bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectra of vinyltrimethylsilane and vinyltri(methyl‐d3) silane
Authors: Smolinsky G. , Vasile M. J. 
Published: May 2005

AbstractThis paper reports the mass spectrum of vinyltrimethylsilane over the range of electron‐impact energy of 9 to 70 eV as determined with a quadrupole mass spectrometer. Less extensive data obtained with magnetic spectrometers are included for comparison as well as the spectrum of vinyl‐tri(methyl‐d3)silane. Plots of ion intensity as a function of electron energy, nominal appearance potentials and metastable ion transitions are given.The primary ionization results in an electron deficiency on the silicon atom, followed by loss of either ·CH3, C2H4 or ·C2H3 to give fragments of mass 85, 73 or 72, respectively. The primary fragment of mass 85 loses C2H2 to give the mass 59 ion. The primary fragment of mass 73 loses successively C2H4 and H2 to give first the mass 45 ion and then the mass 43 ion. At 15 eV, the relative intensities of the ions are 85 > 72 > 100 > 59 > 73. At 70 eV, the relative intensities are 59 > 85 > 43 > 45 > 73 > 72 > 100.
Mass spectrometry of organic compounds in the group V elements–III: Amides, acylphosphines and vinylogues
Authors: Kostyanovsky R. G. , Plekhanov V. G. , Khafizov Kh. , Zagurskaya L. M. , Kadorkina G. K. , Elnatanov Yu. I. 
Published: May 2005

AbstractDistinct differences are observed on comparison of the fragmentation of tertiary amides (I to XI), and acylphosphines (XII to XVII) and (XX to XXII) under electron‐impact, as well as of their vinylogues (XXIII to XXXI) and (XXXIV to XXXV).
Specific and stereospecific water eliminations in the mass spectra of bicyclo[3.3.1]nonanols
Authors: Cable J. , MacLeod J. K. , Vegar M. R. , Wells R. J. 
Published: May 2005

AbstractBy the use of site‐specific and stereospecific deuterium labelling, it has been possible to show that loss of the elements of water from all possible bicyclo[3.3.1]nonanols (I to V) in the mass spectrometer, takes place in a substantially stereospecific manner. The position of abstraction of the hydrogen atom by the hydroxyl group can be related to the proximity effects that are present in the ground state conformers, while the [M]+ / [M – H2O]+ ratio appears to depend on the minimum H–‐OH intramolecular distance in the more stable conformations.
Sur la Fragmentation d'Isosteres Phenanthreniques Soufres et Selenies
Authors: Jacquignon P. , Croisy A. , Renson M. , Iteke E. , Christiaens L. 
Published: May 2005

AbstractDans le présent travail nous avons étudié six composés isostères du phénanthrène contenant simultanément un atome de soufre et un atome de sélénium ou deux atomes de sélénium.La configuration de ces molécules influence la fragilité des liaisons CSe, laquelle semble liée au degré d'aromaticité du noyau auquel l'hétéroatome de sélénium est fixé.Si l'allure générale des spectres est assez voisine de celle des spectres des analogues sulfurés, du benzothiophène, il n'en reste pas moins, comme c'est le cas pour tous les hétérocycles séléniés étudiés jusqu'à présent que la dégradation essentielle de tels composés est la perte du sélénium hétéroatomique, sans que le cycles adjacents soient affectés par cette fragmentation.
Negative ion mass spectra of dicarboxylic acids
Authors: Ito Akihiko , Matsumoto Kozo , Takeuchi Tsugio 
Published: May 2005

AbstractThe negative ion mass spectra of dicarboxylic acids show [M]−˙ and prominent [M – H]−ions. These ions can therefore be used to determine the molecular weight of dicarboxylic acids which do not give positive molecular ions. The [C2H3]− ion is a base peak in the spectra of maleic and fumaric acids. Isomeric phthalic acids are readily differentiated.
Etude Quantitative de la Reactivite–XXI: Comportement sous l'Impact Electronique de Bromures de Cyclopentyle et Cyclohexyle α‐substitutes cis et trans
Authors: Gounelle Yves , Péchiné Jean‐Marie , Solgadi Daniel 
Published: May 2005

