bluuebunny/crossref_metadata_2025_split huggingface dataset:
Negative ion mass spectra of a series of fluorinated β‐diketones
Authors: Gregor I. K. , Jennings K. R. , Sen Sharma D. K. 
Published: May 2005

AbstractElectron capture by and the subsequent fragmentation of a series of eleven fluorinated β‐diketones of general formula CF3COCH2COR has been studied in an MS‐50 mass spectrometer. Consecutive loss of two HF molecules from molecular anions occurs with all compounds, as does elimination of CHF3 from [M  H]− ions. Elimination of CO occurs from either \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm M - HF}} \right]_{}^{_.^ - } $\end{document} or \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm M - 2HF}} \right]_{}^{_.^ - } $\end{document} ions for five compounds where R  CF3 or a cyclic substituent. Kinetic energy release in metastable transitions associated with these HF and CO eliminations has been measured. Intensities of various fragment ions are in part influenced by the ion source temperature. Interaction of \documentclass{article}\pagestyle{empty}\begin{document}$ \left[{{\rm O}} \right]_{}^{_.^ - } $\end{document} reagent ions with five of the β‐diketones under chemical ionization conditions gave [M  H]− ions as the only significant ion‐molecule reaction product.
Recherches en série azabenzodiazépine. VI—etude en spectrométrie de masse de pyrazolo [3,4‐b]diazépines‐1,4
Authors: Affane‐Nguema Jean‐Paul , Lavergne Jean‐Pierre , Viallefont Philippe 
Published: May 2005

AbstractLes spectres de masse de 21 pyrazolo[3,4‐b]diazépines‐1,4 dans lesquelles le cycle diazépine peut présenter cinq structures différentes, sont décrits et analysis. Chaque structure a été caractérisée par un ensemble original de ruptures. Parmi celles‐ci un mode de fragmentation commun à tous les composés étudiés a été identifié: il s'agit de la rupture des liaisons C‐5C‐6 et C‐7N‐8 avec formation d'ions pyrazoloimidazoles.
Anionen‐Massenspektroskopie von Naturstoffen. VI—Anionen‐Massenspektroskopische Untersuchungen ausgewählter Gibberellin‐Verbindungen
Authors: Voigt D. , Adam G. , Schmidt J. , Schreiber K. 
Published: May 2005

AbstractDie Elektronenanlagerungsmassenspektren (2‐4 eV) der Gibberelline A1, A3, A4, A5, A7, A8, A9, 3‐epi‐GA1 und 3‐epi‐GA3 sowie 1β‐Hydroxy‐GA1 werden diskutiert und mit den entsprechenden Kationenmassenspektren verglichen.
Mass spectrometric investigation of stereosomeric 1,2‐dimethyl‐4‐substituted decahydroquinol‐4‐ol N‐oxides. Concerning the configuration of the asymmetric nitrogen atom
Authors: Zaikin V. G. , Bakaev A. A. , Wulfson N. S. , Akhrem A. A. , Ukhova L. I. , Marchenko N. F. 
Published: May 2005

AbstractThe main fragmentation pathways of the N‐1, C‐2 and C‐4 stereoisomers of the 1,2‐dimethyl‐4‐R‐transdecahydroquinoline‐4‐ol N‐oxides (R=CCH, CHCH2 and C2H5) under electron impact are discussed. The correlation between the mass spectrometric chromatographic behaviour and the configuration of polar groups in the N‐oxides examined is discussed. The mass spectra of the N‐1 stereoisomers may be subdivided into two groups, depending only on the orientation of N→O group and not of the 4‐OH group. The spectra of N‐oxides with the axial N‐oxide group reveal less intense ions and much more intense [MCH3]+, [MO]+, [MOH]+ and ions, whereas in the spectra of their equatorial epimers the abundance of the ions exceeds the intensities of the latter ions.
Electron impact studies CX—+E spectra from negative ions. Ortho effects and skeletal rearrangement reactions from sulphur compounds
Authors: Bowie J. H. , White P. Y. , Wilson J. C. , Larsson F. C. V. , Lawesson S.‐O. , Madsen J. Ø , Nolde C. , Schroll G. 
Published: May 2005

