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排序方式: 共有410条查询结果,搜索用时 15 毫秒
361.
Alexey V. Salin Albert R. Fatkhutdinov Anton V. Il'in Evgeniy I. Sotov Alexandr A. Sobanov Vladimir I. Galkin Brian R. James 《Journal of Physical Organic Chemistry》2013,26(8):675-678
Kinetic data provide evidence that proton transfer to the carbanion centre of a phosphonium zwitterion is the rate‐determining step in quarternization reactions of triphenylphosphine with electron‐deficient alkenes in acetic acid solution. This conclusion is based on the third‐order rate equation, the reactivity of the alkenes, and solvent isotope effects in deuteroacetic acid. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
362.
Alexandr Jegorov Ladislav Cvak Roman Bednář Jan Čejka Michal Hušák Bohumil Kratochvíl Ivana Císařová 《Structural chemistry》2006,17(1):131-137
Crystal forms of N-[3-(dimethylamino)propyl]-N-(ethylcarbamoyl)-6-allyl-ergoline-8β-carboxamide (cabergoline) originating from various solvents have been examined by X-ray diffraction at 298 or 150 K. Crystal structures of cabergoline anhydrate, (form II, P212121) and solvates (all P212121) with tert-butyl methyl ether (form VIII), cyclohexane (form XV), toluene (form IX), p-xylene (form XVI), and 1,2,4-trimethylbenzene (form XVII) are described. Conformation of cabergoline in these forms was compared with crystal structures of forms I and VII of cabergoline (P21) described in the literature. Despite a high degree of molecular conformational freedom, cabergoline possesses similar conformation in forms I, II, VIII, IX, XV, XVI, and XVII. Molecular conformations, crystal packing and the effect of the solvent on the former two properties are examined. 相似文献
363.
Maxim Sergeevitch Egorov Galina Leonidovna Starova Alexandr Grigorievitch Shavva 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):o170-o171
The Birch reduction of 3‐methoxy‐B‐nor‐8‐isoestra‐1,3,5(10)‐trienes followed by acid hydrolysis produces steroid androgen 19,B‐dinor‐8,10‐iso‐analogues. By means of X‐ray analysis and correlation NMR spectroscopy of 16,16‐dimethyl‐D‐homo‐19,B‐dinor‐8‐isotestosterone, C20H30O2, it is demonstrated that the main conformations in the crystal and in solution for two 19,B‐dinor‐8,10‐iso‐analogues are, in general, the same. 相似文献
364.
Jegorov A Paizs B Zabka M Kuzma M Havlícek V Giannakopulos AE Derrick PJ 《European journal of mass spectrometry (Chichester, England)》2003,9(2):105-116
High-performance liquid chromatography and tandem mass spectrometry (HPLC/MS/MS) was used for the detection of cyclic hexadepsipeptides roseotoxins produced by Trichothecium roseum. Roseotoxins were found in both submerged standard cultivation on CzapekDox medium and in vivo cultivation extract obtained from an apple. Roseotoxin chromatographic profiles from these two experiments were compared. Product-ion collision-induced dissociation (CID) spectra obtained on an ion trap (electrospray ionisation, ESI) were used for the identification of natural roseotoxins A, B, C and of minor destruxins A and B. The dissociation behavior of roseotoxins is discussed in terms of a fragmentation scheme proposed for describing the dissociation pathways of cyclic peptides. This scheme involves opening of the cyclopeptide ring via formation of oxazolone derivatives and fragmentation of the resulting linear species, which have a free N-terminus and an oxazolone ring at the C-terminus. Some aspects of this fragmentation scheme are underlined by modeling the dissociation channels of roseotoxin A using quantum chemical calculations. The structures of roseotoxin A and destruxin B were verified by nuclear magnetic resonance (NMR) spectroscopy. Structures of three new minor natural roseotoxins [Val(4)]RosA, [MeLxx(4)]RosA and [MeLxx(4)]RosB were deduced by ion cyclotron resonance Fourier transform mass spectrometry (ICR-FT-MS) and ion trap tandem mass spectrometry by examining the pre-separated roseotoxin fraction. 相似文献
365.
