bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation and structure of [C8H8O]+˙ ions, generated from gas phase ions of phenyl‐cyclopropylcarbinol and 1‐phenyl‐1‐(hydroxymethyl)cyclopropane
Authors: Dallinga J. W. , Nibbering N. M. M. , Louter G. J. 
Published: May 2005

AbstractThe structure and formation of [C8H8O]+. ions generated from phenylcyclopropylcarbinol and 1‐phenyl‐1‐hydroxymethylcyclopropane upon electron impact, have been studied using kinetic energy release measurements, by determination of ionization and appearance energies and by collisional activation. It is shown that the non‐decomposing [C8H8O]+˙ ions have exclusively the structure of the enol ion of phenylacetaldehyde, although it is less stable than the enol ion of acetophenone by about 45 kJ mol−1. This has been interpreted as an indication that the [C8H8O]+˙ ions from phenylcyclopropylcarbinol are formed by an attack of either the phenyl ring or the hydroxyl group upon the C‐1C‐2 (or C‐1C‐3) bond of the cyclopropane ring under a simultaneous expulsion of ethene and migration of the attacking group to the C‐1 position. The [C8H8O]+˙ ion from 1‐phenyl‐1‐(hydroxymethyl)cyclopropane is formed by opening of the cyclopropane ring via a benzylic cleavage. A kinetically controlled hydrogen shift in the resulting ring opened ion prior to or during ethene loss then leads to the formation of [C8H8O]+˙ ions which have the structure of the enol ion of phenylacetaldehyde.
Mass spectra of some β‐keto esters. A high resolution study
Authors: Moldovan Zaharie , Palibroda Nicolae , Mercea Victor , Mihǎilescu Gheorghe , Chiriac Maria , Vlasa Mircea 
Published: May 2005

AbstractThis paper presents low and high resolution mass spectra as well as fragmentation processes under electron impact for methyl, ethyl and propyl‐pivaloyl acetate. The fragmentation patterns have been established using elemental compositions of ions determined by high resolution, metastable transitions and deuterium labelling.
Deuterium labelling and thermochemical studies of dissociative ionization of methyl substituted monosilacyclobutanes. Ring expansion in the molecular ion of 1,1,3‐trimethyl‐1‐silacyclobutane
Authors: Gusel'nikov L. E. , Volkova V. V. , Tarasenko N. A. , Tishenkov A. A. , Zaikin V. G. , Eremina E. I. , Nametkin N. S. 
Published: May 2005

AbstractDissociative ionization of 1,1‐dimethyl‐1‐silacyclobutane, 1,1‐bis(trideuteromethyl)‐1‐silacyclobutane, 1,1,3‐trimethyl‐1‐silacyclobutane, 1,1‐bis(trideuteromethyl)‐3‐methyl‐1‐silacyclobutane and 1,1,2‐trimethyl‐1‐sila‐cyclobutane have been studied. Low energy electron impact fragmentation of 1,1‐bis(trideuteromethyl)‐3‐methyl‐1‐silacyclobutane results mainly in the loss of ethene with the involvement of the C‐methyl group from the rearranged molecular ion. No fragment ions indicating rearrangement of the molecular ion have been detected in mass spectra of 1,1‐bis(trideuteromethyl)‐1‐silacyclobutane. The ionization energies for 1,1,3‐trimethyl‐1‐silacyclobutane, 1,1,2‐trimethyl‐1‐silacyclobutane and 1,1‐dimethyl‐1‐silacyclopentane, and also the appearance energies for the [M − 28]+˙ and [M − 42]+˙ ions, have been measured by photoioniza‐tion mass spectrometry. The heats of formation of these ions and of 1,1,3‐trimethyl‐1‐silacyclobutane and 1,1‐dimethyl‐1‐silacyclopentene molecules have been calculated as have the enthalpies of the transformation processes.
Ion cyclotron resonance studies of ambident nucleophiles. The reactions of the trimethylsilyl cation with alkenyl ethers and alkoxy ketones
Authors: Dottore Marie F. , Trenerry V. Craige , Stone David J. M. , Bowie John H. 
Published: May 2005

