bluuebunny/crossref_metadata_2025 huggingface dataset:
The benzoyl cation: The participation of isolated electronic excited states in the dissociation of molecular ions of the form [C6H5COX]+˙
Authors: Benoit F.
Published: May 2005

The heat of formation of the benzoyl cation generated from [C6H5COX]+˙ is found to depend on X, while the heat of formation of the phenyl ion produced therefrom is, with one exception, independent of X. The excess energy of the benzoyl cation can be accounted for by an electronic excited state of the ion in the mass spectra of benzoic acid, benzaldehyde, benzamide, methyl benzoate and possibly benzophenone; the benzoyl cation is not excited in the mass spectra of acetophenone and benzoyl chloride.
Mass spectral studies on 7‐azabicyclo (2.2.1) heptane systems
Authors: Das K. G. , Kulkarni P. S. , Roy S. K.
Published: May 2005

An attempt has been made to rationalise the major fragmentation modes of a few C2, C3 disubstituted 7‐p‐toluene sulphonyl and 7‐carbobenzyloxy‐7‐azabicyclo (2.2.1) heptanes.
Field ionisation mass spectrometry of acetylpyridine isomers
Authors: Migahed M. D. , Hetal A. I. , El‐Kholy S. B.
Published: May 2005

An investigation of the metastable transition in the field ionisation mass spectra of acetylpyridine isomers has established that the reaction pathway is greatly influenced by the ring position of the substituent. It is suggested that the pyridine nitrogen atom induces a rearrangement process in the case of 2‐acetylpyridine. In other acetylpyridines it has a little effect and the cleavage reaction occured prior to rearrangement.
The mass spectra of some pyridazines, pyrido‐pyridazines and related compounds
Authors: Kramer V. , Medved M. , Stanovnik B. , Tišler M.
Published: May 2005

The mass spectral fragmentation behaviour of substituted sulphur containing pyridazines, pyrido (2,3‐d) pyridazines and pyrido‐thiazolo‐pyridazines has been investigated and fragmentation patterns proposed.
Using model ionization efficiency curves to evaluate the methods for determining appearance potentials
Authors: Occolowitz J. L. , Cerimele B. J. , Brown Peter
Published: May 2005

Six methods of estimating appearance potentials from ionization efficiency curves of ions arising from single, competitive, consecutive and isolated ionic reactions are evaluated, using computed electron‐impact ionization efficiency curves as ‘experimental’ data.

Of the linear extrapolation, semi‐log, second derivative, energy compensation, Warren and critical slope methods, a modified critical slope method gives the most accurate appearance potentials for fragment ions. Experimental data are presented to support this conclusion.
Photoionisation and fragmentation of the stereoisomers of 4‐t‐butylcyclohexyl acetate and 4‐t‐butylcyclohexyl methyl ether
Authors: Akhtar Zinat M. , Brion C. E. , Hall L. D.
Published: May 2005

The fragmentation of the stereoisomers of 4‐t‐butylcyclohexyl acetate and 4‐t‐butylcyclohexyl methyl ether has been studied by photoionisation mass spectrometry at 1216 Å and 584 Å. Deuterium substitution and high resolution mass spectrometry have been used to gain further insight into the fragmentation pathways.
Mass spectrometry of the trimethylsilyl derivatives of medicinal barbiturates
Authors: Falkner Fred C. , Throck watson J.
Published: May 2005

The electron ionization mass spectra of the trimethylsilyl derivatives of a number of medicinal barbiturates have been examined. The trimethylsilyl derivatives are useful in the identification of barbiturates by gas liquid chromatography/mass spectrometry (g.l.c.‐m.s.). Mass spectra of these derivatives are characterized by abundant high mass ions which permit the ready distinction of one barbiturate from another. The prominent and characteristic [M ‐ 15] ion is an effective monitor of molecular weight, while other unique fragmentations and/or varying patterns of relative abundance serve to differentiate isomers.
The rational use of a dynamic on‐line data processing system for high and low resolution mass spectrometry
Authors: Van 'T Klooster H. A. , Vaarkamp‐Lijnse J. S. , Dijkstra G.
Published: May 2005

Some of the factors determining the configuration of a mass spectrometry data processing system are discussed. A rationalisation is given for a laboratory situation dealing with a variety of mass spectrometric problems. The effective use of a dynamic on‐line system in such an environment is demonstrated. Conversational procedures are described for the acquisition, reduction and interpretation of mass spectral data, using a CRT visual display terminal as a fast man‐computer interactive communication medium.
Conformations of highly hindered aryl ethers. XXI—fragementation paths involving intramolecular π‐complexes and cyclizations in the mass spectra of 2,4‐dinitrophenyl 2′‐alkylphenyl ethers
Authors: Jáuregui J. Fernando , Lehmann F. Pedro A.
Published: May 2005

The mass spectrometric study of 2,4‐dinitrophenyl 2′‐R‐phenyl ethers (R  H, Me, Et, i‐Pr, tert‐Bu) showed that (1) fragmentation proceeds differently from unsubstituted and 4‐nitro‐substituted diphenyl ethers; (2) important fragmentation routes involve interannular migrations and cyclizations; (3) these occur between two groups ortho to the ether linkage while the ethers are in unfavorable endo, endo twist conformations; (4) the observed interannular interactions can be ustified by the existence in these compounds of an intramolecular π‐complex which stabilizes the sterically unfavorable conformation and explains the observed fragmentations.
Mass spectrometry in structural and stereochemical problems. CCXXXVII—Electron‐impact‐induced hydrogen losses and migrations in some aromatic amides
Authors: Duffield A. M. , DeMartino G. , Djerassi Carl
Published: May 2005

The mass spectra of a series of benzamides and naphthamides have been investigated with respect to their propensity to lose an aromatic hydrogen atom from their molecular ions. Deuterium labeling and a study of model compounds have led to a plausible mechanistic rationalization for the formation of the [M — 1] ions. The other principal fragmentation processes observed with these compounds are discussed, including the specificity of a previously uninvestigated rearrangement process.
Mechanisms of mass spectrometric fragmentations: X–Interaction between remote or‐groups in decalin‐1,5‐diols and their dimethyl ethers
Authors: Grützmacher Hans‐Friedrich , Fechner Karl‐Heinz
Published: May 2005

