bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the mechanism of isomerization reactions in the esters of some simple α,β‐unsaturated carboxylic acids
Authors: Burgers Peter C. , Terlouw Johan K. , Vijfhuizen Peter C. , Holmes John L. 
Published: May 2005

AbstractIt is shown from a detailed examination of first field free region metastable peak shapes that the molecular ion of the methyl ester of acrylic acid rearranges into 2‐ and 3‐butenoic acid ions prior to metastable fragmentations involving the losses of H2O, CH3˙ and CO. The key intermediate ion in this ester‐acid isomerization is shown to be the enol form of ionized γ‐butyrolactone. The C‐5 homologues methylmethacrylate and ethylacrylate display a similar mechanism for H2O loss, but the loss of CH3˙ shows additional mechanistic complexities. It was shown from the metastable peak shapes of 13C and deuterium labelled compounds that the larger part of the methyl loss does not occur from acid type ions, but directly from methyl substituted enol ions of γ‐butyrolactone. The mechanistic proposals also account for the presence of a pronounced loss of CH3˙ from the isomeric ester methylcrotonate and the absence of H2O loss in both methylcrotonate and the methyl ester of 3‐butenoic acid.
Electron impact mass spectra of some salts of carboxylic acids with alkali (group Ia) metals
Authors: White V Edward 
Published: May 2005

AbstractThirteen of the salts of the alkali metals (Li, Na, K, Rb, Cs) with acetic, 2,2‐dimethylpropionic, trifluoroacetic and heptafluorobutyric acid have been found to be sufficiently volatile to give mass spectra under normal electron impact conditions. The metal containing ions observed include (M=metal): [M]+, [MO]+, [MCO2]+, [M2]+·, [M2O]+·, [M2CO2]+· and the cluster ions [Mn (carboxylate)n‐1]+ for n = 2–8.
The time dependence of the competing processes leading to the loss of C2H4 from tetralin
Authors: Levsen K. , Borchers F. , Stolze R. , Budzikiewicz H. 
Published: May 2005

AbstractField ionization kinetic measurements indicate that loss of C2H4 from the molecular ion of tetralin occurs via competing processes, viz. (a) at short times the retro Diels‐Alder decomposition which is a high energy process, (b) loss from positions 1+2 (=3+4) and (c) loss after complete C and H scrambling which gains in importance for long ion lifetimes.
Effects of annulation on the mass spectral behaviour of monosubstituted bicyclo[4.3.0]‐3‐nonenes and bicyclo[4.3.0]‐3,7‐nonadienes
Authors: Tureček František , Hanuš Vladimir 
Published: May 2005

AbstractThe mass spectra of the title compounds differ considerably depending on the annulation of the bicyclic skeleton. For a series of alkyl derivatives the cis‐annulated compounds show a higher abundance of the products due to the retro Diels‐Alder cleavage than the corresponding trans isomers. The cis‐annulated esters and alcohols lose a molecule of ethanol and water, respectively, more easily than the corresponding trans isomers. Effects of conformation and configuration are discussed.
Electron impact induced formation of ions by skeletal rearrangement of some phenyl substituted cyclic ketones
Authors: van den Heuvel C. G. , Nibbering N. M. M. 
Published: May 2005

AbstractThe base peak at 70 eV for 7‐phenylbicyclo [3.1.1] heptan‐6‐one is due to the ion only. The direct formation of this ion from the molecular ion, as deduced from metastable ion decompositions in the field free regions, involves a rearrangement of 7‐phenylbicyclo [3.1.1] heptan‐6‐one to its 7‐phenylbicyclo [3.2.0]‐heptan‐6‐one isomer. Evidence for this rearrangement has been obtained from 13C labelling of 7‐phenyl‐bicyclo [3.1.1] heptan‐6‐one, from investigation of its independently synthesized bicyclic [3.2.0] isomer and of related compounds, and from measurements of kinetic energy release in fragmentations generating the various ions.
Chemical ionization of aliphatic nitro compounds
Authors: Chizhov Oleg S. , Kadentsev Valentin I. , Palmbach Galina G. , Burstein Konstantin Ia. , Shevelev Svyatoslav A. , Feinsilberg Albert A. 
Published: May 2005