Abstract+E spectra derived from the non‐decomposing anion of some sulphur compounds are independent of the pressure of the collision gas. The compounds chosen for study contain peaks produced from either ortho effects or skeletal rearrangement fragments in their conventional positive ion spectra. The dissociative +E spectra are either devoid of skeletal rearangement ions or alternatiely contain such peaks in small abundance. In contrast, peaks derived from ortho reactions are present in high abundance.
Beiträge zum Studium einiger Heterocyclen. XLIV—Massenspektrometrische Untersuchungen einiger 2‐(p‐X‐Phenyl)‐5‐Y‐4‐acetylthiazole
Authors: Simiti I. , Demian H. , Luputiu Georgeta , Munteanu R. 
Published: May 2005

AbstractEs wurden massenspektrometrische Untersuchungen einiger neuen 2‐Phenyl‐4‐acetylthiazole durchgeführt. Die Substanzen besitzen hohe Molekülpeaks. Die Substituenten in p‐Stellung des Benzolrings üben keinen Eintluss auf das Fragmentierungsmuster aus, sondern nur auf die relativen Intensitäten von Molekülionen und der Fragmentionen. Die Einführung von Chlor bzw. Brom in Stellung 5 des Thiazols führen zu beträchtlichen Änderungen der Fragmentierung (‘ortho Effekt’). Es findet eine Umlagerung über einen fünfgliedrigen Übergangszustand statt. Ebenfalls sind doppelt geladene Ionen erkennbar, die durch Anwesenheit mehrerer leicht ionisierbarer Gruppen erklärbar sind.
The electron impact induced fragmentation of aromatic aldoximes—II. Substituent effects on the loss of MCN
Authors: Vijfhuizen Peter C. , Dijkstra Geo 
Published: May 2005

AbstractLoss of HCN from the molecular ion of benzaldoximes occurs via two distinct involving a 4‐membered and a 5‐membered intermediate, respectively. Both low energy high energy molecular ion decomposition were investigated by means of metastable peak shapes and the energetics of further decomposition of ions, respectively. Substituent effects previously held responsible for differences in the behaviour of m‐ and p‐methoxybenzaldoximes are shown to be negligible; the differences are due to the differense in internal energy contents.
Ionic dehydration reactions: The effect of location of the activated complex on kinetic energy release
Authors: Gross M. L. , Deroos F. L. , Hoffman M. K. 
Published: May 2005

AbstractA broad range of kinetic energy release has been found for the 1,4 elimination of water in a series of ortho substituted benzyl alcohols and benzoic acids. It is suggested that the trend reflects, in part, the position of the activated complex on the reaction coordinate. More specifically, reactions which proceed via an ‘early’ transition state release only small quantities of energy, whereas those processes occurring ‘later’ release a larger fraction of the available energy. Consequently, the o‐ methyl derivatives give large kinetic energy release compared to o‐ amino or hydroxy substituted compounds. Father verification is obtained from the small kinetic energy release observed for the 1,4 ionic dehydration in simple,acyclic alcohols.
Transfert d'un Atome de Chlore lors d'un Réarrangement de Type McLafferty
Authors: Arseniyadis S. , Gore J. , Roumestant M. L. 
Published: May 2005

AbstractLes spectres de trois allènes ω‐chlorés mettent en évidence deux réarrangements de type McLafferty; l'un s'effectue avec transfert d'hydrogène, I'autre avec transfert de l'atome de chlore.
Mass spectrometric studies on a β‐ketosulfone
Authors: Diller Dov , Bergmann Felix 
Published: May 2005

AbstractThe fragmentation of the β‐ketosulfone‐γ‐methylsulfonyl‐γ‐benzoylbutyronitrile under electron bombardment follows a number of different pathways: formation of the benzoyl ion (Major path); remova of acrylonitrile; liberation of the methylsulfonyl radical or of methylsulfonic acid; and finally elimination of a methylenecyano radical. The fragments observed can be explained by these five degradation paths. The reactions are compared with the photochemical cleavage of this β‐ketosulfone in benzene solution.
Electron impact induced fragmentation of some 1,2,4‐triazole derivatives
Authors: Kallury R. Krishna Mohan Rao , Upadhyaya Pramod V. , Surendra Nath Tumbalam G. , Srinivasan Vankipuram R. 
Published: May 2005