The mass spectra of the five stereoisomers of decalin‐1,5‐diol and its dimethyl ether have been investigated. The differences in the mass spectra of stereoisomers I to III with a trans‐ decalin ting system are small. The differences are much larger in the mass spectra of the two isomers IV and V of the cis‐decalin series and the elimination of CH2O, formed by interaction between the two methoxy groups, from the molecular ion is only observed in the mass spectrum of Vb.
On the 1,1‐elimination of nitrous acid and the loss of hydroxyl from the molecular ion of the methyl ester of γ‐nitrobutyric acid
Authors: Molenaar‐Langeveld T. A. , Nibbering N. M. M.
Published: May 2005

It is shown by D labelling experiments that nitrous acid and hydroxyl, eliminated from the methyl ester of γ‐nitrobutyric acid upon electron‐impact, contain a γ‐hydrogen atom to the extent of ∼ 85% and ∼ 100%, respectively. The loss of nitrous acid is the third case of a highly specific 1,1‐elimination from a molecular ion1a,1b reported hitherto and arguments are presented for the essential role played by carbomethoxy group in this reaction, i.e. it converts the nitro structure of the molecular ion to its acinitro structure. The results obtained further point to a stepwise character of the McLafferty rearrangement, at least for the present case.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen. XI—Energetische Betrachtungen zum Mas Senspektro‐Metrischen Zerfall Einiger Offenkettinger und Isomerer Cyclischer Kohlenwasserstoffe
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Mit Hilfe von AP/IP‐Messungen und deren Korrelation mit thermochemischen Daten werden die Bildungsenthalpien stabiler Ionen einiger C8H6‐, C10H10 und C12H10‐Kohlen‐wasserstoffe bestimmt. Es wird gezeigt, dass sowohl offenkettige als auch cyclische Ionen‐Strukturen bei der elektronenstossinduzierten Fragmentierung von Aromaten und isomeren Acetylenverbindungen ausgebildet werden können.
Electron‐impact‐induced rearrangements of organic ions: IV—Hydrogen and carbon scrambling in [t‐C3H8N]+ metastable ions
Authors: Cum Giampietro , Romeo Giovanni , Uccella Nicola
Published: May 2005

Independent loss of positional identity of the hydrogen and carbon atoms in [t‐C3H8N]+ metastable cations prior to fragmentation in the gas phase with loss of ethylene, has been demonstrated by 2H and 13C labelling experiments. The scrambling reaction is interpreted as a rearrangement in competition with the high activation energy unimolecular decompositions. The study of this fragmentation process indicates the occurrence of a primary isotope effect discriminating in favour of 2H and 13C retention in the original methylene group.
Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen: XIII—Einfluß der Dissoziationsenergie auf intramolekulare aromatische Substitutionen in den Molekül‐Ionen von N,N‐Dimethyl‐N′‐phenylformamidinen
Authors: Kuschel Heinz , Grützmacher Hans‐F.
Published: May 2005

Der Einfluß der Dissoziationsenergie der CX‐Bindung (X = H, F, Cl, Br, J) auf die Bildung von Benzimidazolium‐Ionen (b) durch Abspaltung von X aus den Molekül‐Ionen der ortho‐substituierten N,N‐Dimethyl‐N′‐phenylformamidinen (I bis V) wird untersucht. Zwischen den Intensitäten von b und den Dissoziationsenergien besteht keine einfache Beziehung. Weiterhin werden die Auftrittspotentiale der lonen b nur wenig von den Dissoziationsenergien beeinflußt, obwohl fur eine einfache Spaltungsreaktion Unterschiede von ca. 2.5 eV erwartet werden. Dieses Verhalten der Molekül‐Ionen von I bis V steht irn Einklang mit einem zweistufigen Additions‐Dissoziations‐Mechanismus [M]+· → a → b, bei dem der erste Additionsschritt die hohere Aktivierungsenergie besitzt. Analoge Mechanismen sind bei aromatischen Substitutionen in kondensierter Phase bekannt, für massenspektrometrische Fragmentierungen bisher jedoch noch nicht nachgewiesen worden. Der Nachweis zusätzlicher kinetischer Energie T in den Reaktionsprodukten mit Hilfe einer Analyse der metastabilen Übergange für [M]+· → b bestätigt den vorgeschlagenen Mechanismus.
Alkyl–oxygen bond formation in the mass spectra of α‐chloromethyl aryl sulphones
Authors: Pratanata Miss Itawati , Williams L. R. , Williams R. N.
Published: May 2005

When subjected to electron‐impact, chloromethyl aryl sulphones (II, X = Cl) fragment predominantly by the loss of CH2Cl from the molecular ion followed by the loss of SO2 and in most cases the appropriate metastable peaks are present to confirm the transitions. In addition, alkyl–oxygen bond formation in the molecular ion was revealed by the presence of prominent peaks corresponding to the [Rϕ‐SO]+ ions. In most spectra no evidence for aryl–oxygen bond formation could be found and thus the presence of the chlorine atom was able to effectively reverse the direction of skeletal rearrangement reported for aryl methyl sulphones.
Rearrangement processes in the mass spectra of N‐substituted sulphoximines
Authors: Whittle C. P. , Macdonald C. G. , Katekar G. F.
Published: May 2005

The electron‐impact mass spectra of a range of N‐substituted sulphoximines have been recorded and rationalised. Intense peaks consistent with oxygen‐to‐sulphur and sulphur‐to‐sulphur migrations were observed in the spectra of some of the compounds.
Massenspektrometrie isomerer Diazaphenanthrene—I
Authors: Schmidtberg G. , Bluhm Th.
Published: May 2005

Die Massenspekiren von fünf durch photochemische Cyclodehydrierung von Styryldiazinen gebildeten Diazaphenanthrenen werden untersueht. Sic zeigen, daß die Fragmentierung dieser Verbindungen fast ausschließlich vom hctcrocyclischen Teil des Moleküls ausgeht und durch konkurrierende α‐Spaltungen zustande kommt. Aus den Intensitatsverhältnissen der dabei gebildeten Ionen [M  H˙]+, [M  HCN]+˙, [M  N2]+˙ und [M  2 HCN]+˙ läßt sich das jeweilige Isomer eindeutis bestimmen.
Heuristic programming as an ion generator in mass spectrometry. II—Generation of primary ions from simple cyclic structures
Authors: Delfino Allan B. , Buchs Armand
Published: May 2005