AbstractThe chemical ionization mass spectra of various aliphatic nitro compounds have been studied. Almost all the nitro compounds form stable [M+H]+ ions in sharp contrast to the instability of their ions produced by other ionization techniques. The fragmentations of the [M+H]+ ions are discussed, the mechanisms and structures of fragment ions proposed being supported by quantum mechanical calculations. Correlations between chemical ionization mass spectra and structures of compounds studied are outlined. Reliable identification of mono‐ and polynitroalkanes and some related derivatives may be made by analysis of their chemical ionization mass spectra.
Stable gaseous aziridinium ions
Authors: Van de Sande Christian C. , Ahmad Syed Zahoor , Borchers Friedrich , Levsen Karsten 
Published: May 2005

AbstractGaseous protonated aziridine ions are produced at the threshold from β‐phenoxyethylamine molecular ions. The evidence for this is collisional activation spectra, using various precursors (including labelled analogues) under electron impact and field ionization conditions. Partial conversion to the acyclic \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = }\mathop {\rm N}\limits^ + {\rm H}_{\rm 2} $\end{document} isomer occurs at higher electron energies and is rationalized by means of a potential energy surface constructed from energetic data.
Ionization and appearance potentials in organic chemistry. I—energetic aspects of the mass spectra of stereoisomeric 4‐substituted N‐alkyl‐2‐methyldecahydroquinol‐4‐ols
Authors: Zaikin V. G. , Wulfson N. S. 
Published: May 2005

AbstractThe ionization potentials for the stereoisomers of trans‐fused 1,2‐dimethyl‐ and 1‐ethyl‐2‐methyl‐4‐R‐decahydroquinol‐4‐ols (RCCH, CHCH2 or C2H5) and the appearance potentials for the [M–CH3]+ and [M–C2H5]+ ions (loss of 2‐CH3 and 4‐C2H5 groups potential, respectively) were measured by using the electron impact method. The ionization and appearance potential for [M–CH3]+ are always lower for the isomers with the axial 2‐CH3 group. For the C‐2 epimers, the difference between the appearance potentials for the [M–CH3]+ ion values is likely to be equal to the enthalpy differences between the ground states of the epimers and the dissociation energy differences between the axial and equatorial C2–CH3 bonds. The appearance potentials for [M–C2H5]+ for the C‐4 epimers possessing the 4‐C2H5 group were very similar. At the same time, the appearance potentials for the [M–CH3]+ ions were lower for less stable epimers which had an axial 4‐C2H5 group.
Reactions of [CH3]+ and [CD3]+ with alcohols
Authors: Smith Richard D. , Futrell Jean H. 
Published: May 2005

AbstractThe reactions of [CH3]+ and [CD3]+ with a number of C1 to C5 alcohols were studied at approximately thermal energies (0.1 eV) using a tandem Dempster ion cyclotron resonance mass spectrometer. Branching ratios obtained under single collision conditions are reported for [CH3]+ and [CD3]+ with methanol, perdeutero methanol, ethanol, allyl alcohol, 1‐propanol, 2‐propanol, perdeutero‐2‐propanol, 1‐butanol, 2‐butanol, t‐butanol, cyclopentanol and 1‐pentanol. The results are examined in terms of the mechanism of reactions and indicate that upon progression to larger alcohols, the formation of a long‐lived adduct becomes less important in determining the reaction products.
Mass spectrometry of heterocyclic compounds. XV—The mechanism of the fragmentation under electron impact of 3‐p‐NH2‐phenyl‐5‐phenyl‐1,2,4‐oxadiazole. A CNDO/2 treatment
Authors: Selva A. , Traldi P. , Fantucci P. 
Published: May 2005

AbstractMolecular orbital calculations using the semi‐empirical CNDO/2 method were carried out on the molecular ion of 3‐p‐NH2‐phenyl‐5‐phenyl‐1,2,4‐oxadiazole, whose structure had been determined by X‐ray diffraction. The calculated diatomic interaction energy values are consistent with the mechanistic proposals made previously in terms of the quasi‐equilibrium theory concerning the cleavage of the heterocycle ring after electron impact.
Potential energy profiles for unimolecular reactions of organic ions: [C3H8N]+ and [C3H7O]+
Authors: Bowen Richard D. , Williams Dudley H. , Hvistendahl G. , Kalman John R. 
Published: May 2005

