π-Bindungsbeitrag in Boranen, 2. Mitt.:Ab initio- und Kraftfeld-Rechnungen von Vinyldifluorboran

Ab initio calculations on vinyldifluoroborane yield a content/vq107uj27766g3p8/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-contribution of 23 kJ/mol (5.5 kcal/mol) mainly due to the C=C bond and not to the lone pairs of the fluorine atoms. The rotational barrier was also determined. The force field calculations favour the interpretation of the bond structure derived from the theab initio results.

     

Absence of p,π-conjugation in the Cl2C=CHOMe molecule from data ofab initio calculations

ab initio Calculation of the Cl₂C=CHOMe molecule has been carried out with geometrical optimization in the split valence basis set in the RHF/6-31G^*//RHF/6-31G^* approximation. An analysis of the populations of the p-orbitals of the Cl atoms implies the absence of p,content/m885386139465882/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-conjugation between the unshared electron pairs of these atoms and the content/m885386139465882/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">-bond. The asymmetry parameters of the electric field gradient at the³⁵Cl nuclei, calculated from the 3p-orbital populations of the Cl atoms, practically coincide with the experimental values.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2369–2372, December, 1995.The authors are grateful to G. S. Beloglazov for assistance in accomplishingab initio calculations.     

Phosphorescence lifetime of naphthalene and phenanthrene in aggregated aromatic molecule-β-cyclodextrin-precipitant complexes

Aggregated aromatic molecule-content/n172l724h5304v21/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin-precipitant complexes exhibit long-lived phosphorescence at room temperature in water after the chemical binding of oxygen. The temperature dependences of the phosphorescence lifetimes of naphthalene-h₈, naphthalene-de, and phenanthrene in the aggregates were measured. For example, the phosphorescence lifetimes of naphthalene-d₈ aggregated with content/n172l724h5304v21/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin and cyclohexane are equal to 25.1, 17.6, and 6.8 s at 77, 276, and 347 K, respectively, and that of phenanthrene aggregated with isooctane and content/n172l724h5304v21/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin are 3.24, 3.06, and 1.26 s at 268, 274, and 335 K, respectively. The temperature dependences of the phosphorescence lifetimes at room temperature are determined by the rate constants of the radiative and nonradiative transitions from the triplet state of an aromatic molecule.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2225–2228, September, 1996.     

A novel vapor phase process for aromatic ketone synthesis

The vapor phase catalytic reaction between aromatic carboxylic acid and acetic acid was investigated. Many metal oxides catalyzed the reaction between 2content/m1274j4038230616/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">methylbenzoic acid (OTA) and acetic acid (AA) to produce 2content/m1274j4038230616/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">methylacetophenone (OMA), and weakly acidic oxides such as Th, U, Ce, and La oxide exhibited higher yield of OMA. The OMA yield depended on the catalyst support. SiO₂, Al₂O₃, TiO₂, and ZrO₂ with a surface area of less than 200 m² g^–1 appeared to be suitable as industrial catalyst supports. CeO₂ on Al₂O₃was chosen as an industrial catalyst for the synthesis of OMA because of higher productivity, longer catalyst life, and lifting of legal restrictions on catalyst handling. This catalyst system can also be applied to the syntheses of acetophenone, nitroacetophenone, and chloroacetophenone.     

Michael and ring expansion reactions of 6-carboethoxy-3,5-diaryl-2-cyclohexen-1-ones

When content/g64n853265325683/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-keto-ester1 a was reacted with dimethyl acetylenedicarboxylate ring expansion occurred to give substituted cyclooctadienones.Michael reactions of the title compounds1 with unsaturated ketones gave adducts, some of which underwent further cyclization reactions. A new route to content/g64n853265325683/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-tetralone ring system10 via cyclization of the intermediateMichael adduct9 is described.

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Michael- und Ringerweiterungsreaktionen von 6-Carboethoxy-3,5-diaryl-2-cyclohexen-1-onen

Zusammenfassung Bei der Reaktion von content/g64n853265325683/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-Keto-ester1 a mit Dimethyl-acetylendicarboxylat wurden unter Ringerweiterung substituierte Cyclooctadienone erhalten. DieMichael-Reaktion der Titelverbindung1 mit ungesättigten Ketonen ergab Addukte, von denen einige weitere Cyclisierungsreaktionen eingingen. Es wird ein neuer Weg zum content/g64n853265325683/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-Tetralonsystem10 über die Cyclisierung des intermediärenMichael-Addukts9 beschrieben.

     

Application of water as a solvent in microwave-assisted extraction for analysis of PCBs and CBzs in fly ash

Polychlorinated biphenyls (PCBs) and chlorobenzenes (CBzs) are two classes of dioxin precursors formed in municipal solid waste incinerators (MSWIs); they produce negative health effects similar to those of dioxins. Reducing the analytical time required for determining the concentrations of these compounds in MSWIs is important for quickly evaluating their importance and assessing associated health risks. In the present study, water is used as a safe and environmentally friendly solvent in microwave-assisted extraction (MAE) for PCB and CBz analyses. MAE is compared with traditional Soxhlet extraction (SE) to determine the extraction efficiencies. The evaluation of extraction efficiencies shows that MAE has a high extraction efficiency compared with that of SE when water content is lower than 60%. Furthermore, the extraction time and organic solvent consumption are reduced with MAE compared with SE.     

Characterization of high-temperature superconductors by electron microprobe analysis

In order to optimize the physical properties of HTSC small single crystals grown from a melt for basic studies of their physical properties the influence of the environment on their impurity content was investigated by EPMA. This requires quantitative analysis of all elements being present in the crystals. The accuracy of results was affected by problems with the choice and quality of standards, by contamination but also by malfunction of microprobe electronics. The HTSC materials were found to react with mills, milling balls, crucibles and the atmosphere. These problems are being discussed and some reactions being studied for Y₁Ba₂Cu₃O_6+x (0 < x < 1) HTSC in A1₂O₃ and ZrO₂ crucibles. The crystals grown contain reproducible amounts of impurities depending on boundary conditions and exhibit a zone structure in composition particularly for Y and Ba within their range of homogeneity.     

聚丙烯改性研究

采用马来酸酐、二甲基丙烯酸乙二醇酯、三羟甲基丙烷三基丙烯酸酯对聚丙烯进行改性。以自由基反应机理为基础，讨论了引发剂用量、反应时间、改性试剂的种类、用量等因素对改性ＰＰ凝胶含量及性能的影响，提出了力学性能的优选条件。得到了力学性能优良的改性ＰＰ，为其进一步功能化提供了理论参考。     

New approach to nonracemic 1-alkylamino-3-aryloxypropan-2-ols belonging to β-blockers via cyclic sulfites

Nonracemic content/jl1450776wp32677/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-blockers, viz., (S)-propranolol and (S)-timolol, were prepared from (S)-glycidol in three steps consisting in the reaction with SOCl₂ followed by the reaction of the resulting (4S)-4-chloromethyl-2-oxo-1,3,2-dioxathiolanes with the corresponding phenol and the final cleavage of (4R)-aryloxymethyl sulfites under the action of amines in DMF.     

头发锌含量测定的应用价值评价

以114例2－5岁儿童为对象，同时取其末梢血和头发，测定锌含量。以全血锌值为标准，评价头锌测定的应用价值。结果显示，头发锌测定的灵敏度可达86．1％，特异度为52．4％，符合率为73．7％。