bluuebunny/crossref_metadata_2025_split huggingface dataset:
The role of charge‐site location in fragmenting ions. 1—[CH3 CHXCOOCH3]+˙ and [CH2XCH2 COOCH3]+˙ ions and the structures of daughter ions derived from the loss of X (X = I, Br, Cl and CH3)
Authors: Burgers Peter C. , Holmes J. L. , Lossing F. P. , Povel Frank R. , Terlouw Johan K. 
Published: May 2005

AbstractThe structures of the m/z 87, [C4H7O2]+, ions generated by dissociative ionization of CH3CGXCOOCH3 and XCH2CH2COOCH3 (X = CH3, Cl, Br, and I) have been investigated via their unimolecular and collisionally activated fragmentations and by apperance energy measurements. For both precursors loss of X = CH3 produced, via H atom transfer, ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_2 = CH}\mathop {\rm C}\limits^{\rm + } \left({{\rm OH}} \right){\rm OCH}_{\rm 3} $\end{document} (a), ΔHf = 386 kj mol−1. In marked contrast, loss of I˙ from ionized CH3CHICOOCH3 and ICH2CH2COOCH3 proceeded without rearrangement to yield respectively ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH_3}\mathop {\rm C}\limits^{\rm + } {{\rm HCOOCH_3}} $\end{document} (b), ΔHf = 480 kJ mol−1 and (c), ΔHf = 450 kJ mol−1. These different fragmentation behaviours are explained via photoelectron spectra which show that the formal charge site in the precursor ion is at the carbonyl oxygen when X = CH3 but at the halogen atom when X = I. The precursor molecules X = Cl and Br display both of the above characteristics, CH3CHXCOOCH3 yielding mixtures of a and b and XCH2CH2COOCH3 producing a and c ions.
Mass spectra of aurones
Authors: Varma Rajender S. , Bowen Richard D. 
Published: May 2005

AbstractThe mass spectra are reported for 19 aurones (2‐benzylidenecoumaran‐3‐ones) having a wide variety of functional groups and substitution patterns. The principal ions in these spectra are consistent with the operation of proximity effects demonstrated previously for 6‐methoxyaurones.
Charge reversal of the enolate ions of acetaldehyde and acetone
Authors: Lehman Thomas A. , Bursey Maurice M. , Hass J. Ronald 
Published: May 2005

AbstractCollisionally activated charge reversal of HCOCH2− and CH3COCH2− produces positive ions whose fragments differ from those of other [C2H3O]+ ions formed by fragmentation of positive molecular ions, including the [C2H3O]+ ions from 2,2‐dichlorethanol, considered formerly to have the HCOCH2+ structure. The fragmentations of the charge reversed ions are concordant with the RCOCH2+ structures. Least‐squares correlations of the collisional activation spectra [C2H3O]+ are probed as a useful guide to claiming similarity or dissimilarity of ionic structure.
Extended mass range by multiple charge: Sampling quadruply charged quasimolecular ions of poly(ethylene glycol) 4000
Authors: Chan Kelvin W. S. , Cook Kelsey D. 
Published: May 2005

AbstractMass spectrometric sampling of quasimolecular ions with charge as high as 4+ has been achieved by Electrohydrodynamic Ionization Mass Spectrometry (EHMS). Triply and quadruply charged sodium ion adducts of poly(ethylene glycol) 4000 oligomers with mass exceeding 3500 u were sampled from glycerol solution without fragmentation. Although the mass of these ions exceeded the nomical mass range of the spectrometer, they were detected because of multiple charge which lowered their mass‐to‐charge ratio. From the mass spectral intensities of these oligomer ions, the number average molecular weight of the polymer was caculated, and found to be in good agreement with results of an ASTM standard method.
The unorthodox loss of propyl from the molecular ions of methoxycyclohexane
Authors: Molenaar‐Langeveld Tineke A. , Nibbering Nico M. M. 
Published: May 2005

