Substituent effects in the migration step of the Baeyer-Villiger rearrangement. A theoretical study

Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger (BV) rearrangements of some acetophenones, p-RC6H4COCH3 (R = CN, Cl, H, CH3, CH3O) with m-chloroperbenzoic acid. The energy barriers, charge distributions, and frontier molecular orbitals determined for the aryl migration step explain the effects of substituents on the reactivity of these ketones. A plot of the log of relative oxidation rates of the ketones versus their corresponding calculated energy barriers of the migration stage showed a downward deviation for the p-OCH3 derivative. This result is consistent with a change in the rate-determining step, from the aryl migration to the carbonyl addition, in the case of p-methoxyacetophenone, according to the suggestion that the rate-determining step of the BV oxidation can change with variations in the substituent group.     

Providing Support in Favor of the Existence of a PdII/PdIV Catalytic Cycle in a Heck‐Type Reaction

The complex [Pd(O,N,C‐L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6‐diacetylpyridine, reacts with 2‐iodobenzoic acid at room temperature to afford the very stable pair of Pd^IV complexes (OC‐6‐54)‐ and (OC‐6‐26)‐[Pd(O,N,C‐L)(O,C‐C₆H₄CO₂‐2)I] (1.5:1 molar ratio, at ?55 °C). These complexes and the Pd^II species [Pd(O,N,C‐L)(OX)] and [Pd(O,N,C‐L′)(NCMe)]ClO₄, (X=MeC(O) or ClO₃, L′=another monoanionic pincer ligand derived from 2,6‐diacetylpyridine), are precatalysts for the arylation of CH₂?CHR (R?CO₂Me, CO₂Et, Ph) using IC₆H₄CO₂H‐2 and AgClO₄. These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd^IV complexes was detected by ESI(+)‐MS during the catalytic process. All the data obtained strongly support a Pd^II/Pd^IV catalytic cycle.     

New synthetic method for cycloalkanedione

Ｔｈｅｓｙｎｔｈｅｔｉｃｍｅｔｈｏｄｓｉｎｌｉｔｅｒａｔｕｒｅｆｏｒｐｒｅｐａｒｉｎｇｃｙｃｌｏａｌｋａｎｅｄｉｏｎｅｃｏｍｐｏｕｎｄｓｕｓｅｄａｓｖａｌｕａｂｌｅｐｅｒｆｕｍｅｕｓｕａｌｌｙａｒｅｓｐｅｃｉａｌ,ｔｈｅｓｙｎｔｈｅｓｅｓｏｆｓｏｍｅｃｙｃｌｏａｌｋａｎｅｄｉｏｎｅｃｏｍｐｏｕｎｄｓａｒｅｅｘｔｒｅｍｅｌｙｄｉｆｆｉｃｕｌｔ.1,6ＣｙｃｌｏｄｏｄｅｃａｎｅｄｉｏｎｅｗａｓｐｒｅｐａｒｅｄｐｒｅｖｉｏｕｓｌｙｂｙＦｏｎｋｅｎｅｔａｌ.[1]ｖｉａｍｉｃｒｏｂｉｏｌｏｇｉｃａｌｈｙｄｒｏｘ…     

基于双间苯-32-冠-10穴醚超分子组装体的设计与构筑

由于具有三维空腔结构及良好的应用前景, 穴醚逐渐成为超分子研究领域的热点之一. 近年来, 我们课题组设计合成了一系列基于双间苯-32-冠-10穴醚主体分子, 并利用这些穴醚分子构筑了不同的超分子组装体. 首先, 将双硫代四硫富瓦烯(STTFS)引入到穴醚的第三个臂上, 成功构筑了具有氧化还原响应性的穴醚主体分子. 该穴醚与客体间的解离-穿环过程可以利用STTFS的氧化态来进行控制; 其次, 设计合成了两种含有P=O官能团桥连的穴醚, 在固态结构中得到了近似线型和Z字型的不同超分子聚[2]准轮烷; 最后, 合成了具有两种不同性质空腔的柱[5]芳烃稠合穴醚主体分子, 该穴醚通过正交作用同时络合两个不同的客体分子. 基于两种不同主客体作用力, 我们构筑了一种新型的超分子聚合物. 以上研究为分子器件和超分子材料的进一步研究奠定了良好的基础.     

Cyclic group and knapsack facets

 Any integer program may be relaxed to a group problem. We define the master cyclic group problem and several master knapsack problems, show the relationship between the problems, and give several classes of facet-defining inequalities for each problem, as well as a set of mappings that take facets from one type of master polyhedra to another. Received: May 24, 2001 / Accepted: August 2002 Published online: March 21, 2003 Mathematics Subject Classification (1991): 20E28, 20G40, 20C20     

Low-frequency ultrasound induces oxygen vacancies formation and visible light absorption in TiO2 P-25 nanoparticles

Low-frequency ultrasound (LFUS) irradiation induces morphological, optical and surface changes in the commercial nano-TiO₂-based photocatalyst, Evonik-Degussa P-25. Low-temperature electron spin resonance (ESR) measurements performed on this material provided the first experimental evidence for the formation of oxygen vacancies (V_o), which were also found responsible for the visible-light absorption. The V_o surface defects might result from high-speed inter-particle collisions and shock waves generated by LFUS sonication impacting the TiO₂ particles. This is in contrast to a number of well-established technologies, where the formation of oxygen vacancies on the TiO₂ surface often requires harsh technological conditions and complicated procedures, such as annealing at high temperatures, radio-frequency-induced plasma or ion sputtering.Thus, this study reports for the first time the preparation of visible-light responsive TiO₂-based photocatalysts by using a simple LFUS-based approach to induce oxygen vacancies at the nano-TiO₂ surface. These findings might open new avenues for synthesis of novel nano-TiO₂-based photocatalysts capable of destroying water or airborne pollutants and microorganisms under visible light illumination.     

Cold Atmospheric Pressure Plasma Can Induce Adaptive Response in Pea Seeds

Plasma Chemistry and Plasma Processing - This study investigated the effect of cold atmospheric pressure air plasma pre-treatment on pea (Pisum sativum L.) seeds. The aim of our study was to verify...     

On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

In this work, the use of the area-averaged void fraction and bubble chord length entropies is introduced as flow regime indicators in two-phase flow systems. The entropy provides quantitative information about the disorder in the area-averaged void fraction or bubble chord length distributions. The CPDF (cumulative probability distribution function) of void fractions and bubble chord lengths obtained by means of impedance meters and conductivity probes are used to calculate both entropies. Entropy values for 242 flow conditions in upward two-phase flows in 25.4 and 50.8-mm pipes have been calculated. The measured conditions cover ranges from 0.13 to 5 m/s in the superficial liquid velocity j _f and ranges from 0.01 to 25 m/s in the superficial gas velocity j _g. The physical meaning of both entropies has been interpreted using the visual flow regime map information. The area-averaged void fraction and bubble chord length entropies capability as flow regime indicators have been checked with other statistical parameters and also with different input signals durations. The area-averaged void fraction and the bubble chord length entropies provide better or at least similar results than those obtained with other indicators that include more than one parameter. The entropy is capable to reduce the relevant information of the flow regimes in only one significant and useful parameter. In addition, the entropy computation time is shorter than the majority of the other indicators. The use of one parameter as input also represents faster predictions.