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1998 (1)
1991 (1)
1Author    W. Müncha, L. Walz, M. KönigbRequires cookie*
 Title    Magnetische Eigenschaften von [C u JO C ^ C F ^ N ^ H t^ IN C O ^ im Bereich von 10 bis 240 K Magnetic Properties of [Cu{OCH2CH2N(C4H9)2 }NCO]4 in the Temperature Range from 10 to 240 K  
 Abstract    The magnetic properties of the title compound were re-investigated, since a new phase below 240 K has recently been identified. The exchange parameters were evaluated from the temperature dependence of the magnetic susceptibility with a Heisenberg operator taking into account the high pseudo-symmetry of the tetrameric units observed. 
  Reference    (Z. Naturforsch. 53b, 58—62 [1998]; eingegangen am 16. Oktober 1995 -31. Oktober 1997) 
  Published    1998 
  Keywords    Copper Complexes, Magnetic Properties, Theoretical Calculations 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0058.pdf 
 Identifier    ZNB-1998-53b-0058 
 Volume    53 
2Author    Ulrike Holzgrabe, Willy Friedrichsen, Rl-FH. EsseRequires cookie*
 Title    Keto-Enol-Tautomerism and Configurational Isomerism of 2,6-Disubstituted 4-Piperidone-3,5-dicarboxylates [1]  
 Abstract    The dialkyl 2,6-dialkylsubstituted 4-piperidone-3,5-dicarboxylates were synthesized by a M annich procedure. Depending on the substitution at the nitrogen keto-enol-tautomerism and a configurational isomerism at C 2 is observed. The structure o f the N-substituted piperi-done 24 E (C 18H 29N 0 5) has been determined by X-ray analysis: it is characterized by an enol structure o f the /?-ketoester and an axial position o f the alkyl group at C 2 and an equatorial one o f the alkyl group at C 6. The O -H -O hydrogen bond shows characteristic values o f a strong hydrogen bond. The N-unsubstituted piperidones adopt a ketone structure with the all-equatorial position o f all substituents. This stereochemistry is confirmed for other enolic and ketone analogues by N M R spectroscopic methods. To work out the reason for the different thermodynamic stabilities o f the different stereochemical structures o f N-substituted and N-unsubstituted piperidones, various semiempirical calculations were done for series o f simple pairs o f carbonyl/enol tautomers, substituted acetoacetates, oxoglutarate as well as o f syste­ matically varied substituted cyclohexanone, 4-oxacyclohexanone and 4-piperidone deriva­ tives. 
  Reference    Z. Naturforsch. 46b, 1237—1250 (1991); received Novem ber 2 1990 
  Published    1991 
  Keywords    2, 6-Disubstituted 4-Piperidone-3, 5-dicarboxylates, High-resolution N M R, X-Ray, Theoretical Calculations 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-1237.pdf 
 Identifier    ZNB-1991-46b-1237 
 Volume    46