Structures of 2-, 3-, and 4-methyl-9-oxothioxanthenes

The structures of 2-, 3-, and 4-methyl-9-oxothioxanthenes (2-, 3-, and 4-TX, respectively) were determined by single crystal x-ray methods. The molecules are folded by 2–3° about their SC=O lines. Bond distances and angles vary only slightly as a function of the methyl substitution position, and reveal no inherent structural reason for the long-range nmr couplings observed between the ring and methyl protons. The molecular packings exhibit interesting similarities as well as subtle differences that result from variation of the methyl position. Crystals of 2-TX are orthorhombic, space groupPn2₁ a,a=10.807(1),b=4.024(2),c=24.827(3) Å,Z=4,R=0.059 for 715 observed reflections. Crystals of 3-TX are orthorhombic, space groupPbc2₁,a=3.999(1),b=25.051(2),c=10.758(1)Å,Z=4,R=0.041 for 1382 observed reflections. Crystals of 4-TX are triclinic, space groupP¯1,a=7.118(1),b=7.907(2),c=10.415(2) Å,=77.74(1),=74.35(1), =73.96(1)°,Z=2,R=0.043 for 1542 observed reflections.Deceased.     

Fate of Petroleum Hydrocarbons in the Sediment of Coastal Water

Assessment of the concentrations of petroleum hydrocarbons and their fate in marine environment is very important and necessary for marine environment scientists. In order to study the ecotoxicological effects of this kind of pollutants on marine ecological system, the fate of petroleum hydrocarbons in sediment of coastal water has been studied under natural conditions by Chromatography-FID.     

Zur Bestimmung und Trennung des Chroms und zur Analyse von Chrom enthaltenden Substanzen

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Total synthesis and determination of the absolute stereochemistry of the squalene synthase inhibitors CJ-13,981 and CJ-13,982

The absolute and relative stereochemistries of the potent squalene synthase inhibitors CJ-13,981 and CJ-13,982 were determined to be 3S,4S by total synthesis of their antipodes using, as a key step, the diastereoselective alkylation of a chiral dioxolanone.     

Über die notwendigen und hinreichenden Bedingungen für das Bestehen eines Kleinschen Oszillationstheorems

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Von reinem Whisky

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Growth of PTCDA crystals on H:Si(1 1 1) surfaces

The room temperature deposition of PTCDA on hydrogen passivated Si(1 1 1), as a function of evaporation temperature and dosing time, has been studied by STM. At low evaporation temperature, 200 °C, clusters with an average size of 3.5 nm are formed on the surface. The mobility of the small clusters is so high, even at room temperature, that most of the clusters are trapped at surface defects. By increasing the evaporation temperature to 230 °C, larger clusters are formed which have lower mobility. The growth process is identified as a Volmer-Weber mechanism. On increasing the evaporation temperature further to 250 °C, crystals with dendritic shape are formed with an average size of 150 nm. The terraces of the crystal are formed with the (1 0 2) basal plane of the α-phase. Molecular resolution on the terrace also allows us to identify the molecular mechanism involved in the growth of the dendritic crystals.     

Numerical simulation method for viscoelastic flows with free surfaces—fringe element generation method

To simulate filling flow in injection moulding for viscoelastic fluids, a numerical method, based on a finite element method and a finite volume method, has been developed for incompressible isothermal viscoelastic flow with moving free surfaces. The advantages of this method are, first, good applicability to arbitrarily shaped mould geometries and, second, accurate treatment for boundary conditions on the free surface. Typical filling flows are simulated, namely filling flow into a 1:4 expansion cavity with and without an obstacle. Numerical results predict the position of weld lines and air-traps. The method also indicates the effects of elongational flow on molecular orientation.     

Micromolar ammonia analysis and atmospheric contamination

Summary Measurement of micromolar quantities of ammonia is generally done by spectrophotometric methods. However, these methods do not protect the sample from atmospheric contamination. Atmospheric contamination of samples with ambient ammonia during analysis is therefore investigated. A modification of Kjeldahl's apparatus for extracting micromolar quantities of ammonia from small samples without atmospheric contamination is proposed.