bluuebunny/crossref_metadata_2025_split huggingface dataset:
Collisionally activated decomposition of poly(ethylene glycol)s: An investigation of high‐mass ion abundances in the collisional activation technique with large molecules
Authors: Kiplinger Jeffrey P. , Bursey Maurice M. 
Published: May 2005

AbstractThe utility of the collisional activation technique in structure determination of ions is limited as parent ion mass increases. Optimum collisionally activated dissociation yield is often obtained at parent masses of 1000–2000 u, after which daughter ion yield decreases. The apparent decrease in the efficiency of the collisional activation process has been thought of as a degree‐of‐freedom effect: as new rotational‐vibrational modes are added to the parent ion, its lifetime with respect to dissociation increases. We have investigated this effect using an easily characterized system of several poly(ethylene glycol) homologs from the 15‐mer to the 35‐mer. Observed trends in the collisional activation spectra as parent mass increases support the postulated ‘degree‐of‐freedom’ effect in general. The loss of C2H4O from the [M − H]− parents, a fragmentation which has a high activation barrier, however, actually becomes more favored as the parent ion becomes larger. This effect is explained in terms of statistical rate theory.
Secondary ion emission from glycerol under continuous and pulsed primary ion current
Authors: Todd Peter J. 
Published: May 2005

AbstractSecondary ion intensity from glycerol is measured as a function of 5 keV primary ion current density and is found to be linear over the range 0.1–1 μA cm−2. The possibility that protonated glycerol, or some other condensed‐phase precursor to secondary protonated glycerol, exists in solution and enhances secondary ion emission from glycerol is investigated. Kinetics for formation of such precursors by the primary ion beam are described and evaluated by pulsed primary ion beam experiments. Depletion rates are calculated assuming diffusion from the surface as the major loss mechanism Results of this analysis indicate that the mechanism for secondary emission of protonated glycerol does not involve formation of precursors, e.g. solution‐phase protonated glycerol, directly or indirectly by the primary ion beam.
The gas‐phase amino–claisen rearrangement of protonated N‐allylaniline
Authors: Kingston Eric E. , Beynon John H. , Flammang Robert , Maquestiau André 
Published: May 2005

AbstractMetastable molecular protonated ions of N‐allylaniline dissociate with significant losses of ethene and ammonia in the flight path of a mass spectrometer. The structures of the daughter ions formed on the loss of ethene have been elucidated using collision‐induced dissociation and it is postulated that two isomeric structures are formed, one corresponding to molecular protonated ions which have undergone an amino–Claisen rearrangement. The relative proportion of this rearranged species is dependent on the exothermicity of the proton‐transfer reaction between the sample molecule and the chemical ionization reagent gas ion. It is proposed that the two isomeric parent species differ in the site of protonation.
Formation of thioacylium ions in the gas phase
Authors: Abd. Rahman Noorsaadah , Fisher Cindy L. , Caserio Marjorie C. 
Published: May 2005

AbstractA study of the ion chemistry of benzenethioic acid using ion cyclotron resonance techniques shows that a long‐lived ion of composition C7H5S+ is formed from the reaction of the neutral acid with primary fragment ions, m/z 77 (phenyl) and m/z 105 (benzoyl). The product is assigned the thiobenzoyl structure on the basis df its mode of formation from benzoyl cations and tbe neutral acid. Other reactant ions (acetylium and thioacetylium) derived from mixtures of benzenethioic acid with ethanethioic acid or acetate esters similarly lead to thiobenzoyl ions as the major product The significance of these results as support for the thioacetylium structure of C2H3S+ ions from ethanethioic acid is discussed.
Do the aminopyridine molecular ions display aniline‐ or pyridine‐type behaviour?
Authors: Hop C. E. C. A. , Dakubu M. , Holmes J. L. 
Published: May 2005

