Fluorination with xenon difluoride; Part IX. Reaction with phenylsubstituted sulphides

Fluorination of phenyl-methylsulphide with xenon difluoride yields phenyl-fluoromethylsulphide. Further fluorination leads to phenyl-difluoromethylsulphide. Reaction with cis-2,6-diphenyltetrahydro-1-thio-4-pyrone results in the dehydrogenated product 2,6-diphenyldihydro-1-thio-4-pyrone, while further reaction leads to 2,6-diphenyl-1-thio-4-pyrone; thiochroman-4-one yields thiochromen-4-one. No evidence for precursors of the products isolated at room temperature was found.     

Hierarchical clustering of infrared spectra

The generation of a hierarchical tree of 500 infrared spectra, using the recently proposed fractal or 3-distances-clustering method is described and discussed. The objects of clustering are infrared spectra of polymer compounds which are represented as sets of 80 complex Fourier coefficients, obtained by fast Fourier transformation of digitized absorbance spectra. The generated hierarchical tree, with a maximum height of 20 and an average height of 12 levels, yields a very satisfactory clustering scheme with respect to the structure of the compounds involved. In addition to very good clustering, a 100% retrieval (prediction) ability was obtained. This was achieved by the use of an iterative procedure after the initial tree had been generated. Additionally, the tree was tested with 240 infrared spectra of different compounds which were taken into account during the generation of the tree. The retrieval success of these test runs is discussed with respect to the structural similarity of the compounds to which the “unknown” spectra were linked.     

Selective and effective fluorination of organic compounds in water using Selectfluor F-TEDA-BF4

[reaction: see text] Selective and effective fluorination of various types of organic compounds performed in water as the reaction medium using 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor F-TEDA-BF4) is reported. 2-Naphthole and 2-methoxynaphthalene were thus transformed to 1,1-difluoro-2(1H)naphthalenone, estrone to 10beta-fluoro-1,4-estradien-3,17-dione, phenyl-substituted alkenes to vicinal fluorohydrins, and various ketones, 1,3-diketones, or beta-ketoesters to corresponding alpha-fluoro or alpha,alpha-difluoro ketones.     

Chemistry of organo halogenic molecules,LXXV. Polymer-supported hydrogen fluoride

Polymer-supported hydrogen fluoride prepared by reaction of hydrogen fluoride with crosslinked poly(styrene-$\text{co}$-4-vinyl- pyridine) containing 40–45 mol % of 4-vinylpyridine did not react with $\text{trans}$-stilbene, 1,2-diphenylacetylene, and cyclohexanol under various conditions, whereas 1-phenyl-1-hydroxy- 4-tert-butylcyclohexane was converted to 1-phenyl-4-tert-butylcyclohexene. Bromofluorination of various phenyl-substituted olefins with N-bromosuccinimide in the presence of polymer supported hydrogen fluoride in methylene chloride proceeds with Markovnikov type regioselectivity. Fluorination and halofluorination of norbornene with xenon difluoride or N-bromosuccinimide or N-chlorosuccinimide in the presence of polymer- supported hydrogen fluoride resulted in up to five products, with a large increase in halonortricyclane formation, compared to reactions in the presence of hydrogen fluoride-pyridine. Polymer-supported hydrogen fluoride, in comparison to hydrogen fluoride-pyridine, enhanced the $\text{endo}$ attack of the electrophile on norbornadiene by fluorination or halofluorination.     

Flame retardant activity of SiO2-coated regenerated cellulose fibres

An alternative route to lower the flammability of viscose fibres is presented. Instead of adding a flame retardant to the viscose dope chemically, we have grown a layer of silica (SiO₂) on the surface of a regenerated cellulose fibre via a sol-gel process. One set of samples was used as-received, while the other was pre-treated in an 18% NaOH solution, giving a rough, etched surface to the fibre. The different surface morphology of both fibre types triggered a different growth of silica layers. On an untreated fibre, silica formed a 300-400 nm thick surface layer containing a high density of cracks and holes. Conversely, on a NaOH pre-treated fibre, the silica layer intruded into fibre interior, adhered more tightly to the fibre structure and formed an almost defect-free, thin (100 nm) layer on the outer fibre surface. This type of silica layer increased the temperature at which the fibre started to decompose by 20 °C. It also hindered significantly the flow of oxygen to the generated volatiles during the thermal decomposition, and increased the temperature of glowing combustion of the residual char; the temperature of the corresponding exothermic peaks increased by ca. 20 °C and 40 °C. In contrast, the thermal effects of silica coatings that grew on an untreated fibre were much smaller.     

