bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemical ionization mass spectra of chlorine‐substituted aryl‐propio‐ and ‐butyro‐nitriles: Occurrence of an unusual radical‐induced cyclization process
Authors: Madhusudanan K. P. , Seth M. , Bhaduri A. P. 
Published: May 2005

AbstractThe chemical ionization (CI) induced reactions in certain chlorine‐containing aryl‐substituted alkyl nitriles have been studied using different reagent gases including ND3 and CD4 and with the help of collisional activation spectra. A few fragmentations can be explained only on the basis of protonation of or electrophilic attachment to neutral products formed in the CI source. A detailed investigation of the unusual dehalogenation and dehydrohalogenation reactions occurring in some of these molecules has shown that radical‐induced cyclization processes give rise to these ions.
Chemical ionization mass spectrometric characteristics of morphine alkaloids
Authors: Liu Ray H. , Low I. A. , Smith Frederick P. , Piotrowski Edwin G. , Hsu An‐fei 
Published: May 2005

AbstractThe ion‐molecular reaction behavior of ten morphine alkaloids with several commonly used reagent gases are studied under chemical ionization mass spectrometry conditions. These studies emphasize the correlation of the structural characteristics of the 10 alkaloids with the following four mass spectrometric parameters: (i) mass shifts of the protonated ion as a result of replacing ammonia with deuterated ammonia as the reagent gas, (ii) relative tendencies of the adduct ion and the protonated ion to lose molecules of water, (iii) relative intensity ratio of the adduct ion and the protonated ion and (iv) tendency of a compound to undergo a reduction reaction.
Interference to linear superposability of collisionally activated decomposition spectra at high resolution
Authors: Bursey Maurice M. , Hass J. Ronald 
Published: May 2005

AbstractA new factor causing the superposability of collisionally activated decomposition spectra of ions to fail has been established for isobaric ions. If the two isobaric ion beams are not transmitted in their entirety simultaneously to the collision cell, the resulting spectrum is not a linear combination of the two spectra of the individually transmitted complete ion beams. Apparently the energy content of collimated ions varies across the ion beam, so that transmission of different portions of the ion beam produces samples of ions with different energy contents.
An algorithm for estimating the enthalpies of formation of amine molecular ions and immonium fragment ions
Authors: Maccoll Allan 
Published: May 2005

AbstractA method of estimating the enthalpies of formation of amino molecular ions, ΔH⊖ ([CnH2n+1NH2]+˙) and of immonium ions ΔH([CnH2n+1N]+) is reported. It is based on the fact that CH3 is isoelectronic with NH2, CH2 with NH and CH with N. Some calculated values of the enthalpies of formation of amine molecular ions and immonium ions are reported and estimates are made of the accuracy of such calculation.
Stereochemical effects in mass spectrometry. 3—Detection of chirality by chemical ionization mass spectrometry
Authors: Suming Hua , Yaozu Chen , Longfei Jiang , Shuman Xue 
Published: May 2005

AbstractIt was found that the chemical ionization mass spectra of the enantiomers of some α‐amino acids and α‐hydroxy acids could be definitely distinguished when a chiral compound, l‐amyl alcohol, was used as a component of the reagent gases. The relative abundances of some characteristic ions produced through ion‐molecule reactions in the gas phase were much higher in the D isomers than in the L isomers. The results were highly reproducible. This approach proved to be a convenient way for the detection of the chirality of these compounds by chemical ionization mass spectrometry.
Energy deposition in [Fe(CO)5]+˙ upon collision with a metal surface
Authors: DeKrey Michael J. , Kenttämaa Hilkka I. , Wysocki Vicki H. , Cooks R. G. 
Published: May 2005

AbstractCollision of the title ion upon a stainless steel surface at near‐normal incidence leads to deposition of internal energy in a well‐defined narrow distribution. The energy deposited increases with laboratory collision energy and exceeds 7 eV (average) for 100 eV collisions. The translational‐to‐vibrational energy transfer efficiency is 15% (assuming an infinitely massive target) at 25 eV collision energy. Comparison is made with the internal energy distributions associated with gas‐phase collisional activation using both low and high ion kinetic energies. The narrowness of the distribution of internal energies, the easy access to ions excited to different extents, and the high internal energies accessible, make the ion/surface collision process superior to gas‐phase collisional activation for this system.
Gas‐phase protonation of unsaturated ethers: Experimental and theoretical study of 2,3‐and 2,5‐dihydrofuran and related compounds
Authors: Bouchoux Guy , Djazi Faycal , Hoppilliard Yannik , Houriet Raymond , Rolli Eric 
Published: May 2005