AbstractBy means of collisionally induced dissociative ionization mass spectrometry it was shown that the three isomeric aminopyridine molecular ions display ion chemistry similar to aniline molecular ions; i.e. metastable HNC loss, rather than losing the more stable neutral species HCN, behaviour typical of ionized pyridine. The molecular ions do not isomerize to a common intermediate prior to fragmentation and can readily be distinguished from their collisional activation and charge‐stripping mass spectra.
Gas‐phase electrophilic addition reactions of chlorinated alkyl ions
Authors: Burinsky David J. , Campana Joseph E. 
Published: May 2005

AbstractChemical ionization was used to study gas‐phase electrophilic addition reactions of chloromethyl ions ([CHxCl3‐x]+, x = 0, 1, 2) with a number of substituted benzenes (C6H5Y, Y = NH2, OH, CHO, CN, NO2). Mass‐analyzed ion kinetic energy spectrometry was used to characterize the reaction products with respect to the site of electrophilic addition (ring v. substituent). In some cases, examination of secondary reaction products (ion–molecule adduct which has undergone an elimination reaction in the ion source) aided in establishing the original site of electrophilic addition. Aniline, benzonitrile and nitrobenzene exhibited preferential substituent interaction, while phenol and benzaldehyde gave a mixture of ring and substituent reaction products. These gas‐phase results differ considerably from solution‐phase Friedel–Crafts alkylation; however, they are consistent with the notion of preferential σ‐bond formation at polarizable centers of negative charge.
A comparative study on the behaviour of 1,3‐diheterocyclopentanes (X = O, O; S, S; O, S) under electron impact. The formation of thioacetyl and thiiranyl cations
Authors: Pihlaja Kalevi , Kuosmanen Pentti , Vainiotalo Pirjo 
Published: May 2005

AbstractThe electron‐impact‐induced mass spectra of 1,3‐dioxolane (la), 1,3‐dithiolane (2a) and 1,3‐oxatbiolane (3a) and their 2‐methyl (1b–3b) and 2,2‐dimethyl [(CH3)2: 1c–3c or (CD3)2: 1d–3d] derivatives have been studied in detail to gain further insight into their ion structures and competing reaction pathways with low‐resolution, high‐resolution, metastable and collision‐induced dissociation (CID) techniques. For compounds 1a–1d the most significant reaction is loss of H˙ and CH3˙ by α‐cleavage and a subsequent formation of CHO+ and C2H3O+ ions. The [M  H]+ ions from 1a and 1b give a C2H3O+ ion which does not have the acyl cation structure as shown by their CID spectra. In compounds 3a–3d the sulphur‐containing ions predominate, the C2H3O+ now having the acyl cation structure. 1,3‐Dithiolanes (2a–2d) exhibit the most complicated fragmentation patterns. Furthermore the [M  H]+ ion from 2a and [M  CH3]+ ion from 2b have different structures as well as the [M − H]+ ion from 2b and [M  CH3]+ ion from 2c, as shown by their CID spectra. This can be utilized to explain why 3a–3c and 2a give principally a thiiranyl cation, whereas 2b gives a mixture of this and the thioacyl cation and 2c practically only the open‐chain thioacetyl cation.
Gas‐phase reactions of electrons, halide ions and radicals with (meso‐tetraphenylporphinato)metal(II) complexes under negative ion chemical ionization conditions
Authors: Dillow G. W. , Gregor I. K. 
Published: May 2005

