bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isomerization and fragmentation of methyl benzofuran ions and chromene ions in the gas phase
Authors: Spilker Rüdiger , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractThe rearrangement of the molecular ions of the isomeric 2‐ and 3‐methyl benzofurans (1 and 2), 2H‐chromene (3) and 4H‐chromene (4) has been studied as a further example of the isomerization of oxygen‐heteroaromatic radical cations via a ring expansion/ring contraction mechanism well documented for molecular ions of alkyl benzenes. The ions 1+˙−4+˙ fragment mainly by H loss into identical chromylium ions a. The process exhibits consistently a large kinetic energy release and an isotope effect kH/kD, which arise from a rate‐determining energy barrier of the last dissociation step. Differences of the kinetic energy releases, the isotope effects and the appearance energies of the methyl benzofuran ions and the chromene ions indicate a large energy barrier also for the initial hydrogen migration during the rearrangement of the methyl benzofuran ions. This is substantiated by an MNDO calculation of the minimum energy reaction path. In contrast to the behaviour of alkyl benzene ions, a unidirectional isomerization of the methyl benzofuran ions by ring expansion takes place but no mutual interconversion of the molecular ions of methyl benzofurans and chromenes.
Fragmentation reactions of the enolate ions of 2‐pentanone
Authors: Donnelly Allen , Chowdhury Swapan , Harrison Alex. G. 
Published: May 2005

AbstractThe reaction of [OH]− with 2‐pentanone produces two enolate ions, [CH3CH2CH2COCH2]− and [CH3COCHCH2CH3]−, by proton abstraction from C(1) and C(3), respectively. Using deuterium isotopic labelling the fragmentation reactions of each enolate have been delineated for collisional activation at both high (8 keV) and low (5–100 eV) collisional energies. The primary enolate ion fragments mainly by elimination of ethene. Two mechanisms operate: elimination of C(4) and C(5) with hydrogen migration from C(5), and elimination of C(3) and C(4) with migration of the C(5) methyl group. Minor fragmentation of the primary enolate also occurs by elimination of propane and elimination of C2H5; the latter reaction involves specifically the terminal ethyl group. The secondary enolate ion fragments mainly by loss of H2 and by elimination of CH4; for the latter reaction four different pathways are operative. Minor elimination of ethene also is observed involving migration of a C(5) hydrogen to C(3) and elimination of C(4) and C(5) as ethene.
Differentiation of the isomeric 1,2‐cyclopentanediols by ion‐molecule reactions in a triple‐quadrupole mass spectrometer
Authors: Meyerhoffer William J. , Bursey Maurice M. 
Published: May 2005

AbstractCollisionally activated decompositions and ion‐molecule reactions in a triple‐quadrupole mass spectrometer are used to distinguish between cis‐ and trans‐1,2‐cyclopentanediol isomers. For ion kinetic energies varying from 5 eV to 15 eV (laboratory frame of reference), qualitative differences in the daughter ion spectra of [MH]+ are seen when N2 is employed as an inert collision gas. The cis −1,2‐cyclopentanediol isomer favors H2O elimination to give predominantly [MH‐ H2O]+. In the trans isomer, where H2O elimination is less likely to occur, the rearrangement ion [HOCH2CHOH]+ exists in significantly greater abundance. Ion‐molecule reactions with NH3 under single‐collision conditions and low ion kinetic energies can provide thermochemical as well as stereochemical information. For trans −1,2‐cyclopentanediol, the formation of [NH4]+ by proton transfer is an exothermic reaction with the maximum product ion intensity at ion kinetic energies approaching 0 eV. The ammonium adduct ion [M + NH4]+ is of greater intensity for the trans isomer. In the proton transfer reaction with the cis isomer, the formation of [NH4]+ is an endothermic process with a definite translational energy onset. From this measured threshold ion kinetic energy, the proton affinity of cis −1,2‐cyclopentanedioi was estimated to be 886 ± 10 kJ mol−1.
Effect of ammonium formate as ionizing additive in thermospray liquid chromatography‐mass spectrometry for the determination of triazine, phenylurea and chlorinated phenoxyacetic acid herbicides
Authors: Barceló D. 
Published: May 2005

