bluuebunny/crossref_metadata_2025_split huggingface dataset:
Appearance energies and the kinetic shift. Loss of HCN from the benzonitrile molecular ion
Authors: Baldwin Michael A. 
Published: May 2005

AbstractMeasurement of the appearance energy of the [C6H4]+⋅ ion from benzonitrile molecular ions fragmenting in the second field free region of a reverse geometry double focusing mass spectrometer, gives a value free of any significant kinetic shift. The heat of formation of the [C6H4]+⋅ ion calculated using this appearance energy is 1348 kJ mol−1, which is consistent with the ion having the benzyne structure.
On the loss of ethylene from [C3H7O]+ ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {{\rm CHOH}}\limits^{\rm + } $\end{document}
Authors: Holmes John L. , Rye R. T. B. , Terlouw J. K. 
Published: May 2005

AbstractThe results of some 3C and 2H labelling experiments plus some measurements of reaction thermochemistry and translational energy releases, permit a significant simplification of the mechanistic pathways by which [C3H7O]+ ions of structure
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fragment by loss of C2H4. The relationships between these ions and some of their isomeric forms are explored and clarified.
Oxygen equilibration in the electron impact mass spectra of aryl esters and carbamates
Authors: Rowe Jeffrey E. 
Published: May 2005

AbstractThe positional integrity of an 18O label is partially lost in the molecular ion in the electron impact mass spectra of 4‐methylphenyl benzoate, 4‐methylphenyl 4‐nitrobenzoate and 4‐methylphenyl N,N‐dimethylcarbamate.
The mechanism of elimination of an H2O molecule in desmethylencecalin under electron impact
Authors: Nakayama Mitsuru , Eguchi Shizuko , Hayashi Shûichi , Tsukayama Masao , Nakata Hisao 
Published: May 2005

AbstractThe mass spectrum of desmethylencecalin has been measured and a fragmentation mechanism for the loss of a water molecule from the [MCH3]+ ion is proposed on the basis of isotope labelling and metastable peak observations. The eliminated water has been shown to involve the carbonyl oxygen and hydrogen atoms of the hydroxyl and acetyl groups.
The ‘even‐electron rule’
Authors: Karni Miriam , Mandelbaum Asher 
Published: May 2005

AbstractMany (>170) exceptions to the ‘even‐electron rule from the literature (unrecognized in most cases) and from the authors’ laboratory are presented and discussed. The large number of violations suggests that although the generalization may be a helpful guide for the explanation of mass spectral behaviour of many organic compounds, the term ‘rule’ seems to be unjustified.
Chemical ionization mass spectrometry of some aromatic and aliphatic oximes
Authors: Maquestiau André , Van Haverbeke Yves , Flammang Robert , Meyrant Philippe 
Published: May 2005

AbstractAromatic and aliphatic oximes are protonated under methane or isobutane chemical ionization conditions. The structural identity of the [MHH2O]+˙ ions with nitrilium cations is established by the mass analysed ion kinetic energy method after collisional activation. The results also show the stereospecific nature of the transposition in the gas phase.
Contributions to the study of some heterocycles: LII—Mass spectra of some 3‐phenyl‐5‐(R‐thio)1,2,4‐triazoles and some thiazolo[3,2‐b]‐1,2,4‐triazoles
Authors: Simiti I. , Demian H. , Palibroda Aurelia Marie N. , Palibroda N. 
Published: May 2005

AbstractThe fragmentation patterns of thiazolotriazoles are in agreement with the individual character of each heterocycle but there are also peaks arising both from their combined influence and from the nature of the substituents in positions 5 and 6.
Site of protonation in the chemical ionization mass spectra of olefinic methyl esters
Authors: Harrison Ale X. G. , Ichikawa Hiroshi 
Published: May 2005

AbstractThe H2 and CH4 chemical ionization mass spectra of the olefinic esters methyl acrylate, methyl methacrylate, methyl crotonate, methyl 3‐butenoate, methyl 2‐methyl‐2‐butenoate, methyl 3‐methyl‐2‐butenoate and methyl cinnamate have been determined. In addition to the expected loss of CH3OH from [MH]+, in many cases the protonated molecules also show loss of CO or CH2CO with methoxy group migration to the positive ion centre, indicative of protonation at the double bond. These rearrangement reactions, which have analogies in electron impact mass spectra, result in chemical ionization mass spectra of isomeric molecules which show more substantial differences than the electron impact mass spectra. In the case of methyl cinnamate, isotopic labelling experiments show considerable interchange of the added proton with the ortho and meta phenyl hydrogens prior to CH3OH or CH2CO loss, although the extent of interchange is not the same for both cases.
Negative ion mass spectrometry: The generation of high concentrations of low energy molecular negative ions at high source pressures
Authors: Szulejko J. E. , Howe I. , Beynon J. H. , Schlunegger U. P. 
Published: May 2005