AbstractThe negative ion chemical ionization mass spectra of a series of (meso‐tetraphenylporphinato)metal(II) (metal = Mg, Co, Ni, Cu, Zn) complexes obtained with the electron‐energy‐moderating/reagent gases argon, NF3, CF2Cl2 and CF3Br are presented. Formation of the negative ions identified in the mass spectra is accounted for in terms of the chemistry which occurs in the gaseous plasmas. In argon plasmas, the metal complexes undergo resonance electron capture with comparable facility to produce stable molecular ions. In the NF3, CF2Cl2 and CF3Br plasmas, ionization occurs as a result of ion–molecule reactions as well as resonance electron capture, and is quite selective. Only fluoride ions react with each of the metal complexes, producing metal‐containing ions by nucleophilic addition and proton abstraction as well as by inducing ring closure. The less reactive chloride and bromide ions react readily by nucleophilic addition only with the magnesium and zinc complexes. Negative ions are also produced in the plasmas by radical‐molecule reactions followed by ionization of the neutral products of these encounters.
Mass spectroscopic studies of riboflavin and isotopically labelled lumiflavins
Authors: Holzmann Gerhard , Bock Michael , Elsner Martin , Kurreck Harry , Müler Franz 
Published: May 2005

AbstractUnder electron impact conditions 3‐methylriboflavin is attacked at the ribityl side chain to generate 3‐methyl‐lumiflavin. This is verified by analysis of metastable fragmentations and comparison with model ions. Formation of 1,3‐dimethyl‐lumkhrome through migration of the methyl group from N(10) to position N(1) is positively excluded. A general fragmentation scheme for ionized 3‐methyl‐lumiflavin is developed based on exact mass measurements using various2H,13C and15N isotopically labelled derivatives. The predominating initial loss of CH3NCO exclusively involves the 3‐ and 4‐positions, for which an asynchronous mechanism is discussed.
Low‐energy, low‐temperature mass spectra. 10—urethanes
Authors: Bowen Richard D. , Maccoll Allan 
Published: May 2005

AbstractThe 12.1 eV, 75°C electron impact mass spectra of 24 urethanes, RNHCO2C2H5 [R  H, C2H2n +1 (n = 1‐8), CH2CHCH2, Ph, PhCH2 and PhCH2CH2], and seven symmetrically disubstituted urethanes R2NCO2C2H5 (R  Cn H2n + 1 (n = 1−4)) are reported and discussed. All 31 spectra show appreciable molecular ion peaks. For n −Cn H2n +1 NHCO2C2H5, M+ ˙ usually is the most abundant ion in the spectrum. A peak at m/z 102 of comparable intensity also is present; this corresponds to formal cleavage of the bond connecting the α‐ and β‐carbon atoms in the N‐alkyl group, though it is unlikely that the daughter ion has the structure [CH2NHCO2C2H5]+. In the RNHCO2C2H5 series, branching at the α‐carbon atom enhances the relative abundance of the ion arising by notional α‐cleavage at the expense of that of M+ ˙. Formal cleavage of the bond between β‐ and γ‐carbon atoms occurs to some extent for [RNHCO2C2H5]+˙ ions; this reaction provides information on the degree of branching at the β‐carbon, especially if metastable molecular ions are considered. The higher n‐CnH2n +1NHCO2C2H5 (n = 5−8) urethanes exhibit two other significant ions in their mass spectra. First, there is a peak at [M  C2H5]+. Secondly, a peak is present at m/z 90; the most plausible structure for this ion is [H2N(HO)COC2H5]+, arising by double hydrogen transfer from the alkyl group and expulsion of a [CnH2n −1]˙ radical. Ions originating from secondary decomposition of the primary ionic species are generally of only very low abundance in these spectra.
Relation between alkali ion affinity and ionic radius ratio by means of fast atom bombardment tandem mass spectrometry
Authors: Isa Kimio , Takeuchi Yasutaka 
Published: May 2005

AbstractCationization of organic molecules has been studied using fast atom bombardment mass spectrometry and tandem mass spectrometric methods. The order of the A+ affinity to G (G − H + A) and AX was determined by this tandem mass spectrometric approach, where G, A and X represent glycerol, alkali metal element and halogen element, respectively. The affinity orders of most alkali halides are divided into three classes. By analogy with the ionic radius ratio rule in solid ionic crystals, this particular parameter, ionic radius ratio, was introduced to analyse the experimental results. This classification is thought to be caused by the ionic radius ratio (X−/A+). These ratios of the I, II and III classes exist between 0.657 and 1.026, 1.096 and 1.776, and 1.856 and 2.289, respectively. The ionic radius ratio plays an important role for determination of the order of alkali ion affinity.
On the mechanism of secondary ion formation from poly(methylmethacrylate) under static secondary ion mass spectrometry conditions
Authors: Lub J. , Benninghoven A. 
Published: May 2005