AbstractA comparison between the use of ammonium acetate and ammonium formate in thermospray liquid chromatography‐mass spectrometry with positive and negative ion modes using ‘filament‐on’ mode has been applied for the determination of simazine, atrazine, propazine, monuron, diuron, linuron, 2,4,‐D, 2,4,5‐T and silvex. By using ammonium formate, the positive ion mode showed for triazine and phenylurea herbicides [M + H]+ and [M + NH4]+, respectively, and the formation of other adduct ions different from ammonium acetate. In the negative ion mode, chlorinated phenoxyacetic acid herbicides exhibited [M + acetate]− or [M + formate]−, depending on the ionizing additive. Applications are reported for the determination of triazine and chlorinated phenoxyacetic acid herbicides in spiked soil and water samples, respectively.
Electron ionization mass spectrometry of systematically modified ligands in chromium(III) β‐diketonates
Authors: Schultze Peter , Wenclawiak Bernd W. 
Published: May 2005

AbstractThe positive ion mass spectra of several chromium(III) β‐diketonates with aliphatic α‐substituents have been investigated. Metastable peaks in the spectra confirm that ions containing substituents with γ‐H atoms undergo propene loss. This implies a McLafferty rearrangement of an open‐chain ligand structure. Ethyl radicals are lost from n‐butyl substituents; methyl groups are cleaved from the molecular ions of complexes formed from methyl‐substituted ligands. The main fragment is, as expected, [ML2]+; however, its further fragmentation is different from that of [ML3]+. Electron donating substituents stabilize doubly charged molecular ions.
Cyclization of 1,2,3,5‐polysubstituted pyrroles in electron impact
Authors: He Meiyu , Yu Zhenpei , Hua Wenting 
Published: May 2005

AbstractMass spectra of eight new 1,2,3,5‐polysubstituted pyrroles were studied by methods of electron impact, mass‐analysed ion kinetic energy and high‐resolution data. It has been found that five‐membered or six‐membered cyclic ions were formed and other rearrangement ions were observed in the mass spectra.
Fast atom bombardment and secondary ion mass spectra of thiamine hydrochloride
Authors: Brown Stephen M. , Busch Kenneth L. , Burinsky David J. 
Published: May 2005

AbstractThe ratio of the fragment ions at m/z 122 and m/z 123 in the positive ion fast atom bombardment or secondary ion mass spectra of thiamine hydrochloride varies with sample preparation and experimental conditions. For all mass spectra that contained significant abundances of matrix (S) ions [S + H]+, the fragment at m/z 123 is the more abundant of the two ions. If [S + H]+ ions are not observed in the mass spectrum under the conditions selected, the ion at m/z 122 is more abundant. This correlation suggests that hydrogen transfer to the fragment ion occurs in the gas phase, with the composition of the ion‐solvent cluster ions in the selvedge region being the key factor. The ratio of the fragment ions at m/z 123 and m/z 122 is thus an indicator of the extent of protonation in the selvedge, the region immediately above the solvent surface created by primary particle bombardment.
Experimental determination of the double ionization energies of the perhalomethanes, CF3Br, CF2Br2, CFBr3 and CF2ClBr
Authors: Griffiths W. J. , Harris F. M. 
Published: May 2005

AbstractThe double ionization energies of the perhalomethanes CF3Br, CF2Br2, CFBr3 and CF2ClBr have been determined using the technique of double‐charge‐transfer spectroscopy. The values found are compared with those of other perhalomethane molecules also determined in this laboratory.
Ortho effects in organic molecules on electron impact: 19—Competing oxygen transfers from nitro group to sulphur and acetylinic carbons in 2‐nitrophenylphenylethynylsulphides
Authors: Ramana D. V. , Krishna N. V. S. Rama 
Published: May 2005

