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171.
A series of 2-(5-nitro-2-furyl)-2-oxoethylarylsulphides 3a–3h has been prepared by the reaction of 5-nitro-2-furylbromomethylketone 1 with 4-substituted thiophenols 2a–2h. The determined rates of carbanion formation (log k'), pK values as well as 1H NMR data show that in these compounds transmission of polar effects by the substituents through the -S- group occurs. Compounds 3a–3h react with aromatic aldehydes affording sulphur chalcone derivativěs of the 5-nitrofuran series 4a–4h. 1H NMR, IR and UV spectra of prepared compounds are discussed. 相似文献
172.
Four 9H and four 7H tautomers of DNA base xanthine were studied by the ab initio LCAO-MO method at the MP2/6-311G**//HF/6-31G** and MP2/6-31G**//HF/6-31G** approximations. All calculated structures are minima at the HF/6-31G** potential energy surface with the dioxo 7H tautomer (A1) being the global minimum. The second most stable tautomer, dioxo-9H (B1) is by 9 kcal/mol less stable. For the A1 B1 transition the calculated MP2 energy gap corresponds to the equilibrium constant of 2 × 10–7. Therefore, only the major tautomeric form A1 is predicted to be detectable in the gas phase. The 7H and 9H groups of tautomers are discussed separately. Within both groups, the dioxo form (A1-7H, B1-9H) is the most stable one and is succeeded by the 2-dihydroxy (A2, B2) form. However, while the energy difference between A1 and A2 is 10 kcal/mol, the energy difference between B1 a B2 is only 2 kcal/mol. The effect of polar environment was estimated by the SCRF method, using a spherical cavity, at the HF/6-31G** level. These calculations did not change the gas phase stability order of the tautomers. However, the energy difference between A1 and B1 decreased from 9 kcal/mol at the HF/6-31G** level to 4 kcal/mol at the SCRF HF/6-31G** level. 相似文献
173.
K. Rybáček L. Wilhelmová M. Tomášek 《Journal of Radioanalytical and Nuclear Chemistry》1994,186(3):245-255
Radiocesium in ground layer atmospheric aerosol and fallout in Prague has been examined. After a decline in 1986–1988, controlled by a sum of two negative exponentials,137Cs aerosol concentration reached a constant level based on an equilibrium between its deposition and resuspension. Deposition velocity was compared to that of7Be and226Ra. It confirmed the supposed source of137Cs as resuspension from the ground. Resuspension factor of the order of magnitude of 10–9 was determined, reminding similar values found earlier in Prague as well as those found in Munich. It also agrees well with the USAEC resuspension model. Solubility of137Cs was measured in combined wet and dry fallout. The average undissolved fraction of137Cs was found to be about 70% which can be explained by the conditions of the137Cs aerosol formation in Chernobyl. 相似文献
174.
Milan Melník Peter Mikuš 《Phosphorus, sulfur, and silicon and the related elements》2020,195(5):367-370
AbstractIn this review, the structural data of monomeric platinum(II) complexes with inner coordination spheres of Pt(η2-P2L)(SiL)2, Pt(η2-P2L)(η2-Si2L) and Pt(η2-P,SiL)2 are classified and analyzed. These complexes crystallize in three crystal systems: monoclinic (8 examples), triclinic (4 examples) and orthorhombic (4 examples). Distorted square-planar environments about the Pt(II) atoms are built up by combination of homobi-P,P with two monodentate Si donor ligands; homobi-PP with homo-Si,Si donor ligands, or heterobi-P,Si donor ligands. The chelating ligands create metallacycles with the following angles: 65.0° (SiOSi) < 83.1° (SiC2Si) < 85.2° (PC2P) < 88.8° (SiSi2Si)). The mean Pt-P and Pt-Si bond distances in Pt(η2-P2L)·(SiL)2 complexes are 2.319 and 2.365?Å; in Pt(η2-P2L)(η2-Si2L) the values are 2.316 and 2.360?Å. The complex [Pt{η2-Me2P(C2B10H10)SiMe2}2] exists in two isomeric forms, a monoclinic cis- and a triclinic trans-isomer. The structural data are compared and discussed with the complexes of inner coordination spheres: Pt(η2-P2L)(XL)2 (X?=?O, N, CN, BL, Cl, SL, SeL, Br, or I) and Pt(η2-P2L)(η2-X2L) (X?=?OL, NL, SL or SeL). 相似文献
175.
