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1983 (1)
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1978 (1)
1Author    Helmut Schwarz, Chrysostomos WesdemiotisRequires cookie*
 Title    -und 2-Methylallylkationen aus isomeren Vinylbromidradikalkationen 1-and 2-Methylallyl Cations from Cation Radicals of Isomeric Vinyl Bromides  
 Abstract    It is demonstrated by collisional activation mass spectrometry that dissociative ionization of E-and Z-l-bromobutene-1 (3, 4), 2-bromo-butene-1 (5) and 2-bromobutene-2 (6) yields exclusively 1-methylallyl cation (a). Unimolec-ular Br -loss from the molecular ion of 1-bromo-2-methylpropene (7) gives rise to the specific formation of the isomeric 2-methylallyl cation (b). Kinetic energy release measurements sup-port the interpretation that Br' loss from the cation radicals 3-7 is preceded (or accompanied) by an exothermic isomerization of the incipient C4Ü7+ ions. 
  Reference    Z. Naturforsch. 35b, 1486—1487 (1980); eingegangen am 18. Juli 1980 
  Published    1980 
  Keywords    Ion Structures, Collisional Activation, Gas Phase Ion Chemistry 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1486_n.pdf 
 Identifier    ZNB-1980-35b-1486_n 
 Volume    35 
2Author    Jörn Müller, Frerk LüdemannRequires cookie*
 Title    Stoßaktivierungs-Massenspektren von C6H6M + -und C7H7M + - Fragment-Ionen aus Übergangsmetall-^-Komplexen Collisional Activation Mass Spectra of C6H6M+ and C7H7M+ Fragment Ions from Transition Metal ^-Complexes  
 Abstract    Comparative structure investigations of simple gaseous ions formed by electron impact of organometallic -complexes have been carried out by use of the collisional activation (CA) technique. The CA mass spectra of C6H6M+ ions (M — V, Cr, Fe) arising either from benzene or from methylcyclopentadienyl metal compounds show significant differences indicating different structures of these fragments. Similar observations were made with C7H7M+ ions produced from benzyl or cycloheptatrienyl chromium tricarbonyl derivatives, although the metal-free ligand ions exhibit identical CA mass spectra. The CeHßV 1 -ion arising from C5HsVC7H7 by a rearrangement fragmentation was shown to have the ^-benzene vanadium structure. 
  Reference    (Z. Naturforsch. 36b, 74—77 [1981]; eingegangen am 21. Oktober 1980) 
  Published    1981 
  Keywords    Collisional Activation, Gas Phase Ion Structure Analysis, ^-Complexes 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0074.pdf 
 Identifier    ZNB-1981-36b-0074 
 Volume    36 
3Author    Bernhard Ciommer, Helmut Schwarz, Azzedine Maaroufi, ManfredT. Reetz, Karsten LevsenRequires cookie*
 Title    Silyl-Assistierte Etherspaltung bei Radikalkationen von Hydroxylaminderivaten [1] Silyl-Assisted Ether Cleavage in Radical Cations of Hydroxylamine Derivatives [1]  
 Abstract    It is demonstrad by means of various mass spectrometric techniques that the dissociative ionization of N.N-bis-silylated hydroxylamine derivatives (5 a) and (5 b), giving rise to the cleavage of the (O-C) bond, is anchimerically assisted by migration of the trimethylsilyl group to the ether oxygen, thus generating ion (7). 
  Reference    Z. Naturforsch. 36b, 771—773 (1981); eingegangen am 11. März 1981 
  Published    1981 
  Keywords    Mass Spectrometry, Collisional Activation, Anchimeric Assistance, Silyl Ether 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0771_n.pdf 
 Identifier    ZNB-1981-36b-0771_n 
 Volume    36 
4Author    Chrysostomos Wesdemiotis, Helmut Schwarz, Friedrich Borchers, Heinz Heimbach, Karsten LevsenRequires cookie*
 Title    Massenspektrometrische Untersuchungen zur Genese von [M—Me] [M-Et] [C7H7]+ und [C7H8]+ aus n-Butyl-und n-Pentylbenzol: Zeitabhängige Nachbargruppeneffekte, Isomerisierungen und kompetitive Wasserstoff-Umlagerungen Mass Spectrometric Investigations on the Formation of [M-Me]+, [M-Et]+, [C7H7] + and [C7H8] + - from w-Butyl and w-Pentyl Benzenes: Time Dependent Neighbouring Group Participation, Isomerization and Competitive Hydrogen Rearrangements  
 Abstract    The details of the elimination of CH3 1 and C2Hs -from the molecular ions of n-butyl and n-pentyl benzenes as well as the formation of C7H7+ and C7Hs + -have been established using a combination of different mass spectrometric techniques. Among these techniques are field ionization kinetics (FIK), collisional activation (CA), unimolecular decomposi-tion of metastable ions (MI), kinetic energy release determinations (Tkin)> appearance potential measurements (AP) as well as high resolution mass spectrometry. The appli-cation of these methods and the investigation of nine 13 carbon and eleven deuterium labelled n-butyl and n-pentyl benzenes clearly demonstrate that 1) the loss of methyl and ethyl from terminal positions of the alkyl chains are accompanied by an interaction with the phenyl ring and 2) the regioselectivity of these processes is time dependent. Contrary to previous conclusions it is shown that hydrogen transfer in the formation of C7H8 + -occurs via five-, six-and seven-membered transition states. The time dependence of the hydrogen exchange reaction preceding the alkene eliminations is discussed in detail. 