AbstractOxygen transfers to both the acetylenic carbons and sulphur are noticed in parallel fragmentation pathways during the electron‐impact induced decompositions of 2‐nitrophenylphenylethynylsulphides. Single oxygen transfer to acetylinic carbons leads to the most abundant ion corresponding to the benzoyl cation whilst double oxygen transfers to both the acetylenic carbons followed by the ejection of two CO units from the M+˙ ion afford another abundant fragment corresponding to the phenothiazine radical cation. However, the oxygen transfers to sulphur yield a less abundant [M  SO2H]+ ion. The proposed fragmentation pathways and the ion structures are sup ported by high‐resolution data, collision‐induced dissociation Linked‐scan spectra and chemical substitution.
Reactivity in the gas phase. Behaviour of isoxazoles under negative ion chemical ionization conditions
Authors: Guarna Antonio , Moneti Gloriano 
Published: May 2005

Abstract[M  H+]− ions of isoxazole (la), 3‐methylisoxazole (1b), 5‐methylisoxazole (1c), 5‐phenylisoxazole (1d) and benzoylacetonitrile (2a) are generated using NICI/OH− or NICI/NH2− techniques. Their fragmentation pathways are rationalized on the basis of collision‐induced dissociation and mass‐analysed ion kinetic energy spectra and by deuterium labelling studies. 5‐Substituted isoxazoles 1c and 1d, after selective deprotonation at position 3, mainly undergo N  O bond cleavage to the stable α‐cyanoenolate NC  CH  CR  O− (R = Me, Ph) that fragments by loss of RCN, or RH, or H2O. The same α‐cyanoenolate anion (R = Ph) is obtained from 2a with OH−, or NH2−, confirming the structure assigned to the [M  H+]− ion of 1d, On the contrary, 1b is deprotonated mainly at position 5 leading, via NO and C(3)C(4) bond cleavages, to HC ≡ C O − and CH3CN. Isoxazole (1a) undergoes deprotonation at either position and subsequent fragmentations. Deuterium labelling revealed an extensive exchange between the hydrogen atoms in the ortho position of the phenyl group and the deuterium atom in the α‐cyanenolate NC  CD = CPh  O−.
The electron impact mass spectra of some cevine orthoacetates
Authors: Waight Eric S. 
Published: May 2005

AbstractThe most important fragmentation in the electron impact mass spectra of dihydrocevine orthoacetate and some analogues involves loss of an acetoxyl radical from the molecular ion, and is associated with strain in the orthoacetate group bridging a six‐membered ring. The process is much less important in the less‐strained dihydrocevine isoorthoacetate, which gives the ion m/z 112, characteristic of cevine alkaloids, as the most abundant. A further important difference concerns an ion involving the loss of C(20) and its substituents together with a hydrogen atom from M+˙, also relatively unimportant in the isoorthoacetate.
Application of on‐line HPLC‐FAB mass spectrometry to the analysis of enzymatic digests of ribonuclease B
Authors: Mock K. , Firth J. , Cottrell J. S. 
Published: May 2005

AbstractA tryptic digest of bovine ribonuclease B was analysed by on‐line HPLC‐FAB mass spectrometry to verify the primary sequence. Peptides obtained by digestion with trypsin before and after treatment with N‐glycanase were separated on a slurry‐packed fused silica LC column. The entire eluent was introduced into the mass spectrometer source via a continuous flow interface. A single injection of 100 pinoles of material provided data covering over 70% of the sequence.
Negative ions generated by reactions with oxygen in the chemical ionization source. II. The use of wall‐catalyzed oxidation reactions for differentiation of polycyclic aromatic hydrocarbons and their methyl derivatives
Authors: Stemmler Elizabeth A. , Buchanan Michelle V. 
Published: May 2005

