bluuebunny/crossref_metadata_2025 huggingface dataset:
The mass spectrometric fragmentation of n‐alkanes
Authors: Lavanchy André , Houriet Raymond , Gäumann Tino
Published: May 2005

The 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

The 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

The 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

The 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

La 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

Le 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

Der 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

The 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

First 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

Die 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

Both 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

Dehydration 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

Mass 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

Multiply 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

Stoßaktivierungsspektren 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

The 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

The 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

Precursors 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.
Appearance energies and the kinetic shift. Loss of HCN from the benzonitrile molecular ion
Authors: Baldwin Michael A.
Published: May 2005

Measurement 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

The 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
equation image
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

The 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

The 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

Many (>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

Aromatic 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

The 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

The 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

The 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

The 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

Intermolecular 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

This 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

The 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

The 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

The 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

Electron 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

Some 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

The [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

The 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

The 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

The 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

Mass 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

The 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

The 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

The 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

Structures 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

The 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

Electron 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

The 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.
Skeletal rearrangements on chemical ionization of dibenzyl ether and derivatives
Authors: Kingston Eric E. , Shannon James S. , Diakiw Vladimir , Lacey Michael J.
Published: May 2005

Protonated molecular ions of dibenzyl ether, formed by chemical ionization using hydrogen and isobutane as reagent gases, undergo skeletal rearrangements to lose water and formaldehyde, both in the ion source and the flight path. The rearrangements have been elucidated by deuterium labelling and chemical substitution. The water lost contains the reagent proton and an aromatic hydrogen atom, and the aromatic hydrogen atoms have been shown to be mobile prior to the reaction. It is proposed that the skeletal rearrangement for water loss is initiated by protonation on the ether oxygen atom, followed by benzyl migration. The formaldehyde lost contains benzylic hydrogen atoms exclusively, and it is proposed that the skeletal rearrangement is preceded by hydrogen rearrangement of an oxygen protonated molecular ion to a ring protonated molecular ion. Daughter ion structures are supported by comparisons of their collision induced dissociation spectra with those of isomeric ions prepared by alternative routes.
Fragmentation mechanisms of isoxazole
Authors: Bouchoux G. , Hoppilliard Y.
Published: May 2005

Fragmentation pathways of isoxazole giving ions [C3H2ON]+, [C2H3N]+˙ and [C2H2N]+ are elucidated by means of metastable ion studies and thermodynamic properties. Rearrangement reactions are demonstrated to occur with H and HCO loss. Elimination of carbon monoxide leads to [C2H3N]+˙ ions whose reacting configuration is the same as for acetonitrile. All these results can be rationalized in terms of a prior isomerization of isoxazole involving ring opening and 1,2 H migration.
Stereochemical effects in the electron impact mass spectra of cis‐trans isomeric 1,2,3,4‐tetramethylcyclohexanes
Authors: Herzschuh R. , Werner H. , Mann G.
Published: May 2005

The mass spectra of six cis‐trans isomeric 1,2,3,4‐tetramethylcyclohexanes are discussed. The intensity ratio of [MCH3]+/[MC2H5]+ correlates with the strain energies of the stereoisomers. Therefore, the identification of cis‐trans isomers is possible by means of their mass spectra. The mass spectra of deuterium labelled compounds demonstrate favoured fragmentation of the axial methyl groups and ring opening between the cis substituted carbon atoms of the cyclohexane.
Plenary lecture: Ion enthalpies and their application in mass spectrometry
Authors: Maccoll Allan
Published: May 2005

The experimental determination of ionization and appearance energies is discussed, together with the calculation of heats of formation of ions. Results are presented for the ions [CnH2n+1]+, [CnH2n+2N]+ and [CnH2n+1O]+. The low temperature (∼350K), low energy (12.1eV) mass spectra of some alkanes, amines and alcohols are presented and discussed.
Comparative study of [Xe]+ and [Ar]+ bombardment in secondary ion mass spectrometry for bioorganic compounds
Authors: Kambara Hideki
Published: May 2005

Secondary ion mass spectra obtained by [Xe]+ bombardment are compared with those obtained by [Ar]+ bombardment. Although [Ar]+ ions are commonly used as primary ions in secondary ion mass spectrometry for organic compounds, [Xe]+ ions seem better as primary ions because they give a larger sputtering yield for a metal substrate than [Ar]+ ions. Cationized molecular intensities of sucrose, raffinose and stachyose, and quasimolecular ion intensities of tuftsin and eledoisin related peptide are investigated using [Xe]+ and [Ar]+ bombardments. The observed molecular species are 2–4 times more intense for [Xe]+ bombardment than for [Ar]+ bombardment, although the secondary ion mass spectra are almost the same in both cases.
Some stereochemical effects in gaseous ion decompositions
Authors: Reddy A. Mahender , Nayar M. S. B. , Reddy G. Sudhakar , Das K. G.
Published: May 2005

