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1.
Paula Mayorga Burrezo Wangdong Zeng Michael Moos Marco Holzapfel Sofia Canola Fabrizia Negri Concepci Rovira Jaume Veciana Hoa Phan Jishan Wu Christoph Lambert Juan Casado 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14609-14613
A complete experimental and theoretical study has been carried out for aromatic and quinoidal perylene‐based bridges substituted with bis(diarylamine) and bis(arylimine) groups respectively. The through‐bridge inter‐redox site electronic couplings (VAB) have been calculated for their respective mixed‐valence radical cation and radical anion species. The unusual similitudes of the resulting VAB values for the given structures reveal the intervention of molecular shapes with balanced semi‐quinoidal/semi‐aromatic structures in the charge delocalization. An identical molecular object equally responding to the injection of either positive or negative charges is rare in the field of organic π‐conjugated molecules. However, once probed herein for perylene‐based systems, it can be extrapolated to other π‐conjugated bridges. As a result, this work opens the door to the rational design of true ambipolar bulk and molecular conductors. 相似文献
2.
Minshou Zhao Xinbo Zhang Yujun Chai Changying Sun 《Research on Chemical Intermediates》2006,32(5):403-417
The structures and the electrochemical characteristics of La0.7−x
CexMg0.3Ni2.8Co0.5 (x = 0.1–0.5) alloy, Ti0.25−x
ZrxV0.35Cr0.1Ni0.3 (x = 0.05–0.15) alloy and AB3<x<5-type alloy, which are the representative examples of AB3-type alloy, solid solution alloy and non-AB5-type alloy, respectively, have been investigated, and the performances of MH-Ni battery in which AB3<x<5 type alloy is used as the negative electrode material are examined at relatively low temperature. 相似文献
3.
4.
The theory for deceptive simplicity in the NMR spectra of oriented molecules is discussed in terms of degeneracy of subspectra. The conditions for the degeneracy of AB, AB2 and AA′BB′ spectra leading to deceptive simplicity in the spectra of the type ABX, AB2X, AA′BB′X and AA′XX′ are reported. It is shown that the conditions for deceptive simplicity are easily fulfilled for ABX, AA′BB′X and AA′XX′ cases. It is further demonstrated that deceptive simplicity is not so common in AB2X spectra. The proton spectra of partially oriented 2,4,5-trichloronitrobenzene (AB) and 2,6-dibromo-pyridine (AB2) are use to illustrate degeneracy and those of p-chloro- and p-bromo-fluorobenzenes are reported to demonstrate deceptive simplicity. 相似文献
5.
Metal-hydride electrodes made of an AB2 alloy of the composition Zr0¨5Ti0¨5V0¨6Cr0¨2Ni1¨2 are studied for AC impedance behaviour at several of their state-of-charge values. Impedance data at any state-of-chargecomprisetwoRC-time
constants and accordingly are analysed by using a nonlinear-least-square-fitting procedure. Resistance of the electrode and
frequency maximumf* of the lowfrequency semicircle are found useful for predicting state-of-charge of the metalhydride electrodes. 相似文献
6.
镍氢电池的循环性能与活性物质微结构的研究 总被引:1,自引:0,他引:1
与循环试验大致同步, 用静态(初态和终态)或准动态(增加若干个中间态)的模式对MH/H电池循环性能、电极(包括负极和正极)材料的微结构进行了X射线衍射(XRD)研究, 发现循环性能衰减与正极材料β-Ni(OH)2的点阵参数、平均晶粒尺度、微应变和总的层错几率均随循环周期增加而减小以及负极材料中腐蚀产物A(OH)3和B相出现和增加有一定的对应关系, 发现MH/Ni 电池循环性能的衰减是正极材料和负极材料的结构和微结构随着循环次数的增加发生明显变化, 恶化了正负极材料的电化学性能, 同时消耗和恶化了电解液的综合结果. 为了提高电池的循环性能, 采用不同正极材料的添加剂. 结果表明, CaF2和Lu2O3有明显的效果, 其中CaF2效果最好, 并有广泛的实用性. 相似文献
7.
F. Corre 《Journal of Molecular Structure》1981,86(1-2)
The use of pAB = ΣμA ΣνB μν Sμν as bond index in the CNDO approximation is theoretically justified as it is an elaborated form of Coulson's bond order and an approximation of Roby's shared electron density. This bond index correlates with diatomic energy EAB, a measure of binding energy, and with interatomic distance RAB, for several bonds involving hydrogen and atoms of the n = 2 period. As an example of utilization of pAB bond lengths in butadiene and a series of ethylenic compounds are determined. 相似文献
8.