AbstractThe unimolecular decompositions of two isomers of [C3H8N]+, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm CH} = \mathop {\rm N}\limits^ + {\rm H}_2 $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm N}\limits^ + {\rm H = CH}_{\rm 2} $\end{document}, are discussed in terms of the potential energy profile over which reaction may be considered to occur. The energy needed to promote slow (metastable) dissociations of either ion is found to be less than that required to cause isomerization to the other structure. This finding is supported by the observation of different decomposition pathways, different metastable peak shapes for C2H4 loss, the results of 2H labelling studies, and energy measurements on the two ions. The corresponding potential energy profile for decomposition of the oxygen analogues, \documentclass{article}\pagestyle{empty}\begin{document}${\rm CH}_{\rm 3} {\rm CH}_{\rm 2} {\rm CH =\!= }\mathop {\rm O}\limits^ + {\rm H} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH}_{\rm 2} \mathop {\rm O}\limits^ + {\rm = CH}_{\rm 2} $\end{document}, is compared and contrasted with that proposed for the [C3H8N]+ isomers. This analysis indicates that for the oxygen analogues, the energy needed to decompose either ion is very similar to that required to cause isomerization to the other structure. Consequently, dissociation of either ion is finely balanced with rearrangement to the other and similar reactions are observed. Detailed mechanisms are proposed for loss of H2O and C2H4 from each ion and it is shown that these mechanisms are consistent with 2H and 13C labelling studies, the kinetic energy release associated with each decomposition channel, the relative competition between H2O and C2H4 loss and energy measurements.
Formation of doubly charged ions in field ionization mass spectra of para substituted acetophenones
Authors: Helal A. I. , Zahran Nagwa F. 
Published: May 2005

AbstractThe doubly charged [M]2+, [M+1]2+ and [M‐O]2+ ions are observed in the field ionization mass spectra of para substituted acetophenones. The effect of the type of the substituent on the formation of the doubly charged ions is described.
Intermolecular methyl transfer on pyrolysis of carpronium chloride
Authors: Ohya Kazumi , Yotsui Yasuhiko , Sano Mitsuji 
Published: May 2005

AbstractThe methyl transfer occurring in the production of methyl N,N‐dimethyl‐γ‐aminobutyrate by pyrolysis of carpronium chloride was examined by means of pyrolysis gas chromatography mass spectrometry with the aid of some deuterated compounds. The mass spectra of methyl N,N‐dimethyl‐γ‐aminobutyrate, produced from deuterated derivatives of carpronium chloride, showed inter alia, characteristic molecular ion peaks which indicated that the methyl of the trimethylammonium group transfers and displaces the methyl of the carbomethoxy group of the tertiary amino compound. The results show that an intermolecular methyl transfer occurs in part on pyrolysis of carpronium chloride, to form methyl N,N‐dimethyl‐γ‐aminobutyrate in which the methyl oxygen is replaced by a methyl from the nitrogen of the original compound. The mechanism presented involves the bimolecular reaction between zwitterionic intermediates formed by ionic O‐demethylation of carpronium chloride.
The use of a mass spectrometer of mattauch‐herzog geometry for the determination of the kinetic energy release in ionic decompositions
Authors: Herzig Ulrike , Krenmayr Peter 
Published: May 2005

AbstractA double focusing mass spectrometer of Mattauch‐Herzog geometry has been modified to allow the evaluation of the kinetic energy (T) released during ionic fragmentations within the first field free region. The data obtained are consistent with, though less accurate than those determined on Nier‐Johnson type mass spectrometers. Kinetic energy release values for the decomposition of metastable [C2H3O]+ ions formed from a series of compounds containing the acetyl group are reported. A ‘degrees‐of‐freedom’ effect on T was not detected.
The mass spectrometric fragmentation of n‐alkanes
Authors: Lavanchy André , Houriet Raymond , Gäumann Tino 
Published: May 2005