AbstractIt is shown by field ionization kinetics, D and 13C labelling and metastable ion studies that the loss of a propyl radical from the molecular ion of methoxycyclohexane occurs via two routes. At a molecular ion lifetime of <10−10 s propyl is eliminated in the ‘classic’ way, i.e. by successive cleavage of the C(1)C(2) bond, 1,5‐H shift from C(6) to C(2) and cleavage of the C(4)C(5) bond. At 10−10 s the other pathway for propyl loss starts to take place, which is initiated by a hydrogen shift from position 3 or 5 to the methoxy group. This leads in a series of steps to the formation of the 3‐methoxyhexene‐1 ion, which eventually eliminates a propyl radical. In some of the steps specific hydrogen‐deuterium exchange processes have been observed.
Mass spectra of chlorinated aromatics formed in pulp bleaching: I—chlorinated catechols
Authors: Knuutinen Juha , Korhonen Ilpo O. O. 
Published: May 2005

AbstractA systematic study on the electron impact mass spectra of all nine chlorinated catechols in presented. Metastable ion analysis was used to elucidate the fragmentation pathways. The influence of the position of the chloro substituents can be used to distinguish the structural isomers. In this respect the most characteristic fragment ions are [MCHl]+˙, [MHCOOH]+˙, [MCOCl]+, [MHClCO]+˙, [MCHOCl]+˙ and [MHClHCl]+˙.
Energy transfer in the collision induced decomposition of peptide ions formed by field desorption
Authors: Neumann Gregory M. , Derrick Peter J. 
Published: May 2005

AbstractIn the collision induced decomposition of a number of peptide ions formed by field desorption, it has been found that at the optimum pressure of collision gas the translational energy lost by an incident peptide ion increases as peptide ions of increasing mass are considered. The internal energy taken up by any individual peptide ion appears to be directly proportional to its mass.
Quick screening of major constituents in plant tissue by temperature programmed fractionation mass spectrometry
Authors: Mak C. K. , Tse R. S. 
Published: May 2005

AbstractTemperature programmed fractionation mass spectrometry can be used to quickly screen for the major constituents in plant and herbal tissues. The method is particularly useful if one is searching for a good plant source of a desired compound. It is also shown that simple extraction followed by mass spectrometry has no advantage over the quick screening method. Limitations and possible improvements of the method are discussed.
The mass spectrometric isomerization of 1‐benzoyl‐2‐(2′‐hydroxy)phenylcyclopropane and 2‐phenyl‐2,3,4,5‐tetrahydro‐2,5‐epoxy[1]‐benzoxepin to a common structure
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Daolio Sergio , Traldi Pietro 
Published: May 2005

AbstractThe mass spectrometric isomerization of 1‐benzoyl‐2‐(2′‐hydroxy)phenylcyclopropane and 2‐phenyl‐2,3,4,5‐tetrahydro‐2,5‐epoxy[1]benzoxepin has been studied in detail with the aid of different ionization methods (electron impact, chemical ionization, field ionization, charge exchange) in conjunction with collisionally activated dissociation experiments.
The effect of configuration of gas phase protonated ethenedicarboxylates on their low energy collision induced dissociation behaviour
Authors: Weisz A. , Mandelbaum A. , Shabanowitz J. , Hunt D. F. 
Published: May 2005

AbstractLow energy collision induced dissociation (CID) spectra were measured by a triple stage quadrupole mass spectrometer for the [MH]+ ions of diethyl and dimethyl esters of maleic, fumaric, citraconic and mesaconic acids. A very high degree of stereospecificity was observed for the geometrically isomeric diethyl esters. The cis esters give rise to very abundant [MHEtOH]+ and [MHEtOHC2H4]+ ions, while the trans isomers exhibit very abundant [MHC2H4]+ and [MH2 C2H4]+ ions. The highly stereospecific processes indicate that the double bond configuration is retained in the protonated species under the conditions of the experiment.
The fast atom bombardment mass spectra of xanthane dyes
Authors: Brown R. M. , Creaser C. S. , Wright H. J. 
Published: May 2005