AbstractLes spectres de dix couples de bromures de cyclopentyle et de cyclohexyle α‐substitués cis et trans sont enregistrés pour onze énergies d'ionisation distinctes comprises entre 10 et 20 eV. Pour chaque isomère un calcul du spectre de masse et de ses variations avec l'accélération électronique basé sur la théorie du quasi‐équilibre nous a permis une estimation des énergies d'activation dela rupture principale [M – Br]. Ces évaluations montrent que les différences observées entre les spectres de masse de diastéréoisomères dépendent essentiellement soit de la différence d'enthalpie entre les ions isomères àl'état fondamental lorsque le substituant est un fluor ou un oxygène, soit de la différence d'enthalpie entre les états de transition isomères de la rupture [M – Br] lorsque le substituant est un chlore ou un brome; ce qui dans ces derniers cas s'interprète par l'intervention d'une participation de l'halogène au départ du brome pour les isomères trans.
Stereospecific hydrogen migration in retro‐diels‐alder fragmentation of some polycyclic imides
Authors: Lesman Thila , Deutsch Joseph 
Published: May 2005

AbstractA stereospecific ‘retro‐Diels‐Alder’ fragmentation followed by hydrogen migration was found in the mass spectra of imides and phenyl imides of decahydroindacene 4,5‐dicarboxylic acid. The fragmentation involves a one hydrogen atom rearrangement when the charge is retained on the diene moiety and double hydrogen rearrangement when the charge is on the dienophilic moiety.
Mass spectra of some syn‐ and anti‐aromatic aldoximes
Authors: Brown Ellis V. , Hough Lindsay B. , Plasz Andrew C. 
Published: May 2005

AbstractThe mass spectra of eight pairs of geometric isomers of aromatic oximes and four other single aromatic oximes are reported. The loss of H2O, HO and HCN are major fragmentations from the molecular ion of all the benzaldoximes studies; however, the loss of HCN from the molecular ion did not occur in the oximes of 9‐phenanthraldehyde, 1‐naphthaldehyde and 2‐naphthaldehyde. The halogen substituted benzaldoximes eliminate HCNO and H2CNO forming an additional fragmentation pathway from the molecular ion. In general, variations were found for each pair of syn‐ and anti‐oximes but no consistent patterns could be found in the spectra for all the syn‐isomers versus all of the anti‐isomers. The geometric isomerism of four oximes previously reported in the literature have been established for the first time as anti‐m‐bromobenzaldoxime, syn‐9‐phenanthraldoxime, syn‐1‐naphthaldoxime and syn‐2‐naphthaldoxime. Three new oxime acetates were prepared and their mass spectra are discussed.
Mechanism of enolic ion tautomerization
Authors: Eadon George 
Published: May 2005

AbstractEvidence of enolic ion‐enolic ion tautomerization was observed in the mass spectra of several alkylcyclobutanols and aliphatic ketones. Extensive deuterium labeling experiments on 1‐butylcyclobutanol, 5‐nonanone and 7‐tridecanone demonstrated that the process did not involve the intermediacy of the ketonic ion. The predominant mechanism involves reciprocal hydrogen transfers through large ring transition states, rather than a direct 1,3 hydrogen shift. Other decomposition reactions of the enolic ions were observed.
Continuous wave laser induced degradation of polystyrene monitored by time‐of‐flight mass spectrometry
Authors: Coloff Stanley G. , Vanderborgh Nicholas E. 
Published: May 2005

AbstractThe laser induced degradation of polystyrene within the ion‐source housing of a time‐of‐flight mass spectrometer is described. A low power, CO2 laser was used to produce a steady state flux of degradation products. This method permits the use of normal recording techniques. The degradation of polystyrene is reported using this technique. Evidence is presented that the monomer is ejected from the irradiated surface. Degradation in the presence of oxygen and nitrogen is also described. Oxygen promotes the fragmentation of styrene while nitrogen shows the opposite effect.
The mass spectra of some pentafluorophenylthio derivatives
Authors: Jamieson W. D. , Peach M. E. 
Published: May 2005

AbstractIonic fragmentations induced by electron‐impact on compounds of the type C6F5SX (X  H, CH3, COCH3, Cl, C6F5) and (C6F5S)2, (C6F5S)2Hg, (C6F5S)3As and (C6F5SCH2)2 have been studied. Principal features of the mass spectra are reported. The [C6F5S]+ ion (m/e 199) is predominant and its mode of fragmentation has been deduced. The precursor ions for m/e 199 have been examined in (C6F5)2S, (C6F5S)2, (C6F5S)2Hg, (C6F5S)3As and C6F5SCl. Ion kinetic energy spectra of (C6F5)2S, (C6F5S)2, (C6F5S)2Hg and C6F5SCl have been recorded, and all contain peaks corresponding to the fragmentation of the [C6F5S]+ ion.
1,1‐Elimination of HCN from propionitrile under electron‐impact. Hydrogen migration in the molecular ion
Authors: Meyerson Seymour , Karabatsos G. J. 
Published: May 2005