  Reference    Z. Naturforsch. 33b, 1150—1164 (1978); eingegangen am 1. März 1978 
  Published    1978 
  Keywords    Hydrocarbons, Hydrogen Rearrangement, Metastable Ions, Collisional Activation, Field Ionization Kinetics 
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 TEI-XML for    default:Reihe_B/33/ZNB-1978-33b-1150.pdf 
 Identifier    ZNB-1978-33b-1150 
 Volume    33 
5Author    Bernd Kohne, Klaus Praefcke, Helmut SchwarzRequires cookie*
 Title    CO2 Elimination from Gaseous Radical Cations of Thiol Esters: Intramolecular Oxygen Transfer of (C +3 /C +3 )-Type  
 Abstract    It is shown for the first time that under electron impact conditions an intramolecular oxygen transfer is possible from the thiol ester funtion onto the carbon atom of a second thiol ester group. The reaction sequence is terminated by CO2 elimination and the proposed structure of the resulting product ion is based on 13 carbon labelling experiments and collisional activation mass spectrometry. In addition, some unusual examples of ring contraction processes in the gas phase are reported. Eliminierungen kleiner Neutralteile unter Einbe-ziehung von Wasserstoff-Umlagerungen sind wohl-bekannte Reaktionen ionischer Systeme, die zweck-mäßig im Massenspektrometer analysiert werden können [3]. In die gleiche Kategorie gehören -formal besehen -auch die viel seltener studierten Redoxprozesse [4], unter denen in jüngster Zeit intramolekulare Sauerstoff-Übertragungen [4-10] besonderes Interesse gefunden haben. Bei der Mehr-zahl der Sauerstoff-Wanderungen im Massenspektro-orr 5 ^ (1 c—s CH, CH, CH, meter fungiert eine N02-Gruppe [6-10] als Sauer-stoff-Donator, während als Acceptor Atome ver-schiedenartigster chemischer Natur, Oxidations-stufen und Sauerstoffaffinitäten möglich sind [4-10]. Einen bemerkenswerten Sonderfall stellt das 
  Reference    Z. Naturforsch. 34b, 316—320 (1979); eingegangen am 14. August 1978 
  Published    1979 
  Keywords    Sulphur Compounds, Thiol Esters, Collisional Activation, Oxygen Transfer, Ring Contraction 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-0316.pdf 
 Identifier    ZNB-1979-34b-0316 
 Volume    34 
6Author    Helmut Schwarz, Chrysostomos Wesdemiotis, Thomas Weiske, Klaus-Peter Zeller, Roland MüllerRequires cookie*
 Title    H. Schwarz et al. * Methyl-Eliminierung aus dem metastabilen Homoadamantan-Radikalkation 219 Methyl Loss from Metastable Homoadamantane Cation Radical  
 Abstract    It is demonstrated that methyl loss from ionized homoadamantane (1) yields exclusively the 1-adamantyl cation (4); there is no experimental evidence for the formation of the secondary adamantyl cation (5). From both model calculations and the investigation of [4-13 C]-homoadamantane (la) and l(13 C-methyl)adamantane (2a) it is concluded, that 24% of the metastable homoadamantane cation radicals dissociate after one isomerization (1 2); the remaining 76% are able to undergo at least a second (degenerate) isomerization cycle (2->l->2) prior to methyl loss. 78% of metastable 1-methyl-adamantane cation radical, obtained upon direct ionization of the corresponding neutral hydrocarbon, dissociate directly, whereas the loss of methyl from the remaining 22% is preceded by an isomerization 2 ->1 ->2. 
