排序方式: 共有45条查询结果,搜索用时 15 毫秒
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(39):11931-11935
Atomic‐scale mechanochemistry is realized from force exerted by a C60‐functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage‐metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density‐functional calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process cannot be achieved by electrical means. 相似文献
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Daniel C. Lee Victoria K. Kensy Christopher R. Maroon Brian K. Long Andrew J. Boydston 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(17):5695-5698
Herein we report the discovery of the intrinsic mechanochemical reactivity of vinyl‐addition polynorbornene (VA‐PNB), which has strained bicyclic ring repeat units along the polymer backbone. VA‐PNBs with three different side chains were found to undergo ring‐opening olefination upon sonication in dilute solutions. The sonicated polymers exhibited spectroscopic signatures consistent with conversion of the bicyclic norbornane repeat units into the ring‐open isomer typical of polynorbornene made by ring‐opening metathesis polymerization (ROMP‐PNB). Thermal analysis and evaluation of chain‐scission kinetics suggest that sonication of VA‐PNB results in chain segments containing a statistical mixture of vinyl‐added and ROMP‐type repeat units. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(24):6907-6911
17O NMR spectroscopy has been the subject of vivid interest in recent years, because there is increasing evidence that it can provide unique insight into the structure and reactivity of many molecules and materials. However, due to the very poor natural abundance of oxygen‐17, 17O labeling is generally a prerequisite. This is a real obstacle for most research groups, because of the high costs and/or strong experimental constraints of the most frequently used 17O‐labeling schemes. Here, we show for the first time that mechanosynthesis offers unique opportunities for enriching in 17O a variety of organic and inorganic precursors of synthetic interest. The protocols are fast, user‐friendly, and low‐cost, which makes them highly attractive for a broad research community, and their suitability for 17O solid‐state NMR applications is demonstrated. 相似文献
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Gary N. Hermann Peter Becker Carsten Bolm 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(25):7522-7525
In a proof‐of‐principle study, a planetary ball mill was applied to rhodium(III)‐catalyzed C H bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)2, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck‐type cross‐coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution‐based standard protocol. 相似文献
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Although many methods can be employed to transfer energy to a chemical reaction, mechanical energy has not been widely used: It is difficult to apply mechanical forces high enough to lead to breaking bonds to small molecules. Work is the product of force and displacement but when the distances are small, very high forces are needed to obtain sufficient energy to break a bond. The situation is different in polymers, where the path length can be high. Here, bond cleavage, cycloreversions and isomerisations can be observed when mechanical energy is supplied, both in solution and solid systems. Mechanical energy can lead to different mechanistic pathways than those observed under thermal conditions or irradiation. Practical applications of the mechanochemistry of polymers are only just emerging and range from a better understanding of polymer decomposition under force to the development of strain sensors using mechanochromic polymers. 相似文献
26.
Wei Xu Hao Chen Kecheng Jie Zhenzhen Yang Tingting Li Sheng Dai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(15):5072-5076
High‐entropy materials refer to a kind of materials in which five or more metal species were incorporated deliberately into a single lattice with random occupancy. Up to now, such a concept has been only restricted to hard materials, such as high‐entropy alloys and ceramics. Herein we report the synthesis of hybrid high‐entropy materials, polymetallic zeolitic imidazolate framework (also named as high‐entropy zeolitic imidazolate framework, HE‐ZIF), via entropy‐driven room‐temperature mechanochemistry. HE‐ZIF contains five metals including ZnII, CoII, CdII, NiII, and CuII which are dispersed in the ZIF structure randomly. Moreover, HE‐ZIF shows enhanced catalytic conversion of CO2 into carbonate compared with ZIF‐8 presumably a result of the synergistic effect of the five metal ions as Lewis acid in epoxide activation. 相似文献
27.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(14):3900-3904
The quantum yield of a photochemical reaction is one of the most fundamental quantities in photochemistry, as it measures the efficiency of the transduction of light energy into chemical energy. Nature has evolved photoreceptors in which the reactivity of a chromophore is enhanced by its molecular environment to achieve high quantum yields. The retinal chromophore sterically constrained inside rhodopsin proteins represents an outstanding example of such a control. In a more general framework, mechanical forces acting on a molecular system can strongly modify its reactivity. Herein, we show that the exertion of tensile forces on a simplified retinal chromophore model provokes a substantial and regular increase in the trans ‐to‐cis photoisomerization quantum yield in a counterintuitive way, as these extension forces facilitate the formation of the more compressed cis photoisomer. A rationale for the mechanochemical effect on this photoisomerization mechanism is also proposed. 相似文献
28.
Dr. Qun Cao Dr. Deborah E. Crawford Chengcheng Shi Prof. Stuart L. James 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(11):4508-4513
A continuous, scalable, and solvent-free method for the synthesis of various naphthalic imides and perylene diimides (PDIs) using twin-screw extrusion (TSE) is reported. Using TSE, naphthalic imides were obtained quantitatively without the need for excess amine reactant or product purification. With good functional-group tolerance, alkyl and benzyl amine derived PDIs (incl. commercial dyes) were obtained in 50–99 % yield. Use of K2CO3, enabled synthesis of more difficult aniline-derived PDIs. Furthermore, an automated continuous TSE process for Pigments Black 31 and 32 is demonstrated, with a throughput rate of about 1500 g day−1, corresponding to a space time yield of about 30×103 kg m−3 day−1, which is 1–2 orders of magnitude greater than for solvent-based batch methods. These methods provide substantial waste reductions and improved efficiency compared to conventional solvent-based methods. 相似文献
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