AbstractThe dominant primary reactions of propionitrile under electron‐impact effect loss of HCN and loss of H·. Deuterium labeling shows that the hydrogen atom lost as HCN comes chiefly from C‐2, but that lost as a free atom comes chiefly from C‐3. Both reactions are probably preceded by a 1,2 hydrogen migration to yield an allylic‐like molecular ion, \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm CH}_{\rm 3}{\rm C}^+ {\rm HCH = N}^{\rm .} \leftrightarrow {\rm CH}_{\rm 3} \mathop {\rm C}\limits^{\rm .} {\rm HCH = N}} \right]^+ $\end{document}.
Organische Schwefelverbindungen—IV: Elektronenstossinduzierte Redoxreaktion von ortho‐Nitrothiobenzoesäure‐S‐p‐tolylester
Authors: Martens Jürgen , Praefcke Klaus , Schwarz Helmut 
Published: May 2005

AbstractDie elektronenstossinduzierte Fragmentierung der nitrothiobenzoesäure‐S‐p‐tolylester führt bei der ortho‐Verbindung zu einer bisher unbekannten Umlagerung, bei der in Form einer intramolekularen Redoxreaktion ein Sauerstoff der Nitrogruppe zum Schwefel der Thiolester‐Gruppierung wandert. Die Stellung der Nitrogruppe beeinflusst nicht nur wesentlich das Fragmentierungsbild, sondern darüberhinaus in dramatischer Weise die Lebensdauer des Molekül‐Ions.
Mass spectra of monosubstituted trans‐stilbenes
Authors: Güsten H. , Klasinc L. , Kramer V. , Marsel J. 
Published: May 2005

AbstractThe mass spectra of twenty‐eight monosubstituted trans‐stilbenes in ortho, meta, para and alpha positions with N(CH3)2, NH2, OCH3, OH, Br, Cl, F, CH3, COOH, CN and NO2 groups as substituents have been studied. A detailed fragmentation pathway is given for stilbene. This fragmentation, characteristic for most of the substituted stilbenes, takes place either from the molecular or from the [M ‐ Substituent] ion. In o‐nitro‐, o‐methoxy‐,α‐carboxyl‐ and α‐methylstilbene, however, rearrangement reactions prior to fragmentation influence the fragmentation pattern.
The electronic structure of ionised molecules—VIII: Ethylamine
Authors: Krier C. , Lorquet J. C. , Berlingin A. 
Published: May 2005

AbstractWavefunctions for the [C2H5NH2]+˙ ion in its electronic ground state have been calculated by two variants of the CNDO method. The potential energy surface, the reaction paths, the charge distribution and the overlap populations have been calculated as functions of the internuclear distances in order to elucidate the fragmentation mechanism. The results are compared with the description given by other methods in current use, namely the mechanistic approach and the Hirofa method. The reliability and limitations of the three methods are discussed.
The mass spectra of some methyl alkanesulphinates
Authors: Filby W. G. , Penzhorn R.‐D. , Stieglitz L. 
Published: May 2005

AbstractMass Spectra of the methyl esters of ethane, n‐propane, isopropane, n‐butane, sec‐butane and tert‐butane sulphinic acids have been determined. In general, the parent ions are of low abundance and the most prevalent are the hydrocarbon ions which arise by α‐cleavage. Other ions that serve to characterise these compounds are those from the CH4SO2 and HSO2 fragments.
Étude D'une Série de Phénoxazines et D'azaphénoxazines par Spectrométrie de Masse
Authors: Cassan J. , Rouillard M. , Azzaro M. , Mital R. L. 
Published: May 2005

