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101.
Oliver Tietze Birgit Schiefner Burkhard Ziemer A. Zschunke 《Analytical and bioanalytical chemistry》1997,357(5):477-481
The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E,
E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the 1H and 13C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds
N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic
acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding
spectra. To assign the 13C NMR signals we used two-dimensional 13C-1H one-bond (HMQC) and 13C-1H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to
a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition
of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two
CH-O hydrogen bonds.
Received: 31 May 1996 / Revised: 26 June 1996 / Accepted: 1 July 1996 相似文献
102.
Galvanic cells of the type (C+Cl2)(NaCl(s))(MCl2(s))(C+Cl2) give e. m. f. 's above 280°, which are due to the formation of ternary chlorides NanMCln+2. By the change in slope of continuously measured e.m.f.vs. T curves, the temperatures of solid-state reactions in systems NaCl-MCl2 can be found. This method was applied for the systems of NaCl with NiCl2, CoCl2 and CdCl2, and for KCl-NiCl2. With the exception of the system NaCl-NiCl2, all phase diagrams must be corrected.
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 相似文献
Zusammenfassung Mit galvanischen Zellen des Typs (C+Cl2)/NaCl(s)/MCl2(s)/(C+Cl2) lassen sich oberhalb 280° EMK's messen, die auf der Bildung ternärer Chloride NanMCln+2 beruhen. Durch die Änderung der Steigung kontinuierlich gemessener EMK- gegen T-Kurven lassen sich in Systemen NaCl/MCl2 die Temperaturen von Festkörperreaktionen nachweisen. Diese Methode wurde auf die Systeme des NaCl mit NiCl2, CoCl2 und CdCl2 sowie auf das System KCl-NiCl2 angewendet. Alle Phasendiagramme, mit Ausnahme des Systems NaCl-NiCl2, mußten auf Grund dieser Messungen revidiert werden.
(C+Cl2)/NaCl./MCl2./(C +Cl2) 280 °C . . , NanMCln+2. . . , NaCl-MCl2. NaCl NiCl2, CoCl2, CdCl2 KCl-NiCl2. NaCl-NiCl2,ce .
This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. 相似文献
103.
Vyboishchikov SF Bühl M Thiel W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(17):3962-3975
Gradient-corrected (BP86) density functional calculations were used to study alternative mechanisms of the metathesis reactions between ethene and model catalysts [(PH(3))(L)Cl(2)Ru[double bond]CH(2)] with L=PH3 (I) and L=C(3)N(2)H(4)=imidazol-2-ylidene (II). On the associative pathway, the initial addition of ethene is calculated to be rate-determining for both catalysts (Delta G(22-25)*[double bond] kcal mol(-1)). The dissociative pathway starts with the dissociation of phosphane, which is rather facile (Delta G(298)* is approximately equal to 5-10 kcal mol(-1)). The resulting active species (L)Cl(2)Ru[double bond]CH(2) can coordinate ethene cis or trans to L. The cis addition is unfavorable and mechanistically irrelevant (Delta G(298)* is approximately equal to 21-25 kcal mol(-1)). The trans coordination is barrierless, and the rate-determining step in the subsequent catalytic cycle is either ring closure of the complex to yield the ruthenacyclobutane (catalyst I, Delta G(298)*=12 kcal mol(-1)), or the reverse reaction (catalyst II, ring opening, Delta G(298)*=10 kcal mol(-1)), that is, II is slightly more active than I. For both catalysts, the dissociative mechanism with trans olefin coordination is favored. The relative energies of the species on this pathway can be tuned by ligand variation, as seen in (PMe(3))(2)Cl(2)Ru[double bond]CH(2) (III), in which phosphane dissociation is impeded and olefin insertion is facilitated relative to I. The differences in calculated relative energies for the model catalysts I-III can be rationalized in terms of electronic effects. Comparisons with experiment indicate that steric effects must also be considered for real catalysts containing bulky substituents. 相似文献
104.
