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'Ring Contraction' in keywords Facet   section ZfN Section B  [X]
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1991 (1)
1980 (2)
1979 (1)
1Author    William Clegg, Michael Hesse, Uwe Klingebiel, GeorgeM. Sheldrick, Lutz SkodaRequires cookie*
 Title    Ringkontraktion am Cyclotrisilazan -System - Synthese und Molekülstrukturen zweifach silylverknüpfter Cyclodisilazane Ring Contraction in the Cyclotrisilazane System - Synthesis and Molecular Structures of Silyl-Bridged Cyclodisilazanes  
 Abstract    l-(Fluorodiorganylsilyl)-2,2,4,4,6,6-hexamethyl-3-(trimethylsilyl)cyclotrisilazanes react with butyllithium to give the corresponding lithium salts. Ring contraction of the lithium salts with formation of lithiated (fluorodiorganylsilyl)amino-substituted four-membered rings is observed in THF solution. The dimerisation of these cyclodisilazanes with elimina-tion of LiF is demonstrated by crystal structure determinations of three products. Monoclinic and triclinic crystalline modifications of one compound could be isolated. 
  Reference    Z. Naturforsch. 35b, 1359—1365 (1980); eingegangen am 29. Juli 1980 
  Published    1980 
  Keywords    Cyclotrisilazanes, Ring Contraction, Cyclodisilazanes, Crystal Structures 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1359.pdf 
 Identifier    ZNB-1980-35b-1359 
 Volume    35 
2Author    Z. NaturforschRequires cookie*
 Title    Ringerweiterungs-und -Verengungsreaktionen bei BN-Vier-und -Sechsringen  
 Abstract    Expansion and C o n tractio n R eactions w ith BN F our-and Six-M em bered Rings Peter Paetzold3 *, J u tta K iesgena, K arl K ra h éa, H ans-U lrich M eiera und R oland Boeseb By the addition o f im inoboranes R B = N R ' (l a -d) to the corresponding diazadiboretidines (R B N R ')2 (2 a -d), a ring expansion is observed, borazines (R B N R ')3 (3 a -d) being formed. The particular im inoborane iP rB =N /P r (la) can be added to the diazadiboretidines 2 c -g to give borazines B3N 3R2R'2/Pr2 with an unsymmetrical set o f ligands. From P hB =N rB u (lj) and (PhBNzBu), (2j), the Dewar borazine 3j' is formed, which crystallizes in the space group P 2,lc. The diazadiboretidines 2 b -i , the borazines 3 b -d ,f , and the Dewar borazine 3e' are split into the corresponding iminoboranes R B =N rB u at 5 0 0 -6 0 0 °C in the gas phase. The molten bo­ razines 3 b —d ,f and Dewar borazines 3e', j' are contracted to the corresponding diazadiboreti­ dines 2 b -f , j at 1 6 0 -3 2 0 °C. [Ligands R/R': zPr/zPr (a), Me/zBu (b), Et//Bu (c), Pr/?Bu (d), zPr/ ?Bu (e), Bu/rBu (f), /Bu/zBu (g), /Bu/rBu (h), zBu(M e3Si)N/zBu (i), Ph//Bu (j).] 
  Reference    Z. Naturforsch. 46b, 853—8 (1991); eingegangen am 26. N ovem ber 1990 
  Published    1991 
  Keywords    Iminoboranes, Diazadiboretidines, Borazines, Ring Expansion, Ring Contraction 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-0853.pdf 
 Identifier    ZNB-1991-46b-0853 
 Volume    46 
3Author    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 
4Author    Hans-Ludwig Krauss, Erich HumsRequires cookie*
 Title    Oberflächenverbindungen yon Übergangsmetallen, XXIII [1] Die Umsetzung cyclischer Olefine mit Oberflächen-Chrom(II) auf Silicagel bei höherer Temperatur Surface Compounds of Transition Metals, XXIII [1] The Reaction of Cycloolefines with Surface Chromium (II) on Silicagel at Higher Temperature  
 Abstract    By reaction with surface chromium(II) on silicagel at T > 150 °C, cycloolefins can undergo ring contraction, methylation/demethylation, hydrogenation/dehydrogenation, and iso-meri7ation. Furthermore, n-alkanes (Ci... C4) are formed incorporating support hydrogen. -As in the case of the corresponding acyclic olefins, a common intermediate MC3 (metalla-cyclobutane^HM-allyl complex) for all these reactions is postulated; the transfer of Ci units is claimed to proceed via a carbene M = CH2 derived from the MC3 precursor. 
  Reference    Z. Naturforsch. 35b, 848—854 (1980); eingegangen am 21. Februar 1980 
  Published    1980 
  Keywords    Surface Compounds, Ring Contraction, Methylation/Demethylation, Hydrogenation/Dehydrogenation, Carbene Intermediates 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-0848.pdf 
 Identifier    ZNB-1980-35b-0848 
 Volume    35