The Ion Generator computer program has now the ability to fragment cyclic structures Examples of mechanisms which are proposed by the program for the fragmentation of simple ring compounds are presented.
Skeletal rearrangement of allyl acetates after protonation by chemical ionization
Authors: Liehr J. G. , McCloskey James A.
Published: May 2005

In the methane chemical ionization mass spectra of allyl phenylacetate and allyl phenoxyacetate the major reaction paths (>40%σ) involve skeletal rearrangements, which have no analogy in the corresponding, simpler electron‐impact spectra. Substituent and deuterium labeling studies suggest a mechanism involving intramolecular substitution of the phenyl ring by the allyl group. Abstraction of hydrogen from the ortho position of the phenyl ring or from the rearranged allyl group is followed by expulsion of water and carbon monoxide.
The mass spectral fragmentation of 1,1,4a‐trimethyl‐1,2,3,4,4a,9,10,10a‐octahydrophenanthrene, its 2‐oxo and 2‐oxy derivatives, and their deuteriomethyl analogues
Authors: Al‐Jallo H. N. A. , Waight E. S.
Published: May 2005

The mass spectra of the title compounds have been compared with those of their 4a‐trideuteriomethyl and 1,1‐bis(trideuteriomethyl) analogues. Some fragmentation pathways proposed for ring C aromatic diterpenes by earlier workers have been corrected in the light of the shifts in peak positions and metastable refocusing experiments.
Mass spectrometry of onium compounds. XXIII—ionisation potentials in the structural assignment of [M – N2] ions from diazo‐oxides
Authors: Thorstad Olav , Undheim Kjell , Hvistendahl Georg
Published: May 2005

The ionisation potential shows that fulven‐6one is formed pyrolytically from o‐benzo‐diazo‐oxide. Appearance potential measurements show increasing pyrolytic contribution to the [M – N2] species with increase in ion source temperature.
Isotope effects and H/D scrambling in the fragmentation of labelled propenes
Authors: Lau A. Y.‐K. , Solka B. H. , Harrison A. G.
Published: May 2005

The fragmentation reaction [C3(H,D)6]+· → [C3(H,D)5]+ + (H, D) has been examined in the metastable decomposition region for two pairs of labelled propenes: CH3CDCH2,CD3CHCD2 and CD3CHCH2, CH3CDCD2. The results indicate that complete hydrogen scrambling occurs in the propene molecular ion prior to fragmentation. The isotope effect kH/kD is in the range 2·1 to 3·3.
Etude de la Fragmentation Du Benzofuro(3‐2b)Benzofuranne
Authors: Breliere C. , Ricard M. , Dizabo P. , Brun J. P.
Published: May 2005

Sous impact électronique, la fragmentation du benzofuro(3–2b)benzofuranne est caractérisée par la perte d'un groupment C6H4CO avec migration sélective d'un hydrogène et les pertes de radicaux benzoyle et benzoate; Un groupment formyle est éliminé en deux étapes.
Elucidation of elctron‐impact‐induced fragmentations of hydrocinnamaldehyde by 13C labelling; evidence for an ‘ortho attack’ in the molecular ion
Authors: Venema A. , Nibbering N. M. M.
Published: May 2005

The mass spectra of hydrocinnamaldehydes, labelled with 13C in Position 1 and 3, have been studied in order to determine the origins of the carbon atoms in the moieties C2H2O, C3H4O, CH3 and CO, expelled from the molecular ion.
The mass spectra of some 5′‐alkul substituted 5′‐thioadenosine trimethylsilyl derivatives
Authors: Szczepanik P. A.
Published: May 2005

Trimethylsilyl derivatives of 5′‐S‐alkyl substituted 5′‐thioadenosines give mass spectra that are characterized by a number of highly intense ions. These ions are formed by the fragmentation of the alkyl substituted sugar moicty and are specific for the alkyl group in the substitution.
The mass spectra of some α‐aminooxy acids
Authors: Tamás J. , Hegedüs‐Vajda J. , Dancsi L. , Kisfaludy L.
Published: May 2005

The mass spectrometric behaviour of six simple α‐aminooxy acids is described. Comparison is made with the electron‐impact‐induced fragmentation of the parent α‐amino acids. The differences are in accordance with the observed

See Ref. 1.

chemical character of the α‐aminooxy acids.
Studien Über die Saponine aus der Arznei‐Ginseng‐Wurzel: Massenspektren von Ginsenoside‐Rg1‐Decaacetat und Verwandten Verbindungen
Authors: Komori Tetsuya , Tanaka Osamu , Nagai Yumiko
Published: May 2005

Die Massenspektren von Ginsenoside‐Rg1‐decaacetat und verwandte Triterpensaponin‐acetate vom Dammarantyp wurden untersucht. Die von Elyakov u.a. vorgeschlagene Struktur des Panaxoside A ( = Ginsenoside‐Rg1)

Siehe Lit. 3.

wird kommentiert.
Mass spectrometric studies on the effect of sidechains of N‐acetylamino acid methyl esters and N‐methylamides on their photoionisation
Authors: Orlov V. M. , Varshavsky Ya. M. , Miroshnikov A. I.
Published: May 2005

Photoionisation mass spectra of N‐methylamides of N‐acetyl derivatives of the following amino acids have been studied: alanine, valine, leucine, serine, threonine, phenylalanine, tyrosine, tryptophan and proline. The study also included methyl esters of N‐acetyl tyrosine, N‐acetyl phenyl alanine and N‐trideuteroacetyl phenylalanine. The photon energies were within the range of 7.5 to 13.0 eV. The appearance potentials of the main ions were also determined. The compounds under study contain CHCO, CONH and NCα bonds as well as sidechains and may therefore be regarded as models of short peptides.

