglio Gian Angelo , Ferrari Rosa Pia , Mortarini Vittorio , Gasco Alberto , Calvino Rosella
Published: May 2005

The positive and negative ion mass spectra, at 70 eV, of p‐RC6H4N(O)NCOOCH3 (RH, Cl, Br, NO2), C6H5N(O)NCOOC2H5, p‐RC6H4N(O)NCONH2 (RH, Cl, Br, NO2) and p‐RC6H4N(O)NCOC6H5 (RH, Cl, Br, NO2) are reported. The azoxyester derivatives show abundant molecular ions and a number of weak fragment and rearrangement ions in the positive ion mass spectra, whereas weak molecular ions and abundant low mass fragment ions are present in the negative ion mass spectra. Similar behaviour is observed in the mass spectra of the azoxyamides. Conversely, for the azoxycarbonyl compounds the positive molecular ion is absent. A ready cleavage of the NCO bond occurs and only few fragments of low diagnostic value are formed, whereas the negative molecular ion is the base peak for all these compounds with the exception of the p‐NO2 derivative, where [MO]−⋅ is the base peak and [M]−⋅ is the second major ion. The behaviour under electron impact of these classes of compounds is compared with that of azoxycyanides reported previously.
Studies in negative ion mass spectrometry. XIII—Electron attachment to a series of Nickel(II) β‐diketonate complexes
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K.
Published: May 2005

Results of electron attachment reactions and negative ion mass spectra are presented for a group of selected nickel(II) β‐diketonate complexes of formula Ni[R1COCHCOR2]2, where R1 is a perfluoroalkyl group and R2 either an alkyl or aryl group. Molecular negative ions together with ligand ions are the major contributors to the total ion currents for each compound, and the degree of fragmentation has been shown to be dependent on the substituents R1 and R2. Fragmentation schemes have been elucidated for all the major ion decomposition pathways, and all significant ions have been identified in the negative ion mass spectra of each compound. Bis(1,1,1‐trifluoro‐5,5‐dimethyl‐2,4‐hexanedionato) nickel(II), with R1CF3 and R2tert‐butyl is the complex which shows considerable potential for analytical quantitation in the negative ion mode, because of the stability of its negative molecular ion, the high negative ion yield given after electron attachment, as well as the volatility of the compound.
Mass spectrometry of condensed N‐heterocycles: II—A novel ortho effect in the electron impact induced fragmentation of some C‐(2‐nitrophenyl)‐azoles and ‐azoloazines
Authors: Könnecke A. , Lepom P. , Dörre R. , Lippmann E. , Herzschuh R. , Kralj B. , Stanovnik B. , Tišler M.
Published: May 2005

Heterocycles containing an integrated 2‐nitrobenzaldehyde imine moiety produce ions of m/z 134 with high abundance under electron impact. As shown by kinetic energy release measurements these ions have the same structure in all the cases studied, identical to m/z 134 formed from the reference compound 2‐nitrobenzoylpiperidide. The mechanism of formation of m/z 134 most probably involves isomerization of its precursor ion to give a spiro intermediate, from which m/z 134 arises either synchronously or after a second isomerization. Both alternatives formally represent an oxygen transfer from the nitro group to the imino carbon via a 5‐membered transition state.
Exact mass analysis of DNA fragments
Authors: Gaudin D. , Jankowski K.
Published: May 2005

High resolution data for the major ions from the salmon sperm DNA mass spectrum are reported. The presence of two series of ions for each characteristic fragment is shown, the first containing a phosphate moiety and the second having CHNO compositions only.
Ortho effects in schiff bases of diaminodicyanoethene
Authors: Holzmann G. , Rothkopf H. W.
Published: May 2005

In the electron impact mass spectra of azomethines derived from various substituted aromatic aldehydes and diarninodicyanoethene the superposition of two ortho effects concurring with the azomethine group is apparent: one involving the amino group of the diaminodicyanoethene part accounts for the cyclization to [C5H3N4]+ ions and the other involving ortho substituents of the benzylidene part which can interact with the azomethine moiety is responsible for specific fragment ions, suppressing the typical fragmentations of azomethines. The ortho effect was studied for the o‐nitro derivative by labelling experiments, analysis of metastable transitions and collisional activation comparing model ions, demonstrating that the specific [M‐H2O]+˙ and [C7H5NO2]+˙ ions are the result of cyclization processes.
Studies on the mechanism of electron impact induced SH radical loss from the diastereoisomeric 2‐dimethylamino‐2‐thiono‐4‐methyl‐1,3,2‐dioxaphosphorinanes
Authors: Stec W. J. , Zielińska B. , van de Graaf B.
Published: May 2005

The intensity differences between the [MHS]+ peaks in the mass spectra of diastereoisomeric 2‐dimethylamino‐2‐thiono‐4‐methyl‐1,3,2‐dioxaphosphorinanes have been rationalized in terms of fragmentation mechanisms and ion structures. Metastable characteristics together with D labelling experiments support these rationalizations.
Unimolecular decompositions of even‐electron ions
Authors: McLafferty F. W.
Published: May 2005