Stereochemical effects were observed in the electron ionization, methane, isobutane and ammonia positive ion chemical ionization and hydroxy negative ion chemical ionization behaviour of some isomeric triaryl nitrocyclohexenes. cis‐Eliminations leading to loss of HNO2, H2NO2 and arene were found to be stereochemically preferred in gaseous ions.
Loss of hydroxyl radical from isomeric ethylnitrobenzenes
Authors: Baldwin Michael A. , Carter David M. , Gilmore Jeremy
Published: May 2005

The loss of a hydroxyl radical from the molecular ions of o‐, m‐ and p‐ethylnitrobenzene has been studied by metastable ion and collisional activation techniques using electron impact and field ionization. It is shown that for the ortho isomer the mechanism of this reaction is unique, and is totally different from that of the meta and para isomers. The critical energies are also reported, and deuterium labelling is employed to access the role of the α‐hydrogens in hydroxyl loss.
Heterocyclic analogues of steroids: VIII—Mass spectrometry of the stereoisomeric derivatives of 8‐aza‐16‐oxaestrane
Authors: Suboch Victor P. , Lakhvich Fyodor A. , Liss Leo G. , Akhrem Affanassi A.
Published: May 2005

Using high resolution mass spectra, metastable ions and selective deuteration the decomposition pathways of 8‐aza‐16‐oxasteroid derivatives have been investigated. There is a dependence of the mass spectra on the stereochemistry of the C/D ring fusion in 8‐aza‐16‐oxaestrane derivatives.
On the use of collision induced dissociation spectra in the determination of the structural composition of ions
Authors: Bass Lewis M. , Bowers Michael T.
Published: May 2005

The application of the superposition principle of McLafferty and co‐workers to collision induced dissociation or collisional activation spectra to obtain quantitative estimates of the composition of isomeric mixtures of ions is discussed in detail. A set of explicitly stated assumptions is used to derive expressions for the percent composition based on normalized peak heights or peak height ratios in the collision induced dissociation spectra. The simple linear interpolation based on peak ratios which has been used in the past is shown to be invalid. It is demonstrated that the common practice of ignoring those collision induced dissociation peaks where there is interference from non‐collision induced dissociation processes may lead to substantial uncertainty in the final results. It is also demonstrated that the superposition principle may lead to results which are not internally consistent with the model. The final conclusion is that the present method of quantitative structural analysis based on the superposition principle cannot generally be expected to yield reliable results. In specific cases the results may be assumed to be reliable if it is demonstrated that the model is self‐consistent and the inherent experimental uncertainty is reasonably small. Further work may be useful in developing a generally valid method of analysis.
Mass spectral fragmentation pathways in RDX and HMX. A mass analyzed ion kinetic energy spectrometric/collisional induced dissociation study
Authors: Yinon J. , Harvan D. J. , Hass J. R.
Published: May 2005

A collisional induced dissociation study of 1,3,5‐trinitro‐1,3,5 triazacyclohexane (RDX) and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazacyclooctane (HMX) was carried out using mass analyzed kinetic energy spectrometry. High resolution mass spectra and mass analyzed ion kinetic energy/collisional induced dissociation spectra of RDX and HMX were recorded in the electron impact, chemical ionization and negative ion chemical ionization modes. Fragmentation pathways of the compounds investigated were determined in all three modes of ionization. It was found that a major part of the fragment ions in RDX and HMX originate from formation of the aduct ions [M+NO]+ and [M+NO2]+ in electron impact and chemical ionization, and from [M+NO]− and [M+NO2]− in negative chemical ionization, followed by dissociation.
The structures of [C5H5O]+ ions formed from isomers of nitrophenol in the gaseous phase
Authors: Porter C. J. , Proctor C. J. , Larka E. A. , Beynon J. H.
Published: May 2005

Translational energy release measurments on metastable ions are used in the comparison of the structures of isomeric ions. Metastable ions, m2+, formed from m1+ ions as the result of a high energy process in the ion source are compared with isomeric metastable ions formed as daughters from fragmentation of metastable m1+ ions in a field. In the case of o‐, m‐ and p‐nitrophenol the structure of the [C5H5O]+ ions formed from [C6H5O]+ ions by these two independent methods is different as verified by comparison of the behaviour of [C5H5O]+ ions formed from several other compounds.
Unexpected mass spectral skeletal rearrangements in aromatic thioamides
Authors: Ramana D. V. , Viswanadham S. K.
Published: May 2005

