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91.
Geometry optimizations at the UHF/6-31G* and UMP2/6-31G* levels of theory were performed to find the transition state in the interconversion between norbornadiene (N) and quadricyclane (Q) radical cations. Two transition structures, TS+·1 and TS+·2, were obtained which have C1 and C2 symmetry, respectively. Vibrational analysis at the UHF and UMP2 levels of theory and IRC calculation showed that TS+·1 is the true transition state connecting N+· and Q+·, while TS+·2 is a second order saddle point. 相似文献
92.
Jan S. Jaworski 《Monatshefte für Chemie / Chemical Monthly》1984,115(4):415-418
A two parameter approach to solvent variations in the electroreduction rate constants of cobalt complexes and europium cations is presented and discussed in terms of solvent—solute and solvent—solvent interactions.
Ein Zwei-Parameter Donor-Acceptor-Ansatz für Lösungsmitteleffekte bei der Elektrodenkinetik von Kationen (Kurze Mitteilung)
Zusammenfassung Es wird eine Zwei-Parameter-Annäherung der Lösungsmitteleinflüsse auf die Geschwindigkeitskonstanten der Elektroreduktion von Kobalt-Komplexen und Europium-Kationen präsentiert und auf der Basis von Lösungsmittel—gelöster Stoff- und Lösungsmittel—Lösungsmittel-Wechselwirkung diskutiert.相似文献
93.
模式识别—人工神经网络在化学中的若干新应用 总被引:2,自引:0,他引:2
本文通过我们应用模式识别-人工神经网络方法预报新化合物、熔盐相图以及复杂化学反应体系的研究,展示应用模式识别-人工神经网络方法与物理化学理论相结合,研究化学现象的可能性和应用价值。 相似文献
94.
The reaction paths for the transformations of substituted acetylenes (X—CC—Y; X, Y = H, Me, Ph, CN) in reaction with phenylsulfenium cation were studied by quantum-chemical methods. It was shown that the reactions take place with the formation of acyclic and cyclic cationic intermediates. The factor that determines the structure and characteristics of these cations is the induction and polarizing action of the substituents in the acetylenes and to a lesser degree their electron-donor characteristics. The resonance effect of the phenyl substituent has a predominantly levelling action on the distribution of charges. 相似文献
95.
Summary The ion exchange selectivity of trivalent metal ions has been determined on titanium antimonate cation exchanger prepared by coprecipitation of antimony to titanium at different mole ratios. The selectivity sequence Al3+<Cr3+<Ga3+<In3+<Fe3+ was found for trivalent metal ions at an initial concentration of 10–4 mol dm–3 in nitric acid media. A high separation factor Ga/Al = KdGa/KdAl, 4.8×103, was observed for the Ga3+–Al3+ pair on titanium antimonate with an antimony to titanium ratio of 0.34. The effective separation of Ga3+ and In3+ from Al3+ was achieved using a 3 cm×0.5 cm i.d. column containing titanium antimonate with an antimony to titanium ratio of 0.34. 相似文献
96.
Summary The molecular-shape recognition of polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase high-performance liquid chromatography. The examined stationary phases were phenyl-, diphenyl-, triphenyl- and benzyl-bonded silicas. The results of regression analysis inidcated that triphenylsilica is the best packing material to recognize the difference in the molecular-shape of structural isomers. This fact was confirmed by the separation of 4-ring isomers. 相似文献
97.
Summary Two molecularly imprinted polymers (MIP) have been prepared using the acidic drug salicylic acid, which can form intramolecular
hydrogen bond, as the template and acrylamide or 4-vinylpyridine as the functional monomer. HPLC was used to evaluate the
binding performance of the MIP for the template and for several analogues. The results showed that the MIP (P2) prepared using acrylamide as the functional monomer had no molecular imprinting effect whereas that (P1) prepared using 4-vinylpyridine as the functional monomer had a significant molecular imprinting effect. The reason the molecular
imprinting effect was different for the two MIP was elucidated and the molecular recognition properties of P1 were studied in detail. It was confirmed that electrostatic interaction played an important role in the molecular recognition
of P1. Scatchard analysis showed that two types of binding site with distinctly different affinity were formed in P1. Their dissociation constants were estimated to be 7.6×10−5 mol L−1 and 3.2×10−3 mol L−1, respectively. Because P1 has high affinity and selectivity for salicylic acid not only in organic systems but also in water-containing systems, it
gives P1 the potential for use in the enrichment, separation, and detection of salicylic acid in biological fluids. 相似文献
98.