Under photoionisation conditions, decomposition of compounds containing aliphatic sidechains involves mainly CHCO bonds; the appearance potentials of the corresponding fragments decrease with an increase in the size of sidechain. The presence of hydroxyl in the sidechain results in an increase in the appearance potential of a fragment formed due to CHCO bond rupture, whereas the presence of an aromatic moiety favours an even greater increase in the appearance potential and results in predominant rupture of the NCα bond.

Analysis of the mass spectra obtained confirms the conclusion made previously that application of the photoionisation technique enables one to increase considerably the relative intensity of characteristic peaks and to suppress secondary process taking place upon ionisation by the electrons with energy values of the order of 70 eV.
Massenspektrometrische Untersuchung von Amiden X—Notiz zum Mechanismus der H‐Abspaltung aus N,N‐Dimethylbenzamid
Authors: Schwarz Helmut , Bohlmann Ferdinand
Published: May 2005

Die Bildung des [MH]+‐Ions aus N,N‐Dimethylbenzamid erfolgt ausschließlich durch Wechselwirkung der Amidgruppe mit den Wasserstoffen der ortho‐Position. Die übrigen H‐Atome spielen bei der Fragmentierung keine Rolle.
Mass spectrometric studies on azidomorphine derivatives
Authors: Tamás József , Mák Marianna , Makleit Sándor
Published: May 2005

The mass spectrometric behaviour of nine azidomorphine derivatives have been studied. These compounds proved to have surprisingly specific and selective fragmentation under electron‐impact. For 6‐deoxy‐6‐azido‐dihydro‐isomorphine derivatives (I to V) the main decomposition pathway involves the loss of an N2 molecule followed by a very rapid and selective fragmentation process. On the other hand, the molecular ions of 6‐deoxy‐8‐azido‐pseudomorphine derivatives (VI to VIII) and 6‐deoxy‐6‐azido‐14‐hydroxy‐isocodein (IX) primarily decompose by loss of the N3 radical. This is due to the allylic effect of the double bond in ring C, corresponding to the chemical behaviour of these compounds.
Binary decision prediction probabilities and the accuracy of interpretation of mass spectra
Authors: Adams R. A. , Sedgwick R. D.
Published: May 2005

The results of the applications of computer learning techniques to decision making in the evaluation of mass spectral data are used to propose a model in which molecular complexity is related to binary decision prediction probability. This model is tested on the results from a mass spectrum interpretation programme and it is proposed that the method could be used to compare the effectiveness of programmes developed from different basic concepts.
Zur Lokalisierung funktioneller Gruppen in Steroiden mit Hilfe der Massenspektrometrie: XIII—Massenspektren von 3,7,17‐Trihydroxyandrostanen und 7,17‐Dihydroxyandrostan‐3‐onen
Authors: Stock B. , Spiteller G.
Published: May 2005

Androstanes mit trans‐verknüpftem A/B‐Ringsystem und Hydroxylgruppen in den Stellungen 3, 7 und 17 zeigen in ihren Massenspektren Schlüsselionen der Massen 99 und 178. Das Ion der Masse 99 enthält die C‐Atome des Ringes D, das der Masse 178 die der Ringe A und B sowie C‐11. Bei cis‐Verknüpfung des A/B‐Ringsystems wird das Ion der Masse 178 mit bedeutend geringerer Intensität gebildet, das Ion der Masse 99 fehlt nahezu. Die Stellung der Hydroxylfunktion in der Position 7 läßt sich aus den Spektren entsprechender Trimethylsilyläther ableiten: Bei Gegenwart einer 7α‐ständigen Trimethylsilyläthergruppe und trans‐Verknüpfung der Ringe A und B dominieren [M — 131] Spaltstücke. Eine Kontigurationszuordnung der Hydroxylgruppen in Stellung 3 ist nur sehr schwer möglich. Analoge Spaltstücke treten in den Spektren der entsprechenden 7,17‐Dihydroxyandrostan‐3‐one auf.
Intramolecular catalysis in the mass spectrometer: Mechanisms for loss of methanol from methyl esters upon electron‐impact
Authors: Winnik M. A.
Published: May 2005

A review of the literature indicates compelling evidence that: (1) loss of ROH from esters requires protonation of the alkoxy oxygen; (2) the (symmetry forbidden) [1,3] hydrogen migration from protonated carbonyl to alkoxy oxygen does not occur in the mass spectra of esters; (3) hydrogen abstraction in esters occurs almost exclusively to the carbonyl oxygen. Mechanisms are proposed which account for all examples of ROH loss from esters. Alkanol loss from molecular ions in esters requires the presence of a second functional group to act as an intramolecular catalyst, either as a general acid in transferring a proton to the alkoxy oxygen, or as a general base in assisting the [1,3] carbonyl oxygen to alkoxy oxygen proton transfer. Loss of ROH from fragment ions requires proton transfer from an atom α to the positive charge to the alkoxy oxygen. These mechanisms are generalized to include a wide class of bifunctional esters and a selection of natural products.
Spectrométrie de Masse D'hétérocycles Séléniés. III—Etude de la Fragmentation de Quelques Selenolo [2, 3‐b] Pyridines
Authors: Croisy Alain , Jacquignon Pierre , Pirson Pierre , Christiaens Léon
Published: May 2005

Less spectres de treize dérivés dé la sélnoloé[2,3‐b]pyridine sont étudiés et comparése avec ceux du benzo[b]sélénophéne, de la quinoléine et de la thiéno[2,3‐c]pyridine. L'influence de la structure dihétéroatomique du noyau sur le processus de fragmentation des substituants oxygénés est examinée.
Evidence against an ortho attack in the molecular ion of ethyl 3‐phenylpropionate
Authors: Resink J. J. , Venema A. , Nibbering N. M. M.
Published: May 2005

13C labelling at the benzylic position of the title compound has shown that the decomposing m/e 107 [C7H7O]+ ion has the protonated benzaldehyde and not the o‐hydroxybenzyl cation structure, suggested earlier by other authors1.
Field ionisation mass spectra of stereoisomeric dihalogenocyclobutanes, 1, 2‐dibromoethylenes and some alkenes
Authors: Lehmann W. D. , Beckey H. D.
Published: May 2005

