bluuebunny/crossref_metadata_2025_split huggingface dataset:
Skeletal rearrangements on chemical ionization of dibenzyl ether and derivatives
Authors: Kingston Eric E. , Shannon James S. , Diakiw Vladimir , Lacey Michael J. 
Published: May 2005

AbstractProtonated molecular ions of dibenzyl ether, formed by chemical ionization using hydrogen and isobutane as reagent gases, undergo skeletal rearrangements to lose water and formaldehyde, both in the ion source and the flight path. The rearrangements have been elucidated by deuterium labelling and chemical substitution. The water lost contains the reagent proton and an aromatic hydrogen atom, and the aromatic hydrogen atoms have been shown to be mobile prior to the reaction. It is proposed that the skeletal rearrangement for water loss is initiated by protonation on the ether oxygen atom, followed by benzyl migration. The formaldehyde lost contains benzylic hydrogen atoms exclusively, and it is proposed that the skeletal rearrangement is preceded by hydrogen rearrangement of an oxygen protonated molecular ion to a ring protonated molecular ion. Daughter ion structures are supported by comparisons of their collision induced dissociation spectra with those of isomeric ions prepared by alternative routes.
Fragmentation mechanisms of isoxazole
Authors: Bouchoux G. , Hoppilliard Y. 
Published: May 2005

AbstractFragmentation pathways of isoxazole giving ions [C3H2ON]+, [C2H3N]+˙ and [C2H2N]+ are elucidated by means of metastable ion studies and thermodynamic properties. Rearrangement reactions are demonstrated to occur with H and HCO loss. Elimination of carbon monoxide leads to [C2H3N]+˙ ions whose reacting configuration is the same as for acetonitrile. All these results can be rationalized in terms of a prior isomerization of isoxazole involving ring opening and 1,2 H migration.
Stereochemical effects in the electron impact mass spectra of cis‐trans isomeric 1,2,3,4‐tetramethylcyclohexanes
Authors: Herzschuh R. , Werner H. , Mann G. 
Published: May 2005

AbstractThe mass spectra of six cis‐trans isomeric 1,2,3,4‐tetramethylcyclohexanes are discussed. The intensity ratio of [MCH3]+/[MC2H5]+ correlates with the strain energies of the stereoisomers. Therefore, the identification of cis‐trans isomers is possible by means of their mass spectra. The mass spectra of deuterium labelled compounds demonstrate favoured fragmentation of the axial methyl groups and ring opening between the cis substituted carbon atoms of the cyclohexane.
Plenary lecture: Ion enthalpies and their application in mass spectrometry
Authors: Maccoll Allan 
Published: May 2005

AbstractThe experimental determination of ionization and appearance energies is discussed, together with the calculation of heats of formation of ions. Results are presented for the ions [CnH2n+1]+, [CnH2n+2N]+ and [CnH2n+1O]+. The low temperature (∼350K), low energy (12.1eV) mass spectra of some alkanes, amines and alcohols are presented and discussed.
Comparative study of [Xe]+ and [Ar]+ bombardment in secondary ion mass spectrometry for bioorganic compounds
Authors: Kambara Hideki 
Published: May 2005

AbstractSecondary ion mass spectra obtained by [Xe]+ bombardment are compared with those obtained by [Ar]+ bombardment. Although [Ar]+ ions are commonly used as primary ions in secondary ion mass spectrometry for organic compounds, [Xe]+ ions seem better as primary ions because they give a larger sputtering yield for a metal substrate than [Ar]+ ions. Cationized molecular intensities of sucrose, raffinose and stachyose, and quasimolecular ion intensities of tuftsin and eledoisin related peptide are investigated using [Xe]+ and [Ar]+ bombardments. The observed molecular species are 2–4 times more intense for [Xe]+ bombardment than for [Ar]+ bombardment, although the secondary ion mass spectra are almost the same in both cases.
Some stereochemical effects in gaseous ion decompositions
Authors: Reddy A. Mahender , Nayar M. S. B. , Reddy G. Sudhakar , Das K. G. 
Published: May 2005

AbstractStereochemical effects were observed in the electron ionization, methane, isobutane and ammonia positive ion chemical ionization and hydroxy negative ion chemical ionization behaviour of some isomeric triaryl nitrocyclohexenes. cis‐Eliminations leading to loss of HNO2, H2NO2 and arene were found to be stereochemically preferred in gaseous ions.
Loss of hydroxyl radical from isomeric ethylnitrobenzenes
Authors: Baldwin Michael A. , Carter David M. , Gilmore Jeremy 
Published: May 2005