AbstractPolycyclic aromatic hydrocarbons (PAH) undergo wall‐catalyzed oxidation reactions, in conjunction with electron‐and ion‐molecule reactions, when oxygen is present in the chemical ionization source. Under conditions that promote these wall‐catalyzed oxidation reactions (addition of oxygen, elevated ion source temperature) oxidized products are easily detected by measurement of the negative ion chemical ionization (NICI) mass spectra. The NICI mass spectra are dominated by ions that result from electron‐capture ionization of oxidation products such as ketones, quinones and anhydrides. In this study the NICI mass spectra of 30 PAH and 46 methyl‐substituted PAH were measured. These spectra can be used to differentiate certain isomeric PAH based upon differences in molecular structure. Of particular interest are ions that appear in the spectra of methyl‐substituted PAH, which can provide information regarding the position of methyl substituents.
Primary‐particle‐beam‐induced reduction of silver acetate in glycerol solutions to form a silver mirror
Authors: Dean L. K. L. , Busch Kenneth L. 
Published: May 2005

AbstractThe liquid SIMS mass spectra of silver acetate dissolved in a glycerol matrix is discussed, with emphasis on the formation of a ‘silver mirror’ on the surface of the glycerol droplet owing to reduction of the silver acetate. Silver clusters containing up to three silver atoms have been observed from this mirrored surface; Ag3+ cluster ions are not observed in the spectrum when conditions are such that the mirror is not formed. For example, use of a slightly oxidizing matrix (o‐nitrophenyl octyl ether or m‐nitrobenzylalcohol) prevents formation of the ‘mirror’; only Ag+ is sputtered from this surface.
Unusual fragmentation of trimethylsilylated enols derived from m‐ and p‐hydroxyacetophenones
Authors: Kraus Rupert , Spiteller Gerhard 
Published: May 2005

AbstractWhen 4‐hydroxyacetophenone is treated with MSTFA the corresponding bis‐trimethylsilylated enol ether (1a) is obtained. The mass spectrum of la is characterized by a [M – 1]+ base peak. Extensive deuteration experiments revealed that the hydrogen is mainly removed from a ring position, but originates also to some extent from the side chain (methylidene group) and even to a very small amount from the hydrogens of the methyl groups of the enolic trimethylsilyl group. A mechanism for this fragmentation behaviour is formulated.
Dissociation dynamics of halotoluene ions, production of tolyl, benzyl and tropylium ([C7H7]+)ions
Authors: Olesik Susan , Baer Tomas , Morrow J. C. , Ridal Jeffrey J. , Buschek John , Holmes John L. 
Published: May 2005

AbstractThe dissociation rates and energetics of the loss of halogen atoms from energy‐selected halotoluene ions were investigated by photoelectron photoion coincidence (PEPICO) and collisional activation (CA) mass spectrometric experiments. Dissociation onsets, determined from the dissociation rates measured as a function of the internal energy of the parent ion, revealed the formation of three [C7H7]+ isomers, which were identified, on the basis of the CA data, as the tolyl, benzyl and tropylium ions. All of the ions investigated produced a mixture of isomeric ions. Only iodotoluene ions produced any tolyl product ions by a direct bond cleavage. The bromo‐ and chlorotoiuene ions produced mixtures of benzyl and tropyl ions. The observed two‐component decay rates of the iodotoluene ions revealed the participation of a lower energy [C7H7I]+ ˙ isomer in the dissociation process. The identity of this isomer is not known but it probably does not have the cycloheptatriene ion structure because considerable kinetic energy was released in this dissociation.
Determination of the fragmentation mechanisms of organophosphorus ions by H2O and D2O atmospheric‐pressure ionization tandem mass spectrometry
Authors: Snyder A. Peter , Harden Charles S. 
Published: May 2005