AbstractThe Fast Atom Bombardment mass spectra of a number of xanthane dyes are reported. These dyes are insufficiently volatile to give spectra by conventional electron impact ionization. Fragmentation pathways have been determined by metastable linked scan techniques and accurate masses obtained by peak matching. The xanthane dyes may be readily identified from their FAB spectra by the presence of characteristic ions.
Electron impact and chemical ionization mass spectra of nitro‐substituted polyfunctional isomers
Authors: Kulkarni P. S. , Kamath H. V. , Kulkarni Sheshgiri N. 
Published: May 2005

AbstractThe electron impact and methane and ammonia chemical ionization mass spectra of some selected nitro‐substituted isomeric benzalacetophenones, benzyl ketones and aromatic epoxides have been examined. The isomeric pairs show significant differences in the electron impact and chemical ionization spectra. The EI spectra show cleavage α to the carbonyl as the major fragmentation mode. Under CI conditions subtle differences in the fragmentation modes of isomeric pairs are more enhanced, and elimination reactions are more favoured in the o‐nitro‐substituted compounds than in the para isomers.
Mass spectrometric investigation of phenylthiovinyl chlorides
Authors: Paradisi Cristina , Scorrano Gianfranco , Daolio Sergio , Traldi Pietro 
Published: May 2005

AbstractThree isomeric phenylthiovinyl chlorides (β‐, E and Z, and α‐) have been examined under EI and FI conditions with particular attention paid to the fragmentation leading to [C8H7S]+ ions via loss of Cl˙. Kinetic energy release data, MIKE and CAD MIKE spectra obtained with these precursors, as well as with model compounds, suggest the thioacylium ion PhCH2CS+ as the predominant structure observed for the [C8H7S]+ species in all cases examined. A comparison is made with the solution behaviour of incipient β‐thiovinyl carbenium ions, which are known to rearrange to the S‐bridged thiirenium structure.
The formation of the anilinium ion from the ammonium ion in the ammonia chemical ionization of substituted benzenes
Authors: Stone John Alfred , Splinter Dena Ellen , McLaurin Joanne , Wojtyniak Anastasia C. M. 
Published: May 2005

AbstractCompounds C6H5X(X  F, Cl, Br, NO2, CN, OCH3) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C6H5NH3]+ (m/z 94). [NH4]+ reacts with C6H5X(X  F, Cl, Br) to yield m/z 94 but C6H5X (X  CN, NO2) forms this ion only by reactions involving either [NH3]+ or [C6H5X]+. C6H5OCH3 does not form m/z 94.
Low energy, low temperature mass spectra 2—low energy, low temperature mass spectra of some small saturated alcohols and ethers
Authors: Bowen Richard D. , Maccoll Allan 
Published: May 2005

AbstractThis paper reports the low energy, low temperature mass spectra of the 27 alcohols and ethers containing up to five carbon atoms. The observed fragmentation pathways are discussed in energetic terms. Except in one instance, pentan‐1‐ol and 3‐methylbutan‐1‐ol, the spectra are diagnostic of the structure of the compounds; even in this case, subtle differences can be used to determine structure. The advantage of the low energy, low temperature mass spectra in identifying low energy fragmentation routes is emphasized.
Mass spectra of ethenol and its deutero analogues
Authors: Tureček František , Hanuš Vladimír 
Published: May 2005