AbstractThe protonation of 2,3‐ and 2,5‐dihydrofuran is examined in gas‐phase equilibrium proton transfer reactions conducted in an ion cyclotron resonance spectrometer. The thermodynamically favoured site of protonation in the two compounds is seen to be different: whereas the first isomer forms a carbocation upon protonation, the second isomer protonates on the oxygen atom to form an oxonium ion. The results obtained with substituted derivatives and with linear analogues confirm these conclusions. Molecular orbital calculations on the various structures for protonated bases are performed at the 4–31G level with correction for configuration interaction effects and at the 4–31G* level. The latter basis set provides the best results owing to the introduction of d‐type orbitals on the oxygen atom. The calculation results substantiate the experimental observations and provide details on the molecular structure of the protonated species.
Charge separation reactions of doubly charged benzene ions
Authors: Richardson P. J. , Eland J. H. D. , Lablanquie P. 
Published: May 2005

AbstractPhotoion‐photoion coincidence spectra of benzene and benzene‐d6 photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge‐separation reactions of the [C6H6]2+ ion. Three main groups of ion pairs are related to [C3H3]+ + [C3H3]+, [C2H3]+ + [C4H3]+ and [CH3]+ + [C5H3]+, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C6H6]2+, and subsequent hydrogen loss by the singly charged fragments.
Molecular weight adjustment to probability based matching of unknown mass spectra
Authors: Stauffer Douglas B. , McLafferty Fred W. 
Published: May 2005

AbstractFor an unknown mass spectrum of lower molecular weight, there should be relatively fewer compounds in the reference file giving similar mass spectra. Testing this with the Probability Based Matching (PBM) algorithm, for a specific degree of match a reference compound of low molecular weight has a higher probability of being correct. Modifying the predicted reliability values for such matches statistically improves the overall performance of PBM appreciably at high reliability values.
Rapid characterization of biomaterials by field ionization
Authors: Schulten H.‐R. , Halket J. M. 
Published: May 2005

AbstractThe direct application of field ionization to complex biomaterials is described. Volatiles are characterized by gas chromatography mass spectrometry. Complex involatile materials are investigated by thermal degradation in high vacuum. The methodology and typical analytical features of pyrolysis of biopolymers and soft ionization of their pyrolysates in the high electric field are described. The combination of direct, in‐source pyrolysis mass spectrometry and pyrolysis gas chromatography mass spectrometry is used in two steps. Firstly, for fast profiling of the complex materials and, secondly, for identification of significant products of the controlled thermal degradation process. In particular, temperature programmed/time‐resolved pyrolysis field ionization mass spectrometry has been shown to be an efficient analytical tool as demonstrated for typical examples such as chitin, cellulose, hemicellulose, lignin, wood, peat and coal. Recent results on foodstuffs such as coffee, chocolate, tea and biscuits illustrate the potential of the combined methods for routine work.
Electron impact ionization of unstable enols: H2CCHOH, H2CC(OH)CH3 and H2CC(OH)C2H5
Authors: Iraqi Muhammad , Pri‐Bar Ilan , Lifshitz Chava 
Published: May 2005

AbstractEthenol, 2‐hydroxypropene and 2‐hydroxybutene‐1 were prepared by low‐pressure pyrolysis of cyclobutanol, 1‐methylcyclobutanol and 1‐ethylcyclobutanol, respectively. Mass spectra, ionization energies, appearance energies of metastable ions and kinetic energy releases were determined on a reverse Nier‐Johnson double‐focusing mass spectrometer. Mercury and CH3 radicals from the pyrolysis of dimethylmercury were employed for calibration of the energy scale. The ionization energy of 2‐hydroxybutene‐1 is 8.55 ± 0.1 eV and the appearance energies of [C2H5CO]+ and [CH3CO]+ from that molecule are 10.25 ± 0.1 and 10.40 ± 0.1 eV, respectively. Changes observed in metastable peak shapes for certain fragmentation reactions upon pyrolysis are discussed.
Study of ion structures produced by the reaction of 2‐propyl cations with water and methanol; covalently bound v. Hydrogen‐bridged adducts
Authors: Terlouw Johan K. , Weiske Thomas , Schwarz Helmut , Holmes John L. 
Published: May 2005