AbstractThe mass spectra of eight 1,2,4‐triazole derivaties have been recorded and found tao reveal extensive hydrogen and skeletal migrations. The structures of the fragments have been confirmed by deuterium labelling and exact mass measurement. The compounds revealed striking differences in their spectra depending on the nature of the substituents.
Pyrolysis mass spectrometry of methionine
Authors: Posthumus M. A. , Nibbering N. M. M. 
Published: May 2005

AbstractThe mechanisms of some fragmentation of methionine upon Curie‐point pyrolysis have been studied by the use of deuterium labelling. They lead to products having the same nominal mass but essentially different elemental compositions compared with ions generated by electron impact on methionine. For exaple, upon pyrolysis the product with mass 116 is due to a 1,2 elimination of hydroxylamine from the title compound, whereas upon electron impact the ion with m/e 116 is generated by successive loss of a molecule of water and of a methyl radical from the molecular ion; the generated of product m/e 101 proceeds via successive loss of a molecule of water, carbon monoxide and of hydrogen upon pyrolysis, but via a one‐step elimination of methanethiol upon electron impact. No evidence has been found for a diketopiperazine formation by a bimolecular process upon pyrolysis, although this type of reaction is well known for α‐amino acids.
Fragmentation of a new type of 6‐phenyl‐2‐pyridone, bearing a 5‐methylsulfonyl substituent, under electron impact
Authors: Bergmann Felix , Diller Dov 
Published: May 2005

AbstractThe mass pectra of 5‐methylsulfonyl‐6‐pyridone and its 3,4‐dihydro derivative show that the most important fragmentations involve the methylsufonyl substituent, which is eliminated in various forms (CH3SO˙; CH3SO2˙; CH3SO2H or SO2H˙). Other fissions like the removal of CO, which is the predominant event in simple 2‐pyridones and in 6‐pyridone, appear only after breakdown of the sulfonyl group. Only 5‐methylsulfonyl‐6‐phenyl‐2‐pyridone eliminates an OH radical from the molecular ion.
The mass spectral rearrangements of aryl propenyl sulfones. An electron impact induced smiles type rearrangement
Authors: Hill Charlotte J. , Thyagarajan B. S. , Bates D. K. , Spangler R. J. 
Published: May 2005

AbstractThe mass spectral behavior of trans‐1‐arylsulfonyl‐2‐arylsulfenyl‐propenes, trans‐1‐arylsulfonyl‐2‐arylsulfinyl‐propenes and trans‐1, 2‐(arylsulfonyl)‐propenes was examined. A Smiles type rearrangement was present in the sulfonyl‐sulfides, but was completely absent in the trans‐1‐arylsulfonyl‐2‐arylsulfinyl‐propenes and trans‐1, 2‐(arylsulfonyl)‐propenes. Vinyl migration to the sulfone oxygen predominates over aryl migration in all of the compounds studied. The mass spectra of the cis and trans isomers of 1‐p‐tolylsulfenyl‐2‐p′‐tolysulfonyl‐propene and 1, 2‐(p‐tolylsulfonyl)‐propene are also described.
Field ionization kinetics: Phenylhexanone
Authors: Patterson Donald G. , Scott Richard B. , Brown Peter 
Published: May 2005

AbstractA Varian Atlas SMIB double focusing mass spectrometer has been modified for field ionization kinetics measurements. Computer programs have been written for the calculation and display of potential maps, ion trajectories, and the transformation to ion lifetimes and phenomenological rate constants. The previously studied cyclohexene system has been used to check the accuracy of our method. The fragment ions generated by phenylhexanone after field ionization have also been examined by field ionization kinetics, including cleavage and rearrangement reactions, H/D randomization and temperature effects.
Etude par Spectrométrie de Masse du Di‐O‐isopropylidene‐1,2;5,6‐α‐D‐ribo‐hexofurannosul‐3‐ose
Authors: Glangetas Alain , Buchs Armand , Tronchet Jean M. J. 
Published: May 2005

AbstractLa fragmentation du di‐O‐isopropylidène‐1,2:5,6‐α‐D‐ribo‐hexofurannosul‐3‐ose a été étudiée à I'aide de molécules marquées avec du deutérium et de I'oxygéne 18O. Des mécanismes sont proposés pour la formation des principaux ions.
Electron impact induced fragmentation of dibenzo‐18‐crown‐6 polyether and its nitro derivatives
Authors: Gomes Ailton De Souza , Oliveira Clara Marize Firemand 
Published: May 2005