AbstractNous avons effectué les spectres de masse de phénoxazines et d'azaphénoxazines substituées. Ces composés sont caractérisés par la présence d' un hydrogéne sur l'azote hétérocyclique et la position de substituants NO2et Cl sur les cycles aromatiques. A l'aide de mécanismes classiques, nous avons rationalisé les processus de fragmentation et expliqué les pics principaux de ces specters. La présence de substituants Cl et NO2perturbent totalement la fragmentation observée dans le cas de la molécule de phénoxazine. Ils favorisent la localisation de la charge suivant leur position sur le cycle, soit sur l'azote, soit sur l'oxygéne hétérocycliques. Quant au gropement NO2par isomérisation (forme nitroso), il donne lieu éa une fragmentation spécifique.
A comparative, vapor‐phase (G.L.C.‐M.S.) study of various derivatives of prostaglandins A and B
Authors: Watson J. Throck , Sweetman Brian J. 
Published: May 2005

AbstractThe isomeric prostaglandins, A and B, can be readily distinguished by differences in the mass spectra of their derivatives. The mass spectra of the PGA1‐ or PGA2‐methyl ester (ME)‐trimethyl silyl (TMS) ether derivatives have a prominent ion at [M − 71]+ or [M − C5H11]+ while those of the PGB1‐ or PGB2‐ME‐TMS derivatives have a predominant ion at [M − 99]+ or [M − C6H11O]+ in addition to that at [M − 71]+. Ions of similar origin characterize the spectra of the PGA1‐ or PGA2‐TMS ether‐TMS ester and PGB1‐ or PGB1‐TMS‐TMS derivatives, respectively. The fragmentation of other derivatives of PGA1, PGA2, PGB1 and PGB2 such as the ME‐t‐Bu‐DMS (t‐butyl‐dimethylsilyl ether); ME‐MO (methoxime)‐TMS; ME‐MO‐Ac (acetate), and ME‐Ac are also described comparatively. The composition of important ions was confirmed by deuterium labeling and/or high resolution mass spectroscopy, where appropriate. The potential advantages and limitations of the derivatives for quantitative analysis of prostaglandins by the specialized technique of multiple ion detection (MID) are described.
Etude Comparée de la Fragmentation de Trois Composés Médicamenteux a Structure Hétérocyclique: la Primaclone, le Glutethimide et le Phenobarbital
Authors: Bourgeois G. , Brachet‐Liermain Mme A. , Ferrus Mlle L. 
Published: May 2005

AbstractLes spectes de masse de ces trois composés ont éteacute; comparé. L'utilisation de la haute résolution et de la méthode de marquage au deuté a permis de mettre en évidence un mécanisme de fragmentation particulier commun aux trois dérivés. Ce mécanisme consiste en un transfert électronique cyclique á six centres donnant naissance á un ion radical aromatique. Les mécanismes de fragmentation propres aux barbituriques ont également été observé.
Nachbargruppeneffekte bei der Elektronenstoß‐Induzierten Fragmentierung von Acetylierten 2.2′‐Diamino‐Diphenylmethanen
Authors: Eckhardt G. , Fehlhaber H.‐W. , Volk H. , Welzel P. 
Published: May 2005

AbstractDie mono‐und bis‐acetylierten 2.2′‐Diamino‐diphenylmethane (I bis V) spalten beim Elektronenstoß‐induzierten Zerfall in starkem Maße aus den Molekúlionen Wasser ab. Die zugrundeliegenden Fragmentierungsprozesse wurden mit Hilfe deuterierter Verbindungen untersucht.
Charge localization and aromatic stabilization in large ring ions: Mass spectra of ms‐porphyrins
Authors: Meot‐Ner M. , Adler A. D. , Green J. H. 
Published: May 2005

AbstractThe major mass spectrometric fragments of ms‐tetraphenylporphin and ms‐tetra(p‐chloro)phenylporphin are [M  H]+˙ and [M  Cl]+˙, respectively. Metal derivatives of these compounds give a modified characteristic fragmentation pattern with peak groups ending in the ions [M  4H]+˙, [M  ϕ  5H]+˙ and [M  2ϕ  2H]+˙ for the metallo ms‐tetraphenylporphins, and [M  ϕCl  2Cl  3H]+˙ and [M  2ϕCl  Cl  H]+˙ for Mgms‐tetra(p‐chloro)phenylporphin. Deuterated metal derivatives indicate random hydrogen loss from both phenyl and pyrrole carbons. However, metal substituents do not significantly modify the fragmentation pattern in the case of ms‐tetra(p‐methoxy)phenylporphin. These patterns can be explained in terms of aromatic stabilization of the fragmentation products, coupled with charge localization on the π system in the free base, on the metal atom in the metallo derivatives and on the methoxy function in the p‐methoxyphenyl derivative.
Massenspektroskopische Fragmentierungsreaktionen. V—Zur Frage des Quasi–Thermischen RDA–Zerfalls
Authors: Budzikiewicz H. , Linscheid M. 
Published: May 2005

