Low temperature crystal and molecular structure of nitrobenzene

The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects.     

Beiträge zur Chemie der Pyrrolpigmente, 44. Mitt.: Gallenfarbstoffe als Ionophore

The carrier mediated transport of cations using model compounds of the verdinoid and rubinoid bile pigment structural type as ionophores is studied. Verdinoid bile pigments turn out to be very effective carriers for cations exhibiting a pronounced selectivity for certain transition metal ions like Cr^+-+, Fe⁺⁺, Cu⁺⁺ and Zn⁺⁺. The scope of this behaviour of verdinoid bile pigments is compared to [18]-crown-6 and meso-tetraphenylporphin and is discussed with regard to structural, biological, analytical and technical implications.

     

Tetrakis(trifluormethyl)tellur (CF3)4Te [1]

(CF₃)₄Te is formed from the reaction of (CF₃)₂TeCl₂ with (CF₃)₂Cd·glyme in CH₃CN at ?10°C via the intermediate (CF₃)₃TeCl as a yellow liquid and identified by n.m.r. and mass spectra.     

Multi-element trace analysis of tungsten

Investigations carried out in order to determine traces of 25 elements in tungsten in the lower g/g range are reported on. Atomic absorption spectrometry and plasma atomic emission spectrometry as well as solution photometry and activation analysis were the main techniques used.     

Synthese von 2-methylalanin-peptiden,die pH-Abhängiggkeit ihrer 13C-NMR-spektren und eine neue methode zur auswertung über CS-diagramme

The uncommon amino-acid 2-methylalanine (α-aminoisobutyric acid, Aib) was investigated by ¹³C-NMR. The chemical shifts of amino- or carboxy-protected derivatives of Aib and of protected oligopeptides are discussed with respect to neighbouring groups and amino acids. The pH-dependence of the ¹³C-NMR spectra of Aib, Aib-Ala, Ala-Aib, Aib-Ala-Aib and Aib-Ala-Aib-Ala-Aib was studied. Using these examples, a new and advantageous method is demonstrated for the first time for the evalutions of NMR titration curves, which uses so-called chemical shift diagrams (CS diagrams).     

Syntheses of dictyopterene B (hormosirene) and its enantiomer via asymmetric ScN′ reactions

Stereocontrolled syntheses of dictyopterene B (hormosirene) (1) and its enantiomer (ent-1) are reported. Key steps are highly stereoselective S_cN′ reactions of esters of alcohols 2 and 5 derived from (+)-camphor.     

Branched Star-Type Polysilyllithium Compounds: The Effects of beta-Silyl Substitution and of Complexation on Their Molecular Structure

No Abstract     

Reaktionen an komplexgebundenen liganden: XXXVI. Synthese und oxidationsverhalten von M(CO)5-komplexen (M = Cr,Mo, W) mit amin- und benzochinondiimin-liganden

The oxidation of yellow Cr(CO)₅NH₂R complexes (NH₂R = aniline, m-toluidine, 3,5-xylidine, m-anisidine) with Pbac₄ gives deep blue to deep purple coloured compounds, which have been identified as the respective [Cr(CO)₅(N-phenyl-1,4-benzochinon-diimine)] complexes. Oxidation of the p-phenylenediamine complex yields [(OC)₅CrHNC₆H₄NHCr(CO)₅], which is also deep blue. The binuclear blue complex [{Cr(CO)₅}₂HNC₆H₄NC₆H₅] is obtained by treating Cr(CO)₅THF with the free ligand in THF/hexane; it dissociates rapidly in acetone to form [Cr(CO)₅HNC₆H₄NC₆H₅] and Cr(CO)₅. Analogous Mo(CO)₅ and W(CO)₅ complexes could not be obtained. The oxidation of [W(CO)₅(m-anisidine)] by I₂ yields [W(CO)₄I]₂. All the compounds were characterized by spectroscopic methods as well as by elemental analysis.     

Enantioselective 1,4-Addition of Aliphatic Grignard Reagents to Enones Catalyzed by Readily Available Copper(I) thiolates derived from TADDOL. Preliminary communication

Two simple thiols derived from the parent TADDOL, α,α,α′,α′ tetraphenyl-2,2-dimethyl-1,3-clioxolan-4,5-dimethanol, are used to prepare Cu¹ complexes C and D to catalyze (0.05 equiv.) 1,4-additions of Grignard reagents RMgCl to cyclic enones with enantioselectivities which are comparable to or better than previously reported (enantiomer ratios up to 92:8).