The field ionisation investigation of some stereoisomeric alkenes and alkyl halides reveals differences in the fragmentation behaviour with respect to direct bond rupture. As observation by itself of the thermodynamic stability of stereoisomeric molecules, or rather of their structure, does not suffice entirely to explain the observed differences, we offer here an interpretation of experimental results based on the interaction of the stereoisomeric compounds with the strong electric field. Finally, some fundamental conclusions are drawn about the applicability of the field ionisation method to the differentiation between stereoisomers.
Photodimers of cinnamic acid and related compounds. A stereochemical study by electron‐impact and field desorption mass spectrometry
Authors: Caccamese S. , Montaudo G. , Przybylski M.
Published: May 2005

The low energy (13 eV) electron‐impact and field desorption mass spectra of some photodimers of cinnamic acid and related compounds containing the cyclobutane ring are reported and the fragmentation patterns analysed in order to obtain stereochemical information on the substituent position on the cyclobutane ring. Both symmetrical and asymmetrical splittings of the cyclobutane ring were detected, allowing characterisation of the head‐to‐head and head‐to‐tail structures of the title compounds. A ring opening rearrangement of the McLafferty type was also found.
Criteria for distinguishing between [M]+· and [M+H]+ ions in field desorption mass spectra
Authors: Schulten Hans‐Rolf , Beckey Hans Dieter
Published: May 2005

Ten criteria are introduced to distinguish between molecular ions and protonated parent molecules in field desorption mass spectrometry.
Ionisation et Fragmentation en Spectrometrie de Masse. V—Appreciation de L'Energie D'Activation Pour des Fragmentations Competitives
Authors: Bouchoux Guy
Published: May 2005

L'existence d'un ‘déplacement cinétique compétitif’ est mis en évidence lors de la fragmentation d'un ion moléculaire conduisant à des ruptures concurrentielles. Un mode de calcul de ce ‘déplacement cinétique compétitif’ est proposé.
Fragmentations des Hydroxyesters a Longue Chaine: Effet Sterique Provoque par un Noyau Benzenique Intercale Entre les Deux Fonctions
Authors: Wolff R. E. , Greff M. , Teller G. , Wolff G.
Published: May 2005

L'introduction d'un noyau benzénique entre les groupes hydroxyle et carbométhoxyle d'hydroxyesters aliphatiques à longue chaîne introduit une contrainte stérique qui s'oppose aux interactions entre les deux groupes fonctionnels et aux fragmentations qui en résultent. L'étude d'une série de p‐(hydroxyalkyl)benzoates de méthyle montre que l'importance de ces interactions diminue considérablement lorsque le transfert de l'hydrogène hydroxylique sur le groupe carbométhoxyle nécessite un état de transition de (9+ ϕ) chaînons, ou moins, au profit des fragmentations qui ne résultent pas de ces interactions. Il est montré qu'un transfert spécifique d'un hydrogène benzylique sur le groupe carbométhoxyle s'opère via le groupe hydroxyle qui sert de relais.
Determination of the appearance potentials of [C3H7]+ ions by a computerized electron distribution difference procedure
Authors: Gross M. L. , Wilkins C. L. , Williams R. C. , Leung G.
Published: May 2005

A simple computerized electron distribution difference method has been developed using a conventional mass spectrometer and an on‐line computer. Using the system, ionization potentials for various propyl halides were measured and found to agree well with photoionization data. The appearance potentials for [C3H7]+ agreed well with literature values, except for 1‐propyl bromide and 1‐ propyliodide which gave values approximately 0.7 eV lower than previous reports. The results are interpreted to indicate threshold formation of the sec‐propyl ion from all propul halides.
Massenspektrometrische Untersuchung Organischer Stickstoffverbindungen. XIV—Mechanismus der Piperidin‐Eliminierung aus N.N′‐(o‐Xylylen)‐Dipieridin
Authors: Schwarz Helmut , Wesdemiotis Chrysostomos , Bohlmann Ferdinand
Published: May 2005

Mit Hilfe der unsymmetrisch deuterierten Verbindung wird der Mechanismus der elektronenstoßinduzierten Piperidin‐Abspaltung aus der Titel‐Verbindung aufgeklärt. Eine 1.1‐Eliminierung kann eindeutig ausgeschlossen werden.
Massenspektrometrische Untersuchung von 2‐Alkoxybenzoesäuremethylestern: Mechanismus der Alken‐Eliminierung und Cyclisierungsreaktionen von Fragmentionen Durch Nachbargruppenwechselwirkung
Authors: Schwarz Helmut , Wesdemiotis Chrysostomos , Bohlmann Ferdinand
Published: May 2005

Die ‘instabilen’ [M – C2H4]+·‐Ionen (Lebensdauer<10−6 s) aus 2‐Alkoxybenzoe‐säuremethylester entstehen bevorzugt durch H‐Transfer vom terminalen C‐Atom (80%), aber auch durch solchen von der am Sauerstoff gebundenen Methylengruppe (20%). Die Übertragung findet ausschließlich auf den Sauerstoff und nicht auf den aromatischen Ring statt, und das Produkt‐Ion besitzt die Struktur eines ionisierten Salicylsäuremethylesters. Durch die Untersuchung einer l8O‐markierten Verbindung und mehrerer deuterierter Derivate werden zwei bisher unbekannte elektronenstoßinduzierte Nachbargruppeneffekte nachgewiesen. Die Produkte dieser Abbaureaktionen sind am besten durch cyclische Strukturen beschreibbar.
Negative ion mass spectra of metal complexes: Secondary electron capture and CS2 elimination from nickel (ii) dithiocarbamates
Authors: Fraser I. W. , Garnett J. L. , Gregor I. K. , Jessop K. J.
Published: May 2005

Negative ion mass spectra of series of bis‐(N, N‐dithiocarbamato)nickel(II) complexes of formula [NiS2C·NR1R2]2 (where·NR1R2  ·NEt2 ·NPr2, ·NBu2, pyrrolidinyl, piperidyl, morpholinyl, and ·NEtPh) have been obtained by secondary electron capture. Intense molecular anions are given for all compounds, with most fragments originating from these ions. Metastable data indicate that CS2 is eliminated from all molecular anions.
Studies in mass spectrometry. I—Common intermediates in the fragmentation of isomeric compounds under electron‐impact
Authors: Derocque Jean‐Luc
Published: May 2005

