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排序方式: 共有338条查询结果,搜索用时 15 毫秒
41.
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A. Kandasamy R. Mohan M. Lydia Caroline S. Vasudevan 《Crystal Research and Technology》2008,43(2):186-192
Nucleation parameters such as solubility, induction period, interfacial energy and metastable zone width have been investigated for the aqueous solution growth of a semi‐organic nonlinear optical (NLO) material of L‐Proline cadmium chloride monohydrate (L‐PCCM) single crystal. Metastable zone width and induction period values were determined experimentally in order to optimize the growth parameters. The grown crystals are transparent (dimensions: 16 x 8 x 5 mm3) and characterized by powder X‐Ray Diffraction and dielectric studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
43.
Dr. Lydia M. Peschel Carina Vidovič Dr. Ferdinand Belaj Dr. Dmytro Neshchadin Prof. Nadia C. Mösch-Zanetti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3893-3902
The synthesis and structural determination of four tungsten alkyne complexes coordinated by the bio-inspired S,N-donor ligand 2-(4′,4′-dimethyloxazoline-2′-yl)thiophenolate (S-Phoz) is presented. A previously established protocol that involved the reaction of the respective alkyne with the bis-carbonyl precursor [W(CO)2(S-Phoz)2] was used for the complexes [W(CO)(C2R2)(S-Phoz)2] (R=H, 1 a ; Me, 1 b ; Ph, 1 c ). Oxidation with pyridine-N-oxide gave the corresponding W-oxo species [WO(C2R2)(S-Phoz)2] (R=H, 2 a ; Me, 2 b ; Ph, 2 c ). All W-oxo-alkyne complexes ( 2 a , b , c ) were found to be capable of alkyne release upon light irradiation to afford five-coordinate [WO(S-Phoz)2] ( 3 ). The photoinduced release of the alkyne ligand was studied in detail by in situ 1H NMR measurements, which revealed correlation of the photodissociation rate constant ( 2 b>2 a>2 c ) with the elongation of the alkyne C≡C bond in the molecular structures. Oxidation of [WO(S-Phoz)2] ( 3 ) with pyridine-N-oxide yielded [WO2(S-Phoz)2] ( 4 ), which shows highly fluxional behavior in solution. Variable-temperature 1H NMR spectroscopy revealed three isomeric forms with respect to the ligand arrangement versus each other. Furthermore, compound 4 rearranges to tetranuclear oxo compound [W4O4(μ-O)6(S-Phoz)4] ( 5 ) and dinuclear [{WO(μ-O)(S-Phoz)}2] ( 6 ) over time. The latter two were identified by single-crystal X-ray diffraction analyses. 相似文献
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Xuan B. Nguyen Yuji Nakano Nisharnthi M. Duggan Lydia Scott Martin Breugst David W. Lupton 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11607-11614
Direct polarity inversion of conjugate acceptors provides a valuable entry to homoenolates. N‐heterocyclic carbene (NHC) catalyzed reactions, in which β‐unsubstituted conjugate acceptors undergo homoenolate formation and C?C bond formation twice, have been developed. Specifically, the all‐carbon (5+1) annulations give a range of mono‐ and bicyclic cyclohexanones (31 examples). In the first family of annulations, β‐unsubstituted acrylates tethered to a divinyl ketone undergo cycloisomerization, providing hexahydroindenes and tetralins. In the second, partially untethered substrates undergo an intermolecular (5+1) annulation involving dimerization followed by cycloisomerization. While enantioselectivity was not possible with the former, the latter proved viable, allowing cyclohexanones to be produced with high levels of enantiopurity (most >95:5 e.r.) and exclusive diastereoselectivity (>20:1 d.r.). Derivatizations and mechanistic studies are also reported. 相似文献
47.
Mechanistic Studies on the Organocatalytic α‐Chlorination of Aldehydes: The Role and Nature of Off‐Cycle Intermediates
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M. Sc. Sebastian Ponath M. Sc. Martina Menger M. Sc. Lydia Grothues Manuela Weber Prof. Dr. Dieter Lentz Prof. Dr. Carsten Strohmann Prof. Dr. Mathias Christmann 《Angewandte Chemie (International ed. in English)》2018,57(36):11683-11687
Herein we report the isolation and characterization of aminal intermediates in the organocatalytic α‐chlorination of aldehydes. These species are stable covalent ternary adducts of the substrate, the catalyst and the chlorinating reagent. NMR‐assisted kinetic studies and isotopic labeling experiments with the isolated intermediate did not support its involvement in downstream stereoselective processes as proposed by Blackmond. By tuning the reactivity of the chlorinating reagent, we were able to suppress the accumulation of rate‐limiting off‐cycle intermediates. As a result, an efficient and highly enantioselective catalytic system with a broad functional group tolerance was developed. 相似文献
48.
alpha-Pyrene functionalised poly(methyl methacrylate) (PMMA) chains were synthesised by RAFT polymerisation and found to be highly efficient to solubilise and disentangle multi walled carbon nanotubes that can now self-organise as liquid crystalline phases in PMMA and PEG 400 matrices. 相似文献
49.
Hövelmann CH Streuff J Brelot L Muñiz K 《Chemical communications (Cambridge, England)》2008,(20):2334-2336
Palladium catalysed intramolecular guanidine transfer to alkenes can be accomplished with copper chloride as the oxidant to give bicyclic guanidines with complete selectivity and in high yields. 相似文献
50.
Lydia Außenhofer 《Mathematische Zeitschrift》2007,257(2):231-237
We construct a quotient group of an uncountable product of integers which is not Pontryagin reflexive. 相似文献