AbstractThe effect of the addition of argon and other gases upon the intensities of negative ion species formed in an electron impact source has been investigated. The negative ion current generated for a series of aromatic compounds has been investigated as a function both of sample and argon pressure in the ion source of a ZAB‐2F mass spectrometer. For all compounds studied, a striking enhancement of molecular negative ion current occurred on increasing either the presure of the sample or of argor. The results are consistent with thermalization of the 50 eV electrons by collisions with neutral molecules in the high pressure ion source and collisional stabilization of the negative ions initially formed. Analytical applications of the technique are discussed.
Isobutane chemical ionization mass spectrometry of β‐amino alcohols. Evaluation of populations of conformers at equilibrium in the gas phase
Authors: Longevialle Pierre , Girard Jean‐Pierre , Rossi Jean‐Claude , Tichý M. 
Published: May 2005

AbstractThe conformer populations of conformationally mobile β‐amino alcohols in the gas phase, can be evaluated from the relative intensity of the dehydration peak [MHH2O]+ in isobutane chemical ionization mass spectrometry.
Mass spectrometry of quaternary ammoniohexanoates: Intermolecular alkyl transfer during field desorption
Authors: Sanders R. A. , DeStefano A. J. , Keough T. 
Published: May 2005

AbstractIntermolecular alkyl transfer occurs during field desorption of quaternary ammoniohexanoates, resulting in mass spectra containing structurally diagnostic adduct ions. Methyl, ethyl and propyl groups attached to nitrogen readily undergo intermolecular transfer to give [M+CH3]+, [M+C2H5]+ and [M+C3H7]+ ions, respectively. Evidence is presented that alkyl groups even as large as C10H21 can transfer intermolecularly at high emitter temperatures. In addition to the alkyl ion adducts, the field desorption spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C}_{10} {\rm H}_{21} \mathop {\rm N}\limits^ + \left({{\rm CH}_3 } \right)_2 \left({{\rm CH}_2 } \right)_5 {\rm COO}^ - $\end{document} show several other adduct and fragment ions whose relative intensities depend strongly on emitter current. The field desorption results are compared with earlier pyrolysis electron impact results on similar compounds.
The scope of metastable peak observations
Authors: Holmes John L. , Terlouw Johan K. 
Published: May 2005

AbstractThis short review focuses attention upon the present status of metastable ion studies with emphasis upon the relationship between metastable peak shapes, ion structur and fragmentation mechanisms. Some recommendations are made concerning nomenclature and the reporting of observations on Gaussian‐type metastable peaks. Experimental methods for recording relative abundances of metastable peaks are critically appraised. The relationship between metastable ion phenomena and isomerization of gaseous ions is reviewed with particular attention drawn to the effect of rate‐determining isomerizations. The shapes of Gaussian‐type metastable peaks are discussed in some detail and selected examples from recent studies are used to show that such peaks may, by appropriate experiments, be separated into two Gaussian‐type components thus revealing new features of the fragmentation reaction. The magnitude and significance of released kinetic energies, T, are considered and it is stated that few conclusions can be drawn from the evaluation of T alone; the importance of accurate thermochemical data as an aid to understanding and interpreting kinetic energy release data is emphasized. Other topics discussed include composite metastable peaks, metastable peaks produced in chemical ionization and field ionization and the partitioning of internal energy of the fragmenting ion into translational degrees of freedom of the products, for reactions with and without a reverse energy barrier.
Unimolecular and collision induced fragmentations of molecular ions of polycyclic aromatic hydrocarbons
Authors: Shushan Bori , Boyd Robert K. 
Published: May 2005

AbstractThe unimolecular and collision induced fragmentation reactions of 19 polycyclic aromatic hydrocarbons have been investigated, using B/E linked scans, accelerating voltage scans, and measurements of appearance energies. From the point of view of simple analytical fingerprinting within isomeric series, B/E linked scans without collision gas offered the best compromise. Attempts to correlate trends observed in fragmentation intensities with various molecular parameters were generally unsuccessful, although some tentative conclusions have been drawn. The evidence concerning fragmentation mechanisms and ion structures is also discussed.
Some aspects of the electron impact induced fragmentation of diastereoisomeric thymidine cyclic 3′,5′‐phosphoranilidothioates
Authors: Leśnikowski Zbigniew J. , Stec Wojciech J. , Zielińska Barbara 
Published: May 2005