Fragmentations of even‐electron ions of lifetimes ≥10−5s caused by electron and chemical ionization and by collisional activation have been correlated. Proposed reaction classifications include: cleavage of one bond with charge migration; cleavage of one bond through cyclization‐displacement; cleavage of two bonds in a cyclic ion with charge retention; and cleavage of two bonds in an acyclic ion with rearrangement and charge retention. Such reactions are compared with those of odd‐electron ions; despite a higher tendency for rearrangement, the decompositions of a positive even‐electron ion, in particular as displayed in its collisional activation spectrum, have substantial utility for characterizing its structure.
Kinetic energy release and ion structure: [C6H6O]+˙
Authors: Maquestiau A. , Flammang R. , Glish G. L. , Laramée J. A. , Cooks R. G.
Published: May 2005

It is shown that, contrary to a recent report, the kinetic energy release for CO loss from phenol does not decrease as the ion accelerating voltage is decreased. In fact, an increase is observed which is attributed, at least in part, to greater discrimination against off‐axis ions at low voltage. The kinetic energy release data do not demand the tautomerization of ionized phenol before decarbonylation.
The use of two linked scanning modes in alternation to analyse metastable peaks
Authors: Lacey Michael J. , Macdonald Colin G.
Published: May 2005

Analyses of masses and relative kinetic energies for metastable peaks may be achieved by the use in alternation of two types of linked scans of the electric sector voltage and magnetic field. The method is demonstrated by an appraisal of hydrogen exchange in molecular ions of 2‐methyl‐[2H3]‐benzoic acid.
Charge stripping mass spectra: A method for identifying isomeric [C5H8]+˙ and [C3H6]+˙ ions
Authors: Holmes John L. , Terlouw Johan K. , Burgers Peter C. , Rye Robin T. B.
Published: May 2005

Charge stripping (collisional ionization) mass spectra are reported for isomeric [C5H8]+˙ and [C3H6]+˙ ions. The results provide the first method for adequately quantitatively determining the structures and abundances of these species when they are generated as daughter ions. Thus, loss of H2O from the molecular ions of cyclopentanol and pentanal is shown to produce mixtures of ionized penta‐1,3‐ and ‐1,4‐dienes. Pent‐1‐en‐3‐ol generates [penta‐1,3‐diene]+˙. [C3H6]+˙ ions from ionized butane, methylpropane and 2‐methylpropan‐1‐ol are shown to have the [propene]+˙ structure, whereas [cyclopropane]+˙ is produced from ionized tetrahydrofuran, penta‐1,3‐diene and pent‐1‐yne.
Mass spectrometric fragmentation of S‐(1‐aryltetrazol‐5‐yl)‐monothiocarbonic acid esters
Authors: Löster Heinz , Herzschuh Rainer , Lippmann Eberhard
Published: May 2005

The mass spectra of S‐(1‐aryltetrazol‐5‐yl)‐monothiocarbonic acid esters have been studied. The stability of the ester molecular ions is lower than the stability of the corresponding 1‐aryl‐5‐mercaptotetrazoles. Substituents at the phenyl group increase the stability, whereas the influence of the ester alkyl groups is very small. The esters undergo fragmentation via four different fragmentation pathways. The elimination of carbon dioxide is influenced by an ‘ortho effect’ of the substituents.
Metastable peak study in methylactophenone isomers
Authors: Rabbih M. A. , Selim Ezzat T. M.
Published: May 2005

The relative intensity of the metastable peaks at 70 eV appearing at m/z 105.7 and 69.6 in the mass spectra of methylacetophenone isomers, as well as the kinetic energy (T1/2) released with the peaks at 14 and 70 eV respectively, are reported. The profile of all the metastable peaks studied has been found to be approximately flat‐topped. For the same transition it is found that the kinetic energy released with the metastable peaks formed by unimolecular decomposition of the three isomers decreases from the ortho to the para isomer. In addition, the kinetic energy released during the same transition is found to be roughly directly proportional to their corresponding intensity ratios. This result, together with the observation that the energy released with each metastable peak decreases by lowering the electron energy, may reveal the role of the internal energy of the reacting ions in producing the kinetic energy associated with the metastable peaks produced from methylacetophenone isomers.
Electron impact induced intramolecular hydrogen transfer reactions in polymethylene glycol di‐p‐toluenesulfonates
Authors: Blane Pierre‐Alain , Gülaçar Fazil O. , Buchst Armand
Published: May 2005

The mechanisms of formation of the ionized acid and the protonated acid fragments in the electron impact induced fragmentation of the title compounds were investigated. The well known mechanisms of hydrogen transfer through mono‐ and bicyclic transition states that occur in the molecular ions of carboxylic esters are not the main pathways giving rise to these fragments. The major component of the m/z 172 peak corresponding formally to ionized p‐toluenesulfonic acid in fact has a different structure; its formation involves a complex mechanism including a double hydrogen transfer reaction.
Mass spectrometric studies of 2‐nitrosophenols
Authors: Charalambous J. , Fysh R. R. , Herbert C. G. , Johri M. H. , Shutie W. M.
Published: May 2005

