The synthesis of N-substituted ureas II: Nucleophilic substitution of ureas at the carbonyl group

Summary N-Arylsubstituted ureas undergo exchange of the N-residue upon reaction with amines. Using kinetic measurements, investigation of product distribution, regioselectivity, catalysis, and substrate influences, it was shown that this reaction proceeds via a second order nucleophilic substitution at the urea carbonyl center. By means of semiempirical calculations using the MNDO method the alternative mechanism of fragmentation was investigated.

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Zur Synthese N-substituierter Harnstoffe II: Nucleophile Substitution von Harnstoffen an der Carbonylgruppe

Zusammenfassung N-Arylsubstituierte Harnstoffe erleiden bei der Reaktion mit Aminen einen Austausch des N-Restes. Durch kinetische Messungen, Untersuchung der Produktverteilung, Regioselektivität, Katalyse und des Einflusses des Edukts konnte abgeleitet werden, daß es sich hiebei um eine nucleophile Substitution zweiter Ordnung am Carbonylzentrum des Harnstoffs handelt. Durch semiempirische Rechnungen mit Hilfe der MNDO Methode wurde der alternative Reaktionsmechanismus einer Fragmentierung untersucht.

     

Die Kristallstruktur von AgCu3Cu(AsO4)3 und ihre strukturellen Beziehungen zu AgCo3H2(AsO4)3 bzw. AgZn3H2(AsO4)3

Crystal Structure of AgCu₃Cu(AsO₄)₃ and its Structural Relations to AgCo₃H₂(AsO₄)₃ and AgZn₃H₂ (AsO₄)₃ The compound AgCu₃Cu(AsO₄)₃ was synthesized and investigated by X-rays. It crystallizes in the monoclinic space group C2/c with a = 1 212.7(2), b = 1 249.0(2), c = 727.8(1) pm, β = 117.94(1)°, Z = 4. The structure is closely related to the structures of AgCo₃H₂(AsO₄)₃ and AgZn₃H₂(AsO₄)₃. Only two hydrogen atoms are replaced by an additional copper atom forming a copper coordination square instead of two hydrogen bridges. The remaining copper atoms are sixfold coordinated with the generally observed Jahn-Teller distortion. Whereas in AgCo₃H₂(AsO₄)₃ and AgZn₃H₂(AsO₄)₃ silver has a (4+4) coordination, it is in this compound distinctly eightfold coordinated.     

Über P–P-haltige cyclische Verbindungen. II

On P? P Containing Cyclic Compounds. II. Reaction of N,N'-dimethylthiourea with phenyl dichlorophosphane yields 1.4-dimethyl-2. 3-diphenyl-1.4.2.3-diazadiphospholidine-5-thione-2-sulfide ( II ). The compound is characterized by its nmr, vibration and mass spectra as well as the results of an X-ray structural analysis. Byproduct of the reaction is N-(N,N'-dimethylcarbamimidoyl)-N,N'-dimethyl thiourea hydrochloride ( III ), which crystallizes with pyridinium chloride. Molecular and crystal structure are reported. With methyl dichlorophosphane N,N'-dimethylthiourea forms 1.2.3.4-tetramethyl-1.4.2.3-diazadiphospholidine-5-thione-2-sulfide ( IV ), which is characterized by its nmr and vibration spectra.     

Beiträge zur Chemie der Pyrrolpigmente, 31. Mitt.: Die Spin-Gitter-Relaxation in den1H-NMR-Spektren von Bilatrienen-abc

The¹H-NMR spin lattice relaxation times of aetiobiliverdin-IV- and biliverdindimethylester were determined using the inversion recovery technique. The relaxation times of protons attached to the terminal rings A and D are longer than those situated at the rings B and C which points to a higher mobility of rings A and D. Moreover these measurements allowed an independent assignment of the¹H-NMR-signals of the methyl groups of biliverdindimethylester.

30. Mitt.:H. Falk undT. Schlederer, Ann. Chem., im Druck.