AbstractThe similarities between the electron impact induced fragmentation of diastereoisomeric 4‐methyl‐2‐thio‐2 amino‐1,3,2‐dioxaphosphorinanes and thymidine cyclic 3′,5′‐phosphoranilidothioates are discussed.
Isomerization of imidazoline to imidazolidine derivatives under electron impact
Authors: Moskal Janusz , Nagraba Krzysztof , Moskal Alexandra 
Published: May 2005

AbstractThe electron impact induced fragmentation of some new derivatives of imidazolidin‐2,4‐dione and 4‐imidazoJin‐2‐one has been examined. The main fragmentation pathways have been established with the help of appropriate metastables and high resolution measurements. The effect of isomerization of 4‐aryliminoimidazolidin‐2‐ones to 4‐arylamino‐4‐imidazolin‐2‐ones and conversely, 4‐aryldo‐4‐imidazolin‐2‐ones to 4‐aryliminoimidazolidin‐2‐ones on fragmentation has been investigated by temperature dependence measurements and deuterium labelling.
The influence of ligand substituents and donor atom sets on the gas phase electron attachment reactions of bis‐chelates of nickel(II)
Authors: Dakternieks D. R. , Fraser I. W. , Garnett J. L. , Gregor I. K. , Guilhaus M. 
Published: May 2005

AbstractElectron attachment reactions and negative ion mass spectra which were obtained under negative chemical ionization conditions have been examined for a series of 21 nickel(II) bis‐chelates of formula Ni[R1CXCHCYR2]2. Three ligand donor atom sets (X, Y), respectively O4, O2S2, S4 were investigated for each of the substituent combinations, viz.: R1=CH3, CF3 or C2H5O, R2=CH3; R1=C6H5, CH3 or CF3, R2=C6H5; and R1 = R2 = tert−C4H9. While the ligand substituent combinations exerted considerable influence over the various ion decomposition reactions, the relative molecular ion stabilities were largely dependent on the ligand donor atom sets and followed the sequence O4⩾ O2S2>S4 for most substituent combinations. Rationalizations are offered in terms of reductive electron capture reactions involving metal‐based orbitals, as well as the increasing stabilities of reaction products as sulphur is incorporated into the ligand donor atom sets. A comparison is also given of negative ion mass spectral data obtained under electron impact conditions as well as negative chemical ionization conditions when methane was used as an electron energy moderating gas.
Mechanism of formation of doubly charged fragments from bis‐benzyltetrahydroisoquinolines under electron impact
Authors: Bel Peter , Mandelbaum Asher 
Published: May 2005

AbstractSome bis‐benzyltetrahydroisoquinolines [α,α′‐di‐N,N‐(1‐benzyl‐1,2,3,4‐tetrahydroisoquinoline)‐p‐xylene and various substituted analogues] give rise to very abundant doubly charged fragment ions under electron impact, corresponding to the loss of the two benzyl groups. Substituent effects, ionization and appearance energy measurements and metastable transitions show that these doubly charged ions are formed (at least in part) from singly charged precursors by a heterolytic cleavage (charge separation).
Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)CHCH2]+˙ and [CH2CHCHCH(OH)]+˙ and their relationship with their keto counterparts
Authors: Terlouw Johan K. , Heerma Wigger , Holmes John L. , Burgers Peter C. 
Published: May 2005

AbstractThe [C4H6O]+˙ ion of structure [CH2CHCHCHOH]+˙ (a) is generated by loss of C4H8 from ionized 6,6‐dimethyl‐2‐cyclohexen‐1‐ol. The heat of formation ΔHf of [CH2CHCHCHOH]+˙ was estimated to be 736 kJ mol−1. The isomeric ion [CH2C(OH)CHCH2]+˙ (b) was shown to have ΔHf,  761 kJ mol−1, 54 kJ mol−1 less than that of its keto analogue [CH3COCHCH2]+˙. Ion [CH2C(OH)CHCH2]+˙ may be generated by loss of C2H4 from ionized hex‐1‐en‐3‐one or by loss of C4H8 from ionized 4,4‐dimethyl‐2‐cyclohexen‐1‐ol. The [C4H6O]+˙ ion generated by loss of C2H4 from ionized 2‐cyclohexen‐1‐ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH2CHCHCHOH]+˙ and [CH2C(OH)CHCH2]+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH3˙ and CO, [CH2CHCHCHOH]+˙ and [CH2C(OH)CHCH2]+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C4H6O]+˙ ion [CH2CCHCH2OH]+˙ are also reported.
Temperature effect on the single and double hydrogen atom transfer reactions in o‐, m‐and p‐toluic acid butyl esters
Authors: Tajima Susumu , Yanagisawa Tamae , Azami Tadashige , Tsuchiya Toshikazu 
Published: May 2005

