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871.
872.
A method is described for the determination of selenium, based on its catalytic effect on the picrate—sulfide reaction. The determination involves a variable-time kinetic procedure using potentiometric monitoring with a picrate-selective electrode and automatic measurement of the time required for the potential to change by a preselected amount (5.0 mV). Selenium in the range 3–30 μg was determined with an average error of about 4% and relative standard deviations of about 2%. The reaction can also be followed spectrophotometrically. 相似文献
873.
J. C. Favier P. Sigwalt M. Fontanille 《Journal of polymer science. Part A, Polymer chemistry》1977,15(10):2373-2379
A kinetic study in tetrahydrofuran of the addition of 1,1-diphenylethylene on para-substituted styrylcarbanions (with Cs+ as counterion) has given the reactivities of free ions and ion-pairs. For both species, the addition rate constant increased in the following sequence for the substituent of the phenyl ring: pH < p-CH3 <p-CH3O. It was also shown that in the same solvent, the dissociation constants of the polystyryl ion-pairs decreased with the electron-donating power of the substituent. 相似文献
874.
875.
876.
877.
878.
R. A. Gavar L. Kh. Baumane Ya. P. Stradyn' S. A. Giller 《Chemistry of Heterocyclic Compounds》1974,10(3):280-284
Anion radicals of 2-vinylene derivatives of 5-nitrofuran were obtained by electrochemical generation. The hyperfine structure (hfs) of the ESR spectra of these anion radicals indicates delocalization of the unpaired electron over their entire π-electron system. The effect of the vinylene grouping on the distribution of the unpaired electron in the anion radicals and on the distribution of the unpaired electron in the vinylene grouping itself was examined on the basis of the hfs constants. It was found that the vinylene grouping by localizing more than 10% of the density of the unpaired electron on itself reduces, by a factor of 1.4, the effect of substituents in the 2 position of 5-nitrofuran on the distribution of the spin of the unpaired electron in the nitrofuran framework. 相似文献
879.
Chemistry of Natural Compounds - The epigeal part ofArtemisia santolina Schrenk has yielded a new sesquiterpene lactone, artesin, C14H22O3, having the structure... 相似文献
880.
R. O. Kochkanyan M. M. Nechitailov P. Byszewski A. N. Zaritovskii A. F. Popov 《Russian Journal of Organic Chemistry》2004,40(7):957-961
Reaction of C60 fullerene with ferrocene in the presence of aluminum chloride and aluminum in an inert atmosphere gave ferrocenyl-substituted fullerene 2C60 ·1.5(C5H5)2Fe ·3H2O. The product is a thermally stable iron-containing carbon cage in which the intersphere cavity is formed by three C60 polyhedra and is closed by cyclopentadienyl ligands via formation of four carbon-carbon bonds. 相似文献