AbstractThe loss of a hydroxyl radical from the molecular ions of o‐, m‐ and p‐ethylnitrobenzene has been studied by metastable ion and collisional activation techniques using electron impact and field ionization. It is shown that for the ortho isomer the mechanism of this reaction is unique, and is totally different from that of the meta and para isomers. The critical energies are also reported, and deuterium labelling is employed to access the role of the α‐hydrogens in hydroxyl loss.
Heterocyclic analogues of steroids: VIII—Mass spectrometry of the stereoisomeric derivatives of 8‐aza‐16‐oxaestrane
Authors: Suboch Victor P. , Lakhvich Fyodor A. , Liss Leo G. , Akhrem Affanassi A. 
Published: May 2005

AbstractUsing high resolution mass spectra, metastable ions and selective deuteration the decomposition pathways of 8‐aza‐16‐oxasteroid derivatives have been investigated. There is a dependence of the mass spectra on the stereochemistry of the C/D ring fusion in 8‐aza‐16‐oxaestrane derivatives.
On the use of collision induced dissociation spectra in the determination of the structural composition of ions
Authors: Bass Lewis M. , Bowers Michael T. 
Published: May 2005

AbstractThe application of the superposition principle of McLafferty and co‐workers to collision induced dissociation or collisional activation spectra to obtain quantitative estimates of the composition of isomeric mixtures of ions is discussed in detail. A set of explicitly stated assumptions is used to derive expressions for the percent composition based on normalized peak heights or peak height ratios in the collision induced dissociation spectra. The simple linear interpolation based on peak ratios which has been used in the past is shown to be invalid. It is demonstrated that the common practice of ignoring those collision induced dissociation peaks where there is interference from non‐collision induced dissociation processes may lead to substantial uncertainty in the final results. It is also demonstrated that the superposition principle may lead to results which are not internally consistent with the model. The final conclusion is that the present method of quantitative structural analysis based on the superposition principle cannot generally be expected to yield reliable results. In specific cases the results may be assumed to be reliable if it is demonstrated that the model is self‐consistent and the inherent experimental uncertainty is reasonably small. Further work may be useful in developing a generally valid method of analysis.
Mass spectral fragmentation pathways in RDX and HMX. A mass analyzed ion kinetic energy spectrometric/collisional induced dissociation study
Authors: Yinon J. , Harvan D. J. , Hass J. R. 
Published: May 2005

AbstractA collisional induced dissociation study of 1,3,5‐trinitro‐1,3,5 triazacyclohexane (RDX) and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazacyclooctane (HMX) was carried out using mass analyzed kinetic energy spectrometry. High resolution mass spectra and mass analyzed ion kinetic energy/collisional induced dissociation spectra of RDX and HMX were recorded in the electron impact, chemical ionization and negative ion chemical ionization modes. Fragmentation pathways of the compounds investigated were determined in all three modes of ionization. It was found that a major part of the fragment ions in RDX and HMX originate from formation of the aduct ions [M+NO]+ and [M+NO2]+ in electron impact and chemical ionization, and from [M+NO]− and [M+NO2]− in negative chemical ionization, followed by dissociation.
The structures of [C5H5O]+ ions formed from isomers of nitrophenol in the gaseous phase
Authors: Porter C. J. , Proctor C. J. , Larka E. A. , Beynon J. H. 
Published: May 2005

AbstractTranslational energy release measurments on metastable ions are used in the comparison of the structures of isomeric ions. Metastable ions, m2+, formed from m1+ ions as the result of a high energy process in the ion source are compared with isomeric metastable ions formed as daughters from fragmentation of metastable m1+ ions in a field. In the case of o‐, m‐ and p‐nitrophenol the structure of the [C5H5O]+ ions formed from [C6H5O]+ ions by these two independent methods is different as verified by comparison of the behaviour of [C5H5O]+ ions formed from several other compounds.
Unexpected mass spectral skeletal rearrangements in aromatic thioamides
Authors: Ramana D. V. , Viswanadham S. K. 
Published: May 2005

