制备方法对WO_3/ZrO_2结构的影响

用XRD、比表面测定、LRS定性和定量的方法对用Zr（OH）4和已晶化的ZrO2作载体制得的两类WO3／ZrO2催化剂进行了表征．揭示了样品比表面、载体物相、活性组分的存在状态与制备方法、WO3含量、焙烧温度之间的关系．结果表明，WO3能单层分散在ZrO2上；单层覆盖在Zr（OH）4上的WO3使载体在焙烧时晶粒生长受阻，形成介稳的四方ZrO2，并阻止载体微粒间的烧结，使从Zr（OH）4出发制得的WO3／ZrO2比表面明显增大，在WO3含量达到单层分散容量时以上作用表现得最充分；WO3与Zr（OH）4（或四方ZrO2）在高温（～800℃）可能发生了某种化学结合，开创出超强酸位．用以上观点可对文献中已报导的主要实验事实作出较满意的解释.     

Theoretical investigation of isotopic scrambling mechanisms in 2-chloroethyl methyl sulfide

Ab initio and semiempirical molecular orbital calculations have been applied to study the concerted and stepwise isotopic scrambling mechanisms of 2-chloroethyl methyl sulfide in the gas phase and in aqueous solution. The calculations reveal the structural details of the reactants, transition structures, and intermediates involved in this reaction and provide relative energy estimates. The concerted mechanism is found to be competitive with the stepwise mechanism in the gas phase, but the stepwise mechanism is favored in aqueous solution as no true transition structure for the concerted mechanism could be found using the solvation models. A combined approach of evaluating solvation energies with the generalized-Bom-plus-surface-tensions SM _x solvation models of Cramer and Truhlar at ab initio optimized geometries is found to deliver the best agreement with experimentally determined reaction barriers. Together with the recent experimental results of McManus and co-workers, the present study provides insights into the controlling factors involved in the elementary reaction steps of sulfur mustards and a solid foundation for investigations into more complex reactions of related compounds.     

Temperature-sensitive luminescence of tris (β-diketone) europium chelates for monitoring high-speed cationic photopolymerizations

The temperature-dependent luminescence of tris (β-diketone) chelates of europium was used for in situ temperature measurements during cationic photopolymerizations of vinyl ethers. These molecular-level luminescent probes provided a real-time, noninvasive method for monitoring temperature during these high-speed polymerizations. Two specific probes, tris (benzoyl-1, 1, 1-trifluoroacetone) europium and tris (1,1,1,5,5,5,-hexafluoroacetylacetone) europium, met several stringent spectral and performance requirements for application in our system. The luminescence from these probes exhibits a reproducible temperature dependence over a wide temperature range and is not sensitive to changes in viscosity. In situ temperature profiles obtained using this novel technique verified the importance of thermal effects during these highly exothermic photopolymerizations. These studies have demonstrated the utility of the tris(β-diketone) europium chelates for characterizing the temperature during high-speed photopolymerizations that cannot be monitored using conventional techniques. © 1995 John Wiley & Sons, Inc.     

Measurements of HO2 uptake coefficient on aqueous (NH4)2SO4 aerosol using aerosol flow tube with LIF system

The γ(HO₂) was elevated with increase of Cu(II) concentrations in aqueous (NH₄)₂SO₄ aerosol. The threshold of Cu(II) concentration was 10^-3 mol/L for the dramatic increase of γ(HO₂) to 0.1, suggesting sensitive γ(HO₂) value to concentration of transition metal ions in aerosol.     

Spin density distributions in radical anions of heterocyclic amine N-oxides

The unrestricted Hartree-Fock (UHF) method of Snyder and Amos is used to calculate, in the -electron approximation, the spin density distributions in radical anions of heterocyclic amine N-oxides. The computed spin densities are observed to be in good agreement with the experimental values. The computed spin density distribution of the radical anion of pyridine N-oxide is consistent with the greater susceptibility of pyridine N-oxide relative to pyridine to electrophilic nitration. Also, the calculations are consistent with the lower basicity of the N-oxides relative to the parent bases.     

19F and 1H NMR spectra of halocarbons

19F NMR chemical shifts and coupling constants are reported for 215 compounds. For 77 of these compounds, 1H NMR spectral data are also given. Long-range couplings, including 8J(F,F) and 5J(F,H), are reported. The complexity of halocarbon spectra owing to the presence of rotational isomers, asymmetric centers, long-range couplings, and chlorine isotope effects are illustrated, and the methods used for analyzing such complex spectra are briefly discussed.     