AbstractThe fragmentation of n‐hexane, n‐nonane and n‐tetradecane under electron impact has been investigated, using 13C labelled compounds. The mechanism of the formation of the alkyl radical ions is quantitatively explained by using a method of calculation developed in an earlier publication for n‐heptane. It is assumed that these ions are formed either by a direct C‐C bond cleaveage or by a secondary olefin loss from an alkyl radical ion. In the latter case the probability for a particular carbon to be lost in the neutral fragment is assumed to be random. The probability for a direct cleavage to an alkyl ion is about 80% for an ion containing at least half of the number of carbon atoms of the molecular ion and 15% for the smaller ions. The [MH]+ ion seems to be a special case not yet clearly understood. Former results about the loss of methyl from the molecular ion are confirmed.
Ortho effects in organic molecules on electron impact. VI—Ortho effects of a carboxyl group in N‐substituted anilines
Authors: Ramana D. V. , Vairamani M. 
Published: May 2005

AbstractThe unusual fragments noticed in the mass spectra of N‐benzyl‐ and N,N‐dibenzylanthranilic acids have been explained on the basis of the ortho interaction of the carboxyl group with the N‐benzyl‐ and N,N‐dibenzyl moieties.
Electron impact studies. CXXIV—Negative ion mass spectra of organic functional groups. Thioacetanilides
Authors: Clausen K. , Pedersen B. S. , Scheibye S. , Lawesson S.‐O. , Bowie J. H. 
Published: May 2005

AbstractThe thioacetanilide negative molecular ion (produced by secondary electron capture) is stable, but it fragments after collisional activation to yield [C6H5NH]− by cleavage α to the CS grouping. The negative molecular ions of (substituted) o‐nitrothioacetanilides undergo a series of extremely complex rearrangement reactions. For example, the molecular anion derived from o‐nitro‐N‐methylthioacetanilide yields both acetate and thioacetate anions as major fragment ions.
Photoionization of the C‐1C‐4 monosubstituted alkyl benzenes: Thermochemistry of [C7H7]+ and [C8H9]+ formation
Authors: McLoughlin R. G. , Morrison J. D. , Traeger J. C. 
Published: May 2005

AbstractThe appearance energies for the [C7H7]+ and [C8H9]+ fragment ions produced in the fragmentation of the C‐1C‐4 monosubstituted alkyl benzenes have been measured by photon impact. The mean heat of formation calculated for [C7H7]+ is 205.3 ± 1.9 kcal mol−1 which is consistent with a threshold tropylium structure. For [C8H9]+ the mean heat of formation is calculated to be 199.2 ± 1.3 kcal mol−1 which can be equated with either a methyl tropylium or α‐phenylethyl structure at threshold. Some evidence is provided for the existence of the α‐phenylethyl ion.
Mécanismes de Fragmentation en Spectrométrie de Masse par Ionisation Chimique. IV—Fragmentation des Ions Oxiranes Protonés
Authors: Audier H. E. , Milliet A. , Perret C. , Varenne P. 
Published: May 2005

AbstractLa fragmentation, par ionisation chimique des oxiranes conduisant à un ion ayant perdu une molécule D'eau advient après plusieurs étapes. L'étape déterminante est l'ouverture du cycle. Le profil réactionnel de cette fragmentation est détaillé pour le cas du méthyl‐2 tétrahydrofurane.
Mécanismes de Fragmentation en Spectrométrie de Masse par Ionisation Chimique. V–Echanges d'Atomes d'Hydrogène dans les Ions ‘aldehyde protoné’ à Longue Chaine Linéaire
Authors: Audier H. E. , Milliet A. , Perret C. , Varenne P. 
Published: May 2005