AbstractAlkenyl ethers react through oxygen with Me3Si+ to yield intermediates which undergo characteristic fragmentations. In the particular case of allyl ethers, the decomposing adduct undergoes several fragmentations through the allyl substituent via 6‐membered transition states. The reaction between Me3Si+ and alkoxy carbonyl derivatives yields both ‘ether’ and ‘keto’ adducts, characterized by their fragmentation patterns. The ‘ether’ adducts formed from Me3Si+ and alkoxy acetones undergo the same basic eliminations as those observed for the allyl ether/Me3Si+ systems.
Gaseous alkyne ions
Authors: Wagner‐Redeker Winfried , Levsen Karsten , Schwarz Helmut , Zummack Waltraud 
Published: May 2005

AbstractUsing the relative abundance of metastable ions, collisional activation spectra, field ionization kinetic measurements, isotopic labelling, appearance energy and kinetic energy release data, it is shown that linear alkyne radical cations with more than six carbon atoms do not isomerize to equilibrating structures prior to decomposition. At the shortest ion lifetimes the molecular ions of linear alkynes decompose mainly by simple β‐bond fission which allows an unequivocal localization of the triple bond. At medium ion lifetimes fragmentation occurs predominantly via a McLafferty rearrangement, while at long ion lifetimes competing alkyl losses prevail. These alkyl losses occur via cyclic intermediates leading to thermochemically stable cycloalkenyl ions. All these reactions occur with a high specificity with respect to the carbon and hydrogen atoms involved and are preceded by little or no hydrogen exchange reactions.
Mass spectrometry of pyrazolium salts
Authors: Pande Umesh C. , Egsgaard Helge , Larsen Elfinn , Begtrup Mikael 
Published: May 2005

AbstractA series of pyrazolium bromides were investigated by field desorption, field ionization and electron impact mass spectrometry. Dealkylation was found to be the predominant thermal decomposition. The nature of the substituents controls the pyrazole formed. The application of field ionization was found to facilitate the interpretation of the thermolytic decomposition products. Field ionization and electron impact mass spectra of N‐phenylpyrazole and N‐benzylpyrazole were obtained.
Effect of protonation exothermicity on the reaction of gaseous Brønsted acids with halobenzene derivatives
Authors: Liauw Wie Giap , Lin Margaret S. , Harrison Ale X. G. 
Published: May 2005

AbstractThe protonation of haloaromatics by [N2H]+ and [CO2H]+ has been studied by chemical ionization mass spectrometry. In general, the fragmentation reactions following protonation by [CO2H]+ are similar to those observed following protonation by [CH5]+, while the fragmentation reactions induced by protonation by [N2H]+ are intermediate between those observed on reaction with [CH5]+ and with [H3]+. These results are consistent with the conclusion that the fragmentation mode is determined by the protonation exothermicity since the proton affinity of CO2 is the same as that of CH4 while the proton affinity of N2 is intermediate between that of CH4 and H2.
Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivatives
Authors: Liauw Wie Giap , Harrison Alex G. 
Published: May 2005

AbstractThe site of protonation in the reaction of gaseous Brønsted acids with chlorobenzene and fluorobenzene derivatives has been examined using deuterium labelling of chlorobenzene and deuterated reagent gases (D2 and N2/D2). In the protonation of chlorobenzene by [H3]+ ∼30% of the [MHHCl]+ fragment ions arise from a chlorine‐protonated species while ∼70% arise from a ring‐protonated species in which complete hydrogen scrambling has occurred. In the reaction of [N2H]+ with chlorobenzene ∼75% of the fragment ions arise from the chlorine‐protonated form with ∼25% arising from the ring‐protonated form of [MH]+. By contrast fluorobenzene fragments almost entirely from the fluorine‐protonated form. Similar results are obtained for dihalobenzenes. The mechanistic implications are discussed.
An electron impact study of HCN elimination from indole by use of 13C labelling
Authors: Corval Madeleine 
Published: May 2005