AbstractDimethylmethyl phosphonate (DMMP), dimethyl phosphite (DMPI), trimethyl phosphite (TMPI) and trimethyl phosphate (TMP) were investigated using H2O and D2O atmospheric‐pressure ionization (API) tandem mass Spectrometry. All daughter ions could be explained by losses of one or a successive number of stable molecules as opposed to losses of radicals such as the hydride, methyl and methoxy species. Losses of neutral methanol and dimethyl ether and of protonated methanol and formaldehyde ions from all four organophosphorus pseudo‐molecular ions were observed. The DMMP and DMPI MH+ pseudomolecular ions produced the losses of neutral C2H6 and water, respectively. Formaldehyde loss was not observed for the MH+ ions, but it was well represented in the decomposition pathways of daughter ions. The D2O reagent gas highlighted the role of the ionizing proton/ deuteron in the various daughter ions, including m/z 95, 79, 65, 49, 33, 31 and 47. The last ion was found to be isobaric in that m/z 47 and 48 both appeared with similar abundances in the D2O‐API daughter ion mass spectra of TMPI and TMP.
Mass spectrometry of some methyl esters of N‐4‐pyrimidinylamino acids: Rearrangements of the ions occurring on electron‐impact ionization
Authors: Plaziak Adam S. , Celewicz Lech , Spychala Jaroslaw , Golankiewicz Krzysztof 
Published: May 2005

AbstractThe electron‐impact‐induced mass fragmentations of methyl esters of N‐(1H‐2‐oxo‐4‐pyrimidinyl)ainino acids are reported. The loss of a ·COOCH3 radical and the elimination of a methanol molecule were observed and possible mechanisms of these processes are proposed. The loss of a ·COOH radical and elimination of water were established, which suggests the rearrangement of the investigated esters into isomeric N‐4‐pyrimidinylamino acids.
Odd‐electron molecular ion and loss of toluene in fast atom bombardment mass spectra of some carotenoids
Authors: Caccamese Salvatore , Garozzo Domenico 
Published: May 2005

AbstractPositive‐ion fast atom bombardment (FAB) and B/E linked scan FAB mass spectra of seven carotenoids are reported. In all cases the M +· ions are observed, and the [M + H]+ ions are absent in the hydrocarbons and weak in the oxygenated compounds. The usefulness of B/E linked scan FAB mass spectra to distinguish isomers and to attribute the loss of toluene from the M +· to an ionic fragmentation and not to a thermal process is discussed.
Formation of β‐carbolines from 1‐[(1′ ‐carboxy‐2′‐indol‐3′‐yl‐ethyl)amino]‐1‐deoxy‐D‐fructose under electron impact conditions
Authors: Yaylayan Varoujan , Paré J. R. Jocelyn , Laing Richard , Sporns Peter 
Published: May 2005

AbstractInterest in β‐carbolines has recently increased owing to their detection in human tissue and in some food products; one of the possible sources of their formation in food is the Amadori rearrangement product (ARP) of tryptophan with glucose, l‐[(1′‐carboxy‐2′‐indol‐3′‐ylethyl)amino] ‐1‐deoxy‐D‐fructose. Based on the intermediates identified in the high‐resolution electron impact spectrum of the tryptophan Amadori product and by B/E and B2/E linked‐scan experiments, a mechanism is proposed for their formation under electron impact conditions. The proposed mechanism is an intramolecular nucleophilic substitution reaction of the dehydrated tryptophan ARP, leading to the formation of 3‐substituted β‐carbolines; this mechanism might shed some light on the origin of their abundant formation in food.
H–D Exchange in some macrocyclic complexes of nickel(II) under electron impact
Authors: Palii Sergiu P. , Indrichan Konstantin M. , Gerbeleu Nikolai V. , Arion Vladinir B. , Zagorevskii Dmitrii V. , Nekrasov Yurii S. 
Published: May 2005

AbstractThe electron impact mass spectra of coordination compounds of nickel(II) containing 14‐membered hexaaza macrocyclic ligands composed of S‐substituted isothiosemicarbazide and β‐diketone units with cis and trans arrangement of SR groups were studied. The molecular ions exhibited the most in tense peaks in all cases. The loss of peripheral groups is a common feature of the decomposition of the molecular ions for the compounds studied. Exchange between the hydrogen atoms of the alkylthio groups and the hydrogen at γ‐carbon atoms of the β‐diketonate fragments was observed in the mass spectra of compounds with trans‐SR groups. The molecular ions of the complexes with cis‐SR groups selectively eliminated the radical R˙.
Mndo study of fragmentations in mass spectrometry. Part II. Substituent effects in the ioinization of [CH3COR] compounds and their enol tautomers
Authors: Hrušák Jan , Tkaczyk Martin 
Published: May 2005