The mass spectra of 2‐nitrosophenols are independent of the insertion temperature, suggesting that the compounds either do not exhibit tautomerism in the vapour phase or that the enthalpy of isomerization is low. However, their fragmentation patterns suggest tautomerism in the molecular ion.
The mass spectral rearrangements of 1,6‐bis(arylsulfenyl)‐2,4‐hexadiynes and 1,6‐bis(arylsulfonyl)‐2,4‐hexadiynes
Authors: Thyagarajan B. S. , Glaspy P. E. , Baker E. , Brown Peter
Published: May 2005

The mass spectral. behavior of 1,6‐bis(arylsulfenyl)‐2,4‐hexadiynes and 1,6‐bis(arylsulfonyl)‐2,4‐hexadiynes were examined. The sulfenyl derivatives extruded the hexadiynyl moiety with the formation of ArSSAr fragments. The sulfonyl derivatives, on the other hand, showed no extrusion of the hexadiyne fragment but an expulsion of SO2 and even two SO2 units.
The electron impact mass spectrometry of some para substituted trans‐2‐styryl‐6‐carboxychromones. An unusual cleavage of the chromone ring
Authors: Tonani Roberto
Published: May 2005

The electron impact mass spectrometry of some para substituted trans‐2‐styryl‐6‐carboxychromones shows a new fragmentation of the chromone ring in addition to the well known retro Diels‐Alder reactions with and without hydrogen transfer. The observed primary fragments are supported by metastable transitions and exact mass measurements.
Stereochemical applications of mass spectrometry. II—Chemical ionization mass spectra of isomeric dicarboxylic acids and derivatives
Authors: Harrison Alex. G. , Kallury R. Krisha Mohan Rao
Published: May 2005

The H2 and CH4, chemical ionization mass spectra of the cis dicarboxylic acids, maleic and citraconic acid, show much more extensive loss of H2O from [MH]+ than the trans isomers, fumaric acid and mesaconic acid. Similarly, esters of maleic acid show a much more facile loss of ROH (R=alkyl or phenyl) from [MH]+ than do esters of fumaric acid. Similar differences are observed in the chemical ionization mass spectra of the isomeric phthalic and isophthalic acids and derivatives, where the ortho isomers show more extensive fragmentation of [MH]+ than the meta isomers. The facile fragmentation of [MH]+ for the cis and ortho isomers is attributed to ROH elimination involving interaction between the two carboxylate functions and forming the stable cyclic anhydride structure for the fragment ion. By contrast ROH elimination from [MH]+ for the trans and metu isomers requires a symmetry‐forbidden [1,3]‐H migration in the carboxyl protonated species and cannot lead to the cyclic anhydride structure. The chemical ionization mass spectra of cis and trans cyclohexane‐1,2‐dicarboxylic acids are essentially identical and show extensive fragmentation of the [IMH]+ ion. Experiments using deuterium labelling show extensive carboxyl group interactions for both isomers. The chemical ionization mass spectra of maleanilic and phthalanilic acids and of the related anhydrides and imides also are reported, as are the electron impact mass spectra of diphenyl maleate, diphenyl fumarate, diphenyl phthalate, maleanilic acid and phthalanilic acid.
Mass spectrometry of aryl substituted di‐ and trisiloxanes
Authors: Swaim Robert E. , Weber William P. , Boettger Heinz G. , Evans Margaret , Bockhoff Frank M.
Published: May 2005

The mass spectra of arylpentamethyldisiloxanes, sym‐diaryltetramethyldisiloxanes and 1,5‐diaryl‐1,1,3,3,5,5‐hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M‐15]+ ions is important. Phenylpentamethyldisiloxane, sym‐tetramethyldiphenyldisiloxane and 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M‐15]+ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH3)2SiO] and phenylmethylsilanone [PhCH3SiO] to yield daughter siliconium ions. The [M‐15]+ ion of sym‐tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M‐15]+ ion of 1,1,3,3,5,5‐hexamethyl‐1,5‐diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di‐ and trisiloxanes discussed.
Chemical ionization mass spectrometry of dimethyl acetals and diethyl dithioacetals of aldopentoses and aldohexoses, and the influence of stereochemical configuration
Authors: Blanc‐Muesser Michèle , Defaye Jacques , Foltz Rodger L. , Horton Derek
Published: May 2005

Chemical ionization mass spectra have been recorded for the title compounds having the four pentose configurations and the eight hexose configurations, with ammonia and isobutane as the reagent gases. The ammonia mediated spectra display [NH4]+ capture ions with successive loss of one or two molecules of methanol (acetals) or ethanethiol (dithioacetals), whereas when isobutane was the reagent gas, loss from the protonated acetals of one or two molecules of methanol and of water, and loss from the protonated dithioacetals of one or two molecules of ethanethiol and of water were featured. Significant differences in the ion intensities as a function of stereochemistry in the precursor are noted, and are discussed in terms of the ease of formation of cyclic fragment ions.
Rule‐based mass spectrum prediction and ranking: Applications to structure elucidation of novel marine sterols
Authors: Lavanchy Andre , Varkony Tomas , Smith Dennis H. , Gray Neil A. B. , White William C. , Carhart Raymond E. , Buchanan Bruce G. , Djerassi Carl
Published: May 2005