AbstractLe mécanisme d'élimination d'eau des aldéhydes protonés à longue chaǐne, par ionisation chimique, fait intervenir deux phénomènes, d'une part un échange de l'hydrogène porté par l'oxygène avec ceux de la chaǐne, cet échange est faible pour les aldéhydes ayant moins de six atomes de carbone–un mécanisme d'échange est proposé–d'autre part, un transfert d'un atome d'hydrogène sur l'atome d'oxygène qui conduit à l'élimination d'une molécule d'eau. Cet hydrogène provient pour la plus grande part, des positions 3 et 4 de la chaǐne alkyle.
Massenspektroskopische Fragmentierungsreaktionen. XX—Zur Frage der elektronenstoß‐induzierten Carbenabspaltung
Authors: Budzikiewicz H. , Roth G. , Vogel E. 
Published: May 2005

AbstractDer elektronenstoß‐induzierte Zerfall von 1,6‐Methano[10]annulen und Derivaten mit Brücken‐Substituenten (11‐Stellung) wurde im Hinblick auf die Möglichkeit untersucht, daß die Brücke unter gleichzeitiger Bildung von ionisiertem Naphthalin als Carben eliminiert wird. Während die Carbenabspaltung beim 1,6‐Methano[10]annulen selbst nicht beobachtet wird (<0,5% rel. Int.), ist diese bei seinen 11‐Halogen‐ und 11,11‐Dihalogen‐Derivaten ein wichtiger Fragmentierungsweg. Komplette Eliminierung der Brücke wird auch bei 1,6‐Methano[10]annulen mit C‐Substituenten in 11‐Stellung beobachtet, doch läß sich hier nicht entscheiden, ob die Brücke als Carben order als umgelagerte neutrale Spezies austritt. Auf die Parallelität zwischen thermischem und elektronenstoß‐induzierten Verhalten der 1,6‐Methano[10]annulene wird hingewiesen.
Anomalous ions in the chemical ionization mass spectra of aromatic nitro and nitroso compounds
Authors: Brophy Joseph J. , Diakiw Vladimir , Goldsack Robert J. , Nelson Derek , Shannon James S. 
Published: May 2005

AbstractThe appearance of [MH‐30]+ ions in the chemical ionization mass spectra of aromatic nitro compounds may be due to their initial reduction to the corresponding amines within the ion source. Aromatic nitroso compounds may be similarly reduced to yield [MH‐14]+ ions. The hydroxy derivatives of the nitroso compounds yield further anomalous ions at [MH‐16]+ probably due to the reduction of the hydroxy groups.
Mass spectra of transition metal π‐complexes. VI—The metastable ion mass spectrum of (η1‐Toluene)‐tricarbonylchromium
Authors: Davis R. , Webb M. L. , Millington D. S. , Parr V. 
Published: May 2005

AbstractFirst field free region metastable fragmentations of (η6‐PhCH3)Cr(CO)3 have been examined by means of the linked scan technique. The molecular ion is shown to fragment exclusively by single and multiple CO loss. The ion [C7H8Cr(CO)2]+⋅ also fragments directly to [C7H8Cr]+⋅.
Stereospezifische massenspektrometrische fragmentierungen von cyclohexandicarboxamiden. 34–Über massenspektrometrische untersuchungen
Authors: Süess Hans , Hesse Manfred 
Published: May 2005

AbstractDie massenspektrometrische Fragmentierung der 1,3‐ and 1,4‐Cyclohexandicarboxandicarboxamide ist bezüglicn zweier Reaktionen sehr stereospezifisch: Nur die cis‐Isomere spalten CONH ab, Während der Verlust von (NH3+CO) bei den tren‐Isomeren intensiver. In den Spektren der 1,2‐Isomeren sind die Unterschiede zwischen cis‐ und trans‐ Verbindungen weniger ausgeprägt.
Regiospecificity of intramolecular hydrogen transfer in cyclohexanol following chemical ionization
Authors: Fenselau Catherine , Green Mark M. , Jardine Ian 
Published: May 2005