AbstractThe study of the loss of HCN from the molecular ions of [2‐13C]indole and [3‐13C]indole shows that, to a good approximation, only the two carbon atoms of the pentagonal ring are involved in this fragmentation process, contrary to the behaviour of the H atoms; the C‐2 atom is eliminated predominantly, chiefly in the ion source (85–90%) and a little less in the metastable energy range (75–80%). The losses of 13CCH3˙ and C2H3˙ from the [MH12CN]+˙ ions of the two compounds suggest the occurrence of different structures, providing evidence for several mechanisms of HCN elimination.
Mass spectra of heterocyclic compounds: V—dihydro‐1,3,5‐dioxazines
Authors: Corral René A. , Orazi Orfeo O. , Zinczuk Juan 
Published: May 2005

AbstractN‐Substituted dihydro‐1,3,5‐dioxazines show a general fragmentation pattern supported by metastable ions, exact mass measurements and deuterium labelling. There are two well‐defined pathways: one is initiated by elimination of the N‐substituent and the other by loss of a hydrogen atom from the heterocyclic ring.
Mass spectral cycloreversion reactions of 2‐chloro‐3,6‐diaryl‐3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides
Authors: Gogte V. N. , Kulkarni P. S. , Modak A. S. , Tilak B. D. 
Published: May 2005

AbstractThe mass spectral fragmentation modes of various 2‐chloro‐3,6‐diaryl‐3,4‐dihydro‐1,3,2‐oxazaphosphorin‐2‐oxides—a novel ring system—reveal cycloreversion by two pathways. Retro Diels‐Alder reaction by a stepwise mechanism is prominent in this system. The relative abundances of the enone and dienophile ions depend on the nature of the substituent attached to the double bond in this ring. Another retro Diels‐Alder fragmentation process, involving the loss of PO2Cl from the molecular ion, is preceded by a 1,3‐allylic rearrangement and is the major fragmentation mode in the metastable time scale. Further fragmentation of the [MPO2Cl]+ imine ion seems to occur from cyclic dihydroquinoline intermediates by substitution elimination steps.
Doubly charged benzene and isomeric dications. Fragmentation energetics and charge distributions calculated by MINDO/3 molecular orbital theory
Authors: Bentley T. William , Wellington C. Anthony 
Published: May 2005

AbstractMINDO/3 calculations for singlet and triplet doubly charged benzene [C6H6]2+ are in satisfactory agreement with the experimentally determined values of the vertical double ionization energy of benzene; calculations for straight chain isomeric structures are consistent with the observed kinetic energy release on fragmentation to [C5H3]+ and [CH3]+. Symmetrical doubly charged benzene ions relax to a less symmetrical cyclic structure having sufficient internal energy to fragment by ring opening and hydrogen transfer towards the ends of the carbon chain. Fragmentation of [CH3C4CH3]2+ to [CH3C4]+ and [CH3]+ is a relatively high energy process (A), whereas both (B): [CH3CHC3CH2]2+ to [CHC3CH2]+ and [CH3]+ and (C): [CH3CHCCHCCH]2+ to [CHCCHCCH]+ and [CH3]+ may be exothermic processes from doubly charged benzene. Furthermore, the calculated energy for the reverse of process (A) is less than the experimentally observed kinetic energy released, whereas larger energies for the reverse of processes B and C are predicted. Heats of formation of homologous series [HCn]+, [CH3Cn]+, [CH2Cn−2CH]+, [CH3Cn−2CH2]+ and [CH2CHCn−3CH2]+ with 1 < n < 6 are calculated to aid prediction of the most stable products of fragmentation of doubly charged cations. The homologous series [CH2Cn−2CH]+ is relatively stable and may account for ready fragmentation of doubly charged ions to [CnH3]+; alternatively the symmetrical [C5H3]+ ion [CHCCHCCH]+ may be formed. Dicoordinate carbon chains appear to be important stabilizing features for both cations and dications.
Collisional activation mass spectra of ions containing polyisotopic elements
Authors: Todd Peter J. , Barbalas Michael P. , McLafferty Fred W. 
Published: May 2005