A novel, computer aided approach to the interpretation of mass spectra is documented by its application to a series of recently isolated marine sterols. The method consists of construction of biosynthetically plausible candidate structures, prediction of their major mass spectral fragmentation paths using class‐specific rules derived from a training set of known compounds, and a system of ranking candidate structures based on a comparison of the predicted and observed spectra.
Electron impact studies: CXXXI—Ion cyclotron resonance studies of ambident nucleophiles. The reaction between the thioacetate anion and thioacetic anhydride. A further example of a negative ion McLafferty rearrangement
Authors: Trenerry V. Craige , Bowie John H.
Published: May 2005

The [MeCOS]− ion undergoes reaction with neutral thioacetic anhydride in an ion cyclotron resonance cell to yield an adduct [M+MeCOS]− which decomposes principally by loss of CH2CS, thus establishing the occurrence of nucleophilic attack through O at the carbonyl centre.
Ion/molecule reactions of ammonia and methylamine with chloro‐ and nitrobenzene. A comparison of chemical ionization and ion cyclotron resonance experiments
Authors: van der Hart W. J. , Luijten W. C. M. M. , van Thuijl J.
Published: May 2005

It is shown by ion cyclotron resonance measurements that ion/molecule reactions, leading to substitution or reduction product ions from chloro‐ and nitrobenzene with the title amines, are those between the molecular ions [RNH2]+ or [C6H5X]+˙ and their respective counterparts C6H5X or RNH2. The protonated reagent gas ions [RNH3]+ are not involved in these reactions. In the case of nitrobenzene, adduct ions [C6H5NO2·RNH3]+ do not decompose within the time scale of the measurements. The results obtained are compared with those found under chemical ionization conditions.
Mechanisms of unimolecular fragmentations of odd‐electron cations in the gas phase: The importance of intramolecular hydrogen migration for [odd]+˙ → [even]+ transitions
Authors: Schwarz Helmut
Published: May 2005

Eighteen quite different examples are discussed in which the unimolecular elimination of a given radical X˙ from an odd‐electron cation cannot be described as a one‐step process. Despite the fact that the radical X˙ eliminated is already present as a structural unit in the decomposing ions, the product analysis and structure determination of the even‐electron ion formed, the investigation of the energetics of the reaction, the analysis of stereochemical factors, and the determination of kinetic isotope effects reveal that the eliminations must be characterized as two‐ or multi‐step reactions. In all cases investigated, the process commences with a specific (intramolecular) hydrogen transfer to a suitable acceptor function. In this way a reactive radical site is created which induces the actual dissociation step (elimination of X˙) by simultaneous double bond formation. Due to the fact that the hydrogen migration takes place within the charge carrying part of the cation radical and that the migrated hydrogen atom remains there throughout the whole process, the intervention of a H‐migration cannot be traced directly by appropriate mass shifts in the spectra of 2H labelled precursors. However, the methods mentioned above can be applied to reveal the details of the reaction mechanism, and the term ‘hidden’ hydrogen migration induced dissociation is suggested to recognize the particular rǒle of H‐rearrangements to trigger radical eliminations from odd‐electron cations in the gas phase.
Electron impact induced fragmentation of 4‐alkyl derivatives of 2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane and the corresponding 1‐oxides, 1‐sulfides and 1‐selenides
Authors: Kenttämaa Hilkka , Enqvist Jouni
Published: May 2005

The electron impact fragmentations of several derivatives of 2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane have been examined by means of high resolution and metastable ion analysis. The principal fragmentation route for bicyclophosphites, phosphates and phosphorothionates involves a loss of formaldehyde, followed by a loss of the PO2X and HPO2X groups (X = ‐, O, S). The behaviour of phosphoroselenates is quite different, due partly to the favoured loss of selenium from the molecular ion before further fragmentation. Fragmentation through CO bond breaking and a rearranged molecular ion is dependent on the exocyclic chalcogen atom (‐, O, S, Se) on phosphorus. The reactions have been rationalized in terms of 1‐ and 4‐substitutions.
Reversal of the ritter reaction as observed under electron impact conditions
Authors: Nagubandi Sreeramulu
Published: May 2005

Fragmentations of various 2‐phenethylamides, trifluoroacylimidates and imidoyl trifluoromethyl sulfonates have been studied and a pathway for the formation of retro‐Ritter reaction products is proposed.
Studies of consecutive reactions of organic ions in a reversed geometry mass spectrometer
Authors: Proctor C. J. , Kralj B. , Brenton A. G. , Beynon J. H.
Published: May 2005