The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate. 相似文献
105.
de Visser SP Shaik S Sharma PK Kumar D Thiel W 《Journal of the American Chemical Society》2003,125(51):15779-15788
The active site of HRP Compound I (Cpd I) is modeled using hybrid density functional theory (UB3LYP). The effects of neighboring amino acids and of environmental polarity are included. The low-lying states have porphyrin radical cationic species (Por(*)(+)). However, since the Por(*)(+) species is a very good electron acceptor, other species, which can be either the ligand or side chain amino acid residues, may participate in electron donation to the Por(*)(+) moiety, thereby making Cpd I behave like a chemical chameleon. Thus, this behavior that was noted before for Cpd I of P450 is apparently much more wide ranging than initially appreciated. Since chemical chameleonic behavior property was found to be expressed not only in the properties of Cpd I itself, but also in its reactivity, the roots of this phenomenon are generalized. A comparative discussion of Cpd I species follows for the enzymes HRP, CcP, APX, CAT (catalase), and P450. 相似文献
106.
Napper AM Head NJ Oliver AM Shephard MJ Paddon-Row MN Read I Waldeck DH 《Journal of the American Chemical Society》2002,124(34):10171-10181
A systematic determination of electronic coupling matrix elements in U-shaped molecules is demonstrated. The unique architecture of these systems allows for the determination of the electronic coupling through a pendant molecular moiety that resides between the donor and acceptor groups; this moiety quantifies the efficiency of electron tunneling through nonbonded contacts. Experimental electron-transfer rate constants and reaction free energies are used to calibrate a molecular-based model that describes the solvation energy. This approach makes it possible to experimentally determine electronic couplings and compare them with computational values. 相似文献
107.
Ab initio coupled cluster calculations with single and double substitutions and a perturbative treatment of connected triple excitations [CCSD(T)] with the augmented correlation-consistent polarized valence triple-zeta aug-cc-pVTZ basis at 51 816 geometries provide a six-dimensional potential-energy surface for the electronic ground state of NH3. At 3814 selected geometries, CBS+ energies are obtained by extrapolating the CCSD(T) results for the aug-cc-pVXZ(X=T,Q,5) basis sets to the complete basis set (CBS) limit and adding corrections for core-valence correlation and relativistic effects. CBS** ab initio energies are generated at 51,816 geometries by an empirical extrapolation of the CCSD(T)/aug-cc-pVTZ results to the CBS+ limit. They cover the energy region up to 20,000 cm-1 above equilibrium. Parametrized analytical functions are fitted through the ab initio points. For these analytical surfaces, vibrational term values and transition moments are calculated by means of a variational program employing a kinetic-energy operator expressed in the Eckart-Sayvetz frame. Comparisons against experiment are used to assess the quality of the generated potential-energy surfaces. A "spectroscopic" potential-energy surface of NH3 is determined by a slight empirical adjustment of the ab initio potential to the experimental vibrational term values. Variational calculations on this refined surface yield rms deviations from experiment of 0.8 cm-1 for 24 inversion splittings and 0.4 (3.0) cm-1 for 34 (51) vibrational term values up to 6100 (10,300) cm-1. 相似文献
108.
Polysulfonylamines. CLXIII. Crystal Structures of Metal Di(methanesulfonyl)amides. 12. The Orthorhombic Double Salt Na2Cs2[(CH3SO2)2N]4·3H2O: A Three‐Dimensional Coordination Polymer Built up from Cesium‐Anion‐Water Layers and Intercalated Sodium Ions The packing arrangement of the three‐dimensional coordination polymer Na2Cs2[(MeSO2)2N]4·3H2O (orthorhombic, space group Pna21, Z′ = 1) is in some respects similar to that of the previously reported sodium‐potassium double salt Na2K2[(MeSO2)2N]4·4H2O (tetragonal, P43212, Z′ = 1/2). In the present structure, four multidentately coordinating independent anions, three independent aquo ligands and two types of cesium cation form monolayer substructures that are associated in pairs to form double layers via a Cs(1)—H2O—Cs(2) motif, thus conferring upon each Cs+ an irregular O8N2 environment drawn from two N, O‐chelating anions, two O, O‐chelating anions and two water molecules. Half of the sodium ions occupy pseudo‐inversion centres situated between the double layers and have an octahedral O6 coordination built up from four anions and two water molecules, whereas the remaining Na+ are intercalated within the double layers in a square‐pyramidal and pseudo‐C2 symmetric O5 environment provided by four anions and the water molecule of the Cs—H2O—Cs motif. The net effect is that each of the four independent anions forms bonds to two Cs+ and two Na+, two independent water molecules are involved in Cs—H2O—Na motifs, and the third water molecule acts as a μ3‐bridging ligand for two Cs+ and one Na+. The crystal cohesion is reinforced by a three‐dimensional network of conventional O—H···O=S and weak C—H···O=S/N hydrogen bonds. 相似文献
109.