AbstractIf a mass selected ion containing multiple isotopes of an element fragments by loss of a neutral containing the element, the product ions will be observed as multiple peaks. This ‘isotopic cluster’ of peaks, although of a different appearance than those found in normal mass spectra, also indicates the isotopic composition of the precursor ion.
Electron impact mass spectrometry of 3‐cyclohexen‐1‐ol and related compounds
Authors: Braem Daniel , Siles Samuel , Gülaçar Fazil O. , Buchs Armand 
Published: May 2005

AbstractThe electron impact mass spectrum of 3‐cyclohexen‐1‐ol has been studied, especially with regard to the retro Diels‐Alder reaction. Six deuterium labelled analogues and two dimethyl substituted homologues were synthesized. Contrary to what we have observed with 2‐cyclohexen‐1‐ol, the double bond migration which precedes the retro Diels‐Alder reaction plays a minor role.
Consecutive reactions arising from the molecular ions of 14α‐equilenin and 14β‐isoequilenin
Authors: Proctor C. J. , Larka E. A. , Zaretskii Z. V. I. , Beynon J. H. 
Published: May 2005

AbstractIt is shown that two configurational steroidal isomers, 14α‐equilenin and 14β‐isoequilenin, may be easily distinguished by the unimolecular mass analysed ion kinetic energy spectra of their corresponding molecular ions. Furthermore, many of the peaks in these spectra are found to be due to consecutive reactions, whereby product ions of an initial reaction are themselves reactive and can undergo further fragmentation. In each of these cases, the individual steps of the reaction sequence have been separated in the different field free regions of a reversed geometry, double focusing mass spectrometer. Isotopic labelling with 18O in the 17‐position has also helped to clarify reaction sequences.
‘Fast atom bombardment’—A rediscovered method for mass spectrometry
Authors: Devienne F. Marcel , Roustan Jean‐Claude 
Published: May 2005

AbstractIn 1966, Devienne and co‐workers studied extensively the sputtering of various target materials by a high energy molecular beam obtained by charge exchange. They obtained secondary ions that characterized for instance, organic and biological materials. These ions were analysed by mass spectrometry. This method was developed to be patented and many devices were studied. The principle of the apparatus constructed is very simple. An ion source produces an ion current of some microamperes. The ions are accelerated at some keV, and injected into a collision chamber in order to obtain a neutral beam by resonant charge exchange. The residual ions are deflected and this beam bombards the target. The target itself is surrounded by a small metal cylinder which is held at an appropriate potential to extract the positive or negative secondary ions formed. The ion beam is accelerated and focused into the entrance slit of a mass spectrometer. After the first devices, two types of apparatus were built in 1973 and 1975. With the first one, the analysis of the masses was obtained only by an electromagnet. The energy range of the secondary ions varied from 1 to 10 keV. The second apparatus was formed by an electromagnet, a dissociation chamber, and an electrostatic analyser. With this apparatus, it was possible to measure directly masses as large as 6000 daltons. With the first apparatus it was possible to study the adsorption of oxygen on silicon, and to obtain spectra, of many organics such as camphor, nitrodiphenylamine and, as in the earlier device, the spectrum of a non‐volatile organic liquid diethylhexyl azelate, was obtained. After studies on different uranium compounds and their dissociations, the second apparatus was devoted to the formation and study of the chemical properties of clusters.
Electron impact mass spectrometry of 2,2‐disubstituted‐1,3‐benzoxathioles and spiro [1,3‐benzoxathioles‐2,1′‐cycloalkanes]
Authors: Traldi Pietro , Vettori Umberto , Maccioni Antonio , Podda Gianni 
Published: May 2005