Effect of Co-solvent on the Palladium Catalyzed Alkoxycarbonylation of Allyl Bromide in Supercritical CO_2

We have studied the palladium-catalyzed alkoxycarbonylation of allyl bromide in supercritical (sc) CO2 and found the reaction rate in sc CO2 was lower than those in some organic solvents1. The possible reason was the lower solubility of sc CO2 for the palladium catalyst. As an effective approach to improve the solubility of varieties of solutes, cosolvent such as ethanol has been widely used in the sc CO2 extraction2,3. Based on the above consideration, we chose several organic reagents…     

Hydrogen bonding in 2-hydroxy-benzhydrazide and 2-hydroxy-thiobenzhydrazide. Structural and spectroscopic study

Summary X-ray structural data are reported for 2-hydroxy-benzhydrazide(monoclinic; P2₁/n-C _2h ⁵ ;a=10.569(2) Å,b=11.264(2) Å,c=6.074(1) Å, =98.80(1)°;Z=4;R=0.054) and 2-hydroxy-thiobenzhydrazide (monoclinic; P2₁/n-C _2h ⁵ ;a=14.598(6) Å,b=5.975(2) Å,c=9.286(4) Å, =107.80(3)°;Z=4;R=0.044). In both compounds the phenolic OH groups are intramolecularly hydrogen bonded to the (thio)carbonyl oxygens and sulfurs, respectively; the basic intermolecular association patterns consist of closed six-membered hydrogen bonded dimers which are connected via N-H ... NH₂ hydrogen bonds. The spectral characteristics of the intramolecular O-H...O/S hydrogen bonds (solid state (OH)=2800/2700 cm^–1, CCl₄ solution (OH)=3035/3100 cm^–1, CDCl₃ solution (OH)=11.62/10.56 ppm) are similar to those of corresponding primary and secondary amides. The solid state IR spectra are consistent with hydrogen bonded NH groups and free NH₂ groups, the solution IR spectra indicate free NH₂ as well as free NH groups.

---

Wasserstoffbrückenbindung in 2-Hydroxy-benzhydrazid und 2-Hydroxy-thiobenzhydrazid. Strukturelle und spektroskopische Untersuchungen

Zusammenfassung Es werden Röntgenstrukturdaten für 2-Hydroxy-benzhydrazid (monoklin; P2₁/n- C _2h ⁵ ;a=10.569(2) Å,b=11.264(2)Å,c=6.074(1)Å, =98.80(1)°;Z=4;R=0.054) und 2-Hydroxy-thiobenzhydrazid (monoklin; P2₁/n - C _2h ⁵ ;a=14.598(6)Å,b=5.975(2)Å,c=9.286(4)Å, =107.80(3)°;Z=4;R=0.044) berichtet. In beiden Verbindungen bilden die phenolischen OH-Gruppen intramolekulare Wasserstoffbrücken mit den Carbonyl-Sauerstoff-, bzw. den Thiocarbonyl-Schwefel-Atomen. Das intermolekulare Assoziationsmuster wird durch N-H...NH₂ Wasserstoffbrücken bestimmt, die jeweils zwei Moleküle über sechszählige Ringe zu Dimeren verbinden. Die IR- und NMR-spektroskopischen Charakteristika der intramolekularen O-H...O/S Wasserstoffbrücken (kristallin: (OH)=2800/2700 cm^–1, CCl₄-Lösungen: (OH)=3035/3100 cm^–1, CDCl₃-Lösungen: (OH)=11.62/10.56 ppm) sind sehr ähnlich zu denen entsprechender primärer und sekundärer Amide. Die Festkörper-IR-Spektren stehen in Einklang mit assoziierten NH- und freien NH₂-Gruppen, während die Lösungs-IR-Spektren auch auf das Vorliegen freier NH-Gruppen schließen lassen.

     

Catalytic phosphorylation of polyfluoroalkanols. 17. Synthesis and the stereochemistry of tris(α-trifluoromethylbenzyl) phosphates

Catalytic phosphorylation of -trifluoromethylbenzyl alcohols with POCl₃ taken in a ratio of 3 : 1 under particular temperature conditions afforded predominantly symmetrical tris(-trifluoromethylbenzyl) phosphates. The latter were obtained as mixtures of two diastereomers with a statistical ratio of the components.     

Efficient desulfurization of 2-thiopyrimidine nucleosides to the corresponding 4-pyrimidinone analogues using trans-2-(phenylsulfonyl)-3-phenyloxaziridine

A brief treatment of 2-thiopyrimidine nucleosides (s²U^∗) with trans-2-phenylsulfonyl-3-phenyloxaziridine (PSO) results in efficient substrate desulfurization leading to the corresponding 4-pyrimidinone analogues (H²U^∗). The key transformation proceeds through oxidation of the 2-thiocarbonyl group to a sulfur oxyacid derivative and subsequent elimination of sulfur dioxide. 4-Pyrimidinone 1-β-d-riboside (H²U) has been transformed into the respective phosphoramidite, a ready-to-use monomer for the introduction of a modified nucleoside into an oligonucleotide chain. Moreover, the effective desulfurization of the 2-thiouridine nucleotide could be achieved directly at the oligonucleotide level, by treatment of the TdA(s²U)dGdC oligonucleotide with PSO, as verified by MALDI-TOF mass spectrometry.