AbstractA semiempirical MNDO method was used in calculations on monosubstituted neutral and cationic compounds of the [CH3COR] type with a wide range of substituents (R = H, F, Cl, CH3, NH2, OH, OCH3, NHCH3, CHCH2). The results obtained are interpreted with respect to the effect of the individual substituents on the geometry and electron distribution in the systems studied and allow the conclusion that the ratios of partial charges in the individual substructures in a radical cation correspond to those of the respective peak intensities in the mass spectrum.
Effect of collision gas pressure and collision energy on reactions between oxygen and the negative molecular ion of tetrachlorodibenzo‐p‐dioxins in the collision cell of a triple ‐quadrupole mass spectrometer
Authors: Kostiainen R. , Auriola S. 
Published: May 2005

AbstractLow‐energy reactive collisions between the negative molecular ion of a tetrachlorodibenzo‐p‐dioxin (TCDD) and oxygen inside the collision cell of a triple‐stage quadrupole mass spectrometer produce a substitution ion [M  Cl + O]−, a phenoxide ion [C6H4‐nO2Cln]−·, [M  HCl]−·, and Cl− by which 1,2,3,4‐, 1,2,3,6/1,2,3,7‐ and 2,3,7,8‐TCDD isomers can be distinguished either directly or on the basis of intensity ratios. The collision conditions have an important effect on the relative abundances. Energy‐ and pressure‐resolved curves show that the ions formed by a collisionally activated reaction (CAR) process, i.e. [M  Cl + O]− and [C6H4‐n,O2Cln]−·, are favoured by a high pressure of oxygen (3‐6 mTorr) (1 Torr = 133.3 Pa) and a low collision energy (0.1‐7 eV), whereas the ions formed by a collisionally activated dissociation (CAD) process, i.e. [M  HCl]−· and Cl−, are favoured by high pressure and high energy. By choosing a relatively low collision energy (5 eV) and high pressure (4 mTorr), the CAR and CAD ions can be clearly detected.
Mechanism of ionization and initial fragmentation in electron impact mass spectra of 3‐halogenobenzanthrones
Authors: Abliz Zeper , Ueda Toyotoshi , Kubogata Kazuhiko , Iwashima Satoshi , Takekawa Minoru , Aoki Junji , Kan Teruo 
Published: May 2005

AbstractElectron‐impact mass spectra of 3‐halogenobenzanthrones (halogen X = Cl, Br, I) were measured and ionization efficiency curves and three kinds of linked‐scan spectra were obtained for several fragment ions. The fundamental mechanisms of ionization and initial fragmentation were interpreted by the penetration length of an impacting electron or the density distribution on the molecular surface of a rejected electron and its orbital energy. The apparent ionization energy (IE) of a singly charged molecular ion seems to be the lower one of non‐bonding electrons on O or X, and that of a doubly charged molecular ion the sum of three terms, the IE of non‐bonding electron on O, that on X and the electrostatic repulsion between two positive charges. Two competing pathways of decomposition from the molecular ion M+· to an ion [M ‐ CO,‐ X]+ were observed: one is the initial detachment of CO in chloro and bromo compounds and the other is the initial elimination of the iodine atom in the iodo compound. The sequence of these reactions was confirmed by metastable ion analysis with linked‐scan spectra and the relative magnitudes of the appearance energies. They can be explained by the driving force of a localized positive charge or unpaired electron on a heteroatom.
Acetone chemical ionization studies: Olefins
Authors: Vairamani M. , Kumar K. V. Siva , Rao G. K. Viswanadha 
Published: May 2005

AbstractAcyclic, cyclic and bicyclic olefins have been found to undergo acetylation in the gas phase under acetone chemical ionization, giving rise to diagnostic ions. Terminal olefins show enhanced loss of water from the [M + 43]+ adduct. The [M + 43]+ ion of Δ3− Δ4− and Δ5‐olefins give characteristic collision‐induced dissociation spectra.