AbstractIn contrast to an earlier report,1 the collisonally induced dissociation of protonated 2‐propanol and t‐butyl alcohol yields spectra that are indistinguishable from those of the corresponding [C3H7/H2O]+ and [C4H9/H2O]+ ions generated by the (formal) gas phase addition reactions in a high pressure ion source of [s‐C3H7]+ and [t‐C4H9]+ ions with the n‐donor H2O. Similarly, [s‐C3H7/CH3OH]+ ions generated by both gas phase protonation of n‐ and s‐propyl methyl ethers and addition reactions of [C3H7]+ to CH3OH display mode‐of‐generation‐independent collisionally induced dissociation characteristics. However, analysis of the unimolecular dissociation (loss of propene) of the [C3H7/CH3OH]+ system, including a number of its deuterium, 13C‐ and 18O‐labelled isotopomers, supports the idea that prior to unimolecular dissociation, covalently bound [C3H7‐ O(H)CH3]+ ions intercovert with hydrogen‐bridged adduct ions, analogous to the behaviour of the distonic ethene‐, propene‐ and ketene‐H2O radical cations.
Neutralization‐reionization mass spectrometry (NRMS). Structural information from vertical neutralization and reionization efficiencies
Authors: Wesdemiotis Chrysostomos , Feng Rong , Williams Evan R. , McLafferty Fred W. 
Published: May 2005

AbstractThe neutralization‐reionization mass spectra of alkane radical ions indicate significant differences between the structures and geometries of alkane molecules and their molecular ions, confirming recent ab initio predictions. Ionic isomers that are indistinguishable by collisionally‐activated dissociation because of easy interconversion can be characterized by neutralization‐reionization if the corresponding neutrals show different reactivities, as is demonstrated for the [C2H5]+/C2H5˙ system and for [C2H4O2]+˙ isomers. For identification of mixtures of more than one neutral species, the relative efficiency for reionizing each neutral must be determined; e.g. the O2 reionization efficiency of ˙CH2OH radicals is ∼4 times greater than that of CH3O˙. This information and reference reionization spectra of CH3O˙ and ˙CH2OH show that metastable or collisionally activated methyl acetate cations lose CH3O˙, not ˙CH2OH as previously reported; the newly‐formed CH3O˙ undergoes partial (∼20%) isomerization to ˙CH2OH in the ∼10−6s before reionization. Similar results are obtained for [B(OCH3)3]+˙.
Mass spectral behavior of n‐alkynes
Authors: Mercer Roger S. , Harrison Ale X. G. 
Published: May 2005

AbstractThe 70 e V‐electron impact mass spectra of the C7–C10 n‐alkynes have been determined as well as the metastable ion spectra of the molecular ions and the [CS2]+ and [N2O]+ charge exchange mass spectra of the C7‐C9 n‐alkynes. The metastable ion mass spectra provide only a limited opportunity to distinguish between isomers; however, the 70‐eV EI mass spectra of isomeric compounds permit a ready distinction between isomers. The [CS2]+ charge exchange mass spectra of isomeric compounds also show substantial differences. The [N2O]+ charge exchange mass spectra do not show the enhancement of β‐fission fragments observed in field ionization experiments, despite representing ions of similar internal energy, and it is concluded that field dissociation is responsible for the β‐fission fragments in the field ionization experiments.
Tandem mass spectrometry of organophosphate and carbamate pesticides
Authors: Hummel Susan V. , Yost Richard A. 
Published: May 2005

