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排序方式: 共有207条查询结果,搜索用时 15 毫秒
1.
Ksenia Pumpor Elisabeth Windeisen Klaus Burger 《Journal of heterocyclic chemistry》2003,40(3):435-442
The synthesis of heterocyclic α‐mercapto acids starting from (RS)‐thiomalic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building blocks for peptide and depsipeptide modification as well as for drug design. 相似文献
2.
N. V. Shibaeva S. V. Borodaev I. A. Yudilevich A. P. Knyazev A. D. Dubonosov A. I. Pyshchev S. M. Luk'yanov 《Chemistry of Heterocyclic Compounds》1991,27(2):219-223
4-Alkyl-3-azapyrylium salts undergo acylation at the alkyl group under acid-catalyzed conditions to give 4-acylmethyl-3-azapyrylium derivatives, which upon heating in proton-donating solvents recyclize to give 4-acylaminopyrylium salts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 265–269, February, 1991. 相似文献
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A. V. Kazakova N. D. Kushch L. I. Buravov E. B. Yagubskii S. V. Simonov L. V. Zorina S. S. Khasanov R. P. Shibaeva E. Canadell J. Yamada M. Umemiya 《Russian Chemical Bulletin》2007,56(1):49-55
New radical cation salts based on 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) with copper(II) metal complex anions, β-(BDA-TTP)4Cu2Cl6 and (BDA-TTP)2CuCl4, were synthesized and structurally characterized. Single crystals were prepared by electrochemical oxidation of BDA-TTP under
galvanostatic conditions. X-ray diffraction study demonstrated that the salts have a layered structure, in which the conducting
BDA-TTP layers alternate with the [Cu2Cl6]2− or [CuCl4]2− anions. Both salts show the semiconductor-type temperature dependence of the conductivity.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–54, January, 2007. 相似文献
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Ksenia Shilyaeva Nils Elander Evgeny Yarevsky 《International journal of quantum chemistry》2007,107(6):1301-1315
Peaks in collision cross sections are often interpreted as resonances. The complex dilation method, as well as other methods relying on analytic continuation of the scattering formalism, can be used to clarify whether these structures are true resonances in the sense that they are poles of the S‐matrix and the associated Green function. The performance of the Mittag–Leffler expansion and T‐matrix Green function expansion methods are formally and computationally compared. The two methods are applied to two model potentials. Eigenenergies, s‐wave residues, and cross sections are computed with both methods. The resonance contributions to the cross sections are further analyzed by removing the residue contributions from the Mittag–Leffler and Green function expansion sums, respectively. It is suggested that the contribution of a resonance to a cross section should be defined through its S‐matrix residue. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
7.
Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that
- Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions.
- Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications.
- Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library.
- Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra.
8.
K. M. Dyumaev E. P. Popova I. F. Mikhailova L. I. Shibaeva L. D. Smirnov 《Chemistry of Heterocyclic Compounds》1974,10(6):699-701
The nitration of 3-hydroxyquinoline with concentrated nitric acid in sulfuric acid at ?30 to +30°C gives 5-nitro-3-hydroxyquinoline (85–92%) and 7-nitro-3-hydroxyquinoline (7–12%). 4-Nitro-3-hydroxyquinoline is formed in 70% yield by nitration in acetic acid. 4,5-Dinitro-3-hydroxyquinoline is formed by further nitration of 4- and 5-nitro-3-hydroxyquinolines. 相似文献
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