AbstractBoth H2O and HDO are eliminated from protonated d11‐cyclohexanol under chemical ionization conditions using methane as the reagent gas. The elimination of H2O and HDO from the [M+H]+ ions of cyclohexanol specifically labeled with deuterium in the 1; 2,6; 3,5; and 4 positions has been measured. It is found that there is considerable selectivity as to the position from which deuterium is lost in the elimination of HDO. That is, transfer from C‐4 is favored, some transfer from C‐3(5) occurs, little deuterium is lost from C‐2(6) and none is lost from C‐1. A mechanism involving ring protonation and ring opening followed by deuterium transfer to oxygen with subsequent loss of HDO is proposed to account for these observations.
Influence of the interfunctional distance on the dehydration of amino alcohols in Iso‐butane chemical ionization mass spectrometry
Authors: Longevialle Pierre , Girard Jean‐Pierre , Rossi Jean‐Claude , Tichý M. 
Published: May 2005

AbstractDehydration of β‐amino alcohols after chemical ionization with iso‐butane as reagent gas is dependent upon the interfunctional distance. Relative protonation cross‐sections of both functional groups appear to be essentially independent of their relative proton affinities.
Spectra of quaternary ammonium salts taken by fission‐fragment and laser‐induced desorption
Authors: Schueler B. , Krueger F. R. 
Published: May 2005

AbstractMass spectra of quaternary ammonium salts obtained by fission‐fragment induced desorption and laser induced desorption are reported and compared with those obtained by static secondary ion mass spectrometry as well as by field desorption and by field desorption/collisional activation. The principal fragmentation pathways are the same. Certain differences are discussed.
Multiply charged ions in field desorption mass spectra of peptides containing basic amino acids
Authors: Katakuse Itsuo , Matsuo Takekiyo , Wollnik Hermann , Matsuda Hisashi 
Published: May 2005

AbstractMultiply charged ions up to [M+4]4+ were observed in the field desorption mass spectra of five different peptides. The relationship between the charge‐multiplicity and the number of basic sidechains is discussed.
Nachweis einer ‘Wagner‐Meerwein’‐ Ringkontraktion bei der Protoneninduzierten H2O‐Eliminierung aus Cyclohexan‐1.2‐diol
Authors: Wolfschütz Roland , Schwarz Helmut , Blum Wolfgang , Richter Wilhelm J. 
Published: May 2005

AbstractStoßaktivierungsspektren legen den Schluß nahe, daß die H2O‐Abspaltung aus protoniertem cis‐ und trans‐1,2‐Cyclohexandiol zum protonierten Cyclopentylcarbaldehyd führt. Der Mechanismus dieser und alternativer Reaktionen wird diskutiert.
Observations on the electron impact induced fragmentation of methyl and phenyl 4,6‐O‐Benzylideneglucopyranosides
Authors: Kyriakidis N. , Smale T. C. , Waight E. S. 
Published: May 2005

AbstractThe structure of some rearrangement ions in the electron impact induced fragmentation of methyl 4,6‐O‐benzylidene‐2,3‐di‐O‐methyl‐α‐D‐glucopyranoside and phenyl 4,6‐O‐benzylidene‐2,3‐di‐O‐methyl‐β‐D‐glucopyranoside have been investigated using high resolution, deuterium labelling and linked scan (B,E) techniques. Shifts of methoxyl groups from C‐2 and C‐3 to C‐1 have been confirmed.
Mass spectrometry of nitroazoles 1–The mass spectra of methyl substituted nitropyrazoles
Authors: Luijten W. C. M. M. , Van Thuijl J. 
Published: May 2005

AbstractThe mass spectra of all isomers of methylnitropyrazoles are reported. Generally, the spectra are characteristic of nitropyrazoles. In some cases however, ortho effects occur, recognizable by primary losses of, for example, OH., H2O, CHO., CH2O.
Electron impact fragmentation mechanisms of 2,4,6‐trinitrotoluene derived from metastable transitions and isotopic labeling
Authors: Bulusu Suryanarayana , Axenrod Theodore 
Published: May 2005

AbstractPrecursors of the major ions in the electron impact spectrum of 2,4,6‐trinitrotoluene have been determined by observations of metastable peaks and isotope shifts. In 2,4,6‐trinitrotoluene with adjacent CH3 and NO2 groups, the facile transfer of a methyl hydrogen to oxygen followed by loss of an OH group gives rise to the m/z 210 ion which plays a key role in the six important fragmentation sequences that have been identified. A similarity of the reactions in the mass spectrometer to the decomposition pathways induced by other stimuli has been observed.