Georges Leroy Jean-Pierre Dewispelaere Hanan Benkadour Claude Wilante 《Macromolecular theory and simulations》1996,5(2):269-289
In this work, we have calculated the thermodynamic parameters of the first steps of the free radical and anionic polymerizations of various unsaturated monomers, using ab initio methods of quantum chemistry. The enthalpies and entropies of polymerization were estimated assuming that they correspond to those of the model reaction A B(p) + HABAH(p′) → HABABAH(p′) where p and p′ stand for the physical state of the considered species. The enthalpies of polymerization were rationalized using the equation ΔH = −ΔΣ NABEAB + SE(A B) + SE(HABAH) − SE(HABABAH) where NAB is the number of A B bonds, EAB the corresponding bond energy, − ΔΣ NABEAB the variation of the sum of the bond energy terms, and SE(X) the thermodynamic stabilization energy of compound X. The preferential mode of polymerization of each monomer was derived from the enthalpies of the initiation and initial propagation steps of the two types of polymerization. Thus, we were able to make some comments concerning the feasibility of the polymerization of the monomers under consideration. 相似文献
9.
August W. Bosse Vijay R. Tirumala Eric K. Lin 《Journal of Polymer Science.Polymer Physics》2009,47(21):2083-2090
We use polymer random phase approximation (RPA) theory to calculate the microphase separation transition (MST) spinodal for an AB + C diblock copolymer–homopolymer blend where the C homopolymers are strongly attracted to the A segment of the copolymers. Our calculations indicate that one can shift the MST spinodal value of the A ? B segmental interaction parameter (χABN)S to significantly lower values [i.e., (χABN)S < 10.5] upon the addition of a selectively attractive C homopolymer. For a sufficiently attractive C homopolymer, (χABN)S can be pushed to negative values, indicating microphase separation in what would appear to be a completely miscible diblock copolymer. Furthermore, we show that microphase separation can occur in diblock copolymer–homopolymer blends where the segmental interactions between all polymer constituents are attractive. By tuning the value of (χABN)S with a homopolymer additive, one is therefore able to tune the effective copolymer segregation strength and thus dramatically affect the blend phase behavior. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2083–2090, 2009 相似文献
10.
D. Y. Yoon Y. Ando S. Rojstaczer S. K. Kumar G. C. Alfonso 《Macromolecular Symposia》1991,50(1):183-190
Crystal-amorphous interphases in binary polymer blends that are miscible in the melts but phase separate due to crystallization of one polymer have been investigated theoretically by employing lattice models and experimentally by dielectric spectroscopy measurements. Theory predicts the extent of tight adjacent re-entry to depend strongly on the energy Eq disfavoring the tight-fold conformations and to increase slightly with favorable interaction energy - χAB in the blends. The interfacial region of varying composition is predicted to depend strongly on χAB, with the interfacial thickness varying with the reciprocal of |χAB|1/2. Therefore, in the limit χAB → 0 the amorphous polymer, which is miscible in the melt, is predicted to be completely excluded from the interlamellar region, in agreement with experimental results. Dielectric relaxation experiments on semicrystalline blends of poly(vinylidene fluoride) (PVDF) with poly(methyl methacrylate) (PMMA) or poly(vinyl pyrrolidone) (PVP) show the existence of nearly pure PVDF interphase which is not penetrated by PMMA or PVP, despite their strongly favorable interactions with PVDF. These experimental results are discussed and compared with theoretical predictions. 相似文献
11.
The competition among the three different elementary second‐order processes involving the radicals A and B, (1) (2) (3) is frequently established in many combustion and atmospheric chemistry systems. The analytical resolution of the above mechanism for kAB = 2kAA and kAB = 2kBB, that is, for a cross‐combination ratio ? = kAB/(kAAkBB)1/2 = 2, is well‐known, but it has been claimed not to exist for ? ≠ 2. In the present paper an analytical resolution of the system (1)–(3), performed under the condition kAB ≠ 2kAA and kAB ≠ 2kBB, leads to The mathematical procedure leading to this equation and the equation itself are valid independently of the nature of the products of the reactions ( 1 ), ( 2 ) and ( 3 ), that is, recombination or disproportionation products, provided that the reactants and the order of the reactions remain the same. The comparison with numerical integration for exemplary cases is performed. The solutions for the particular cases kAB ≠ 2kBB or kAB ≠ 2kAA are also presented. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 246–251, 2003 相似文献
12.