AbstractEthenol, 1‐d‐ethenol, O‐d‐ethenol and Z‐2‐d‐ethenol were prepared by pyrolysis of corresponding 5‐norbornenols at 800°C/2 × 10−6 Torr. The most important fragments in the electron impact mass spectrum of ethenol are [C2H3O]+ and CHO+ and CH3˙. The hydrogen atom eliminated from the molecular ion comes mainly from the hydroxyl group (68%) and to a lesser extent from C(1) (25%) and C(2) (7%). The loss of the hydroxyl hydrogen is preceded by rate‐determining migration of the hydrogen atom from C(1) onto C(2) to yield CH3COH+˙ions that decompose to CH3CO+ and H˙. The loss of deuterium from O‐d‐ethenol shows a very small primary isotope effect (kH/kD=1.07), whereas a significant effect is observed for the loss of hydrogen from 1‐d‐ethenol (kH/kD=1.28). The appearance energy of [C2H2DO]+ from 1‐d‐ethenol, AE=11.32 eV, gives a critical energy for the hydrogen loss, E=203 kJ mol−1, which is 90 kJ mol−1 above the thermochemical threshold for CH3CO++H˙. The appearance energy of CDO+ from 1‐d‐ethenol was measured as 12.96±0.07 eV, which sets the barrier to isomerization to CH3CDO+˙ at 1121 kJ mol−1. The ionization energy of ethenol was found to be 9.22±0.03 eV.
Reaction gas chromatography/mass spectrometry. 4—structure elucidation of cyclic sulphides by gas chromatography/mass spectrometry with the use of on‐line hydrodesulphurization
Authors: Mikaya A. I. , Trusova E. A. , Zaikin V. G. , Volinsky N. P. , Karaulova E. N. , Gal'Pern G. D. 
Published: May 2005

AbstractA method for structure determination of cyclic sulphides within mixtures is described. It involves the use of a vapour phase hydrodesulphurization micro‐reactor (Raney nickel) located between the chromatographic column and the mass spectrometer (hydrogen and deuterium are used as carrier and reagent gases). A comparative examination of the mass spectra of the cyclic sulphides, as well as of the hydrocarbons and their deuterio analogues (deuterium atoms are bonded to carbon atoms which had been attached to sulphur) derived from the sulphides under the catalytic conditions employed, permits unambiguous determination of the size of the heterocycle and the position of the substituents.
Ortho effects in organic molecules on electron impact. 12—Mechanism of the H2O loss from the molecular ion of 2‐(phenylamino)benzoic acid
Authors: Ramana D. V. , Srinivas R. 
Published: May 2005

AbstractThe mass spectrum of 2‐(phenylamino)benzoic acid is characterized by the presence of the base peak at m/z 195, formed by the expulsion of H2O from the molecular ion. A mechanism for the water loss, involving the COOH and NH functions followed by cyclization leading to the molecular ion of acridone, is proposed based on the study of the substituted derivatives and MIKE spectra.
The generation of triplet methoxy cations
Authors: Burgers Peter C. , Holmes John L. 
Published: May 2005

AbstractThe triplet methoxy cation has been generated in the gas phase by the collision induced charge reversal of methoxy anions. Its heat of formation was estimated to be 1034±20 kJ mol−1, in reasonable agreement with ab initio calculations. 3[H3CO]+ and its isomer [H2COH]+ fragment unimolecularly by loss of H2 via a common transition state and some 60% of the reactant's excess energy appears as translational energy of the products. Large isotope effects are involved in the former's fragmentation. The barrier for the isomerization reaction 3[H3CO]+→[H2COH]+ is small, <20 kJ mol−1. The collision induced dissociation 3[H3CO]+→[H3C]++O proceeds via two reaction channels.
Fragmentation of selected C6H10O isomers: Evidence for a common [C5H7O]+ ion generated by methyl loss from cyclohexene oxide and 5,6‐dihydro‐4‐methyl‐2H‐pyran
Authors: Alai Mehrshid , Rye Robin T. B. 
Published: May 2005

AbstractThe loss of CH3˙ from the molecular ions of cyclohexene oxide and 5,6‐dihydro‐4‐methyl‐2H‐pyran has been investigated. On the basis of metastable peak shape analysis, collision‐induced dissociation/mass‐analysed ion kinetic energy spectra and thermochemical data it is concluded that the same [C5H7O]+ ion is formed in both cases.
Heat of formation for the SH radical by photoionization mass spectrometry
Authors: Traeger John C. 
Published: May 2005

AbstractPhotoionization mass spectrometry has been used to measure the appearance energies for [C2H5]+ from ethanethiol, [C3H7]+ from 2‐propanethiol and [C3H5]+ from 2‐methylthiirane. From the known thermochemistry of these cations and their precursor molecules, a 298 K heat of formation of 138.6±0.4 kJ mol−1 for the SH radical has been derived.
Probing molecular structure by the chemical resolution of hydrogen migrations
Authors: Keough T. 
Published: May 2005