Interesting skeletal rearrangements, resulting in the formation of unexpected fragments, have been noticed in the mass spectra of aromatic thioamides of cyclic amines such as piperidine, morpholine and pyrrolidine. Suitable mechanisms, based on mass analysed ion kinetic energy spectra, high voltage scan spectra and high resolution data, have been proposed for the formation of [MSH]+ ions and the fragment at m/z (103+R) in the mass spectra of these compounds. The mass spectra of the thioamides of non‐cyclic amines and the thioamides of aliphatic acids contain peaks corresponding to a four‐centred skeletal rearrangement followed by the elimination of either the thioalkoxy or the thiophenoxy radical from the molecular ions.
Retrosynthetic reactions in mass spectrometry. Deacylation of ortho phthalamic acids under electron impact
Authors: Selva Antonio , Traldi Pietro , Ventura Paolo , Valle Vincenzo Dalla
Published: May 2005

Ortho Phthalamic acids under electron impact show a retrosynthetic reaction leading to both phthalic anhydride and amine complementary ions, the corresponding neutrals of which are the usual synthetic precursors of the original compounds. The single case of a primary amine derivative is examined, which shows the formation of [MH2O]+˙ ions having the structure of the related N‐substituted imide, by a process which parallels a well known thermal reaction. It also gives the species [C8H6NO2]+ (of the same nominal mass as phthalic anhydride), the structure of which is still under study. Ionic structures are supported by collision induced mass analyzed ion kinetic energy spectra.
The fast atom bombardment mass spectra of glucosinolates and glucosinolate mixtures
Authors: Fenwick G. Roger , Eagles John , Self Ron
Published: May 2005

The behaviour of glucosinolates and desulphoglucosinolates under fast atom bombardment conditions has been investigated. Relatively little fragmentation was noted in the mass spectra of these compounds. The positive ion fast atom bombardment mass spectra of glucosinolates exhibited abundant cationized and protonated molecula ions, thus complementing the previously reported electron impact and chemical ionization mass spectra of these compounds. Desulphoglucosinolates yield only the protonated molecular ion. Under negative ion conditions the spectra of glucosinolates were dominated by the molecular anion and this has been used as a means of analysing a crude plant extract containing a complex mixture of glucosinolates.
Electron impact induced fragmentation of tetramethyl‐substituted dibenzo‐18‐crown‐6 ethers
Authors: Lockhart J. C.
Published: May 2005

A series of tetramethyldibenzo‐18‐crown‐6 molecules with methyl substituents on the ether ring has been subjected to electron impact mass spectrometry, and from the variation of the fragmentation pattern with substituent position, certain fragmentation processes are located and the composition and origin of certain fragment ions can be deduced. The aliphatic CC fission deduced from deuterium labelling studies of benzo‐15‐crown‐5 is not an observable process for the crowns reported here.
Doubly charged ion mass spectra: VI—Amines
Authors: Teleshefsky L. A. , Bostwick D. E. , Abbey L. E. , Burgess E. M. , Moran T. F.
Published: May 2005

Doubly charged ion mass spectra of 22 amines (2–10 carbon atoms) were determined using an Hitachi RMU‐7L double focusing mass spectrometer. Molecular ions were not observed in the spectra of aliphatic amines. The most intense product ion peaks in the spectra of lower molecular weight amines resulted from hydrogen elimination from the molecular ion; however, as amine molecular weight increased the largest peaks resulted from both hydrogen and heavy atom elimination from the molecular ion. Dominant ions in the doubly charged ion spectra of lower molecular weight aliphatic amines were from reactions of [CnH3N]2+ (n:=2, 3, 4) type ions. The spectra of higher molecular weight aliphatic amines spanned a wide mass range. Appearance energies for some of the more prominent ions were measured in the range from 25 to 49 eV. A geometry optimized quantum mechanical self‐consistent field molecular orbital treatment was used to compute the energies and structural parameters of prominent ions in the doubly charged ion mass spectra.
Fragment ion formation of quaternary ammonium salts under fast atom bombardment and field desorption collisionally activated dissociation conditions
Authors: Veith H. J.
Published: May 2005

Comparing fast atom bombardment and field desorption collisionally activated dissociation mass spectra of tetrabutyl ammonium salts it becomes evident that under fast atom bombardment conditions, besides desorption of intact salt cations, the ionization of intact salt molecules must be assumed. Alkyl ions formed under fast atom bombardment and not under field desorption collisionally activated dissociation conditions are ionization products of tetraalkyl ammonium salt molecules. Radical cations are produced by both techniques.
Energy randomization is complete in [C5H10O]+˙ ions with the oxygen on the middle carbon
Authors: McAdoo David J. , Hudson Charles E.
Published: May 2005

The relative intensities of the losses of ethyl groups from opposite sides of the 3‐pentanone ion formed by isomerization from its enol isomer are shown to be equal when corrections for protonated acrolein formation, isotope effects, and overlapping ethane losses are made. Thus the ion decomposes symmetrically, implying ergodic behavior, as concluded by Depke and Schwarz.