Over thirty consecutive reactions of a type m1+ → m2+ → m3+ have been studied in a variety of organic compounds using a reversed geometry mass spectrometer. Two field free regions allow the separation of the two steps that make up the consecutive reaction sequence. Translational energy release measurements are used in the comparison of m2+ ions formed as a result of a high energy process in the ion source with m2+ ions formed as a product of a metastable decomposition. In some cases the structures of such ions have been found to be different. Examples have also been found where consecutive fragmentations of metastable ions do not occur although, when higher energy ions within the source are studied, the two‐step reaction does take place. Furthermore, it has been found that a control over ion internal energy may be achieved by selecting portions of a peak due to the fragmentation of a metastable ion. Unimolecular reactions may then be used to study the reactivity of such ‘energy‐selected’ ions; collision induced reactions can be used to study the structure of both the reactive and unreactive energy selected ions.
The mass spectra of halogeno derivatives of quinoxaline
Authors: Poradowska Henryka , Kaniewska Alicja
Published: May 2005

The mass spectra of seventeen different quinoxaline halogeno derivatives are reported. The fragmentation mechanism is discussed.
Mass spectral fragmentation of metal dithiocarbamate complex salts
Authors: Dias Jerry Ray , Zigon Majda , Gomiscek Sergej
Published: May 2005

A summary of the mass spectra of metal dithiocarbamate complex salts (ML2 and ML3) is presented. Only divalent metal dithiocarbamate ions without an electronic configuration containing an inert s‐orbital electron pair exhibited both expulsion of a ligand radical (L) and the neutral even electron species (L–H) generated from the ligand via hydrogen transfer to the metal‐containing fragment ion. Divalent metal dithiocarbamate ions can be generated either by direct electron impact ionization of gas phase ML2 molecules or ionization of ML3 molecules followed by loss of a ligand radical. A highly stable sp2 hybridized, gas phase ion of a monobidentate lead dithiocarbamate complex is proposed.
Nicotinates as derivatives for the mass spectrometric investigation of long chain alcohols
Authors: Vetter W. , Meister W.
Published: May 2005

The mass spectra of the nicotinates of two methyl branched and one unsaturated long chain alcohol were compared with the mass spectra of the underivatized alcohols and of their trimethylsilyl ethers. It is shown that the structure of the chain is much more clearly shown by the spectra of the nicotinates than in the other spectra.
Chemical ionization mass spectra of selected C3H6O compounds
Authors: Bowen Richard D. , Harrison Alex G.
Published: May 2005

The chemical ionization mass spectra of five isomers of C3H6O (acetone, propionaldehyde, oxetane, propylene oxide and allyl alcohol) have been determined using a variety of reagent gases (H2, D2, N2/H2, CO2/H2 and CO/H2). The [C3H7O]+ ions produced by protonation of these isomers undergo very similar reactions to those reported for analogous [C3H7O]+ metastable ions; however, decomposing ions generated by chemical ionization appear to have somewhat higher internal energies. The results of 2H labelling studies (D2 reagent gas or labelled analogues of C3H6O) indicate that protonation occurs mainly on oxygen and are consistent with previous investigations of metastable oxonium ions. The protonated acetone ion is particularly stable, in agreement with the higher activation energies for fragmentation of this isomer than for other [C3H7O]+ structures. As the calculated heat of protonation of C3H6O is reduced by changing the reagent gas, so the extent to which fragmentation occurs decreases. This is discussed in the context of competition between fragmentation and collisional stabilization of the excited [C3H7O]+* ion. It is concluded that on average a large fraction (approaching 1) of the exothermicity of the protonation reaction resides in the [C3H7O]+* ions produced initially.
Formation and structure of [C8H8O]+˙ ions, generated from gas phase ions of phenyl‐cyclopropylcarbinol and 1‐phenyl‐1‐(hydroxymethyl)cyclopropane
Authors: Dallinga J. W. , Nibbering N. M. M. , Louter G. J.
Published: May 2005

The structure and formation of [C8H8O]+. ions generated from phenylcyclopropylcarbinol and 1‐phenyl‐1‐hydroxymethylcyclopropane upon electron impact, have been studied using kinetic energy release measurements, by determination of ionization and appearance energies and by collisional activation. It is shown that the non‐decomposing [C8H8O]+˙ ions have exclusively the structure of the enol ion of phenylacetaldehyde, although it is less stable than the enol ion of acetophenone by about 45 kJ mol−1. This has been interpreted as an indication that the [C8H8O]+˙ ions from phenylcyclopropylcarbinol are formed by an attack of either the phenyl ring or the hydroxyl group upon the C‐1C‐2 (or C‐1C‐3) bond of the cyclopropane ring under a simultaneous expulsion of ethene and migration of the attacking group to the C‐1 position. The [C8H8O]+˙ ion from 1‐phenyl‐1‐(hydroxymethyl)cyclopropane is formed by opening of the cyclopropane ring via a benzylic cleavage. A kinetically controlled hydrogen shift in the resulting ring opened ion prior to or during ethene loss then leads to the formation of [C8H8O]+˙ ions which have the structure of the enol ion of phenylacetaldehyde.
Mass spectra of some β‐keto esters. A high resolution study
Authors: Moldovan Zaharie , Palibroda Nicolae , Mercea Victor , Mihǎilescu Gheorghe , Chiriac Maria , Vlasa Mircea
Published: May 2005