AbstractThe mass spectra of dibenzo‐18‐crown‐6 polyether and three of its nitro derivatives have been determined. The fragmentation pathways of all the compounds suggested that ring contraction was taking place. The molecular ion of the polyether dissociated by three competing processes, mainly through loss of C2H4O units. The molecular ions of the three derivatives dissociated with ring contraction, as well as through losses of O, No and NO2.
Collisional activation of ions formed by [Li]+ ion attachment
Authors: Röllgen F. W. , Borchers F. , Giessmann U. , Levsen K. 
Published: May 2005

AbstractSince no unimolecular fragmentation is observed with [M+Li]+ ions under normal operating conditions the collisional activation method was used to study the fragmentation behaviour of these ions. It was found that the liberation of the [Li]+ ion is a dominant process only with smaller molecules. In addition, direct bond cleavages and new types of rearrangement reactions lead to fragment ions in which the lithium is normally retained. The decomposition behaviour of [M+Li]+ ions represents an intermediate case between that of [M]+ ions and excited neutral molecules and is quite different from that of [M+H]+ ions.
Unimolekulare CH3‐, CH4‐, C2H4‐ und C3H4‐Eliminierungen aus alkin‐ und arylsubstituierten Isopropylkationen in der Gasphase
Authors: Bobrich Michael , Schwarz Helmut , Levsen Karsten , Schmitz Peter 
Published: May 2005

AbstractDurch die Untersuchung13C‐ und2H‐markierter Modellverbindungen werden die Methyl‐, Methan‐, Äthylenund Allen (bzw. Propin)‐Eliminierungen aus zwei isomeren [C3H6Y]+‐Ionen studiert (Y =p(HCC)C6H4bzw. C6H5CC−). Es wird belegt daß die Zerfallsprozesse von erheblichen Kohlenstoff‐ und Wasserstoffumlagerungen begleitet werden, deren Ausmaß im allgemeinen nicht einem vollständigen C/H‐Scrambling entspricht, sondern in spezifischer Weise durch die jeweilige Fragmentierung bestimmt wird.
Regiospezifische Wasser‐Eliminierung aus stereo‐ und konstitutionsisomeren Hydroxymethyl‐α‐dekalolen durch chemische Ionisation
Authors: Reich Monika , Schwarz Helmut 
Published: May 2005

AbstractDie chemische Ionisation (Reaktionsgas i‐Butan) von spezifisch 18O‐markierten, Hydroxymethyl‐α‐dekalolen, die sowohl eine primäre als auch eine sekundäre Hydroxylgruppe enthalten, belegt zum ersten Mal, daß nahezu ausschließlich (>97%) die sekundäre OH‐Funktion an der Bildung des [M + H − H2O]+‐ Ions beteiligt ist. Die Intensität der protonierten Molekül‐Ionen wird durch die Konstituion, die relativen Konfigurationen und die Konformation der Diole beeinflußt.
Massenspektroskopische Untersuchungen an 2,5‐Diaryl‐1‐(arylimino)‐1λ4,2,5‐thiadia‐zolidin‐3,4‐dionen
Authors: Neidlein Richard , Leinberger Peter , Hotzel Alfred 
Published: May 2005

AbstractDie Massenspektren von 2,5‐diaryl‐1‐(arylimino)‐1λ4,2,5‐thiadiazolidin‐3,4‐dionen wurden untersucht. Das auftreten mehrerer Bruchstücke wird durch die Umlagerung der Titelverbindungen zu 1,3‐(diarylimino)‐5‐aryl‐1λ4,2,5‐thioxazolidin‐4‐onen und 1‐oxo‐2,5‐diphenyl‐3‐(arylimino)1λ4,2,5‐thiadiazolidin‐4‐onen erklärt.
Isomerization of hydrocarbon ions. VIII—The electron impact induced decomposition of n‐dodecane
Authors: Levsen Karsten , Heimbach Heinz , Shaw G. John , Milne G. W. A. 
Published: May 2005