In the particular case where a specific ion [c]+· is generated with different internal energy, the variation of Z(E) = [(f)+]/[(c)+·] vs energy of the electron beam is discussed in relation to the P(Ei) and k(Ei) functions which describe the decay process [c]+· → [f]+. Qualitative application to seven isomeric hydrocarbons suggests that, among these isomers, two pairs might rearrange to a common intermediate before fragmentation occurs. It is found that in such cases the curves Z = f(E) for a given fragmentation are not superimposable but parallel, as suggested by theoretical considerations.
ETUDE EN SPECTROMETRIE DE MASSE DE PHOSPHONATES ENYNIQUES ET DE β‐CETOPHOSPHONATES‐γ, δ‐ETHYLENIQUES
Authors: Peiffer Gilbert , Gaydou Emile M.
Published: May 2005

L'étude des processus de rupture en spectrométrie de masse de dialcoylphosphonates ényniques (I) et de β‐cétophosphonates‐γ, δ‐éthylénique (II)
magnified image
sont caractérisés par des réarrangements au niveau du groupement phosphoré et des ruptures au niveau de la liaison phosphore–carbone. Les composés II conduisent à des schémas identiques à ceux de I par perte d'une molécule d'eau.
Electron‐impact‐induced hydrogen migration in organic molecules I–Substituent effects in the mass spectra of pivlanilides
Authors: Ramana D. V. , Vairamani M. , Kala S.
Published: May 2005

Substited pivalanilides give rise to fragments corresponding to anilies on electron‐impact, which is due to the migration of a hydrogen atom from the t‐butyl group to the nitrogen. The Hammett correlation indicates that the formation of this fragment is favoured by electron‐donating groups. The other interesting feature of these spectra is the migration of the aryl group to the t‐butyl carbon with the elimination of the neutral ketemine.
A detailed analysis of the complete hydrogen and carbon scrambling and fragmantation reactions of boron‐containing cationic species in the mass spectrometer
Authors: Pasto Daniel J. , Timony Peter E.
Published: May 2005

A detailed analysis of the mass spectral behavior of trialkylboranes and deuterium and 13C labeled tri‐n‐butylborane, and comparison with the ion cyclotron resonance behavior, have revealed several unique features and herefore unrecognized rearrangement and fragmantation reactions:(1)the occurrence of intial fragmentation of the parent ion with apparently nearly exclusive loss of one complete alkyl radical; (2) the extensive formation of boron‐containing spiecies (>% of the total ion current)in the mass spectrometer relative to the virtual absence (<5%) of such spieces in the ion cyclotron resonance spectrum; (3) the dominant formation of boron‐containing species of the composition [CnH2n+2B]+ with [C2H6B]+ generally being the base peak; (4) the formation of appreciable quantities of alkane molecular ions (5 to 10% of the total ion current) up to [R2]+. (from R3B); (5) the characterization of a fragmentation reaction involving the loss of CH2; (6) the observation that very extensive hydrogen and carbon scrmbling occurs in the ions formed after the initial fragmentation of the parent ion. A mechanism which satisfactorily accounts for the fragmentation and rearrangement reactions is proposed which involves the reversible formation and rearrangement of protonated boracyclopropanes and cyclopropanes formed by cationic insertions in ß‐CH bonds.
A test of the concept of ‘charge localisation’ in methionine
Authors: Den Heuvel C. G. Van , Nibbering N. M. M.
Published: May 2005

A previous re‐investigation of methionine has shown that the [C2H5S]+ ion is generated via rather complicated routes from the molecular ion. This has been interpreted as evidence against charge localisation in the fragmentation of the title compound. Deuterium labelling, high resolution mass measurements and metastable transitions have revealed, however, that the formation of the [C2H5S]+ ion is not in contradiction with the predicting capabilities of the concept of charge localisation.
Mass spectroscopy of hydroxamic acids: Fragmentation by the loss of the hydroxylamino oxygen
Authors: Akers Hugh A. , Atkin C. L. , Neilands J. B.
Published: May 2005

The mass spectra of three dihydroxamic acids have shown in each case prominent [M – 16]+· and [M – 32]+· ions. The spectrum of biosynthetically labeled rhodotorulic acid indicates that these ions arise from the sequential, specific loss of the hydroxylamino oxygens.
FRAGMENTIERUNGSDIAGRAMME ZUR AUFKLäARUNG DER ABBAUREAKTIONEN ORGANISCHER VERBINDUNGEN I–AROMATISCHE KOHLENWASSERSTOFFE
Authors: Schönfeld Wolfgang
Published: May 2005

Am Beispiel einiger ausgewählter, aromaatisscher Kohlenwasserstoffverbindungen wird die Aussagekraaft der Fraagmentierungsdiaagraamme1,2 demonstriert. Der Haujptzerfallsweg bei allen juntersuchten Verbindungen–Benzol, Diphenyl, Naphthaalin, Anthraacen und Phenaanthrenist eine Kaskaade von Aacetylenaabspaltungen, die vom Molekül‐Ion bis zzum Endprodukt aus zwei Kohlenstoffatomen führt. Die wichtigsten Neutraalfraagmente sind Moleküle, deren freie Valenzen gegebenenfalls durch die Umlagerung von Wasserstoffatomen des entstehenden Ions abgesáttigt wurden. Aanthracen und Phenanthren sind aufgrund ihres Fragmentierungsverhaltens Klar unterscheidbar.
Comparative study of ion kinetic energy, chemical ionisation and field desorption spectra
Authors: Das K. G. , Kulkarni P. S. , Shinde M. B.
Published: May 2005

A comparison of the fragmentation processes operating in the first field free region was made with the fragmentation in the ion source under electron ionisation, chemical ionisation and field desorption conditions for some selected compounds which undergo retro‐DielsI‐Alder fragmentation in the ion source under electron ionisationconditions. The fragmentation processes which com‐ete with retro‐Diels‐Alder fragmentation under chemical ionisation and field desorption conditions are discussed. The complementary nature of these techniques are illustrated.
Use of ion‐molecule reaction equilibria to identify structural isomers
Authors: McIver Robert T.
Published: May 2005