AbstractMethyl chloride chemical ionization mass spectrometry has been used to probe molecular stereochemistry in simple model systems such as cyclic diols and cyclic dicarboxylic acids. The methylation technique, which is based on the chemical resolution of hydrogen migrations, often yields ionic fragments that enable the differentiation of cis and trans isomers. This technique, like protonation methods, fails to differentiate the isomers of 1,2‐cyclohexanediol. However, it does allow differentiation of the isomers of 1,2‐cyclohexanedicarboxylic acid, species that cannot be distinguished via protonation techniques. The utility of methylation in conjunction with MS/MS is also discussed.
Structure determination of [C3H3N2]+ ions, formed from monosubstituted pyrazoles C3H3N2R, by collision‐induced dissociation mass spectrometry
Authors: Van Tilborg M. W. E. M. , Van Thuijl J. 
Published: May 2005

Abstract[C3H3N2]+ ions have been generated under electron impact conditions from some monosubstituted pyrazoles C3H3N2R. Collision‐induced dissociation (CID) mass spectra of deuterium‐labelled precursors suggest that the majority of the [C3H3N2]+ ions formed from 1‐nitro‐ and 4‐bromo‐pyrazole retain their cyclic structure, whereas the ions from 3(5)‐bromopyrazole are mainly linear. This is confirmed by the relative values observed for the overall cross‐sections for CID and for ion loss. An isotope effect of the order of 1.5–1.9 has been found for the collision‐induced loss of H˙ from [C3H3N2]+, generated from 3(5)‐ and 4‐bromopyrazole.
Stereoisomeric fragment ions arising from decomposition of enol cation radicals of different internal energy content
Authors: Weiske Thomas , Halim Herman , Schwarz Helmut 
Published: May 2005

AbstractThe least‐squares analysis of collisional activation mass spectra provides evidence that 1,1‐dihydroxy‐3‐methylbutene cation radical (a) and 1‐hydroxy‐1‐methoxy‐3‐methylbutene cation radical (c) (generated in a McLafferty‐type rearrangement from 2‐isopropyl‐3‐methylbutanoic acid and its methyl ester) give rise to product ions b and d, the stereochemistry of which at the double bond is determined by the lifetime (internal energy) of a and c, respectively. Decompositions of a and c in the ion source yield predominantly the less stable cis‐configurated stereoisomers of b and d, whereas dissociation of a and c at longer lifetimes (lower internal energy) results in the formation of the thermochemically more stable trans isomers of b and d. A qualitative MNDO analysis is provided which takes into account the special features of stereoelectronic control of radical chemistry in the cleavage of a carboncarbon bond.
Basicity of azoles. 5—Experimental gas phase basicities determined by mass spectrometry towards ab initio calculated protonation energies
Authors: Flammang R. , Maquestiau A. , Catalán J. , Pérez P. , Elguero J. 
Published: May 2005

AbstractUsing Cooks' method, the relative gas phase proton affinities of six azoles (imidazole, benzimidazole, pyrazole, indazole, 1‐methylindazole and 2‐methylindazole) have been determined. Ab initio calculations have been carried out for these six molecules and the corresponding cations, thus allowing the determination of protonation energies. Even the correlation between these quantities (‐log K = 0.438+0.0744δΔEp) is far from perfect (r2 = 0.863), the order of basicity is the same. Aqueous basicities, pKa values, are totally uncorrelated.
Unimolecular reactions of ionized methyl acetate and its hydrogen‐rearranged isomers
Authors: Wesdemiotis Chrysostomos , Csencsits Roseann , McLafferty Fred W. 
Published: May 2005