AbstractThe electron impact mass spectrometric behaviour of a series of 2,2‐disubstituted‐1,3‐benzoxathioles and spiro[1,3‐benzoxathioles‐2,1′‐cycloalkanes] has been studied in detail with the aid of linked scans and exact mass measurements. The structures of the more interesting fragment ions have been confirmed by collisional activation experiments. A precise analogy with the chemical degradative processes, obtained by the action of Grignard reagents on these compounds, is emphasized.
Mass spectrometry of allyloxy di‐ and trimethylsilanes
Authors: Steele Kent P. , Weber William P. 
Published: May 2005

AbstractThe mass spectra of allyloxydimethylsilanes and allyloxytrimethylsilanes were examined. Isotopic labelling and metastable peaks support the proposed fragmentation patterns. Siliconium ions dominate the spectra. Loss of neutral fragments from [M—15]+ and [M—1]+ ions is important. These fragmentation patterns are discussed in terms of interaction of siliconium ions with the carbon‐carbon double bond of the allyloxy ligand. Increased substitution on the allyloxy ligand apparently decreases the interaction of siliconium ions with the carboncarbon double bond.
On the nature of the ‘methoxy’ cation
Authors: Bouma Willem J. , Nobes Ross H. , Radom Leo 
Published: May 2005

AbstractAb initio molecular orbital calculations with large, polarization basis sets and incorporating valence‐electron correlation have been used to investigate the structure of the [COH3]+ ion formed at threshold from fragmentation of dimethyl ether in the mass spectrometer. The results indicate that this ion is the hydroxymethyl cation, [CH2OH]+, formed with excess energy in a two‐step rearrangement‐dissociation process involving an initial 1,2‐hydrogen shift in the dimethyl ether radical cation to yield an oxonium ion intermediate, [CH2OHCH3]+˙, followed by CO bond cleavage. The intermediate oxonium ion is predicted to lie slightly lower in energy than the dimethyl ether radical cation and represents a stable, previously unreported [C2H6O]+˙ isomer. It is suggested that at high energies, decomposition of the dimethyl ether radical cation involves dissociation followed by rearrangement.
The mass spectra of some tris(trimethylsilyl)acylsilanes and tris(trimethylsilyl)silanes
Authors: Brook Adrian G. , Harrison Alex. G. , Kallury R. Krishna M. R. 
Published: May 2005

AbstractWhile tris(trimethylsilyl) alkanoylsilanes fragment in the acylsilane form yielding [(Me3Si)3SiCO]+ by α‐cleavage, the molecular ions of their aryl counterparts rearrange to ionized silaethenes prior to cleavage, paralleling known photochemical behaviour. Sila‐allyl type structures are attributed to the stable [MMe˙]+ ions obtained by subsequent cleavage. Metastable ion characteristics reveal the identity of the structures of the monomeric silaethene ions obtained from one of the aroylsilanes and a 1,2‐disilacyclobutane. The non‐compliance of the alkanoylsilanes with their photochemical behaviour is attributed to a preferred elimination of the stable alkyl radical (R˙) from the molecular ions. Several polysilanes display abundant odd‐electron ions which may possess a disilene structure.
The vinyloxonium cation, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 2} = {\rm CH - }\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}, a stable [C2H5O]+ species in the gas phase
Authors: Burgers Peter C. , Terlouw Johan K. , Holmes John L. 
Published: May 2005