AbstractThe negative ion spectrum of a relatively thick layer (± 0. 5 μm) of poly(methylmethacrylate) (PMMA) with M̄w = 1890 and its positive ion spectrum of a very thin layer (± 1. 0 nm) on silver measured with a time of flight secondary ion mass spectrometer are presented. From the negative ion spectrum it is concluded that formation of enolate anions from PMMA under static secondary ion mass spectrometric conditions is an important ion formation process. From fragmentation products of the polymer, detected as silver cationized species in the positive ion spectrum, more evidence was found of a fragmentation mechanism for PMMA under static secondary ion mass spectrometric conditions recently proposed in the literature. From the relation between the information obtained from the two types of spectra an extension of this mechanism is obtained. This mechanism implies scission of the polymer chain by the primary ion bombardment with subsequent formation of enolate anions from the newly formed polymer chain‐ends.
Ortho effects in organic molecules on electron impact: 18—Novel hydrogen transfer from the methoxy group to acetylenic carbon in 2‐methoxyphenylacetylene and 2‐methoxydiphenylacetylenes
Authors: Ramana D. V. , Rama Krishna N. V. S. 
Published: May 2005

AbstractThe transfer of a hydrogen from the ortho methoxy group to the acetylenic carbon in 2‐methoxyphenylacetylene under electron impact conditions affords the rearranged molecular ion corresponding to 2H‐1‐benzopyran. Similar processes leading to cyclic products are also noticed in 2‐methoxydiphenylacetylenes. The ion structures and the mechanism of fragmentations are established through high‐resolution data, collision‐induced decomposition, mass‐analysed ion kinetic energy spectra, B/E linked scan spectra, D‐labelling and chemical substitution.
Collision‐induced fragmentation reactions of doubly charged ions of polycyclic aromatic hydrocarbons
Authors: Sim P. G. , Jamieson W. D. , Boyd R. K. 
Published: May 2005

AbstractUnimolecular and collision‐induced reactions of molecular dications M2 + of polycyclic aromatic hydrocarbons (PAHs) have been investigated. For larger PAHs (three or more rings) charge‐separation reactions, and both dissociative and non‐dissociative electron‐capture collisions, are less important. In both low energy (0‐400 eV) and high energy (16 keV) collision regimes, the dominant processes are expulsion of hydrogen atoms and of neutral acetylene molecules. In the high‐energy collision regime, neutral free radicals are also expelled from these M2 + precursors. Some degree of isomer differentiation is possible via relative intensities of doubly charged fragment ions in the low‐energy collision regime, but not all isomers can be thus distinguished and it seems unlikely that such a scheme could be made predictive. The CID spectra are largely independent of precursor size or structure at lower masses (m/z ⩽ 70). These findings are reviewed in the light of literature data on expulsion of small neutral species from aromatic dications. It is proposed that the charge‐separation reactions characteristic of smaller aromatic systems are charge‐site‐initiated cleavages, while expulsion of small neutral species such as acetylene is a radical‐site‐initiated reaction from M2 + ions possessing considerable diradical character. In all cases an important driving force is the avoidance of anti‐aromatic character for a benzene ring from which two electrons have been removed. The similarity of the CID spectra at low masses is analogous to that discussed recently (S. J. Pachuta et al., J. Am. Chem. Soc. 110, 657 (1988)) for fragmentations of the corresponding singly charged molecular radical cations.
Mass spectra of substituted and annelated benzofurazan‐1‐oxides
Authors: Dyall Leonard K. 
Published: May 2005