  Reference    Z. Naturforsch. 35b, 207—211 (1980); eingegangen am 23. Oktober 1979 
  Published    1980 
  Keywords    Ion Structures, Carbocation Rearrangements, Hydrocarbon Chemistry, Mass Spectrometry, Collisional Activation 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-0207.pdf 
 Identifier    ZNB-1980-35b-0207 
 Volume    35 
7Author    Karsten Levsen, RichardD. Bowen, DudleyH. WilliamsRequires cookie*
 Title      
 Abstract    The non-decomposing molecular ions of methyl cyclopropanecarboxylate (14) are found to rearrange to ionised methyl but-3-enoate (15). For ions with sufficient internal energy to decompose, this isomerization is in competition with -OCH3 loss, via direct cleavage of the ester group. Collisional activation spectroscopy may be used to distinguish between the C3HsCO + ions formed by "OCH3 loss from the molecular ions of 14, 15 and other isomeric precursors. Four distinct C3HsCO+ species (18-21) can be identified in this way; these C3H5CO+ ions may themselves decompose, via CO elimination. Consideration of the metastable peak shape for CO loss, in conjunction with collisional activation spectroscopy on the resulting C3H5 4 -ions, leads to two main conclusions, (i) Two C3H5+ ions (22 and 27) exist in potential energy wells. The very narrow metastable peaks for CO loss from 19 and 21 (leading to 22 and 27, respectively) show that these processes are continuously endo-thermic. In contrast, CO loss from either 18 or 20 gives rise to much broader metastable peaks. This suggests that rate-determining rearrangement of the incipient C3Hs+ cations, to a more stable isomer, occurs prior to decomposition, (ii) Elimination of CO from the [M--OCH3]+ fragment of 14 gives rise to a composite metastable peak, thus indicating the occurrence of two competing channels for dissociation. These channels are assigned to CO loss from 18 (larger kinetic energy release) and CO loss from 19 (smaller kinetic energy release). Die interessanten chemischen Eigenschaften klei-ner Ringe werden seit vielen Jahren intensiv stu-diert [1]. Besondere Beachtung haben substituierte Cyclopropane (1 und 3) gefunden, für die Hoffmann [2] aufgrund von Molekülorbitalrechnungen das folgende Reaktivitätsmuster vorhergesagt hat: Elektronenliefernde Substituenten B schwächen die C(2)-C<3)-Bindung und sollten bei einer chemischen Reaktion (wie z.B. Hydrogenolj'se) zu C-verzweigten Produkten der allgemeinen Konstitution 2 führen. Für elektronenziehende Substituenten A gilt das Umgekehrte: Sie verstärken die C(2)-C(3>-und labili-sieren die C(i)-C(2)-Bindung mit dem Resultat, daß Produkte mit einer unverzweigten C3-Einheit ent-stehen. Tatsächlich konnte Musso [3] beweisen, daß 
  Reference    Z. Naturforsch. 34b, 488—494 (1979); eingegangen am 27. November 1978 
  Published    1979 
  Keywords    Unimolecular Isomerization, Ion Lifetime, Ion Structure, Collisional Activation, Kinetic Energy Release 
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 TEI-XML for    default:Reihe_B/34/ZNB-1979-34b-0488.pdf 
 Identifier    ZNB-1979-34b-0488 
 Volume    34 
8Author    Bernd Richter, Helmut SchwarzRequires cookie*
 Title    Zur McLafferty-Umlagerung bei Radikalkationen von Phenylpyridylalkanonen [1] On the McLafferty Rearrangement of Ionized Phenyl Pyridyl Alkanones [1]  
 Abstract    A detailed investigation concerning the genesis of McLafferty rearrangement products from molecular ions of phenyl pyridyl alkanones reveals the following features: 1) The various products are not formed by competitive dissociations of the molecular ion. Most of the relevant fragment ions are generated from the primary McLafferty product of a hydrogen transfer to the ionized carbonyl group (M +> ->m/z 163, ion k). The ion k plays a decisive role for the generation of the abundant product ions at m/z 93 (ion g) and m/z 106 (ion s) both of which are formed by further dissociation of k. Details of the mechanisms for the decomposition of k are obtained by investigating [D]-labelled isotopomers, the analysis of low and high resolution data, the application of MIKE and CA spectra. The problem of keto/enol tautomerism between some ions, relevant in this context, is discussed and it is shown that these isomerization processes are not involved. A detaüed description is given for the syntheses of various [D]-labelled phenyl pyridyl alkanones. 