AbstractThe proposed formation of [CH3C(OH)OCH2]+˙ (b) as the intermediate in the isomerization [CH2C(OH)OCH3]+˙ (c)⇄b⇄[CH3COOCH3]+˙ (c has been confirmed by preparation of b from CH3COOCH2OCH3. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH3O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a⇄b and b⇄c must be nearly as high as that for CH3O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH2C(OD)OCH3]+˙ and c–D3 ions confirm this, indicating that the barrier for a⇄b is slightly below that for b⇄c. Minor low‐energy dissociations include losses of CH4 and CH3OH from a and losses of ˙CHO and CH2O from b. Comparison of MI and CAD spectra of a–c with those from [CH3(OH)CH2O]+˙ (d) and [CH3COCH2OH]+˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.
Positive ion–molecule reactions in OCS/hydrocarbon mixtures
Authors: Weil David A. , Platzner I. , Miller Larry L. , Dixon David A. 
Published: May 2005

AbstractThe positive ion–molecule reactions of OCS have been investigated in an ion cyclotron resonance spectrometer. A variety of reactions in OCS/hydrocarbon mixtures have been investigated for various C1C4 hydrocarbons—alkanes, alkenes and alkynes. The formation of organosulfur ions is found in reactions in OCS/hydrocarbon (Cn) mixtures with n <4. Formation of organosulfur ions is observed from hydrocarbon ions reacting with OCS and [OCS]+˙ and S+˙ reacting with the hydrocarbons. The proton affinity of OCS has been determined to be 688.7±8 kJ mol−1 while that of CS2 is measured to be 712.1±8 kJ mol−1. Comparison with the proton affinity of CO2 shows that the proton affinity increases as sulfur is substituted for oxygen.
The use of signal averaging techniques for the quantitation and mass measurement of high molecular weight compounds using fast atom bombardment mass spectrometry
Authors: Grotjahn L. , Taylor L. C. E. 
Published: May 2005

AbstractThe measurement and recording of peak signals at high mass is often difficult and susceptible to a large degree of error. Signal averaging of repetitive scans has been used to improve detection limits and aid nominal mass assignment by peak matching. This is illustrated using glucagon as the reference material to determine the mass of the [MH]+ peak in the molecular ion cluster of Vasoactive Intestinal Peptide, and caesium iodide as reference to mass‐measure a 13‐unit oligonucleotide.
A further structural variation of product yield in collisional activation. Study of CH3S+ from dimethyl disulfide with high precursor ion resolution
Authors: Bursey Maurice M. , Hass J. Ronald 
Published: May 2005

AbstractThe isobaric ions CH332S+ and CH34S+ from dimethyl disulfide were separated and collisionally activated in a four‐sector mass spectrometer. The contributions of minor components to the collisional activation spectrum of the unresolved beam are not correctly predicted from consideration of isotope peak corrections using relative intensities of adjacent peaks in the mass spectrum of CH3SSCH3, because the isobaric components not only have different cross‐sections for fragmentation but also different cross‐sections for transmission of the unfragmented beam through the collision gas. Helium collision spectra of the two components are given.
Mass spectral rearrangements of N‐(4′‐arylthio‐2′‐butynyl) N‐(2″‐arylthio‐2″‐propenyl)‐p‐toluidines, N,N‐bis(2′‐arylthio‐2′‐propenyl)‐p‐toluidines and 1,2‐bis(arylthio)acenaphthenes
Authors: Glaspy P. E. , Hancock R. A. , Thyagarajan B. S. 
Published: May 2005

AbstractUnder electron impact the title compounds display, in addition to the sequential loss of the arylthio groups, the elimination of a bisaryl disulphide moiety, but they do not eliminate sulphur. The behaviour of the p‐toluidine derivatives supports the rearrangement pathway proposed earlier for N,N‐bis(4′‐arylthio‐2′‐butynyl)anilines.
Low‐energy, low‐temperature mass spectra: 4—Saturated alkylamines
Authors: Bowen Richard D. , Maccoll Allan 
Published: May 2005

AbstractElectron impact mass spectra obtained with 12.0 eV ionizing electrons at a source temperature of 350 K are reported for 32 saturated alkylamines. The abundances of molecular ions and primary daughter ions are discussed in energetic terms, and the effects of extending the alkyl chain or methylation of the nitrogen atom are considered. A contrast is found between the spectra of amines and those of the analogous alcohols and ethers.