Mojca Dobnikar Marijan Kočevar Andrej Petrič Miha Tišler Bojan Verček 《Monatshefte für Chemie / Chemical Monthly》1989,120(3):269-272
Summary Syntheses of 1-methylimidazo[1,2-c]quinazolinium iodide (3) and 1-methylimidazo[2,1-f]pyrido[3,2-d]pyrimidinium iodide (4) are described. These tricyclic compounds react with nucleophiles derived from active methylene compounds to give the corresponding open-chain enamines.
Reaktionen von quaternisierten Imidazo-Chinazolinen und -Pyridopyrimidinen mit Verbindungen mit reaktiven Methylengruppen
Zusammenfassung Synthesen von 1-Methylimidazo[1,2-c]chinazoliniumjodid (3) und 1-Methylimidazo[2,1-f]pyrido[3,2-d]pyrimidiniumjodid (4) werden beschrieben. Diese tricyclischen Verbindungen reagieren mit einigen Carbanionen aus Verbindungen mit reaktiven Methylengruppen, wobei die offenkettigen Enamine entstehen.相似文献
176.
Analysing experimentally determined P, ?, T data of N2, ethylene, propene, CO2 and Xe by a new mathematical technique, we present evidence that their isothermal pressure-density dependence exhibits behaviour characteristic of a Riemann-Hugoniot catastrophe, in analogy to a van der Waals gas for above and sub critical isotherms. 相似文献
177.
178.
The study of D(?)-ribose complexing with calcium in aqueous solutions less than 1.64 × 10?1M by potentiometric measurements with a calcium selective electrode afforded the value of K1 = 1.70 liters × mole?1 (SD = 1.05 × 10?3). Numerical analysis indicated that complex species with 1:1 and 1:2 calcium to D(-)-ribose ratios are present simultaneously: k1 = 1.13 liters × mole?1 and K2 = 8.47 liters × mole?1 (SD = 0.95 × 10?3).In methanolic medium 1.24 × 10?2M with regard to calcium chloride both stoichiometric proportions were evidenced. A large error accompanying the stability constant K1 = 28 kg × mole?1 (RSD = 82%) renders unreasonable the K2 value obtained from the product K1 × K2 = 96.5 kg2 × mole?2.The results are discussed with respect to the data published for more concentrated (1.27 M) aqueous solutions obtained on the basis of 1H-NMR spectroscopic investigations. 相似文献
179.
The concentration of239,240Pu and238Pu in airborne effluents in the years 1985–1987 from two reactors VVER 440/total power of 880 MW/ of a nuclear power plant V-1 in Jaslovské Bohunice in Czechoslovakia, was determined. The concentration of239,240Pu in effluents ranged from 1.0 to 30.8 Bq.m–3 and of238Pu from 1.6 to 41.1 Bq.m–3. The activity ratio238Pu/239,240Pu in airborne effluents kept within the range of 1.0–2.4. Total annual discharged activities of239,240Pu in 1985, 1986 and 1987 were 28.5, 12.7 and 12.2 kBq, respectively. Total annual discharged activities of238Pu in 1986 and 1987 were 16.6 and 15.1 kBq, respectively. 相似文献
180.
R. Smiljanić D. Novković D. Paligorić Z. Milošević M. Zarić 《Journal of Radioanalytical and Nuclear Chemistry》1989,136(6):437-442
This paper presents the results of measurements of137Cs and134Cs content in air sampled during May 1986. Maximum concentrations:137Cs 2.94±0.01 Bq m–3 and134Cs 1.38±0.01 Bq m–3 were registered on May 3. Several other long lived radionuclides having -energies in the region 33 keV to 1365 keV were registered in the same samples two years later. The results of measurements of the total -activity in air for the same period are also presented. 相似文献