AbstractThe charge stripping mass spectra of [C2H5O]+ ions permit the clear identification of four distinct species: \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} - {\rm O - }\mathop {\rm C}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} - \mathop {\rm C}\limits^{\rm + } {\rm H - OH}$\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 2} = {\rm CH - }\mathop {\rm O}\limits^{\rm + } {\rm H}_{\rm 2}$\end{document}. The latter, the vinyloxonium ion, has not been identified before. It is generated from ionized n‐butanol and 1,3‐propanediol. Its heat of formation is estimated to be 623±12 kJ mol−1. The charge stripping method is more sensitive to these ion structures than conventional collisional activation, which focuses attention on singly charged fragment ions.
Rearrangements and fragmentations of phenyl styryl sulfides: 2—labelling studies
Authors: Dijkstra P. J. , Weringa W. D. 
Published: May 2005

AbstractMetastable molecular ions of phenyl styryl sulfides may decompose by loss of CH3˙, SH˙, CHS˙, C6H5˙, C6H6 or C7H7˙. Labelling with carbon‐13 and deuterium gave information about the mechanisms of these reactions. It appears that extensive rearrangements occur prior to most of these fragmentations. In the case of phenyl β‐styryl sulfide both phenyl groups and both vinyl carbon atoms are found in the C7H7 fragment in comparable amounts. For phenyl α‐styryl sulfide this fragmentation leads more specifically to the loss of the S‐phenyl group and the β‐vinyl carbon atom. It was concluded that rearrangements occur, partly via symmetric diphenyl ethene sulfide structures, to benzyl phenyl thione ions, from which the fragmentation occurs. For the loss of CHS˙ an earlier proposed mechanism was confirmed. From both compounds the S‐phenyl ring can be lost as C6H5˙ or C6H6 as well as the C‐phenyl ring. Fragmentation occurs from one of the initial structures as well as from benzyl phenyl thione. Loss of CH3˙ is thought to occur after ring closure with formation of dihydrobenzo[b]thiophenes followed by ring opening by rupture of a CS bond. While phenyl β‐styryl sulfide shows a strong tendency towards isomerization to a symmetric structure like 1,2‐diphenylethene sulfide, phenyl α‐styryl sulfide easily rearranges in an electrocyclic reaction with formation of benzyl phenyl thione.
Electron impact mass spectra of chlorinated methyl propanoates
Authors: Korhonen Ilpo O. O. 
Published: May 2005

AbstractThe mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3‐dichloropanoate (38%). In most cases α‐cleavage gives the base peak [COOCH3]+, and the loss of a chlorine atom from the molecular ion is characteristic of the 3‐chloro, 3,3‐dichloro and 3,3,3‐trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH3OH, CH2CO, CO2 and CO from the [MCl]+ ion. α‐Cleavage and the loss of Cl˙ gives an intense [MCOOCH3Cl]+˙ peak, which is the base peak in the spectra of the 2,3‐dichloro and 2,3,3‐trichloro compounds.
Ortho, Effects in organic molecules on electron impact: X—unusual ortho effects of the methyl group in o‐picolinotoluidide
Authors: Ramana D. V. , Sundaram N. 
Published: May 2005

AbstractThe mass spectrum of o‐picolinotoluidide gives rise to three major fragments at m/z 184, m/z 169 and m/z 168, corresponding to the loss of CO from the molecular ion followed by the loss of ṄH2 and ĊH3 by independent pathways. It has been shown that the ortho methyl group and the nitrogen of the pyridine ring in the 2‐position are involved in the formation of these three major fragments observed in the mass spectrum of o‐picolinotoluidide. The mass spectrum of 2‐(o‐toluidino) pyridine, the molecular ion of which can resemble the [MCO]+ ion in o‐picolinotoluidide, also shows loss of CH3 and NH2 radicals from the molecular ions. Based on these observations coupled with the high resolution data, the mass analysed ion kinetic energy spectrometry and high voltage scans of these fragments in both the compounds, two mechanistic pathways have been proposed for the formation of these ions in o‐picolinotoluidide.