This paper presents low and high resolution mass spectra as well as fragmentation processes under electron impact for methyl, ethyl and propyl‐pivaloyl acetate. The fragmentation patterns have been established using elemental compositions of ions determined by high resolution, metastable transitions and deuterium labelling.
Deuterium labelling and thermochemical studies of dissociative ionization of methyl substituted monosilacyclobutanes. Ring expansion in the molecular ion of 1,1,3‐trimethyl‐1‐silacyclobutane
Authors: Gusel'nikov L. E. , Volkova V. V. , Tarasenko N. A. , Tishenkov A. A. , Zaikin V. G. , Eremina E. I. , Nametkin N. S.
Published: May 2005

Dissociative ionization of 1,1‐dimethyl‐1‐silacyclobutane, 1,1‐bis(trideuteromethyl)‐1‐silacyclobutane, 1,1,3‐trimethyl‐1‐silacyclobutane, 1,1‐bis(trideuteromethyl)‐3‐methyl‐1‐silacyclobutane and 1,1,2‐trimethyl‐1‐sila‐cyclobutane have been studied. Low energy electron impact fragmentation of 1,1‐bis(trideuteromethyl)‐3‐methyl‐1‐silacyclobutane results mainly in the loss of ethene with the involvement of the C‐methyl group from the rearranged molecular ion. No fragment ions indicating rearrangement of the molecular ion have been detected in mass spectra of 1,1‐bis(trideuteromethyl)‐1‐silacyclobutane. The ionization energies for 1,1,3‐trimethyl‐1‐silacyclobutane, 1,1,2‐trimethyl‐1‐silacyclobutane and 1,1‐dimethyl‐1‐silacyclopentane, and also the appearance energies for the [M − 28]+˙ and [M − 42]+˙ ions, have been measured by photoioniza‐tion mass spectrometry. The heats of formation of these ions and of 1,1,3‐trimethyl‐1‐silacyclobutane and 1,1‐dimethyl‐1‐silacyclopentene molecules have been calculated as have the enthalpies of the transformation processes.
Ion cyclotron resonance studies of ambident nucleophiles. The reactions of the trimethylsilyl cation with alkenyl ethers and alkoxy ketones
Authors: Dottore Marie F. , Trenerry V. Craige , Stone David J. M. , Bowie John H.
Published: May 2005

Alkenyl ethers react through oxygen with Me3Si+ to yield intermediates which undergo characteristic fragmentations. In the particular case of allyl ethers, the decomposing adduct undergoes several fragmentations through the allyl substituent via 6‐membered transition states. The reaction between Me3Si+ and alkoxy carbonyl derivatives yields both ‘ether’ and ‘keto’ adducts, characterized by their fragmentation patterns. The ‘ether’ adducts formed from Me3Si+ and alkoxy acetones undergo the same basic eliminations as those observed for the allyl ether/Me3Si+ systems.
Gaseous alkyne ions
Authors: Wagner‐Redeker Winfried , Levsen Karsten , Schwarz Helmut , Zummack Waltraud
Published: May 2005

Using the relative abundance of metastable ions, collisional activation spectra, field ionization kinetic measurements, isotopic labelling, appearance energy and kinetic energy release data, it is shown that linear alkyne radical cations with more than six carbon atoms do not isomerize to equilibrating structures prior to decomposition. At the shortest ion lifetimes the molecular ions of linear alkynes decompose mainly by simple β‐bond fission which allows an unequivocal localization of the triple bond. At medium ion lifetimes fragmentation occurs predominantly via a McLafferty rearrangement, while at long ion lifetimes competing alkyl losses prevail. These alkyl losses occur via cyclic intermediates leading to thermochemically stable cycloalkenyl ions. All these reactions occur with a high specificity with respect to the carbon and hydrogen atoms involved and are preceded by little or no hydrogen exchange reactions.
Mass spectrometry of pyrazolium salts
Authors: Pande Umesh C. , Egsgaard Helge , Larsen Elfinn , Begtrup Mikael
Published: May 2005

A series of pyrazolium bromides were investigated by field desorption, field ionization and electron impact mass spectrometry. Dealkylation was found to be the predominant thermal decomposition. The nature of the substituents controls the pyrazole formed. The application of field ionization was found to facilitate the interpretation of the thermolytic decomposition products. Field ionization and electron impact mass spectra of N‐phenylpyrazole and N‐benzylpyrazole were obtained.
Effect of protonation exothermicity on the reaction of gaseous Brønsted acids with halobenzene derivatives
Authors: Liauw Wie Giap , Lin Margaret S. , Harrison Ale X. G.
Published: May 2005