AbstractElectron impact positive ion spectra of ten substituted or annelated benzofurazan‐1‐oxides are reported. While most of the molecular ions lose either NO˙ + NO˙, or NO˙ + CO, some also lose CO as an initial fragment. One of the fragmentation pathways for 4‐methylbenzofurazan‐1‐oxides involves initial ˙CHO loss.With the annelated benzofurazan‐1‐oxides (naphtho[1,2‐c]furazan oxide and quinolo[3,4‐c]furazan oxide), loss of N2O2 is followed by a retro‐Diels–Alder elimination of butadiyne or propynenitrile, respectively from the aryne radical cation. In the case of quinolo[5,6‐c]furazan oxide, loss of N2O2 from the molecular ion must be followed by substantial rearrangement to enable the observed loss of propynenitrile to take place.
Ion formation in fast atom bombardment mass spectrometry: a divided probe investigation of gas‐phase reactions
Authors: Miller Jack M. , Balasanmugam Kesgapillai , Fulcher Adrian 
Published: May 2005

AbstractSome ion‐formation processes during fast atom bombardment (FAB) are discussed, especially the possibility of reactions in the gas phase. Divided (two halves) FAB probe tips were used for introducing two different samples into the source at the same time. Our results showed [M + A]+ ions (where M = crown ethers and A = alkali metal ions), can be produced, at least in part, in the gas phase when crown ethers and sources of alkali metal ion are placed on two halves of the FAB probe tip. The extent of this ion formation depends on the volatility of the crown ether and on steric factors. Cluster ions such as (M + LiCl)Li+, (2M + LiCl)Li+, [2M + K]+ and [2M + Na]+ are also observed to form in the gas phase. Unimolecular decompositions contribute to some ions detected in FAB. When the alkali ion salt and the crown ether are mixed together the probability of [M + A]+ ion formation increases significantly, regardless of the volatility of the crown ether.
Mass spectra of doubly charged ions
Authors: Barber Michael , Bell David J. , Morris Michael , Tetler Lee W. , Woods Michael D. , Monaghan John J. , Morden William E. 
Published: May 2005

AbstractThe mass spectra of biological molecules, whose molecular mass exceeds 10 kDa, invariably contain multiply charged ions. For example, a survey scan of a small protein will produce singly, doubly and triply protonated molecules, the intensity of the doubly charged species often being greater than that of the singly charged entity. Although the spectra resulting from doubly charged peptides have not previously been studied, collisional activation of such doubly charged species may result in significant additional information pertaining to molecular structure. The techniques employed to study ions originating from multiply charged species were linked scanning of constant B/E and tandem mass spectrometry, namely low collision energy spectra acquired on a BEQQ hybrid instrument. The methodology was applied to model compounds whose tandem mass spectrometry characteristics are well known, e.g. gramicidin S and angiotensin I. The results for the product ions of the [M + 2H]2+ species of the models were obtained which highlight the methodology required for high‐mass materials.
Trends in the energies of cation and anion states of alkan‐1‐ols
Authors: Badrinathan D. Mathur C. , Marathe V. R. 
Published: May 2005

AbstractWe report results of a systematic investigation of the energies of positive‐ion and negative‐ion states in alkan‐1‐ol molecules CnH2n+1 OH (n = 1–5) in low‐energy electron impact experiments using a beam of nearly mono‐energetic electrons. The measurements have been conducted in a crossed electron‐beam/molecular‐beam apparatus wherein positive ions are detected using a quadrupole mass spectrometer whereas unstable negative ions are observed as resonance structures in the electron transmission function. Theoretical calculations of anion and cation energies have been carried out using the semi‐empirical HAM/3 technique.
Quantitative variability in the 252Cf plasma desorption mass spectra of triglycerides and waxes
Authors: Showell John S. , Fales Henry M. , Sokoloski Edward A. 
Published: May 2005

