Hydroxid-halogenid-verbindungen des di-t-butyl-substituierten zinns

The di-t-butyltin hydroxide halides t-Bu₂Sn(OH)X (X = F, Cl or Br) have been prepared starting from the dihalides t-Bu₂SnX₂ or the oxide (t-Bu₂SnO)₃. X-Ray analysis of the three compounds shows dimeric molecules: two 5-coordinated tin atoms and the oxygen atoms of the hydroxyl groups are linked to a four-membered ring. As confirmed by the IR spectra, the molecules in the crystal are held together by OH?X hydrogen bonds. These are strong in the hydroxide fluoride but are weak in the analogous chloride and bromide.     

Chlorthionitrenkomplexe des Rheniums Die Kristallstruktur von AsPh4[ReCl4(NSCl)2] · CH2Cl2

Chlorothionitrene Complexes of Rhenium. Crystal Structure of AsPh₄[ReCl₄(NSCl)₂] · CH₂Cl₂ Rhenium pentachloride reacts in POCl₃ solution with (NSCl)₃ forming the chlorothionitrene complexes [(Cl₃PO)ReCl₄(NSCl)] ( I ) and [(Cl₃PO)ReCl₃(NSCl)₂] ( II ). I reacts with AsPh₄Cl in CH₂Cl₂ solution under abstraction of SCl₂ and POCl₃, yielding AsPh₄[ReNCl₄], while II forms the complex AsPh₄[ReCl₄(NSCl)₂] · CH₂Cl₂. The i.r. spectra of the compounds are discussed and assigned. The crystal structure of AsPh₄[ReCl₄(NSCl)₂] · CH₂Cl₂ was determined and refined with X-ray diffraction data (R = 0.031 for 2785 reflexions). It crystallizes in the space group Pī with two formula units per unit cell; the lattice constants are a = 1119, b = 1144, c = 1473 pm, α = 77.6, β = 70.8 and γ = 71.2°. The two NSCl ligands have cis arrangement with nearly linear Re?N?S groups, with interatomic distances corresponding to double bonds. The Re? Cl bonds are somewhat longer than usual and show no trans-effect; this is possibly due to Cl…?H? C bridges.     

Darstellung und strukturen diorganylsubstituierter Silicium-Germanium-Sauerstoff-achtringe

Diphenylgermanium diphenylsilicon oxide and dimethylgermanium diphenylsilicon oxide [(R₂Ge)O(Ph₂Si)O]₂ (R = Ph, Me) have been synthesized by treatment of diorganogermanium dihalides with diphenyldihydroxysilane. The X-ray analysis showed nonplanar eight-membered silicon-germanium-oxygen rings which are more puckered than those of cyclotetrasiloxanes. In the compound with R = phenyl the silicon and germanium atoms are disordered.     

Additionsreaktionen von 3-Dimethylamino-2,2-dimethyl-2H-azirin an Isothiocyanate

Addition Reactions of 3-Dimethylamino-2, 2-dimethyl- 2 H-azirine and Isothiocyanates. The title azirine readily reacts with two molecules of benzyl- or methylisothiocyanate to form the zwitterionic 1:2 addition compounds 4 and 13 , respectively (Scheme 2). The presumed 1:1 addition products, which are intermediates in the formation of 4 and 13 , cannot be detected. The structure of 4 and 13 follows from their spectroscopic and chemical properties. With water they give the thiourea derivates 5 and 14 , respectively; treatment with aqueous acid leads to the Δ²-1, 3-thiazolin-5-on-derivates 7 and 15 , respectively. With sodium borohydride compounds 8 and 16 , respectively, are obtained (Scheme 2). The zwitterionic compounds 4 and 13 are able to react further with one molecule of the isothiocyanates to give, in high-yield, triazines 9 and 18 , respectively (Scheme 3). The structure of these compounds was again derived from their spectroscopic data. The mechanism for the formation of 9 and 18 is given in Scheme 3. Acid catalysed hydrolysis of 9 and 18 lead to the trithiocyanuric acid derivates 12 and 20 , and to the spiro compounds 11 and 19 , respectively (Sceme 6). Reaction of 4 with one molecule of phenylisocyanate gives triazine 10 (Scheme 5). According to the X-ray analysis of the methyl compound 18 , there are strong steric interactions in this molecule which are due to the side chain. This is demonstrated by the small distances between C(2) … C(13), N(7) … C(11), and C(8) … C(11) (Table 4). These steric interactions, in addition, cause widening of the bond angles N(1)? C(2)? N(7) and C(9)? N(10)? C(11) (Fig.2). Furthermore, the triazine ring is no longer planar. This deformation of the ring diminishes repulsion between the methyl groups C(13) and C(15).     

Two new organic reference materials for delta13C and delta15N measurements and a new value for the delta13C of NBS 22 oil

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a delta13C value of -26.24 per thousand relative to VPDB and a delta15N value of -4.52 per thousand relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a delta13C value of +37.76 per thousand and a delta15N value of +47.57 per thousand. The delta13C and delta15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (delta13C=+1.95 per thousand ), L-SVEC lithium carbonate (delta13C=-46.48 per thousand ), IAEA-N-1 ammonium sulfate (delta15N=0.43 per thousand ), and USGS32 potassium nitrate (delta15N=180 per thousand ) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of delta13C is better than 0.13 per thousand, and that of delta15N is better than 0.13 per thousand in 100-microg amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a delta13C value for NBS 22 oil of -29.91 per thousand, in contrast to the commonly accepted value of -29.78 per thousand for which off-line blank corrections probably have not been quantified satisfactorily.     

n-π-Interaction in Enamines and Enaminoketones. A 15N-NMR. Study

¹⁵N-Chemical shifts of 32 enamines, 11 enaminoketones and 28 closely related amines have been determined with the isotope in natural abundance. In order to eliminate substituent effects, differential chemical shifts Δδ(N) are defined as δ_N(amine)-δ_N(enamine). This parameter is shown to correlate well with the free enthalpy of activation ΔG# for restricted rotation about the N? C(α) bond in enamines with extended conjugation. Δδ(N) values of substituted anilinostyrenes correlate also with ¹³C-chemical shifts of the β-carbon in the enamine system and with Hammett σ-constants of the aniline substituents. The experimental results suggest that differential ¹⁵N shifts are a useful probe to study n, π-interaction in enamines.     

Correlations between chemical structure and chain packing in two- and three-dimensional systems

Phosphatidylcholines (PCs) containing a branched chain fatty acid at the sn-1 position of the glycerol backbone were characterized by calorimetric and X-ray diffraction studies with bilayers as well as by thermodynamic studies with monolayers. Branching leads to altered thermal properties which are connected with a modified structural polymorphism. Gel phases with interdigitated chains or nonbilayer liquid-crystalline phases could be found in dependence on the length of the side branches. The pressure-area isotherms of the monobranched PCs were measured over a wide range of temperature. The critical temperatures T_c of the transition between the liquid-expanded and condensed films were estimated and compared with the main transition temperatures T_m of the bulk phase. T_c was found to be either lower or higher or equal to T_m. The correlations between T_c and T_m are discussed in terms of chain packing in the two- and threedimensional systems.