The protonation of haloaromatics by [N2H]+ and [CO2H]+ has been studied by chemical ionization mass spectrometry. In general, the fragmentation reactions following protonation by [CO2H]+ are similar to those observed following protonation by [CH5]+, while the fragmentation reactions induced by protonation by [N2H]+ are intermediate between those observed on reaction with [CH5]+ and with [H3]+. These results are consistent with the conclusion that the fragmentation mode is determined by the protonation exothermicity since the proton affinity of CO2 is the same as that of CH4 while the proton affinity of N2 is intermediate between that of CH4 and H2.
Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivatives
Authors: Liauw Wie Giap , Harrison Alex G.
Published: May 2005

The site of protonation in the reaction of gaseous Brønsted acids with chlorobenzene and fluorobenzene derivatives has been examined using deuterium labelling of chlorobenzene and deuterated reagent gases (D2 and N2/D2). In the protonation of chlorobenzene by [H3]+ ∼30% of the [MHHCl]+ fragment ions arise from a chlorine‐protonated species while ∼70% arise from a ring‐protonated species in which complete hydrogen scrambling has occurred. In the reaction of [N2H]+ with chlorobenzene ∼75% of the fragment ions arise from the chlorine‐protonated form with ∼25% arising from the ring‐protonated form of [MH]+. By contrast fluorobenzene fragments almost entirely from the fluorine‐protonated form. Similar results are obtained for dihalobenzenes. The mechanistic implications are discussed.
An electron impact study of HCN elimination from indole by use of 13C labelling
Authors: Corval Madeleine
Published: May 2005

The study of the loss of HCN from the molecular ions of [2‐13C]indole and [3‐13C]indole shows that, to a good approximation, only the two carbon atoms of the pentagonal ring are involved in this fragmentation process, contrary to the behaviour of the H atoms; the C‐2 atom is eliminated predominantly, chiefly in the ion source (85–90%) and a little less in the metastable energy range (75–80%). The losses of 13CCH3˙ and C2H3˙ from the [MH12CN]+˙ ions of the two compounds suggest the occurrence of different structures, providing evidence for several mechanisms of HCN elimination.
Mass spectra of heterocyclic compounds: V—dihydro‐1,3,5‐dioxazines
Authors: Corral René A. , Orazi Orfeo O. , Zinczuk Juan
Published: May 2005

N‐Substituted dihydro‐1,3,5‐dioxazines show a general fragmentation pattern supported by metastable ions, exact mass measurements and deuterium labelling. There are two well‐defined pathways: one is initiated by elimination of the N‐substituent and the other by loss of a hydrogen atom from the heterocyclic ring.
Mass spectral cycloreversion reactions of 2‐chloro‐3,6‐diaryl‐3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides
Authors: Gogte V. N. , Kulkarni P. S. , Modak A. S. , Tilak B. D.
Published: May 2005

The mass spectral fragmentation modes of various 2‐chloro‐3,6‐diaryl‐3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides—a novel ring system—reveal cycloreversion by two pathways. Retro Diels‐Alder reaction by a stepwise mechanism is prominent in this system. The relative abundances of the enone and dienophile ions depend on the nature of the substituent attached to the double bond in this ring. Another retro Diels‐Alder fragmentation process, involving the loss of PO2Cl from the molecular ion, is preceded by a 1,3‐allylic rearrangement and is the major fragmentation mode in the metastable time scale. Further fragmentation of the [MPO2Cl]+ imine ion seems to occur from cyclic dihydroquinoline intermediates by substitution elimination steps.
Doubly charged benzene and isomeric dications. Fragmentation energetics and charge distributions calculated by MINDO/3 molecular orbital theory
Authors: Bentley T. William , Wellington C. Anthony
Published: May 2005

MINDO/3 calculations for singlet and triplet doubly charged benzene [C6H6]2+ are in satisfactory agreement with the experimentally determined values of the vertical double ionization energy of benzene; calculations for straight chain isomeric structures are consistent with the observed kinetic energy release on fragmentation to [C5H3]+ and [CH3]+. Symmetrical doubly charged benzene ions relax to a less symmetrical cyclic structure having sufficient internal energy to fragment by ring opening and hydrogen transfer towards the ends of the carbon chain. Fragmentation of [CH3C4CH3]2+ to [CH3C4]+ and [CH3]+ is a relatively high energy process (A), whereas both (B): [CH3CHC3CH2]2+ to [CHC3CH2]+ and [CH3]+ and (C): [CH3CHCCHCCH]2+ to [CHCCHCCH]+ and [CH3]+ may be exothermic processes from doubly charged benzene. Furthermore, the calculated energy for the reverse of process (A) is less than the experimentally observed kinetic energy released, whereas larger energies for the reverse of processes B and C are predicted. Heats of formation of homologous series [HCn]+, [CH3Cn]+, [CH2Cn−2CH]+, [CH3Cn−2CH2]+ and [CH2CHCn−3CH2]+ with 1 < n < 6 are calculated to aid prediction of the most stable products of fragmentation of doubly charged cations. The homologous series [CH2Cn−2CH]+ is relatively stable and may account for ready fragmentation of doubly charged ions to [CnH3]+; alternatively the symmetrical [C5H3]+ ion [CHCCHCCH]+ may be formed. Dicoordinate carbon chains appear to be important stabilizing features for both cations and dications.
Collisional activation mass spectra of ions containing polyisotopic elements
Authors: Todd Peter J. , Barbalas Michael P. , McLafferty Fred W.
Published: May 2005

