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1.
A path-integral molecular dynamics technique for strongly interacting atoms using ab initio potentials derived from density functional theory is implemented. This allows the efficient inclusion of nuclear quantum dispersion in ab initio simulations at finite temperatures. We present an application to the quantum cluster H
5
+
. 相似文献
2.
Meerwein reactions of 1,5-anthraquinone bis(diazonium hydrogen sulfate) with sufficiently activated olefins, such as acrylonitrile, acrylic esters, methacrylonitrile and its esters, styrene and α-methylstyrene yielded derivatives of the new heterocyclic system anthra[9,1-bc:10,5-b'c']-2,3,7,8-tetrahydrodipyran. Isolation of derivatives was realized and yields enhanced by using dimethyl methylphosphonate as reaction medium. Compounds 5–18 were isolated as mixtures of diastereomers, some of which were separated by crystallization. Proof of structure and stereochemistry was obtained for some of the compounds by X-ray crystallographic analysis. The 1H- and 13C-nmr data provided further support. Surprisingly large chemical shift differences between some of the proton signals of isomers were observed although the two asymmetric centers are far apart through bonds and through space. The mechanism of formation is explained on the basis of redox modulation of a charge transfer complex in which the aliphatic radical attacks the oxygen atom of the anthraquinone. It is proposed to classify this new type of reaction as an intramolecular Meerwein reaction. 相似文献
3.
O. Weis 《Zeitschrift für Physik B Condensed Matter》1986,64(4):401-407
An elementary derivation is giveni) for the power transfer in a general system of coupled masses within the framework of classical mechanics andii) for the instantaneous energy-current density
which is defined as an average over each unit celln. As a first application of these general expressions, it is shown for lattice waves in a general periodic harmonic lattice that the time average of the mentioned energy-current density is equal to the mean energy density times the group velocity. 相似文献
4.
Treatment of the phenyl-substituted silane 4 with lithium metal afforded the functionalized lithiosilane rac-2 by selective cleavage of one Si-C bond between silicon and a phenyl group. The resulting lithiosilane rac-2 crystallizes as the dimer (2.THF)2, which represents the first example of a dimeric organyl-substituted lithiosilane in the presence of THF. 相似文献
5.
DeClue MS Baldridge KK Künzler DE Kast P Hilvert D 《Journal of the American Chemical Society》2005,127(43):15002-15003
Isochorismate pyruvate lyase (IPL) catalyzes the cleavage of isochorismate to give salicylate and pyruvate, a key step in bacterial siderophore biosynthesis. We investigated the enzyme from Pseudomonas aeruginosa using isochorismate selectively deuterated at C2 as a substrate. Monitoring the reaction by 2H NMR spectroscopy revealed that the label is quantitatively transferred from C2 to C9, producing stoichiometric amounts of [3-2H]pyruvate as product. Moreover, the deuterium kinetic isotope effect of 2.34 +/- 0.08 on kcat indicates that C-H cleavage is significantly rate limiting. Consistent with these data, hybrid density functional theory (HDFT) calculations at the Becke3LYP/DZ+(2d,p) level of theory predict a concerted but highly asynchronous pericyclic transition structure, in which carbon-oxygen bond cleavage is more advanced than hydrogen atom transfer from C2 to C9; the calculated 2H isotope effect of 2.22 at C2 is in excellent accord with the experimental value. Together, these findings indicate that IPL should be added to the small set of proteins that are known to catalyze pericyclic reactions. They also raise the possibility that enzymes, such as chorismate pyruvate lyase, salicylate synthase, 4-amino-4-deoxychorismate lyase, and anthranilate synthase, which accelerate formally similar reaction steps, may also exploit pericyclic mechanisms. 相似文献
6.
Robert Weis Marcel Kaiser Reto Brun Robert Saf Werner Seebacher 《Monatshefte für Chemie / Chemical Monthly》2006,137(10):1365-1374
Summary. 4-Aminobicyclo[2.2.2]octan-2-ones and -ols showed activity against the causative organisms of East African sleeping sickness
and Malaria tropica. Several imino derivatives of the ketones were more active. Now hydrazono analogues and 3-hydroximino
derivatives of the ketones and alcohols were synthesized. The structures of the obtained isomers were elucidated by NMR spectroscopy.
A single phenylhydrazone exhibited quite good antitrypanosomal activity in the range of already known imino analogues. 相似文献
7.
C D Weis 《Helvetica chimica acta》1968,51(7):1572-1581
A simple synthesis of tetrachlorophenanthrene starting from DDT has been realized. 1,1,1,2-tetrachloro-2,2-bis-(4-chlorophenyl)-ethane (I) and its rearranged product 1,1,2,2-tetrachloro-1,2-bis-(4-chlorophenyl)-ethane (V) and other analogs substituted by halogen in the para-position undergo a cycliarylation yielding 3,6,9,10-tetrahalogenophenanthrenes. Partial dechlorination of this tetrachlorophenanthrene yields 3,6-dichlorophenanthrene. Oxidation gives 3,6-dichloro-9,10-phenanthrenequinone, and chlorosulfonation leads to 3,6,9,10-tetrachloro-2,7-bis-(chlorosulfonyl)-phenanthrene. The mechanism of this cyclization reaction in presence of LEWIS acids is discussed and compared with the cyclization of DDT derivatives to yield fluorenones. 相似文献
8.
The oxidation of 2,6-dichloro-3-benzylpyridines and bis(2,6-dichloro-3-pyridyl)methanes, respectively, was accomplished using chromic trioxide in a highly acidic medium. The synthesis of several phenyl-3-(2,6-dichloropyridyl)ketones and of bis(2,6-dichloro-3-pyridyl)ketone are reported. 相似文献
9.
10.
The method of linear frequency modulation of a continuous wave (FM-CW) in sound-echo experiments is demonstrated at a sound frequency of 70 GHz. A reflex klystron with a cw power of only 300 mW and a planar Hertzian resonator are used for the piezoelectric sound excitation. Applying homodyne detection, spectral echo signals are detected in the kHz range by means of a spectral analyzer. The detected echoes show an excellent signal-to-noise ratio. Details of the experimental setup and the underlying theory of the FM-CW sound experiments are presented. We observe experimentally two excited needle-like sound beams in 65 m distance, each about 30 m in diameter. 相似文献