Robustness Screen in Enantioselective Catalysis Enabled Generation of Enantioenriched Heterocyclic Scaffolds in One Pot
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Pradip N. Bagle Valmik S. Shinde Nitin T. Patil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3580-3584
Enantioselective catalysis has emerged as a powerful synthetic paradigm and has accelerated the development of new methods to make diverse chiral molecules. Generally, these reactions are very sensitive to the steric and electronic environment present in the catalyst as well as the substrates. With this scenario, the presence of an additional component in the reaction mixture is expected to add complexity in achieving the enantioselective variants. Herein, we report that various enantioenriched molecules could be obtained from multiple starting materials in one pot. The reaction of aminoaromatics A with alkynols B1, B2, B3…?Bn with a AuI/chiral Brønsted acid catalyst afforded AB1*, AB2*, AB3*…ABn*; while, the reaction of alkynols B with aminoaromatics A1, A2, A3…An under the same reaction conditions gave A1B*, A2B*, A3B*…AnB * . 相似文献
13.
Stefan Liebig Heinrich Billetter Tim Wallraff Stefanie Busch Stefan Müller Uwe Ruschewitz 《无机化学与普通化学杂志》2016,642(1):66-72
Three alkali metal acetylides, namely KNaC2, KRbC2, and NaRbC2, were synthesized and characterized by means of X‐ray powder diffraction. KNaC2 and KRbC2 crystallize as a variant of the anti‐PbCl2‐type structure (Pnma, Z = 4), whereas NaRbC2 crystallizes as a variant of the anti‐PbFCl‐type structure (Pmmn, Z = 2). Based on a simple systematic approach developed by Sabrowsky et al. for inter‐alkali metal chalcogenides all known inter‐alkali metal acetylides can be classified into two classes: variants of the anti‐PbCl2 type structure and variants of the anti‐PbFCl type structure. Acetylides with Q(ABC2) ≤ 1.45 crystallize in the anti‐PbCl2‐type structure, whereas for Q(ABC2) > 1.45 the anti‐PbFCl‐type structure is found (Q(ABC2) = Vm(A2C2)/Vm(B2C2) with Vm(A2C2) > Vm(B2C2); Vm: molar volume, A, B = alkali metals). 相似文献
14.
Elie Younang Jean-Marie Andr Joseph Delhalle 《International journal of quantum chemistry》1992,41(2):257-271
In the framework of our study of the changes of the electric polarizability upon substituting heteroatomic linkages in conjugated hydrocarbon backbones, we have been led to examine the relative stability of eight compounds isoelectronic to the all-trans octatetraene using the Cox and Pilcher concept of stabilization energy (SE ), SE = ΔHa – ΣNABEAB, where ΔHa is the heat of atomization of the species under consideration and the EAB's are bond-energy terms. Full geometry optimizations at the 4-31G level have been performed to obtain the equilibrium geometries needed to deduce reliable semiempirical heats of formation from appropriate isodesmic processes. Some of the compounds containing the ? CH?N? and ? N?N ? groups have electric polarizabilities and stabilization energies comparable to octatetrene. 相似文献
15.
We analyse transient effects in an electrolytic cell submitted to an external voltage and determine the relaxation time of the redistribution of the ions and of the potential. We consider the case in which adsorption effects at the interface with the electrodes are present and show that the typical relaxation time, for applied voltage V 025 mV, is of the order of tens of seconds for commercial nematic liquid crystals. When V 0>25 mV the linearized analysis is no longer valid. In this case, the relaxation time depends on the applied voltage. Increasing V 0, but still remaining in the low amplitude limit, the relaxation time starts increasing. This indicates that the reduction of the actual field in the sample, for moderate values of V 0, plays an important role. For large values of V 0, the relaxation time is a decreasing function of V 0. This result is interpreted in terms of a simple model, according to which the ionic charge is localized in a surface layer whose thickness depends on the amplitude of the applied voltage. 相似文献
16.
E. Klesper 《Journal of polymer science. Part A, Polymer chemistry》1970,8(5):1191-1199
For the evaluation of the configurational parameters in cross propagation, Σs and Σp for binary vinyl type copolymers whose monomer units both contain an asymmetric carbon atom in the chain, a method is proposed which relies on intersecting straight lines in a Σs versus Σp diagram. We define Σs = σAB + σAB and Σp = σAB·σBA, σ being the probability of forming an isotactic enchainment between the monomer units when B adds to a chain ending in A, or A adds to a chain ending in B, respectively. For these definitions it is assumed that σAB and σBA are not necessarily equal in their numerical values. The method described is applicable to triad probabilities obtained both from copolymers and such homopolymers which have been prepared from copolymers under retention of configuration by a polymer analogous reaction. In this work, triad data have been evaluated which were obtained by NMR from methyl methacrylate-methacrylic acid copolymers, wherein the methyl methacrylate units were pentadeuterated on the α? CH3 and β? CH2 groups, as well as from methyl methacrylate homopolymers, the latter being prepared from undeuterated methyl methacrylate-methacrylic acid copolymers by esterification. The approximate values Σs = 0.38, Σp = 0.02 were obtained for the deuterated copolymers, while Σs = 0.392 ± 0.003 and Σp = 0.037 ± 0.003 were found for the undeuterated homopolymers. 相似文献
17.