AbstractA series of mixtures of solid triglycerides and waxes are examined using 252Cf plasma desorption mass spectrometry. The relative abundances of diagnostic ions are found to vary with sample preparation, handling, and composition. It is proposed that the less efficiently packing, shorter chain, compounds are forced to the analysis site, i.e. the surface. This takes place at varying rates that reflect the bulk properties of the mixture as revealed by its phase diagram and thermal history. Mixtures that remain liquids during analysis show ion abundances correctly reflecting their composition. Mixtures of isotopomeric glycerides also show normal ion abundances.
The fragmentation of ionized alkyl phenyl ethers
Authors: Blanchette Marcia C. , Holmes John L. , Lossing F. P. 
Published: May 2005

AbstractThe energetics of olefin loss from ionized alkyl phenyl ethers have been determined by ionization and appearance energy measurements. It is concluded that the reaction is governed by one or more of three features: (i) the strength of the bond between the phenoxy radical and the alkyl ion; (ii) the ease of isomerization of the alkyl ions, chiefly by H‐shifts therein, and (iii) the strength of the CH bond (primary, secondary and tertiary) involved in the H transfer to oxygen which precedes the olefin loss. The possible participation in the reaction of distonic ions and proton bound radical‐molecule pairs is also discussed.
Fused‐ring tropylium ion formation and fragmentation
Authors: Standley Laurel J. , Hites Ronald A. 
Published: May 2005

AbstractFused‐ring tropylium ions, formed in the electron impact mass spectra of methyl phenanthrenes and methyl anthra‐cenes were studied by mass spectrometric and computational methods. These ions form through a cyclopropyl intermediate. As a result of an equilibrium between the benzylium and tropylium ion configurations, partial carlton atom scrambling occurs in the fused‐ring structures. Fragmentation of these ions occurs only in the ring incorporating the methyl carbon. These conclusions are supported by MNDO calculations and by 13C‐labeled methyl‐phenanthrene and methylanthracene fragmentation studies.
Studies of phthalic acid and related compounds by positive‐ and negative‐ion chemical ionization tandem mass spectrometry (± CI/MS/MS)
Authors: Gillespie Todd A. , Urogdi Laszlo , Katritzky Alan R. , Yost Richard A. 
Published: May 2005

AbstractThe positive‐ and negative‐ion chemical ionization (± CI) behavior of phthalic acid and four related compounds (phthalic anhydride, phthalide, biphthalyl, and anthraquinone‐2‐carboxyIic acid) are characterized by tandem mass spectrometry with low‐energy collisionally activated dissociation. Principal fragmentation pathways have been established, and molecular and fragment ions arising from these compounds have been differentiated from adduct and dimer ions, as well as from ions due to impurities. The ubiquitous nature of these compounds in analytical samples makes it important to identify the corresponding ions, and thus to be able to exclude them from consideration in the identification of other sample components.
Fragmentation of enamides derived from 6,7‐dimethoxy‐4‐methyl‐2H‐1,3‐benzothiazin and 3,4‐dihydro‐6,7‐dimethoxy‐1‐methylixopuinoline
Authors: Wang Jian , Smith Richard W. , Fodor Lajos , Macleant David B. 
Published: May 2005

AbstractThe electron impact mass spectra of several enamides have been examined. The enamides were prepared by reaction of aroyl halides with 6,7‐dimethoxy‐4‐methyl‐1,3‐benzothiazin, and with 3,4‐dihydro‐6,7‐dimethoxy‐l‐methylisoquinoline. The fragmentation pathways that have been proposed are supported by ion composition determinations and by mass‐analysed ion kinetic energy spectrometry experiments carried out on the molecular ions and major fragment ions. The spectra are characterized by a loss of carbon monoxide from the molecular ion of each compound, a process which is accompanied by migration of the aryl group.