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[reaction: see text] m- or p-Diiodobenzene undergoes selective double coupling reactions with arylboronic acids and esters. Selectivity for double coupling over single coupling is remarkably strong: even with a diiodobenzene:monoboronic acid ratio of 10:1, the products of double coupling are formed in good yields. Steric hindrance and electronic influences of the boronic acid or ester, and reaction conditions do not appear to impact significantly upon the outcome of the reaction. In contrast, m- and p-dibromobenzenes undergo single couplings with aryl boronic acids with high selectivity. 相似文献
134.
An explanation is given of the apparently paradoxical behaviour of heteropoly acids in the presence of organic complexing agents such as tartaric acid, and methods for selective formation of particular heteropoly acids are suggested. Sensitive and rapid methods for the determination of silicate and phosphate in the presence of each other are described. 相似文献
135.
Casper D Becker-Szendy R Bratton CB Cady DR Claus R Dye ST Gajewski W Goldhaber M Haines TJ Halverson PG Jones TW Kielczewska D Kropp WR Learned JG LoSecco JM McGrew C Matsuno S Matthews J Mudan MS Price L Reines F Schultz J Sinclair D Sobel HW Stone JL Sulak LR Svoboda R Thornton G van der Velde JC 《Physical review letters》1991,66(20):2561-2564
136.
R. Bonnett C. Lambert † E. J. Land + P. A. Scourides R. S. Sinclair † T. G. Truscott § 《Photochemistry and photobiology》1983,38(1):1-8
Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0 -acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).
After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φT = 0.92) and photoionises monophotonically (φI = 0.03). For the O -acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates ( k 1 ˜104 s-1 ) and oxygen quenching constants ( k Q ˜1.5times109 M -1 s-1 ) for the triplet state have been measured. The difference and corrected spectra for the semi-reduced species in methanol and semi-oxidised species in aqueous Triton X-100 are presented.
The photophysical characteristics in fluid solution of haematoporphyrin and its 0 -acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins. 相似文献
After 347 nm irradiation in water containing 2% Triton X-100, haematoporphyrin forms the triplet state (φ
The photophysical characteristics in fluid solution of haematoporphyrin and its 0 -acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins. 相似文献
137.
S. J. Parry M. Asif I. W. Sinclair 《Journal of Radioanalytical and Nuclear Chemistry》1988,123(2):593-606
The radioactive study of Ni–NiS bead fire-assay followed by neutron activation analysis showed nearly quantitative collection of the platinum group elements and gold in the bead. However, there was clearly some loss of gold and ruthenium at the dissolution and filtration stage. A preliminary study of the radiochemical fire-assay method indicates that the technique could overcome the problem of losses. Chemical carrier behaves in the same way as platinum metal concentrate during the analytical procedure and could be used to evaluate yields during each determination. When applied to rock samples, the radiochemical fire-assay gives good sensitivity and could be applied to the determination of nanogram concentrations of the platinum group elements without the problem of high blank values from reagents. 相似文献
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Reactor twin-axis neutron diffraction data have been obtained for vitreous silica at five incident wavelengths and analysed to give the total correlation function T(r). A fit to the first SiO and OO peaks in the Gaussian approximation yields distances of 1.61 and 2.63 Å respectively. The peaks are, however, asymmetric, the form of the asymmetry being qualitatively as predicted for anharmonicity in the SiO bond stretching modes. The results show that, in order to avoid significant static approximation distortions of the distinct scattering, measurements on vitreous silica must be limited to scattering angles less than 80°. The effect of temperature on the interference function is demonstrated by an additional measurement at liquid nitrogen temperature. 相似文献