Tadeusz Michałowski Maja Ponikvar-Svet Agustin G. Asuero Krzysztof Kupiec 《Journal of solution chemistry》2012,41(3):436-446
The pH titration of As(III) in the buffered malonate system with V mL of I2+KI solution is considered. At V≤V
eq (V
eq denotes the equivalence volume), the course of the titration curve depends on thermodynamic effects and the malonate species
act only as an acid–base buffer. For V>V
eq the course of this curve depends on kinetic effects and the malonic acid acts both as a buffering and a reducing agent. The
V
eq value in the titration was obtained as the point of intersection of two segments approximated by hyperbolic functions. The
difference in the slopes of the segments results from the difference in the number of protons evolved in thermodynamic reaction
of iodine with HAsO2 (for V≤V
eq) and in the kinetics of the reaction with malonate species (V>V
eq). The slope of the segment at V>V
eq depends on the titration rate within this volume interval. This paper illustrates an application of the GATES methodology,
and provides the possibility of making reasonable inferences from comparison of preliminary physicochemical knowledge with
experimental data. 相似文献
18.
Yufeng Zhai Hualiang Jiang Weiliang Zhu Jiande Gu Jianzhong Chen Kaixian Chen Ruyun Ji 《中国科学B辑(英文版)》1999,42(1):77-82
Iritramolwular electron transfer of nlctal-containing spiro π-electron system was studied by AM1 method in the MOPAC-ET program
developed by the present group. The results indicated that with the increasing of the outer electric field F, the activation
energy of the reaction decreased. When F reaches a certain threshold value, the activation energy barrirr becomcs zero and
the rate of reaction achieves the largest value. The results also indicated that electron transfer matrix elements VAB and reorganization energy λ were not obviously affected by outer electric field while the exothermicity ΔE was directly proportional to it. 相似文献
19.
Momoka Watanabe Yusuke Asai Atsushi Takano Yushu Matsushita 《Journal of Polymer Science.Polymer Physics》2019,57(14):952-960
Microphase‐separated structures of a series of AB6 block‐graft copolymers were studied by TEM and SAXS. Ten copolymers with the same polystyrene (S) backbone and six polyisoprene (I) grafts on the average but with different graft chain lengths were carefully synthesized by living anionic polymerization, covering the range 0.21 ≤ ?S ≤ 0.90, where ?S denotes polystyrene compositions. From TEM observation of the AB6 block‐graft copolymers, it turns out to be clear that they show four microphase‐separated structures, S‐spheres, S‐cylinders(S‐prisms), alternative lamellae, and I‐cylinders. Among them, for example, the samples with 0.54 ≤ ?S ≤ 0.58 shows prism structures whose cross sections of the S domains are close to hexagons, not circles, due to packing frustration of grafts. Composition dependence of morphologies of the present AB6 block‐graft copolymers reveals their phase diagram is extremely asymmetric with respect to ?S = 0.5. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 952–960 相似文献
20.
T. A. Zotov V. N. Verbetskii T. Ya. Safonova A. V. Garshev O. A. Petrii 《Russian Journal of Electrochemistry》2007,43(3):355-363
Using scanning electron microscopy and x-ray phase analysis techniques, it is shown that the C14-type Laves phase with a wide homogeneity reaching the AB2.3 stoichiometry is the main phase in the Zr0.5Ti0.5NiyV0.5Mn x alloys, where y = 0.8–1.4 and x = 0.1–1.7. With the increase in the nickel and manganese contents and in the stoichiometric ratio B/A, the hydrogen capacity decreases from 2 to 1.6 wt %, the equilibrium pressure of hydride phases increases, and the hydrides become less stable. The highest discharge capacity is reached for stoichiometric ratios AB1.7–2.3, where the maximum discharge capacity at a discharge current density of 100 mA/g is 300 (mA h)/g. Alloys that contain ferrovanadium in place of vanadium are also considered. 相似文献