Samskog J Bergström SK Jönsson M Klett O Wetterhall M Markides KE 《Electrophoresis》2003,24(11):1723-1729
A method for coupling an electrophoretic driven separation to a liquid flow, using conventional fused-silica capillaries and a soft polymeric interface is presented. A novel design of the electrode providing high voltage to the electrophoretic separation was also developed. The electrode consisted of a conductive polyimide/graphite imbedded coating immobilized onto the capillary electrophoresis (CE) column inlet. This integrated electrode gave the same separation performance as a commonly used platinum electrode. The on-column electrode also showed good electrochemical stability in chronoamperometric experiments. In addition, with this electrode design, the electrode position relative to the inlet end of the CE column will always be constant and well defined. The on-line flow injection analysis (FIA)-CE system was used with electrospray ionization (ESI)-time of flight (TOF)-mass spectrometry detection. The preparation of the PDMS (poly(dimethylsiloxane)) interface for FIA-CE is described in detail and used for initial tests of the on-column polymer-imbedded graphite inlet electrode. In this interface, a pressure-driven liquid flow, a make up CE electrolyte and a CE column inlet meet in a two-level cross (95 microm ID) in the PDMS structure, enabling independent flow characterization. 相似文献
110.
UT-7 and UT-8 (University of Toronto, structure numbers 7 and 8) are two novel aluminophosphate materials prepared under non-aqueous conditions. Their structures, extended in one and two dimensions, respectively, have been solved by single-crystal X-ray diffraction and characterized by a variety of methods including powder X-ray diffraction (PXRD), insitu high-temperature PXRD, thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and scanning electron microscopy (SEM). UT-7 ([Al(3)P(5)O(20)H](5)(-)[C(7)H(13)NH(3)(+)](5), triclinic space group P&onemacr;, Z = 2, a = 10.118(3) ?, b = 15.691(4) ?, c = 18.117(3) ?, alpha = 72.91(2) degrees, beta = 85.18(2) degrees, gamma = 79.49(2) degrees ) is built of polymeric one-dimensional chain units, hydrogen-bonded into anionic layers that are charge-compensated by interlamellar cycloheptylammonium cations. UT-7 is isostructural to our previously discovered UT-3 chain structure, isolated in the analogous cyclopentylamine system. UT-8 ([Al(3)P(4)O(16)](3-)[C(4)H(7)NH(3)(+)](2)[C(5)H(10)NH(2)(+)], monoclinic space group P2(1), Z = 2, a = 8.993(4) ?, b = 14.884(8) ?, c = 9.799(9) ?, beta = 103.52(3) degrees ) is a two-dimensional net isostructural to several previously reported [Al(3)P(4)O(16)](3)(-) layers. The interlayer region of UT-8 is occupied by two different cyclic organic amine species, namely piperidinium and cyclobutylammonium. To our knowledge, this is the first report of the crystal structure of an aluminophosphate material containing cyclobutylammonium or a mixture of cyclic amines. Interestingly, UT-7 is observed to thermally transform in the solid state to an as yet unknown layered material that can be independently synthesized in a similar synthetic system. In the same way as UT-3 transforms to the UT-4 layered phase, we believe UT-7 transforms to a layered material by means of a chain to layer transformation. 相似文献