Rotating sector study of the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane

The rate constant for the combination of 2,2-dichloro-1,1,1-trifluoroethyl radicals has been measured by applying the rotating sector technique to the gas phase photochlorination of 2,2-dichloro-1,1,1-trifluoroethane at 315°K. The observed value is 6.89 × 10¹² cc/mole.sec. This value is in excellent agreement with measurements by Wampler and Kuntz which yielded a temperature-independent value of 6.6 × 10¹² cc/mole.sec. The measurement by Wampler and Kuntz was determined from the photochemical system (CF₃CCl₃ + C-C₆H₁₂ + hν). The Arrhenius parameters for the reaction CF₃CCl₂· + Cl₂ → CF₃CCl₃ + Cl were found to be given by the expression log k₃ = 12.10 ? 5830/2.3RT (units in mole, cc, and sec). This is a relatively high activation energy for a chlorination reaction and makes the reaction ever slower than the chlorination of chloroform.     

30th anniversary of zoltán bay’s pioneer lunar radar investigations and modern radar astronomy

Acta physica Academiae Scientiarum Hungaricae - Thirty years ago American and Hungarian groups of researchers announced the detection of radar echoes from the moon. The experiments were performed...     

Studies of radiative losses from multimode optical fibres

We describe measurements in which the radiative losses from a multimode fibre have been resolved into three components. These are the Rayleigh Scatter component from the material, the loss by tunnelling from the modes closest to cut-off into the surrounding material, and the forward scatter loss caused by imperfections in the fibre that are large compared to a wavelength.     

The kinetics of hydrogen-deuterium exchange of methylisothiazoles

The rates of hydrogen-deuterium exchange of 3-methyl, 4-methyl, 5-methyI and 3,5-dimethyl-isothiazole were determined and compared with the rate of exchange of 2-methylpyridine. The rates were measured in dimethylsulfoxide-d₆ -deuterium oxide (90:10), using sodium deuteroxide as catalyst. The relative rates for exchange of both ring protons and methyl protons were 5 > 3 > 4. For exchange of methyl hydrogens, the approximate ratio of rate constants is 100:1:< 10^?4 for positions 5,3, and 4, respectively. Activation parameters are reported for 5-methylisothiazole.     

Asymmetric decarboxylative Claisen rearrangement reactions of sulfoximine-substituted allylic tosylacetic esters

Allylic acetate esters containing a variety of N-arylsulfonyl sulfoximines on the acetyl residue have been prepared and submitted to the decarboxylative Claisen rearrangement reaction. Rearranged products were isolated in generally good yields, and diastereoselectivities up to 82:18 have been obtained. The N-(2,4,6-triisopropylphenylsulfonyl)-S-phenyl sulfoximine moiety gave the best selectivity. The stereochemistry of the major isomer was established by X-ray crystallography. A model to explain the stereochemical course of the rearrangement is proposed.     

Vertex-linked ZnO2S2 tetrahedra in the oxysulfide BaZnOS: a new coordination environment for zinc in a condensed solid

The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) angstroms, b = 12.8541(7) angstroms, c = 6.1175(4) angstroms, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible.     

Synthesis and structure of novel organocycloborates

A series of alpha,omega-boryl(bromo)alkanes of the general formula R2B-(CH2)n-Br (n = 3, 4, 5, 6) was obtained in high yield following a standard hydroboration protocol. Upon treatment with Mg turnings and formation of the respective Grignard species, all alkanes with n = 4 to 6 underwent an unprecedented boron-centered cyclisation reaction with formation of boratacyclopentanes, -hexanes, and -heptanes, respectively. All new compounds were isolated in high yields as colourless, crystalline materials and characterised in solution by multinuclear NMR spectroscopy. Four representative examples were chosen for X-ray diffraction studies, thus providing the first structurally characterised ring systems of that size at a tetraalkyl borate centre.     

Surfactant-free synthesis of amphiphilic diblock copolymer nanoparticles via nitroxide-mediated emulsion polymerization

Amphiphilic hairy nanoparticles are prepared in a one step, batch, heterogeneous polymerization of styrene or n-butyl acrylate, using a water-soluble poly(sodium acrylate) alkoxyamine macroinitiator based on the SG1 nitroxide.