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991.
The temperature dependences of the heat capacities of crystalline tetraphenyltetrahydroxycyclotetrasiloxane, octaphenyltetrahydroxytricyclooctasiloxane, and octaphenylpentacyclosilsesquioxane and of glassy polyphenylsilsesquioxane were measured in the range 6-300 K with an adiabatic vacuum calorimeter, with an accuracy of 0.3%. From these data, the thermodynamic functions C
0
p
(T), H
0(T) - H
0(0), S
0(T) - S
0(0), and G
0(T) - H
0(0) of these substances were calculated for the range 0-300 K. The standard entropies of their formation from elements at 298.15 K,
f
S
0, and the entropies of mutual transformations of these substances in the range 0-298.15 K were calculated. 相似文献
992.
The distribution of the chromium(VI) species CrO(2-)(4), Cr(2)O(2-)(7), HCrO(-)(4), and H(2)CrO(4) in aqueous solutions with total chromium(VI) concentrations of 10(-2)-10(-6)M at pH 1-8 have been calculated. 相似文献
993.
V. Yu. Buz’ko I. V. Sukhno V. T. Panyushkin D. N. Ramazanova 《Journal of Structural Chemistry》2005,46(4):596-602
The structure and relative stability of 1,4-dioxane-water, (Diox)n·(H2O )m (n = 1, 2, m = 1–6), molecular complexes have been calculated by semiempirical MNDO/PM3 method. A considerable variety of (Diox)n·(H2O )m isomeric structures was stated. The mean energy of ODiox…HW-OW hydrogen bond in (Diox)n·(H2O)m complexes formed by 1,4-dioxane molecules in the chair conformation amounts to ?2.293 ± 0.210 kcal/mol with the average bond length 2.797 0.015 Å. 相似文献
994.
The structures of fatty monohydroxy acids of the lipids of the seeds ofGaleopsis bifida Boenn. have been studied by the methods of chromatographic, spectral, and chemical analysis. (31) Acids with chain lengths of from 14 to 20 carbon atoms, with from 0 to 3 double bonds, and with the hydrolyls in positions characteristic for the products of the direct hydroxylation and the lipoxygenase and photosensitized oxidation of unsaturated fatty acids were detected. Of them, the 13-OH-9Z, 11E-17:2, the 15-OH-9, 12-18:2, the 16-OH-9, 12-18:2, and 17-OH-11, 14-20:2 acids were new, while this is the first time that the 15-OH-9Z, 12Z, 16E-18:3 acid has been described as a natural compound. The behavior of the TMS derivatives of the hydroxy acids on a polyester phase in GLC is discussed.Institute of the Chemistry of Plant Substances, Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 744–753, November–December, 1991. 相似文献
995.
T. Kluge D. Pankonin O. Brede 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):103-105
The rate constants of the reactions of the radicals OH? and Cl2 ?? with α-pinene determined by pulse radiolysis in aqueous solution are given. The reaction of Cl? with α-pinene has been studied by laser photolyis in CCl4 solution. Furthermore, the rate constants of the reactions of the formed organic radicals with oxygen as well as those of the deactivation of all radicals were determined. 相似文献
996.
A simple and sensitive polarographic method for determining arsenic in steel is presented. The steel is dissolved in HNO(3), and arsenic reduced with Na(2)S(2)O(5)-K.I. The polarographic wave is recorded for an electrolyte at pH 3.0 and containing Fe(II), Mn(II). citric and ascorbic acids. Levels of 0.2% and 0.003% As can be determined with a coefficient of variation of +/- 6%. 相似文献
997.
The thermodynamic quantities Kn?1 n, ΔG0n?1, n and ΔS0n?1, n for the gas phase equilibrium reactions RNH+3(RNH2)n?1 + RNH2 = RNH+3(RNH2)n, where n ? 3 and R indicates an alkyl group (CH3, C2H5, n-C3H7 and iso-C3H7), have been determined. 相似文献
998.
The corresponding 2-(2-furyl)naphth[1,2-d]imidazoles were obtained by heating Schiff bases, prepared from 1,2-naphthalenediamine and furfural and 5-bromo- and 5-nitrofurfurals, in nitrobenzene. 2-[-(2-Furyl)vinyl]naphth[1,2-d]imidazoles were synthesized by condensation of 2-methylnaphth[1,2-d]imidazole with furfural and 5-bromo- and 5-nitrofurfural. The methylation, nitration, and acetylation of the compounds obtained were studied, and the replacement of the bromine atom in the furan ring by a nitro group was also investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1555–1557, November, 1972. 相似文献
999.
This review highlights mutagenesis studies of terpene synthases, specifically sesquiterpene synthases and oxidosqualene cyclases. Mutagenesis studies of these enzymes have provided mechanistic insights, structure-function relationships for specific enzymatic residues, novel terpene structures and enzymes with novel activities. The literature through 2002 is reviewed and 113 references cited. 相似文献
1000.
Variously cross-linked poly(methylmethacrylates) (PMMAs) are synthesized with three additives incorporated at theoretically 1000 microg of the additive per gram of prepared polymer. The additives are Irganox 1010, Irganox 1076, and Irgafos 168. The in-house" synthesized polyacrylates are then subjected to supercritical fluid extraction (SFE) to determine if additive recovery is a function of percent cross-linking. Although considerable work in this regard has been performed with non-cross-linked polyolefins, the literature is lacking regarding polyacrylates. Some additive degradation apparently occurs during the synthesis, as judged by the increased complexity of the extract high-performance liquid chromatographic trace and the low percent recoveries observed especially for the Irganoxes. For low polymer cross-linking (1%), it appears that both PMMA synthetic reproducibility and readily observed polymer swelling during SFE are serious issues that adversely affect additive percent recovery and precision of results. Higher percent cross-linking yields more consistent analytical data than low percent cross-linking, even though the amount of additive extracted in all PMMA samples (regardless of cross-linking percentage) is essentially the same whether the extraction is via SFE or liquid-solid extraction with methylene chloride. Results for comparably cross-linked poly(ethylmethacrylate) and poly(butylmethacrylate) are similar to PMMA. 相似文献