AbstractAm Beispiel von verschieden substituierten Steroiden wird geziegt, daß auch beim RDA‐Zerfall quasithermische Reaktionen nicht zur Deutung des Fragmentierungsverhaltens herangezogen werden müssen, daß Ergebnisse gegen eine erhebliche Beteilgung solcher Prozesse sprechen.
Mass spectrometry of insect moulting hormones: Trimethylsilyl‐methoxime derivatives of ecdysone and 20‐hydroxyecdysone
Authors: Morgan E. D. , Woodbridge A. P. 
Published: May 2005

AbstractThe mass spectra of trimethylsilyl‐methoxime derivatives of the two insect moulting hormones, ecdysone and 20‐hydroxyecdysone are described together with some model compounds. These steroid derivatives are volatile in the gas chromatograph and their mass spectra provide a sensitive means of detection and structure recognition.
The mass spectra of the trimethylsilyl derivatives of some alkyl and aminoalkyl phosphonates
Authors: Harvey D. J. , Horning M. G. 
Published: May 2005

AbstractThe mass spectra of the trimethylsilyl derivatives of a series of alkyl and aminoalkyl phosphonates were investigated with the aid of deuterium labeling and high resolution mass measurements. The spectra contained several prominent ions characteristic of the phosphonate system and a number of ions produced by inter and intra molecular migration and interaction of trimethylsilyl groups.
Mass spectra of organoarsenic compounds. III—Electron‐impact‐induced fragmentation of trialkylarsenates and penta‐alkoxyarsoranes
Authors: Frøyen Paul , Møller Jørgen 
Published: May 2005

AbstractThe mass spectra of a series of trialkylarsenates are reported, together with those of dimethyl methylarsonate, pentamethoxyarsorane and pentaethoxyarsorane. Their behaviour under electron‐impact is discussed and compared with that reported for trialkylphosphates.
Orientation de la Fragmentation en Spectrométrie de Masse Par Introduction de Groupements Fonctionnels. XII—Ethylene Acetals Derives de Cyclopentanones et Cyclopentanones α Substituees
Authors: Audier Henri‐Edouard , Fétizon Marcel , Tabet Jean‐Claude 
Published: May 2005

AbstractLa fragmentation des éthylénecétals des cétones α substituées a été étudiée. Un nou‐veau type de transposition en spectrométrie de masse a été mis en évidence.
Elektronenstossinduzierte Fragmentierung von Acetylenverbindungen. XIII—Acyclische [C7H7]+‐Ionen Als Intermediate bei der Acetylen‐Eliminierung aus dem [M  Cl]+‐Fragment von Heptin‐(6)‐Dien‐(2.4)‐Ylchlorid‐(l)
Authors: Köppel Claus , Schwarz Helmut , Bohlmann Ferdinand 
Published: May 2005

Abstract[C7H7]+‐Ionen aus offenkettigen Verbindungen isomerisieren unter Elektronen‐stoss nur partiell zu einem Tropylium‐Ion, wobei die Lebensdauer τ bzw. die innere Energie E das Ausmass der Cyclisierung bestimmt.
Mass spectrometric studies of diterpenes: VIII—Epimers
Authors: Enzell Curt R. , Wahlberg Inger , Gunnarsson Lars‐Erik 
Published: May 2005

AbstractDiterpene epimers differing with respect to orientation of a secondary hydroxyl group, ring fusion or configuration at an asymmetric centre carrying carbon–carbon linked substituents were studied, and certain stereostructural‐spectral correlations were achieved for the first two groups. Each of the compounds examined was subjected to multiple scanning at both high and low electron voltage to allow computer assisted statistical calculation and comparison of intensity intervals at a predetermined confidence level for total ion currents and selected peaks.
Zum Mechanismus massenspektrometrischer Fragmentierungsreaktionen: XII‐Einfluß einer sterischen Hinderung der Mesomerie bei der Fragmentierung von N,N‐Dimethyl‐N′‐4‐Biphenylformamidinen
Authors: Kuschel Heinz , Grützmacher Hans‐F. 
Published: May 2005

