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排序方式: 共有106条查询结果,搜索用时 281 毫秒
1.
Alexej Jerschow 《Monatshefte für Chemie / Chemical Monthly》2002,20(2):1481-1496
Most NMR-active nuclei found in the periodic table have a quadrupole moment. In combination with a nonsymmetric electron distribution a strong NMR-active interaction results, which very often overshadows the dipolar and scalar couplings. This article aims at reviewing how these interactions manifest themselves in quadrupolar NMR and how they can be exploited for resonance assignment and structure elucidation, in spite of the presence of a strong quadrupolar interaction. 相似文献
2.
Konstantin Karaghiosoff Thomas M. Klaptke Alexej Michailovski Gerhard Holl 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(9):o580-o581
The title compound (systematic name: 4,10‐dinitro‐2,6,8,12‐tetraoxa‐4,10‐diazatetracyclo[5.5.0.03,11.05,9]dodecane), C6H6N4O8, exhibits the highest density among known N‐nitramines, due to its close‐packed crystal structure. It may be regarded as consisting of a distorted hexagonal close‐packed lattice formed by the isowurtzitane cages, with the nitro groups occupying the free space between the cages. 相似文献
3.
4.
Věra Hamplová Alexej Bubnov Corresponding author Miroslav Kašpar Vladimíra Novotná Yveta Lhotáková Milada Glogarová 《Liquid crystals》2013,40(12):1463-1469
New chiral liquid crystalline materials containing a keto group and two lactate units attached to the mesogenic core have been synthesized and studied. All the new compounds show the paraelectric SmA, ferroelectric SmC* and antiferroelectric SmC*A phases each over rather broad temperature ranges. The properties of the phases were characterized by DSC, electro-optical and dielectric studies. The spontaneous polarization, tilt angle, helical pitch, and switching times were determined for the polar phases. 相似文献
5.
Dr. Youai Qiu Alexej Scheremetjew Dr. Lars H. Finger Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(15):3241-3246
Electrophotochemistry has enabled arene C−H trifluoromethylation with the Langlois reagent CF3SO2Na under mild reaction conditions. The merger of electrosynthesis and photoredox catalysis provided a chemical oxidant-free approach for the generation of the CF3 radical. The electrophotochemistry was carried out in an operationally simple manner, setting the stage for challenging C−H trifluoromethylations of unactivated arenes and heteroarenes. The robust nature of the electrophotochemical manifold was reflected by a wide scope, including electron-rich and electron-deficient benzenes, as well as naturally occurring heteroarenes. Electrophotochemical C−H trifluoromethylation was further achieved in flow with a modular electro-flow-cell equipped with an in-operando monitoring unit for on-line flow-NMR spectroscopy, providing support for the single electron transfer processes. 相似文献
6.
Maximilian Stangier Alexej Scheremetjew Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201654
Electrochemical fluorinations of C(sp3)−H bonds with a nucleophilic fluoride source have been accomplished in a chemo- and site-selective fashion, avoiding the use of electrophilic F+ sources and stoichiometric oxidants. The introduced metal-free strategy exhibits high functional group tolerance, setting the stage for late-stage fluorinations of biorelevant motifs. The synthetic utility of the C(sp3)−H fluorination was reflected by subsequent one-pot arylation of the generated benzylic fluorides. 相似文献
7.
Long Yang Ralf Steinbock Alexej Scheremetjew Rositha Kuniyil Lars H. Finger Antonis M. Messinis Lutz Ackermann 《Angewandte Chemie (International ed. in English)》2020,59(27):11130-11135
A ruthenium‐catalyzed electrochemical dehydrogenative annulation reaction of imidazoles with alkynes has been established, enabling the preparation of various bridgehead N‐fused [5,6]‐bicyclic heteroarenes through regioselective electrochemical C?H/N?H annulation without chemical metal oxidants. Novel azaruthenabicyclo[3.2.0]heptadienes were fully characterized and identified as key intermediates. Mechanistic studies are suggestive of an oxidatively induced reductive elimination pathway within a ruthenium(II/III) regime. 相似文献
8.
Jerschow A 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,176(1):7-14
Spin and spatial tensor manipulations are frequently required to describe the theory of NMR experiments. A Mathematica package is presented here, which provides some of the most common functions for these calculations. Examples are the calculation of matrix representations of operators, commutators, projections, rotations, Redfield matrix elements, matrix decomposition into basis operators, change of basis, coherence filtering, and the manipulation of Hamiltonians. The calculations can be performed for any spin system, containing spins 1/2 and quadrupolar spins alike, subject to computational limitations. The package will be available from upon acceptance of the article. 相似文献
9.
10.
Alexej P. Pynko 《Logica Universalis》2010,4(1):41-66
In this paper, we study multiplicative extensions of propositional many-place sequent calculi for finitely-valued logics arising
from those introduced in Sect. 5 of Pynko (J Multiple-Valued Logic Soft Comput 10:339–362, 2004) through their translation
by means of singularity determinants for logics and restriction of the original many-place sequent language. Our generalized approach, first of all, covers, on
a uniform formal basis, both the one developed in Sect. 5 of Pynko (J Multiple-Valued Logic Soft Comput 10:339–362, 2004)
for singular finitely-valued logics (when singularity determinants consist of a variable alone) and conventional Gentzen-style
(i.e., two-place sequent) calculi suggested in Pynko (Bull Sect Logic 33(1):23–32, 2004) for finitely-valued logics with equality
determinant. In addition, it provides a universal method of constructing Tait-style (i.e., one-place sequent) calculi for
finitely-valued logics with singularity determinant (in particular, for Łukasiewicz finitely-valued logics) that fits the
well-known Tait calculus (Lecture Notes in Mathematics, Springer, Berlin, 1968) for the classical logic. We properly extend
main results of Pynko (J Multiple-Valued Logic Soft Comput 10:339–362, 2004) and explore calculi under consideration within
the framework of Sect. 7 of Pynko (Arch Math Logic 45:267–305, 2006), generalizing the results obtained in Sect. 7.5 of Pynko
(Arch Math Logic 45:267–305 2006) for two-place sequent calculi associated with finitely-valued logics with equality determinant
according to Pynko (Bull Sect Logic 33(1):23–32, 2004). We also exemplify our universal elaboration by applying it to some
denumerable families of well-known finitely-valued logics. 相似文献