Zdzislaw Narankiewicz Alexandr L. Blumenfeld Veronica L. Bondareva Irina A. Mamedyarova Marina N. Nefedova Viatcheslav I. Sokolov 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(3):233-245
Spin-lattice relaxation time measurements in laboratory and rotating frames as well as proton second moment analysis have been used to investigate molecular motions in -cyclodextrin (CD) and its solid inclusion complexes with the title organometallic compounds. Different dynamical processes have been identified in the host lattice along with high mobility of the ferrocene and ruthenocene guest molecules. The Arrhenius parameters of all motions were obtained. The assumption based on the second moment measurements was made about the axial structure of the ferrocene complex and the equatorial one of the ruthenocene complex at low temperatures. The bridged ferrocenophane molecule was shown to be rigid on the NMR time scale. The ternary inclusion complex of -CD with ruthenocene and iodine was also studied and no evidence of redox reactions was observed. 相似文献
366.
A new modification of the adiabatic compressibility method of investigating solvation in solutions is presented and applied
to the analysis of the following structurally-related characteristics of hydrated complexes of seawater electrolytes (NaCl,
KCl, MgCl2, CaCl2, Na2SO4, MgSO4) at different concentrations (0.1 to 5.0 mol⋅kg−1) and temperatures (278.15 to 308.15 K): solvation numbers (h) and their dependences on concentration, volumes of stoichiometric mixtures of ions without their hydration shells (V
2h
), compressibilities (β
1h
) and molar volumes of water in their solvation shells (V
1h
), their dependences on concentration and temperature, etc. 相似文献
367.
An Efficient and Convenient Synthesis of 2-Thio[1,2,4]triazolo[1,5-c]quinazoline and its Derivatives
Alexandr V. Karpenko Sergey I. Kovalenko Svetlana V. Shishkina Oleg V. Shishkin 《Monatshefte für Chemie / Chemical Monthly》2006,137(12):1543-1549
Summary. 4-Hydrazinoquinazoline with carbon disulfide underwent a recyclization reaction. The title compound 2-thio[1,2,4]triazolo[1,5-c]quinazoline was obtained after treatment of 4-hydrazinoquinazoline with potassium ethylxanthogenate via a facile in situ Dimroth-like rearrangement of the expected [4,3-c] system. Its structure was established by X-ray diffraction study and confirmed by an independent synthesis, starting from
o-aminobenzonitrile. 相似文献
368.
Vladimir N. Afanasiev Alexandr N. Ustinov Irina Yu. Vashurina 《Journal of solution chemistry》2006,35(11):1477-1491
The isentropic compressibilities of aqueous solutions of potassium iodide, from dilute to almost saturated, were determined at 288 to 308 K based on precise measurements of the speed of ultrasound. Using proper correlations, the hydration numbers (h) were calculated as well as the molar volume and compressibility parameters of the hydrated complexes (V
h
, β
h
V
h
) of water in the hydration shell (V
1h
, β1h
V
1h), and of the cavity containing stochiometric mixtures of K+ and I−
ions (V
2h, β2h
V
2h). It is revealed that under the studied conditions, the obtained values of h and β
h
V
h are independent of temperature whereas the molar compressibility of the hydration shell β
h
V
h) is independent of concentration. The electrostatic field of the ions is shown to influence the temperature dependence of the molar volume of water in the hydration shell more substantially than a change of pressure alone influences the temperature dependence of the molar volume of pure water. 相似文献
369.
370.
Alexandr L. Antipov Alexey Yu. Bykovsky Anton A. Egorov 《Journal of Russian Laser Research》2008,29(4):322-335
A multiple-valued-logic protected-data coding method is proposed for distant ordering/disordering of a fuzzy logic model accumulated
in a robotic agent. Fuzzy-rule-set disordering is a means to realize the distributed logic lock, preventing a hacker from
unapproved use of the robotic device itself or its internal data. The multiple-valued-logic protected-data coding is the method
used here to increase greatly the secret-key space. Optical-data line is to be used for distant transfer of secret codes between
the key and lock devices.
Talk presented at the oral issue of J. Russ. Laser Res. dedicated to the memory of Professor Vladimir A. Isakov, Professor
Alexander S. Shumovsky, and Professor Andrei V. Vinogradov held in Moscow February 21–22, 2008. 相似文献