A new approach is described for identifying structural isomers which cannot be distin‐guished on the basis of their electron‐impact mass spectra. Using a pulsed ion cyclotron resonance mass spectrometer, equilibrium constsnts are measured for ion‐molecule reactions involving various C8H10 isomers and C7H8O isomers. The equilibrium constants are shown to be highly sensitive to the structural features of the various isomers.
FRAGMENTIERUNGSDIA GRAMME ZUR AUFKLÄRUNG DER ABBAUREAKTIONEN ORGANISCHER VERBINDUNGEN II–PPOLYMETHYL‐ UND CHILORBENZOLE
Authors: Schönfeld Wolfgang
Published: May 2005

Vollständige Zerfallsschemata werden zur Untersuchung der Fragmentierungs‐eigenschaften von Polymethyl‐ und Chlorbenzolen herangezogen. Der Verstärkte + M‐Effekt der Methylgruppe am ionisierten, aromatischen‐Ionen stark methylierter Verbindungen wechselt im Verlauf ihres Abbaus wiederholt zwischen dem Sechs‐ und Siebenringskelett. Mit dem ver‐stärkten + M‐Effekt kann auch der Abbau von Chlorbenzolen erklärt werden. Im Chlortropylium‐Ion ist die CCI‐Bindung in nachweisbarem Maße gefestigt.
Pyrrolo [1,2‐a] [1,3,5] triazine‐2,4(1H, 3H)‐diones. III—Fragementation under electron‐impact
Authors: Traynor J. R.
Published: May 2005

The mass spectra of eight pyrrolo[1,2‐a][1,3,5]triazie‐2,4(1H, 3H)‐diones have been examined. An unusual feature in the fragmentation of those compounds having a 7‐alkoxycarbonyl function, namely loss of the whole ester grouping with concomitant hydrogen rearrangement, is discussed.
Mass spectrometry of p‐toluenesulfonamides: Useful amine identification derivatives
Authors: Singer G. M. , Lijinsky W. , Rainey W. T.
Published: May 2005

The mass spectral fragmentation patterns of p‐toluenesulfonamides have been determined and have been found useful for identification of naturally occurring amines.
Ion structure determination through collisions of ions of high kinetic energy
Authors: Cooks R. G. , Beynon J. H. , Litton J. F.
Published: May 2005

Through studies on [C6H6]+ and [C6H5]+ it is shown that charge stripping provides information on ion structure which is complementary to that given by collision‐induced dissociation. Stripping involves a more uniform sampling over the range of ion internal energies than does collision‐induced dissociation which preferentially samples higher energy ions.
Loss of HX from 2‐haloethanol ions
Authors: Van De Sande C. C. , McLafferty F. W.
Published: May 2005

Contrary to the behavior of 1‐haloalkanes, the loss of HX from 2‐chloro‐and 2‐bromo‐ethanol involves a 1,2 elimination.
Mass spectrometry of heterocyclic compounds VIII–electron‐impact‐induced fragmentation of 1,2‐diphenyl‐pyrazolidine‐3,5‐dione and some 4‐substituted derivatives
Authors: Selva Antonio , Citterio Attilio , Merlini Lucio
Published: May 2005

The mass spectra of 1,2‐diphenyl‐pyrazolidine‐3,5‐dione and twenty‐one 4‐substituted derivatives are reported. Their fragmentation patterns have been studied by deuterium labelling, exact mass measurements, metastable studies by the defocusing technique and low energy spectra. Hydrogen rearrangements from the 4‐position of the heterocycle and/or from the ß‐position of the 4‐substituent groups, lead to the main primary fragment ions [C12H11N2]+ (m/e 183) as shown by the metastables. The 4,4‐d2 derivative shows an appreciable isotope effect even for molecular ions decomposing in the ion source. By comparison with the metastable abundances of competitive reactions, the molecular ions (m/e 252) of the 4‐unsubstituted compound appear to be structurally different from the corresponding m/e 252 fragment ions formed from 4‐derivatives by the loss of 4‐substituent with H rearrangement. If only vinylic or aromatic hydrogen atoms are present, primary cleavage of the heterocyclic ring occurs with loss of OH·, C3O2 and C3HO2. Important rearrangements leading to elimination of C6H6N and C6H7N are typical for unsaturated substituents on position four having allylic hydrogen atoms. Fragment ions, identical to molecular ions of some compounds discussed here, are obtained by electron‐impact and/or thermal decompostion of some complex compounds containing more than one 1,2‐diphenyl‐pyrazolidine‐3,5‐dione system. The [C6H5N2]+ (m/e 105) and [C6H5]+ (m/e 77) ions are common fragments of all the title compounds. Any hydrogen scrambling reactions between phenyl and heterocycle or 4‐substituent groups can be excluded.
Collision‐induced dissociation of the lower alcohols. A thermochemical study
Authors: Cooks R. G. , Hendricks L. , Beynon J. H.
Published: May 2005

Collision‐induced dissociation of the molecular ions and of some of the fragment ions foremed on ionization of methanol, ethanol and n‐propnol have been studied at high energy resolution in a mass spectrometer. The translational energy lost upon collision and the kinetic energy releasedupon fragmentation of the collisionally excited species have been measured by the methods of ion kinetic energy spectromety. The results of the translational energy loss measurements compare well with excitation energies predicted for each reaction form breakdown curves showing the relative abundances of the ionsas a fuction of internal energy. This correspondence is evidebce that the ionic reactions following electron‐impact excitation and those following collisional excitation with neutral molecules at relative traslational energies in the range of several kilovolts are at least qualitatively independent of the method of excitation. The occurrence of the corresponding spontaneous fragmentations in the alcohols has also been studied and the kinetic energy releases accompanying these reactions have been determined. In a few cases, metastable peaks were observed which did not increase in intensity when collision gas added and this phenomenon is associated with particular features of the reaction thermochemistry. Reactions which generally occur to very small extents in mass spectromety, such as methylene elimination, have been observed in highly excited ions. The methods developed in this study allow the decription of the thermochemistry of the reaction of highly excited ions, indlcuding the experimental determination of the partitioning of the nonfixed energy of the activated complex. This procedure complemets and extends energy partitioning studies made on metastable ions in which the partitioning of the reverse activation energy is the more readily accessible.
Transposition des Cycles Satures en Spectrometrie de Masse IV—Dioxolanes Derives de Cetones a Cycle Moyen et Grand
Authors: Audier Henri‐Edouard , Fetizon Marcel , Tabet Jeain‐Claude
Published: May 2005