AbstractWe present tandem quadrupole mass spectrometric data for 26 organophosphate and 16 carbamate pesticides. These data are of use in developing methods for screening samples for specific compounds (by selected reaction monitoring) or specific classes of compounds (by parent scans and neutral loss scans). Optimization of tandem mass spectrometry conditions for maximum sensitivity is also described.
Structures and relative energies of gas‐phase [C2H7N]+˙ radical cations
Authors: Yates Brian F. , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital calculations with split‐valence plus polarization basis sets and incorporating electron correlation and zero‐point energy corrections have been used to examine possible equilibrium structures on the [C2H7N]+˙ surface. In addition to the radical cations of ethylamine and dimethylamine, three other isomers were found which have comparable energy, but which have no stable neutral counterparts. These are \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3} $\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm }, $\end{document} with calculated energies relative to the ethylamine radical cation of −33, −28 and 4 kJ mol−1, respectively. Substantial barriers for rearrangement among the various isomers and significant binding energies with respect to possible fragmentation products are found. The predictions for \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^. {\rm H}_{\rm 2} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^ + {\rm H}_{\rm 3} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm H}\mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 3}$\end{document} are consistent with their recent observation in the gas phase. The remaining isomer, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm N}\limits^{\rm + } {\rm H}_{\rm 2} \mathop {\rm C}\limits^{\rm .} {\rm H}_{\rm 2} {\rm },$\end{document}is also predicted to be experimentally observable.
Fragmentations of protonated acetophenones via intermediate ion–molecule complexes
Authors: Filges U. , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractProtonated acetophenones, substituted with a methoxymethyl group in the para and meta positions, have been generated by electron impact induced fragmentation of the correspondingly substituted 2‐phenylpropan‐2‐ols. The metastable ions, formed in the second field‐free region of a VG ZAb 2F mass spectrometer, react unimolecularly by elimination of CH3OH, formation of CH3CO+ and magnified image ions, loss of CH3COOCH3, and loss of CH2O. The mechanisms of these fragmentations have been elucidated with the aid of deuterated analogues of the protonated acetophenones. It is shown that these reactions are initiated by an endothermic transfer of the proton at the carbonyl group of the protonated acetophenones to the benzene ring. A further migration of the proton to the ether O atom of the methoxymethyl side‐chain leads eventually to the elimination of CH3OH. Protolytic bond cleavages of either side‐chain gives rise to the CH3CO+ and magnified image ions. At low internal energies both these ions may be trapped by the aromatic neutral fragment in ion‐molecule complexes. Reactions within these complexes result in the energetically favourable losses of CH3COOCH3 and CH2O, respectively. With respect to these reactions, the protonated acetophenones behave analogously to the correspondingly substituted and protonated benzaldehydes.
A mass spectrometric study of the dimethyl ester trimethylsilyl enol ether derivatives of some 3‐oxodicarboxylic acids
Authors: Svendsen John S. , Whist Jon E. , Sydnest Leiv K. 
Published: May 2005

AbstractThe fragmentation pathways for the dimethyl ester trimethylsilyl enol ether derivatives of some 3‐oxodicarboxylic acids have been found by using B/E and B2/E linked scans, collisional activated decomposition and isotope substitution techniques. The trimethylsilyloxy group strongly directs the decomposition processes, and induces a fragmentation pattern that intimately reflects the structure of the compounds.
The mass spectrometric behaviour of benzohydroxaraic and benzothiohydroxamic acids under electron impact
Authors: Florěncio M. H. , Heerma W. , Santos M. A. , Tavares M. R. , Lobo A. M. , Prabhakar S. 
Published: May 2005

AbstractPrimary fragmentation reactions in benzohydroxamic and benzothiohydroxamic acids have been studied and compared with those in benzamides and benzothioamides. Mass‐analysed ion kinetic energy spectra, collisional activation spectra and spectral data from labelled compounds were used to elucidate fragment ion structures and reaction mechanisms. The mass spectra are shown to be dependent on ion source temperature. Losses of O and H2O are proved to be thermal in origin. The formation of an S… HO bond, which is analogous to an intramolecular hydrogen bond in solution chemistry, directs many fragmentation pathways. This seems to be the major factor determining the differences between the mass spectra of benzothiohydroxamic acids and those of the corresponding carbonyl compounds.
Charge exchange and charge separation processes of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications
Authors: March Raymond E. 
Published: May 2005

AbstractThe charge exchange and charge separation processes of a series of [C3Hn]2+ and [C3Dn]2+ (n = 1–6) dications have been investigated experimentally in a mass spectrometer of reversed geometry. The relative reaction cross‐sections for charge exchange with nitrogen exhibited a 20‐fold variation which has implications for the interpretation of 2E spectra with respect to dication relative intensities. Charge separation resulting in deprotonation was observed for all [C3Dn]2+ species investigated, while de‐deuteronation was observed for [C3Dn]2+ (n = 1–4) only. Intercharge separations calculated from the observed ion kinetic energies released upon charge separation suggest linear structures for [C3Dn]2+ and [C3Dn]2+ (n = 1–2) and cyclic structures for [C3Dn]2+ (n = 3–6) and [C3Dn]2+ (n = 3–4).
Ion‐neutral complex‐mediated hydrogen exchange in ionized n‐butanol: A mechanism for ‘non‐specific’ hydrogen migrations
Authors: McAdoo David J. , Hudson Charles E. 
Published: May 2005