AbstractDie Entstehung cyclischer [M  H]+Ionen (a) in den Massenspektren von N,N‐Dimethyl‐N′‐arylforrnamidinen wird durch elektronenabgebende Substituenten an der Aryl‐gruppe in para‐Stellung zur Formamidingruppe wegen der Ausbildung von Resonanzstrukturen des Typs c unterdrückt. Dieser Effekt wird auch in den Massenspektren von in 4′‐Stellung substituierten N,N‐Dimethyl‐N‐4‐biphenylformamidinen (III) beobachtet. Durch Finführung von Substituenten in die 2‐, 2′‐, 6‐ und 6′‐Stellung von III wird die Ausbildung der Resonanzstrukturen c′ in den Molekül‐Ionen so erschwert, daß diese Derivate ein noi males massenspektrometrisches Fragmentierungs‐verhalten aufweisen. Dafür reichen zwei Methylgruppen in 2‐ und 2′‐Stellung aus.
Perte Stereoselective du Groupe Methyle 20‐α de la Methyl‐20 Conanine sous L'impact Electronique
Authors: Longevialle P. , Alazard J. P. , Lusinchi X. 
Published: May 2005

AbstractDes expériences de marquage au deuterium des méthyles en 20 de la méthyl‐20 conanine ont permis de montrer la perte stéréosélective du méthyle 20‐α sous l'impact électronique. La perte de l'un ou l'autre méthyle conduisant à des fragments identiques, ce résultat ne peut être interprété qu'en considérant l'état de transition de la réaction de fragmentation.
Mass spectra of aryl substituted N‐t‐ butylbenzamides: Substituent effects on unimolecular ion decomposition
Authors: Tsai S.‐C. , Rubottom G. M. 
Published: May 2005

AbstractThe major reactions of aryl substituted N‐t‐butylbenzamides upon electron‐impact involve direct cleavage of a methyl radical, the loss of a butene molecule with the transfer of one hydrogen, or the loss of a butenyl radical with the transfer of two hydrogens. The last of these processes parallels the mass spectral behavior of aliphatic amides. Substituent effects indicate that electron‐withdrawing groups on the aromatic ring enhance the two hydrogen transfer process, while electron‐donating groups enhance the single hydrogen transfer process. Ion abundances, ionization potentials and appearance potentials are discussed with respect to correlation with σ+ values.
Notiz Über die Elektronenstossinduzierte Fragmentierung 2H‐Markierter Phenylsilane
Authors: Bohlmann Ferdinand , Köppel Claus , Schwarz Helmut 
Published: May 2005

AbstractBei der Bildung der [M  H]+‐Ionen aus Phenylsilan wird sowohl ein Isotopeneffekt i als auch ein Präferenzfaktor p beobachtet. Die Entstehung intensiver [M – 2]+‐ und [M – 3]+‐Ionen ist mit der Vorstellung offenkettiger Systeme verträglich. Eine Entscheidung für oder gegen die Struktur eines Silatropylium‐Ions ist durch die Untersuchung 2H‐markierter Verbindungen nicht möglich.
Susbstituent effects in mass spectrometry IV—an evaluation of empirical methods for calculating the ionisation potentials of para and meta disubstituted benzenes
Authors: Benoit Frank M. 
Published: May 2005

AbstractThree empirical equation which have been used to calculate ionisation potentials of para and meta disubstituted benzenes are evalyated according to their ability to predict the IP's of para and meta YC6H4COX, (where x  OH, NH2, CL).
3‐aryl‐2‐isoxazolines: Electron‐impact fragmentation and substituent effects
Authors: Bettinetti G. F. , Facchetti S. 
Published: May 2005

AbstractThe mass spectra were investigate of six 3‐aryl‐2‐isoxazolines, and three main fragmentation pathways were found to occur through loss of 28 and 30 a.m.u. The losses of 28 (C2H4)and 30 (CH2O) are seen as competitive mass spectrometric retro‐1,3‐dipolar cycloaddition processes. These reactions are also repeated successively, and take place in different ions either following the degradation of the substituent or the attack of the benzene ring. The substituents in the para position influence both these reactions and also the attack upon the rings. A quantitative study has been carried out on the effect of the substituent on the [M‐28] reaction, which can be interpreted in terms of the first ionisation energies. These terms are linearly intercorrelated, for the compounds under examination, with the Hammett type σ‐constants.