AbstractInteresting skeletal rearrangements, resulting in the formation of unexpected fragments, have been noticed in the mass spectra of aromatic thioamides of cyclic amines such as piperidine, morpholine and pyrrolidine. Suitable mechanisms, based on mass analysed ion kinetic energy spectra, high voltage scan spectra and high resolution data, have been proposed for the formation of [MSH]+ ions and the fragment at m/z (103+R) in the mass spectra of these compounds. The mass spectra of the thioamides of non‐cyclic amines and the thioamides of aliphatic acids contain peaks corresponding to a four‐centred skeletal rearrangement followed by the elimination of either the thioalkoxy or the thiophenoxy radical from the molecular ions.
Retrosynthetic reactions in mass spectrometry. Deacylation of ortho phthalamic acids under electron impact
Authors: Selva Antonio , Traldi Pietro , Ventura Paolo , Valle Vincenzo Dalla 
Published: May 2005

AbstractOrtho Phthalamic acids under electron impact show a retrosynthetic reaction leading to both phthalic anhydride and amine complementary ions, the corresponding neutrals of which are the usual synthetic precursors of the original compounds. The single case of a primary amine derivative is examined, which shows the formation of [MH2O]+˙ ions having the structure of the related N‐substituted imide, by a process which parallels a well known thermal reaction. It also gives the species [C8H6NO2]+ (of the same nominal mass as phthalic anhydride), the structure of which is still under study. Ionic structures are supported by collision induced mass analyzed ion kinetic energy spectra.
The fast atom bombardment mass spectra of glucosinolates and glucosinolate mixtures
Authors: Fenwick G. Roger , Eagles John , Self Ron 
Published: May 2005

AbstractThe behaviour of glucosinolates and desulphoglucosinolates under fast atom bombardment conditions has been investigated. Relatively little fragmentation was noted in the mass spectra of these compounds. The positive ion fast atom bombardment mass spectra of glucosinolates exhibited abundant cationized and protonated molecula ions, thus complementing the previously reported electron impact and chemical ionization mass spectra of these compounds. Desulphoglucosinolates yield only the protonated molecular ion. Under negative ion conditions the spectra of glucosinolates were dominated by the molecular anion and this has been used as a means of analysing a crude plant extract containing a complex mixture of glucosinolates.
Electron impact induced fragmentation of tetramethyl‐substituted dibenzo‐18‐crown‐6 ethers
Authors: Lockhart J. C. 
Published: May 2005

AbstractA series of tetramethyldibenzo‐18‐crown‐6 molecules with methyl substituents on the ether ring has been subjected to electron impact mass spectrometry, and from the variation of the fragmentation pattern with substituent position, certain fragmentation processes are located and the composition and origin of certain fragment ions can be deduced. The aliphatic CC fission deduced from deuterium labelling studies of benzo‐15‐crown‐5 is not an observable process for the crowns reported here.
Doubly charged ion mass spectra: VI—Amines
Authors: Teleshefsky L. A. , Bostwick D. E. , Abbey L. E. , Burgess E. M. , Moran T. F. 
Published: May 2005

AbstractDoubly charged ion mass spectra of 22 amines (2–10 carbon atoms) were determined using an Hitachi RMU‐7L double focusing mass spectrometer. Molecular ions were not observed in the spectra of aliphatic amines. The most intense product ion peaks in the spectra of lower molecular weight amines resulted from hydrogen elimination from the molecular ion; however, as amine molecular weight increased the largest peaks resulted from both hydrogen and heavy atom elimination from the molecular ion. Dominant ions in the doubly charged ion spectra of lower molecular weight aliphatic amines were from reactions of [CnH3N]2+ (n:=2, 3, 4) type ions. The spectra of higher molecular weight aliphatic amines spanned a wide mass range. Appearance energies for some of the more prominent ions were measured in the range from 25 to 49 eV. A geometry optimized quantum mechanical self‐consistent field molecular orbital treatment was used to compute the energies and structural parameters of prominent ions in the doubly charged ion mass spectra.
Fragment ion formation of quaternary ammonium salts under fast atom bombardment and field desorption collisionally activated dissociation conditions
Authors: Veith H. J. 
Published: May 2005

AbstractComparing fast atom bombardment and field desorption collisionally activated dissociation mass spectra of tetrabutyl ammonium salts it becomes evident that under fast atom bombardment conditions, besides desorption of intact salt cations, the ionization of intact salt molecules must be assumed. Alkyl ions formed under fast atom bombardment and not under field desorption collisionally activated dissociation conditions are ionization products of tetraalkyl ammonium salt molecules. Radical cations are produced by both techniques.
Energy randomization is complete in [C5H10O]+˙ ions with the oxygen on the middle carbon
Authors: McAdoo David J. , Hudson Charles E. 
Published: May 2005