AbstractThe literature on the mass spectrometry of 2H and 13C labelled higher alkanes is reviewed and the decomposition behaviour of both the molecular and the fragment ions of n‐dodecane, n‐dodecane‐1, 12‐[13C2] and n‐dodecane‐1,1,1,12,12,12‐[2H6] studied with special emphasis on metastable decompositions. It is shown that the elimination of alkane molecules and alkyl radicals from the n‐dodecane molecular ion occurs primarily by simple splitting of the CC bond. In addition, both small alkane molecule and alkyl radicals are eliminated with low probability from centreal parts of the molecular ion. The alkane elimination is less specific than the alkyl elimination. The methyl elimination shows an exceptionally high non‐specificity, but is of negligible abundance in the 70 e V electron impact spectrum. The metastable ion spectra suggest, but do not prove unambiguously, that those small alkyl ions (with up to four carbon atoms) originating directly from the molecular ion, may be formed both by direct cleavage of the terminal groups and from central parts of the molecular ion. However, the majority of the small alkyl fragment ions in the 70 eV spectrum are formed by secondary decomposition explaining their apparent non‐specific formation. The strikingly different fragmentation behaviour of even electron, [CnH2n+1]+, and odd electron magnified image fragment ions, results from differences in the product stabilities. Using collisional activation and metastable ion spectra it is shown that the odd electron fragments have the structure of the linear alkene (most probably the 1‐alkene) molecular ion. In contrast to the molecular ions, alkyl fragment ions decompose with complicated skeletal rearrangements, which lead to substantial, but not complete, carbon randomization. The terminal hydrogen atoms, however, show little scrambling.
Field desorption of electrolytic solutions using untreated wire emitters
Authors: Heinen H. J. , Giessmann U. , Röllgen F. W. 
Published: May 2005

AbstractSimple untreated wire emitters can be used for field desorption of electrolytic solutions, e.g. acids or substances containing alkali salts. The ionization is achieved by the attachment of protons or alkali ions to molecules in the condensed phase which are subsequently desolvated by the action of high electric fields. This field desorption mode is demonstrated and discussed for a few characteristic examples. It is shown that the addition of substances of high viscosity and low vapour pressure in the liquid state favours the field desorption behaviour of many compunds. In general the mass spectra of untreated wires are less complicated than those of activated emitters since field ionization processes occurring at the tip of the field‐enhancing microneedles are avoided.
Massenspektrometrische Fragmentierung von Metallkomplexen des Tropolons
Authors: Grotjahn L. , Krüger P. 
Published: May 2005

AbstractDie Fragmentierung der Metallkomplexe von Tropolonen ist entscheidend vom Metallatom beeinflußt. Im Unterschied zum freien Liganden wird die Eliminierung von Kohlenmonoxid stark zurückgedrängt. Die Bildung von metalltreien Fragmentionen sowie die außergewöhnliche Wasserabspaltung der Cu‐Verbindung werden beschrieben.
Dehydration reactions in the mass spectra of 13‐podocarpen‐12‐ols and 12‐podocarpen‐14‐ols
Authors: Wahlberg Inger , Enzell Curt R. 
Published: May 2005

AbstractElectron impact induced dehydration of allylic cyclohexenols has been examined using 13‐podocarpen‐12‐ols and 12‐podocarpen‐14‐ols as model compounds. Deuterium labelling shows that ring cleavage prior to elimination of water is the principal dehydration route, whereas transannular 1,3 and 1,4 reactions account for only minor portions of the [M−18]+⋅ and [M−33]+ ion currents.
Mass spectra and energetic data for the formation of the [MCH3]+ ion of 10,10‐dimethylphenylthio‐silyn, ‐germyn and ‐stannyn derivatives, and of 9,9‐dimethyl‐thioxantene
Authors: Innorta G. , Torroni S. , Distefano G. , Pietropaolo D. , Ricci A. 
Published: May 2005

AbstractThe formation of the [M  CH3]+ ion from 10,10‐dimethylphenylthio‐silyn, ‐germyn and ‐stannyn derivatives as well as 9,9‐dimethylthioxantene with the aid of appearance and ionization potential measurements.
Effects of pressure on ion‐molecule reactions in the chemical ionization mass spectrometry of carboxylic acids
Authors: Grønneberg Truls 
Published: May 2005