Le mécanisme de frangementation des éthylètals des cyclanones à cycle moyen ou grande a été réétudié. La fragmentation peut ětre entièrement expliquée à l'aide d'un nouveau réarrangement qui implique une contraction de cycle et des migrations d'hydrogène qui ont été vérifiées sur des composés deutériés.
On field desorption mass spectrometry of salts
Authors: Schulten H.‐R. , Röllgen F. W.
Published: May 2005

The types of ion occurring in the field desorption mass spectra of inorganic and organic salts are discussed. In contrast to general experience with field desorption mass spectrometry molecular ions are either absent or of low intensity. The energetically and kindetically favoured process of cluster formation, however, generates ions from which the molecular structure can be easily derved. Some specific aspects for the analyses of salts by field desrption mass spectrometry are outlined.
Combined deuterium labeling and appearance potential measurements to uncover competing reaction mechanisms in the electron‐impact‐induced loss of water from cyclohexanol
Authors: Green Mark M. , Bafus Don , Franklin J. L.
Published: May 2005

The appearance potentials for loss of H2O and DOH from the constitutional isomers 3,5‐dideuterocyclohexanol and 4,4‐ dideuterocyclohexannol show, in agreement with proposals based on stereoselectivites, that 1,3 loss of water is energetically more costly than 1,4 loss of water.
Beurteilungskriterien für Klassifikatoren zur automatischen Spektreninterpretation (pattern recognition)
Authors: Rotter H. , Varmuza K.
Published: May 2005

In den Letzten Jahren wurden zahlreiche Verfahren der Zeichenerkennung für die automatische Interpretation von chemisch‐physikalischen Daten erprobt. Gute Erfolge wurden insbesondere mit Klassiufikatoren für niedrig aufgelöste Massenspektren erzielt. Die Angaben über die Güte der Spektrenklassifikatoren (‘Prozenstsatz richtig klassifizierter Spektren’) waren jedoch oft mathematisch unzureichend definiert. In dieser Arbeit werden mit Hilfe grundlegender Prinzipien der Wahrscheinlichkeitsrechnung und der Informationstheorie objektive Beurteuilungskriterien für binäre Klassifikatoren abgeleitet. Ein Klassifikator ist eine Rechenvorschrift, um aus einem Merkmalsvektor (Massenspektrum) und den a priori‐Wahrscheinlichkeiten der Klassenzugehörigkeiten (chemischen Strukturen) für diesen Merkmalsvektor die a posteriori‐Wahrscheinlichkeiten zu berechnen. Für den Vergleich der Güte von Klassifikatoren sind die Klassifizierungsfähigkeiten für die einzelnen Klassen oder der Informationsgewinn geeignet. Die angegebenen Formeln werden durch Beispiele aus der Massenspektrometrie erläutert.
Electron‐impact‐induced fragmentation of some isomeric cyclopropyl picolyl and pyridyl ketones
Authors: Glenn David F. , Edwards William B.
Published: May 2005

The electron‐impact‐induced fragmentation of three cyclopropyl picolyl ketones and three cyclopropyl pyridyl ketones has been studied with the aid of deuterium labeling, high resolution mass measurements and metastable mode operation.
Ionisation and appearance potentials of alkylketones
Authors: Mouvier G. , Hernández R.
Published: May 2005

The ionisation potentials of a series of alkylketones have been measured by the electron‐impact technique using the second derivative method. The ionisation efficiency curves were obtained with a conventional mass spectrometer and the data treated by means of a minicomputer. These results are compared with those given by photoelectron spectroscopy, which has enabled us to test our mass spectrometric method and to distinguish between the adiabatic and the vertical ionisation potentials. It has been observed that the electron‐impact technique can lead to the adiabatic ionisation potential in favourable cases.

We have determined the appearance potentials of fragmentations [A]+ = [RCO]+ and [B]+ = [CH3CO]+, arising from the rupture of bonds in the α position with respect to CO, for a large series of methylalkylketones. The standard heats of formation of these ions have been calculated. The excess energy of the fragmentation reaction, corresponding to the kinetic shift, is found to be small or negligible for the decomposition giving ion [A]+, requiring a smaller activation energy and high in the case of ions [B]+. This kinetic shift becomes larger for an increase in the activation energy and the vibrational degrees of freedom of the molecular ion, as postulated by the quasi‐equilibrium theory. An important fraction of the kinetic shift is due to the ‘competitive shift,’ i.e. the excess energy that must be supplied to the molecular ion for it to yield [B]+ ions in sufficient amounts to be detected by the mass spectrometer. This is confirmed by the claculation of the fragmentation rate constants for the 2‐butanone molecular ion.
Massenspektroskopische Fragmentierungsreaktionen. X—Zum Mechanismus der Methyl‐ und Äthylabspaltung bei benzanellierten 6‐ und 7‐gliedrigen heterocyclen
Authors: Budzikiewicz H. , Lenz U.
Published: May 2005

Es wird gezeigt, daß Methyl‐ und Äthyleliminierung aus 6‐ und 7‐gliedrigen benzanellierten Heterocyclen in der Regel nach verschiedenen konkurierenden Mechanismen erfolgt, wobei deren Art und relative Bedeutung vom Heteroatom abhängen.
The reactive states of ions: Dimethyl‐hexadienes and tetramethylcyclobutenes
Authors: Rennekamp Michael E. , Hoffman Michael K.
Published: May 2005

The principal decomposition routes of molecular ions of cis, cis‐3,4‐dimethyl‐2‐4‐hexadiene, cis, trans‐3,4‐dimethyl‐2,4‐hexadiene, cis‐1,2,3,4‐tetramethylcyclobutene and trans‐1,2,3,4‐tetramethylcyclobutene were studied using ion kinetic energy spectroscopy. Evidence indecates that loss of radicals from [M]+· appears to proceed via an electronically excited state, while loss of a neutral molecule appears to involve complete equilibration of structure within the system, or may involve both ground state and excited state pathways.