AbstractThe relative intensities of the losses of ethyl groups from opposite sides of the 3‐pentanone ion formed by isomerization from its enol isomer are shown to be equal when corrections for protonated acrolein formation, isotope effects, and overlapping ethane losses are made. Thus the ion decomposes symmetrically, implying ergodic behavior, as concluded by Depke and Schwarz.
Mass spectra of dicyanomethylene derivatives of benzophenone analogs
Authors: Wang Ching‐Bore , Her Guor‐Rong , Watson J. Throck 
Published: May 2005

AbstractThe dicyanomethylene derivative of a benzophenone analog significantly alters the fragmentation pattern observed during electron impact ionization of the underivatized parent compound. A double bond connecting the dicyanomethylene moiety to the parent compound is cleaved during a major fragmentation pathway for many of these compounds. A mechanism involving rearrangement of two hydrogen atoms is proposed to rationalize cleavage of this double bond. Conventional mass spectra as well as collisionally activated dissociation mass spectra of selected ions of several model compounds are reported and described in support of a proposed fragmentation mechanism.
The structure of decomposing [C7H7O]+ ions: Benzyl versus tropylium ion structures
Authors: Russell D. H. , Freiser B. S. , McBay E. H. , Canada D. C. 
Published: May 2005

AbstractThe unimolecular dissociation reactions for [C7H7O]+ ions generated by fragmentation of a series of precursor molecules have been investigated. The metastable kinetic energy values and branching ratios associated with decarbonylation and expulsion of a molecule of formaldehyde (CH2O) from the [C7H7O]+ ions are interpreted as the hydroxybenzyl and hydroxytropylium [C7H7O]+ not interconverting to a common structure on the microsecond time‐scale. In addition, similar measurements on protonated benzaldehyde, methylaryloxy and phenyl methylene ether [C7H7O]+ ions are interpreted as the dominant fraction of these decomposing ions having unique structures on the microsecond time‐scale. These results are supported by experimental heats of formation calculated from ionization/appearance energy measurements. The experimental heats of formation are determined as: hydroxybenzyl ions, 735 kJ mol−1; hydroxytropylium ions, 656 kJ mol−1; phenyl methylene ether ions, 640 kJ mol−1; methylaryloxy ions 803 kJ mol−1. The combination of the results reported in this paper with previously reported experimental data for stable [C7H7O]+ ions (see Ref. 1, C. J. Cassady, B. S. Freiser and D. H. Russell, Org. Mass Spectrom.) is interpreted as evidence that the relative population of benzyl versus tropylium [C7H7O]+ ion structures from a given precursor molecule is determined by isomerization of the parent ion and not by structural equilibration of the [C7H7O]+ ion.
Metastable decompositions of cyclopentanol ions and [C5H10O]+˙ ions with the oxygen on the first carbon
Authors: Hudson Charles E. , McAdoo David J. 
Published: May 2005

AbstractIonized cyclopentanol and [C5H10O]+˙ ions with the oxygen on the first carbon lose methyl, ethylene, ethyl, ethane and water in their metastable decompositions. We show by collisionally activated decompositions of the products that the losses of ethyl form CH3CH2CO+, the losses of ethylene form magnified image, and the losses of methyl probably yield magnified image. Deuterium labeling indicates that ethyl loss from ionized cyclopentanol occurs following α‐cleavage of the ring, isomerization to the enol isomer of ionized n‐pentanal and subsequent isomerization to the 3‐pentanone ion.
Fragmentations of 5,5‐diphenylmonothiohydantoins and their N‐ and S‐methyl derivatives after electron impact
Authors: Záhorszky U. I. , Nyitrai J. , Zauer K. 
Published: May 2005

AbstractThe mass spectra of 5,5‐diphenylmonothiohydantoins and their N‐ and S‐methyl derivatives have been investigated and interpreted in terms of structural correlations. All stable isomers can be easily distinguished by their fragmentation patterns.
Stereochemical applications of mass spectrometry. 3—Energy dependence of the fragmentation of stereoisomeric methylcyclohexanols
Authors: Harrison Alex G. , Lin Margaret S. 
Published: May 2005