AbstractThe temperature effect on the single and double hydrogen atom transfer reactions in o‐, m‐ and p‐toluic acid n‐butyl esters and isobutyl esters has been investigated. For the meta and para isomers, the abundance of the m/z 137 ion [C8H9O2]+ generated by a double hydrogen atom transfer reaction increases relative to the m/z 136 ion [C8H8O2]+˙ generated by a single hydrogen atom transfer reaction upon lowering the temperature of the ionization chamber. On the other hand, the ratio of the peak abundances [137]+/[136]+ for the ortho isomers is nearly constant when the temperature is changed. It is shown that this is due to the difference between the appearance energies of the m/z 136 and m/z 137 ions.
The fragmentation of 5‐ and 3‐substituted thiophene‐2‐carboxamides under electron impact
Authors: Occhipinti Salvatore , Alberghina Gaetano , Fisichella Salvatore , Puglisi Orazio , Ceraulo Leopoldo 
Published: May 2005

AbstractThe 70 eV electron impact mass spectra of twelve 5‐ and 3‐substituted thiophene‐2‐carboxamides are discussed with the aid of exact mass measurements and labelling experiments. All mass spectra exhibit pronounced molecular ions. Some isomeric 5‐ and 3‐substituted title compounds can be differentiated by mass spectrometry. The fragmentation is influenced by a strong ‘ortho‐effect’ which activates the NH3 elimination. In the other cases the most important fragmentation is NH2˙ loss, followed by CO elimination.
Dissociation of the diphenylnitrile imine radical cation into benzonitrile and [phenylnitrene]+˙
Authors: Wentrup Curt , Maquestiau André , Flammang Robert 
Published: May 2005

AbstractThe collision induced dissociation/mass analysed ion kinetic energy mass spectra of 2,5‐diphenyltetrazole demonstrate the decay sequence [diphenyltetrazole]+˙→ [diphenylnitrile imine]+˙→ m/z 91. The m/z 91 ion was shown to be identical to the ion formed by loss of N2 from the phenyl azide radical cation, thus suggesting the phenylnitrene structure for the m/z 91 ion.
Mass spectra of 2,2′‐bridged biphenyls with 12‐membered heterocyclic bridging rings: 2—some tetrabenzo[b, d, h, j][1, 6]diazacyclododecines
Authors: Behnam Basil A. , Hall D. Muriel 
Published: May 2005

AbstractMass spectra of four tetrabenzo[b, d, h, j][1, 6]diazacyclododecines are reported. The common pattern of fragmentation is altered by the presence of ortho methoxycarbonyl groups.
Electron impact induced rearrangement processes for some 1‐trimethylsilyl‐2‐methoxycarbonyl‐3‐alkyl‐Δ1–3‐cyclopropenes
Authors: Vékeym Károly , Tamás József , Okonnishnikova Galina P. , Dolgy Igor E. , Nefedov Oleg M. 
Published: May 2005

AbstractThe electron impact induced decomposition of five of the title compounds with methyl, ethyl, n‐propyl, n‐butyl or n‐pentyl groups, has been investigated in detail. The observed fragmentation can be characterized by two outstanding features: (a) interactions of the silicon centre with the ethereal oxygen atom of the methoxy carbonyl group, (b) strong directing effects of the cyclopropene ring. As a consequence of (a), the loss of a (CH3)3SiOCH3 molecule represents the main decomposition pathway of the molecular ion. It was shown to be a low energy, single dissociation step reaction, not depending on the radical site or charge localization. In spite of the rigid skeleton, ring opening does not take place during this process. As to (b), beside the β‐fission, highly selective and intense δ‐ and ϵ‐cleavages of the alkyl chain have been observed following the (CH3)3SiOCH3 elimination. On the basis of energetic and kinetic considerations, these interesting reactions can be rationalized in terms of through‐space interactions and intramolecular ortho substitution (cyclization) processes.
Intramolecular aromatic substitution reactions in substituted N,N‐dimethylthiobenzamide ions
Authors: Ramana Devalla Venkata , Grützmacher Hans‐Fr. 
Published: May 2005