Intramolecular cyclization reactions of 3,4-bis(indol-3-yl)maleimides 1, 3-(indol-1-yl)-4-(indol-3-yl)maleimides 2, and 3,4-bis(indol-1-yl)maleimides 3 under the action of protic acids were studied in order to estimate the parameters of the interaction between protonated and
unprotonated indole moieties. Geometric parameters, charge distributions, energy characteristics, and information concerning
the frontier orbitals of bisindolylmaleimides 1–3 were obtained from density functional B3LYP/6-31G(d) quantum chemical calculations. Alternative pathways of protonation of
bisindolylmaleimides with differently bonded indole and maleimide moieties were studied and pathways of cyclization of corresponding
conjugated acids leading to polyannelated compounds were analyzed. All the key intermediates of the cyclization reactions
correspond to stationary points on the potential energy surfaces (minima and transition states). Analysis of the potential
energy surfaces revealed almost linear dependences of the activation energies of the cyclization reactions under study on
the distances between the reaction centers, on the angle of approach of intramolecular electrophile, and on the energy gap
(energy difference between frontier orbitals). The key role in the cyclization reactions is played by structural similarity
between the starting indoleninium cations and the activated complexes of the reactions under study.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 754–760, May, 2006. 相似文献
99.
Pittelkow M Nielsen CB Broeren MA van Dongen JL van Genderen MH Meijer EW Christensen JB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(17):5126-5135
Host-guest interactions between the periphery of adamantylurea-functionalized dendrimers (host) and ureido acetic acid derivatives (guest) were shown to be specific, strong and spatially well-defined. The binding becomes stronger when using phosphonic or sulfonic acid derivatives. In the present work we have quantified the binding constants for the host-guest interactions between two different host motifs and six different guest molecules. The host molecules, which resemble the periphery of a poly(propylene imine) dendrimer, have been fitted with an anthracene-based fluorescent probe. The two host motifs differ in terms of the length of the spacer between a tertiary amine and two ureido functionalities. The guest molecules all contain an acidic moiety (either a carboxylic acid, a phosphonic acid, or a sulfonic acid) and three of them also contain an ureido moiety capable of forming multiple hydrogen bonds to the hosts. The binding constants for all 12 host-guest complexes have been determined by using fluorescence titrations by monitoring the increase in fluorescence of the host upon protonation by the addition of the guest. The binding constants could be tuned by changing the design of the acidic part of the guest. The formation of hydrogen bonds gives, in all cases, higher association constants, demonstrating that the host is more than a proton sensor. The host with the longer spacer (propyl) shows higher association constants than the host with the shorter spacer (ethyl). The gain in association constants are higher when the urea function is added to the guests for the host with the longer spacer, indicating a better fit. Collision-induced dissociation mass spectrometry (CID-MS) is used to study the stability of the six motifs using the corresponding third generation dendrimer. A similar trend is found when the six different guests are compared. 相似文献
100.
Metathesis of hex-1-ene in ionic liquids catalyzed by WCl6 was studied. The metathesis is preceded by isomerization of hex-1-ene to hex-2-ene, from which the main reaction product, viz., oct-4-ene, is derived. The WCl6-1-butyl-3-methylimidazolium tetrafluoroborate (BMIM·BF4) system efficiently catalyzes metathesis of linear olefin, the ionic liquid serving as the reaction medium by forming a stable homogeneous catalytic system with WCl6. The yields of the metathesis products increase with increasing reaction temperature. The addition of tin-containing promoters leads to a substantial increase in the reaction rate. In the WCl6-BMIM·BF4-SnBu4 system, the selectivity of the formation of oct-4-ene is significantly enhanced.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2094–2097, October, 2004. 相似文献