AbstractBreakdown graphs have been constructed from charge exchange data for the epimeric 2‐methyl‐, 3‐methyl‐ and 4‐methyl‐cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ∼12 eV recombination energy, significant differences are observed for the epimeric 2‐methyl‐ and 4‐methyl‐cyclohexanols at low internal energies. For the 2‐methylcyclohexanols the ratio ([MH2O]+·/[M]+·)cis/([MH2O]+·/[M]+·)trans is 3.2 in the [C6F6]+· charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis‐1,4‐H2O elimination for the cis epimer. The breakdown graph for trans‐4‐methylcyclohexanol shows a sharp peak in the abundance of the [MH2O]+· ion at ∼10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis‐1,4‐elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C6F6]+· charge exchange mass spectra the ([MH2O]+·/[M]+·)trans/([MH2O]+·/[M]+·)cis ratio is ∼24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.
Electron impact mass spectra of 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐7‐one and isomeric‐5‐one derivatives
Authors: Foti S. , Russo F. , Santagati A. , Santagati M. 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of some 1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐7‐one and isomeric‐5‐one derivatives are discussed with the aid of defocused metastable spectra and exact mass measurements. The compounds are shown to be very stable to electron impact and ring contraction reactions are in most cases the characterstic fragmentations. Most importantly, the 7‐one derivatives fragment by a retro‐Diels–Alder process which does not occur in the 5‐one isomers. This provides a diagnostic tool for differentiation between the isomers and for the unequivocal assignment of the structure.
Electron impact mass spectrometry of some benzodioxole derivatives of pharmacological interest, their synthons and synthetic intermediates
Authors: Podda Gianni , Maccioni Antonio , Fadda Anna Maria , Daolio Sergio , Pelli Beatrice , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric behaviour of two newly synthesized β‐blocking benzodioxole derivatives, their synthons and synthetic intermediates has been studied in detail with the aid of exact mass measurements, linked scans, collisionally activated decomposition mass analysed ion kinetic energy spectra and deuterium labelling experiments. A retrosynthetic process, leading to the original synthons, is described.
The potential energy surface for the [C2H2O]+˙ system: The ketene radical cation [CH2CO]+˙ and its isomers
Authors: Bouma Willem J. , Gill Peter M. W. , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital calculations with large, polarization basis sets and incorporating valence electron correlation have been employed to examine the [C2H2O]+˙ potential energy surface. Four [C2H2O]+˙ isomers have been identified as potentially stable, observable ions. These are the experimentally well‐known ketene radical cation, [CH2CO]+˙ (a), and the presently unknown ethynol radical cation, [CH2COH]+˙ (b), the oxirene radical cation magnified image (c) and an ion resembling a complex of CO with [CH2]+˙, magnified image (d). The calculated energies of b, c and d relative to a are 189, 257 and 259 kJ mol−1, respectively. Dissociation of ions a and d is found to occur without reverse activation energy.
Assigning structures to ions in the gas phase
Authors: Holmes John L. 
Published: May 2005

AbstractThe purpose of this short review is critically to assess the important experiments in gas phase ion chemistry whose correct interpretation can lead to the assigning of structures to organic positive ions. The methods fall into two main categories, (i) the measurement of ion enthalpies and transition state energies for their fragmentations and (ii) the detailed examination of the unimolecular and collision‐induced fragmentation behaviour of cations, anions and neutral species. It is argued that in general, none of the above methods alone can suffice for an ion structure determination, but that in combination these techniques provide a powerful tool by means of which ion structures may confidently be assigned.
Heat of formation for the propanoyl cation by photoionization mass spectrometry
Authors: Traeger John C. 
Published: May 2005

AbstractThe ionization energies and [C3H5O]+ appearance energies for a series of oxygenated organic compounds have been measured by dissociative photoionization mass spectrometry. The adiabatic ionization energy for cyclopentanol is observed to be 9.72 eV. A 298 K heat of formation of 591.2±2.3kJ mol−1, based on the stationary electron convention, is derived for the propanoyl cation in the gas phase. A heat of formation of –86±6 kJ mol−1 is obtained for methylketene, which leads to an absolute proton affinity of 853±8 kJ mol−1.
The mass spectra of benzofuroxans—an example of an ortho effect
Authors: Chafin Andrew P. , Erickson Eric D. 
Published: May 2005

AbstractThe fragmentation behavior of a series of nine benzofuroxans has been studied under electron impact conditions. It was found that benzofuroxans without a nitro group in the 4‐position fragment principally through loss of N2O2 (the furoxan ring), whereas those with a nitro group ortho to the furoxan ring exhibit predominant loss of NO from position 1 of the furoxan ring.