AbstractThe water elimination caused by bifunctional interaction in protonated dicarboxylic acids diminishes as sample pressure increases. This appears to be the result of stabilization of the protonated dixarboxylic acid by reversible formation of a protonted dimmer. The effect reaches a minimum for dicarboxylic acid with interfunctional chain length of 6–9 carbons where the free energy of activation probably also reaches a minimum. Self‐acetylation by water elimination from protonated dimers was observed for the monocarboxylic acids only.
Mass spectra of trimethylsilyl Di‐O‐methyloximes of aldosuloses and dialdoses
Authors: Dizdaroglu Miral , Henneberg Dieter , Sonntag Clemens Von , Schuchmann Man Nien 
Published: May 2005

AbstractAldosuloses and dialdoses are readily converted to the corresponding acyclic methyloxime trimethylsilyl derivatives which give characteristic mass spectra. The gas chromatography mass spectrometry coupling technique also allows trace analysis since full information can be derived from the most intense fragment ions of the mass spectra which mainly arise from fragmentations β and δ to the O‐methyloxime group.
Mass spectrometry of steroid systems. XXIV–The origin of [M – 28]+ and [M – 43]+ ions in equilenin and its 14β‐isomer
Authors: Zaretskii Ze'ev V. I. 
Published: May 2005

AbstractThe formation of the [M43]+ ion in equilenin is due mainly to elimination of Me radical from the [MCO]+ ion and, to a lesser extent, to CO loss from the [MMe]+ ion. In 14β‐isoequilenin the [MCO]+ ion is absent, and the formation of [M43]+ occurs via the [MMe]+ ion. This makes the determination of the mode of junction of the rings C and D in the equilenin series possible, using high resolution mass spectra, even when only one stereoisomer is available.
Mass spectra of o‐aminobenzophenones
Authors: Nudelman N. Sbarbati , Waisbaum R. G. 
Published: May 2005

AbstractThe electron impact induced fragmentation of chlorine substituted o‐aminobenzophenones has been examined. All the compounds show ions formed by α‐cleavage on either side of the carbonyl group. The relative intensity of the resulting ions is predictable from the quasi‐equilibrium theory. The most important features of the mass spectra of these compounds are, however, intense [MH]+ ions for the primary amines and [M – OH]+ ions for the N‐methylated compounds. These and other less intense peaks as well as some metastable ions allows structural elucidation.
Fragmentation sous l'Impact Electronique de Bitriazoles‐5(3),1′ et de Bitriazoles‐4,4′
Authors: Aouial Mohamed , Bernardini Antoine , Viallefont Philippe 
Published: May 2005

AbstractLes spectres de masse d'un certain nombre de bitriazoles‐5(3),1′ et bitriazoles‐4,4′ sont décrits: les principales fragmentations sont données et leur utilité à la détermination des structures de composés isomères est montrée. Des dégradations spécifiques sont également observées à partir du groupement triazolyle en position 4.
Mass spectra of tetraselenafulvalenes, diselenadithiafulvalenes and tetrathiafulvalenes
Authors: Andersen Jan R. , Egsgaard Helge , Larsen Elfinn , Bechgaard Klaus , Engler Edward M. 
Published: May 2005

AbstractThe mass spectra of 13 heterofulvalenes are reported. The spectra show great similarities within the selenium and within the sulphur series. The main difference between the selenium and the sulphur compounds results from the more facile loss of selenium compared with sulphur, and from the first fragmentation of the molecular ion, as the selenium fulvalenes lose an alkyne molecule, whereas the sulphur fulvalenes first lose an (SĊR) radical. An important feature of the spectra of the simple heterofulvalenes is the formation of a rearrangement ion by migration of a heteroatom. The mechanism was elucidated by 13C labelling and is discussed in detail.
Fragmentation en Spectrométrie de Masse D'Imidazobenzodiazépines
Authors: Geneste Patrick , Kamenka Jean‐Marc , Vidal Yves 
Published: May 2005

AbstractL'étude des benzodiazépines a fait apparaǐtre des modes de fragmentations différents pour les imidazo[4,5,1‐jk]benzodiazépines‐1,4 et les imidazo[1,5,4‐ef]benzodiazépines‐1,5. Les ruptures caractéristiques dans ces deux séries ont été identifiées. Elles mettent en évidence l'influence de la nature du cycle diazépine sur les processus caractéristiques de fragmentation et rendent possible l'identification et la différenciation des structures isomères.