bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractIt 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

AbstractMit 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

AbstractIndependent 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

AbstractDer 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

AbstractWhen 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

AbstractThe 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

AbstractDie 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.
Skeletal rearrangement of allyl acetates after protonation by chemical ionization
Authors: Liehr J. G. , McCloskey James A. 
Published: May 2005

AbstractIn 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractSous 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

AbstractThe 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

AbstractTrimethylsilyl 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

AbstractThe 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 observedSee 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

AbstractDie 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

AbstractPhotoionisation 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

AbstractDie 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

AbstractThe 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

AbstractThe 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

AbstractAndrostanes 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

AbstractA 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

AbstractLess 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

Abstract13C 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

AbstractThe 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

AbstractThe 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.
Ionisation et Fragmentation en Spectrometrie de Masse. V—Appreciation de L'Energie D'Activation Pour des Fragmentations Competitives
Authors: Bouchoux Guy 
Published: May 2005

AbstractL'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

AbstractL'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

AbstractA 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

AbstractMit 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

AbstractDie ‘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

AbstractNegative 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

AbstractIn 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

AbstractL'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.