  Reference    Z. Naturforsch. 36b, 865—877 (1981); eingegangen am 16. Dezember 1980 
  Published    1981 
  Keywords    Mass Spectrometry, Hydrogen Rearrangement, Keto Enol Tautomerism, Metastable Ions, Collisional Activation 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-0865.pdf 
 Identifier    ZNB-1981-36b-0865 
 Volume    36 
9Author    Wilfried Franke, Helmut Schwarz, Chrysostomos WesdemiotisRequires cookie*
 Title    Elf stabile C5H9+-Kationen in der Gasphase. Zur dissoziativen Ionisierung von 31 isomeren C6H9Br-Verbindungen Eleven Stable CsHo 4 " Cations in the Gas Phase. On the Dissociative Ionization of 31 Isomeric CsHgBr Compounds  
 Abstract    Collisional activation mass spectrometry (CA) reveals the existence of 11 stable CsH9+ cations in the gas phase, e. g. the substituted allyl cations a, b, c, d,and e, the sub-stituted vinyl cations f, g, h, and i, the methyl cyclobutyl cation j and the cyclopentyl cation k, respectively. The ethyl substituted allyl cation a is formed via dissociative ionization of the isomeric precursors 1, 3, 4, 5, 18, 19, 20, 22, and 28 by means of various mechanistic processes, whereas the 1,3-dimethylallyl cation b is generated from both 2 (by allylic cleavage) and in part from the stereoisomeric cyclopropan derivatives 25, 26 and 27. 6"l + -gives a mixture of the vinyl cations 1 and g. From 13 and 14 the main product generated is the 1,2-dimethylallyl cation d, which is formed directly from 11 and also by quite complicated processes from 13, 14 and to a certain extent from 25, 26 and 27. The dissociative ionization of 9, 15, 16, 21, 24 and (in part) 23 give rise to the formation of the substituted vinyl cation h. Decomposition of 23"!+ • results not only in formation of h but generates also the 1,1-dimethylallyl cation e. From 291+-and 30~l +-both the methylcyclo-butyl cation j and cyclopentyl cation k are produced, whereas the isomeric precursor 28 gives mainly the substituted allyl cation a and a second, as yet, unidentified CsH^ cation. In general, it can be stated that the gas phase chemistry of cation radicals of substituted cyclopropanes is characterised by multistep-reactions, commencing with spontaneous ring opening. The so formed intermediates undergo various rearrangements (including hydrogen and alkyl shifts) prior to expulsion of Br\ Direct elimination of Br' from intact cyclopropan-like structures, followed by ring opening of the intermediate cyclopropyl cation, cannot compete with the above-mentioned multistep-sequences. 
  Reference    Z. Naturforsch. 36b, 1315—1323 (1981); eingegangen am 2. Juni 1981 
  Published    1981 
  Keywords    Isolated Carbocations, Ion Structures, Gas Phase Ion Chemistry, Mass Spectrometry, Collisional Activation 
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 TEI-XML for    default:Reihe_B/36/ZNB-1981-36b-1315.pdf 
 Identifier    ZNB-1981-36b-1315 
 Volume    36 
10Author    Bernhard Ciommer, Helmut SchwarzRequires cookie*
 Title    Zur intermediären Existenz von Ethylenfluoronium-Ionen in der Gasphase On the Intermediary Existence of Gaseous Ethylen Fluoronium Ions  
 Abstract    The long-sought ethylen fluoronium ion (2) is generated as an intermediate in the dissociative ionization of l-fluoro-2-(^-methyl)phenoxy ethane (4). However, prior to collisionally induced dissociation 2 undergoes ring-opening, associated with hydrogen migration, to form 1-fluoroethyl cation (3). Other decomposition pathways of the molecular ions of 4 involve (i) direct formation of 3 via a combination of C-O-cleavage (loss of ArO -) and [1,2] hydrogen migration (18%) and (ii) complete positional loss of the a-and ß-methylene hydrogen atoms (34%). The remaining 48% of the molecular ions of 4 dissociate via anchimeric assistance of the fluorine in the elimination of ArO -, thus giving rise to the formation of 2. 
  Reference    Z. Naturforsch. 38b, 635—638 (1983); eingegangen am 23. Dezember 1982 
  Published    1983 
  Keywords    Fluoronium Ions, Neighbouring Group Participation, Gaseous Ions, Collisional Activation, Mass Spectrometry 
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 TEI-XML for    default:Reihe_B/38/ZNB-1983-38b-0635.pdf 
 Identifier    ZNB-1983-38b-0635 
 Volume    38