Heterocycles. CII. Barriers to rotation in some N′-Heteroaryl N,N-dimethylformamidines

The free energies of activation about the =CH? NMe₂ bond in N′-heteroaryl N,N-dimethylformamidines have been found in the range from 15.6 kcal/mole to 23 kcal/mole.     

Role of the polymer backbone on the reactivity of polymer-supported (dichloroiodo)benzene

-Chlorination of iodinated crosslinked polystyrene with Cl₂ gave polyaryliododichloride containing 1.1 mmol of active chlorine per gram of resin, whilefluorination of the same iodinated resin with XeF₂ gave polyaryliododifluoride, containing 1.05 mmol of active fluorine per gram of resin. Both resins reacted with 1,1-diphenylethylene, reaction withpolyaryliododifluoride giving rearranged 1,1-difluoro-1,2-diphenylethane, while polyaryliododichloride gave 1,2-dichloro-1,1-diphenylethane and 1,1-diphenyl 2-chloroethene. The stereochemistry of chlorine addition with polyaryliododichloride to cis or trans-1-phenylpropene is very similar to that observed in the reaction with Cl₂ under ionic conditions, and its reactivity differs markedly from (dichloroiodo)benzene, which reacts via radical intermediates. Similar studies with 1-phenylalkynes and norbornene are described.     

Suppression of the exaggerated growth of barium ferrite nanoparticles from solution using a partial substitution of Sc<Superscript>3+</Superscript> for Fe<Superscript>3+</Superscript>

The effect of the substitution of Sc³⁺ for Fe³⁺ in barium ferrite on the size of the resulting nanoparticles was studied. These nanoparticles, with the nominal compositions BaFe₁₂O₁₉ and BaFe_11.5Sc_0.5O₁₉, were synthesized hydrothermally at 90–240 °C or by coprecipitation under reflux at 140 °C. The precursors were obtained using (co)precipitation at room temperature. The sizes and morphologies of the precursors and nanoparticles were inspected with transmission electron microscopy, while their structures were confirmed with a combination of X-ray powder and electron diffraction. The samples’ compositions were analyzed with energy-dispersive X-ray spectroscopy. The evolution of the particle size and its distribution with the synthesis temperature and time were studied in pure and Sc-substituted barium ferrite and correlated with the evolution of the magnetic properties. The Sc substitution in the barium ferrite results in the formation of magnetic nanoparticles with applicable magnetic properties and in a significant reduction of the exaggerated particle growth. This was explained on the basis of the reaction kinetics.     

The application of Kohonen neural networks to diagnose calibration problems in atomic absorption spectrometry

In atomic absorption spectrometric measurements calibration lines are measured daily. These lines are not always acceptable. They can, for instance, contain outliers, have a bad precision or can be curved. To evaluate the quality of those lines a method which gives a fast diagnosis is recommended. In this study the use of Kohonen neural networks was examined as an automated procedure to classify these calibration lines. The results were compared with those obtained using a decision support system which uses classical statistical methods to classify the lines. The prediction capabilities of both approaches relative to a visual inspection and classification was found to be comparable, or even slightly better for the Kohonen networks, depending on the training set used. For both techniques a prediction error rate of <10% was obtained, relative to a visual classification.     

On representation of DNA by line distance matrix

Recently Line Distance (LD) matrix has been introduced as a novel route for characterization of DNA sequences. The approach was based on construction of four separate submatrices for the four nucleotides, the first row of each of which records the separation between the selected nucleotide and the remaining nucleotides of the same kind. In this article, we consider an alternative representation of DNA by LD matrix in which we construct a single matrix for each DNA sequence. The approach is illustrated on the DNA sequence of the first exon of human β-globin gene.