AbstractThe molecular ions of N,N‐dimethylthiobenzamide and its ortho substituted derivatives (substituents CH3, Cl, Br, I) lose a hydrogen atom and/or the ortho substituent. The mechanism of this process has been studied by measurements of the ionization energies, appearance energies of the product ions m/z 164 and the kinetic energy release during this process. The structure of the product ions m/z 164 and relevant reference ions have been investigated by mass analysed ion kinetic energy spectra, B/E linked scan spectra and collision induced decompositions. The results show clearly the formation of two different kinds of product ions m/z 164 depending on the substituent lost. Type a ions are formed by loss of a H atom or the CH3 substituent and correspond to protonated 3,4‐benzo‐N‐methylpyroline‐2‐thione. The formation of these ions occurs by a hydrogen rearrangement followed by an intramolecular substitution via a 5‐membered cyclic intermediate and is associated with a large release of kinetic energy. In contrast, the loss of the halogeno substituents to give type b ions probably occurs via a direct displacement reaction by the sulfur atom of the thioamide group giving rise to Gaussian shaped peaks mass analysed ion kinetic energy spectra.
The fragmentation of 1‐phenyl‐2‐propen‐1‐ol under electron impact
Authors: Denhez Jean‐Pierre , Corval Madeleine , Dizabo Pierre 
Published: May 2005

AbstractThe electron impact mass spectra of 1‐phenyl‐2‐propen‐1‐ol and its specifically deuterated analogues have been investigated. Most of the decomposition pathways involve skeletal rearrangements or hydrogen atom transfers, such that a rearrangement of the excited molecular ions of 1‐phenyl‐2‐propen‐1‐ol to molecular ions of cinnamic alcohol and/or cinnamaldehyde can be anticipated.
Structure and formation of [C4H6N]+ ions: 1—Ion structures derived from aliphatic nitriles
Authors: Sarneel Maria M. , Heerma Wigger , Dijkstra Geo 
Published: May 2005

AbstractStructures and formation of the [C4H6N]+ ions present in the mass spectra of eleven α‐substituted and eleven α‐unsubstituted nitriles have been investigated from collisional activation and metastable ion spectra. Collisional activation spectra lead to identification of six structures. The [C4H6N]+ ions from some branched compounds prove to be mixtures. This, as well as the identity of all metastable ion parameters and certain spectral data, shows that energy differences between all structures are small. This is corroborated by MINDO/3 calculations showing a spread from 724 to 891 kJ mol−1 over the structures. Earlier proposals for two different [C4H6N]+ ion structures, based on the mass spectra of deuterium labelled compounds, appeared to be correct. A computer program to calculate the contribution of standard spectra in a measured spectrum has been developed.
Thermochemical aspects of the formation of solvated anions from ethers under ion cyclotron resonance conditions
Authors: van Doorn R. , Jennings K. R. 
Published: May 2005

AbstractThe reactions of [NH2]−, [OH]− and [F]− with diethyl ether, vinyl ethyl ether and vinyl acetate have been investigated, and the relative yields of solvated and unsolvated product ions have been discussed in terms of the thermochemistry of these reactions and the effect this has on the lifetime of the reaction complex.
The loss of SO2H from an imido‐sulfite under electron impact: Structural elucidation by collision activation of the resulting fragment
Authors: Puzo Germain , Promé Jean‐Claude , Zedde Chantal , Cazaux Louis 
Published: May 2005

AbstractElectron impact mass spectrometry of an imido‐sulfite 5,6‐benzo‐2‐imino‐N‐(2,4,6‐trichlorophenyl)‐1,3‐dioxa‐2‐thiacycloheptane shows an intense fragment ion corresponding to the expulsion of SO2H from the molecular ion. A mechanism that requires a rearrangement of the molecular ion is proposed. Structural elucidation of the [MSO2H]+ ion was obtained by recording its metastable ion and collisional activation spectra. Comparison of these spectra with similar spectra recorded from a precursor ion of known structure demonstrated that they were identical. Thus, the results support the proposed structure which derives from the expulsion of SO2H from the molecular ion of the compound 5,6‐benzo‐2‐imino‐N‐(2,4,6‐trichlorophenyl)‐1,3‐dioxa‐2‐thiacycloheptane.
Gas phase ion/molecule reactions in laser desorption mass spectrometry
Authors: van der Peyl G. J. Q. , Isa K. , Haverkamp J. , Kistemaker P. G. 
Published: May 2005

AbstractThe desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process.