AbstractWater elimination from ionized n‐butanol reflects near randomization of all hydrogens in ions decomposing after ∼10−5s. This probably takes place in ion‐neutral complexes by formation of a cyclobutane ion–H2O complex and/or rearrangement within [C4H8]+˙ in open‐chain [C4H8+˙H2O] complexes, in either case accompanied by hydrogen exchange between water and open‐chain hydrocarbon moieties. Extensive hydrogen rearrangements in which restraints on conventional transition‐state ring size have little apparent influence may generally be ion–neutral complex‐mediated processes.
Mechanism of reduction of double bond under chemical ionization conditions
Authors: Madhusudanan K. P. , Murthy V. Sreenivas , Fraisse D. 
Published: May 2005

AbstractThe mechanism of double bond reduction occurring in certain conjugated ketones, nitriles, acids and esters under chemical ionization conditions has been studied. The results indicate that the hydrogen radicals present in the chemically ionized plasma are responsible for the reduction of the double bond. This is further supported by experiments with radical traps.
Negative chemical ionization mass spectrometry of phenols, and their determination in acidic fractions of coal‐derived liquids
Authors: Strachan Michael G. , Anderson Geoffrey B. , Porter Quentin N. , Johns R. B. 
Published: May 2005

AbstractThe use of Freon–113 as a reagent gas in the negative chemical ionization mass spectra of phenolic compounds is reported. The dominant mode of ionization is by chloride attachment producing [M + Cl]− ions. The application of this technique to the highly phenolic acid fractions from coal‐derived liquids gives spectra containing essentially only [M + Cl]− peaks. This allows relative molecular mass profiles to be obtained. The resultant complex spectra are simplified by dividing them into their homologous series components. Since this is a low‐resolution technique, absolute component identification cannot be made; but in conjunction with other analytical methods, tentative identification of series of molecules is possible. Thus, the alkyl‐substituent ranges of the different homologous series can be assessed. Comparisons between coal‐derived liquids produced under different reaction conditions are made, and composition differences detected.
Electron impact mass spectra of some anthracene, anthrafuran and nitroanthrafuran derivatives. A tandem mass spectrometric collisional activation dissociation study
Authors: Sellier Nicole , Cazaussus Annie , Bilger Christine , Demerseman Pierre 
Published: May 2005

AbstractThe 70‐eV electron impact mass spectra of a series of thirty anthracene, seven anthra[2,1‐b]furan and seven 2‐nitroanthra[2,1‐b]furan derivatives are described and discussed. A collisional activation dissociation study of 1‐formyl‐2,6‐dimethoxy‐9‐methyianthracene, 1‐formyl‐2,6‐dimethoxy‐10‐methylanthracene, and 2‐carboxy‐11‐methylanthra[2,1‐b]furan has been carried out using tandem mass spectrometry in order to substantiate the fragmentation schemes.
Mechanism of the [C7H7]+ ion formation in the electron impact induced fragmentation of 3‐dimethylamino‐1‐phenylpropanone (Mannich's base)
Authors: Srzić D. 
Published: May 2005

AbstractThe genesis of the [C7H7]+ ion in the mass spectrum of 3‐dimethylamino‐1‐phenylpropanone (Mannich's base) hydrochloride has been studied by 13C and deuterium labelling and by application of metastable transitions. It has been shown that this ion is formed from [M − OH]+, involving non‐adjacent carbon atoms.
Mass spectral fragmentation pathways in reduction metabolites of 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene. A tandem mass spectrometric collision induced dissociation study
Authors: Yinon Jehuda 
Published: May 2005

AbstractA collision induced dissociation study of a series of reduction metabolites of 2,4‐dinitrotoluene and 2,4,6‐trinitrotoluene was carried out using a tandem BB mass spectrometer. Fragmentation pathways of the metabolites were determined in the electron impact mode. It was found that the dominant fragmentation pathway is loss of OH˙ due to an ortho effect. Other fragmentation routes include loss of NO2˙ and loss of CH2N˙.