If a mass selected ion containing multiple isotopes of an element fragments by loss of a neutral containing the element, the product ions will be observed as multiple peaks. This ‘isotopic cluster’ of peaks, although of a different appearance than those found in normal mass spectra, also indicates the isotopic composition of the precursor ion.
Electron impact mass spectrometry of 3‐cyclohexen‐1‐ol and related compounds
Authors: Braem Daniel , Siles Samuel , Gülaçar Fazil O. , Buchs Armand
Published: May 2005

The electron impact mass spectrum of 3‐cyclohexen‐1‐ol has been studied, especially with regard to the retro Diels‐Alder reaction. Six deuterium labelled analogues and two dimethyl substituted homologues were synthesized. Contrary to what we have observed with 2‐cyclohexen‐1‐ol, the double bond migration which precedes the retro Diels‐Alder reaction plays a minor role.
Consecutive reactions arising from the molecular ions of 14α‐equilenin and 14β‐isoequilenin
Authors: Proctor C. J. , Larka E. A. , Zaretskii Z. V. I. , Beynon J. H.
Published: May 2005

It is shown that two configurational steroidal isomers, 14α‐equilenin and 14β‐isoequilenin, may be easily distinguished by the unimolecular mass analysed ion kinetic energy spectra of their corresponding molecular ions. Furthermore, many of the peaks in these spectra are found to be due to consecutive reactions, whereby product ions of an initial reaction are themselves reactive and can undergo further fragmentation. In each of these cases, the individual steps of the reaction sequence have been separated in the different field free regions of a reversed geometry, double focusing mass spectrometer. Isotopic labelling with 18O in the 17‐position has also helped to clarify reaction sequences.
‘Fast atom bombardment’—A rediscovered method for mass spectrometry
Authors: Devienne F. Marcel , Roustan Jean‐Claude
Published: May 2005

In 1966, Devienne and co‐workers studied extensively the sputtering of various target materials by a high energy molecular beam obtained by charge exchange. They obtained secondary ions that characterized for instance, organic and biological materials. These ions were analysed by mass spectrometry. This method was developed to be patented and many devices were studied. The principle of the apparatus constructed is very simple. An ion source produces an ion current of some microamperes. The ions are accelerated at some keV, and injected into a collision chamber in order to obtain a neutral beam by resonant charge exchange. The residual ions are deflected and this beam bombards the target. The target itself is surrounded by a small metal cylinder which is held at an appropriate potential to extract the positive or negative secondary ions formed. The ion beam is accelerated and focused into the entrance slit of a mass spectrometer. After the first devices, two types of apparatus were built in 1973 and 1975. With the first one, the analysis of the masses was obtained only by an electromagnet. The energy range of the secondary ions varied from 1 to 10 keV. The second apparatus was formed by an electromagnet, a dissociation chamber, and an electrostatic analyser. With this apparatus, it was possible to measure directly masses as large as 6000 daltons. With the first apparatus it was possible to study the adsorption of oxygen on silicon, and to obtain spectra, of many organics such as camphor, nitrodiphenylamine and, as in the earlier device, the spectrum of a non‐volatile organic liquid diethylhexyl azelate, was obtained. After studies on different uranium compounds and their dissociations, the second apparatus was devoted to the formation and study of the chemical properties of clusters.
Electron impact mass spectrometry of 2,2‐disubstituted‐1,3‐benzoxathioles and spiro [1,3‐benzoxathioles‐2,1′‐cycloalkanes]
Authors: Traldi Pietro , Vettori Umberto , Maccioni Antonio , Podda Gianni
Published: May 2005

The electron impact mass spectrometric behaviour of a series of 2,2‐disubstituted‐1,3‐benzoxathioles and spiro[1,3‐benzoxathioles‐2,1′‐cycloalkanes] has been studied in detail with the aid of linked scans and exact mass measurements. The structures of the more interesting fragment ions have been confirmed by collisional activation experiments. A precise analogy with the chemical degradative processes, obtained by the action of Grignard reagents on these compounds, is emphasized.
Mass spectrometry of allyloxy di‐ and trimethylsilanes
Authors: Steele Kent P. , Weber William P.
Published: May 2005

The mass spectra of allyloxydimethylsilanes and allyloxytrimethylsilanes were examined. Isotopic labelling and metastable peaks support the proposed fragmentation patterns. Siliconium ions dominate the spectra. Loss of neutral fragments from [M—15]+ and [M—1]+ ions is important. These fragmentation patterns are discussed in terms of interaction of siliconium ions with the carbon‐carbon double bond of the allyloxy ligand. Increased substitution on the allyloxy ligand apparently decreases the interaction of siliconium ions with the carboncarbon double bond.