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231.
用半经验AM1方法研究了C_(70)与臭氧环加成反应的反应机理。采用Berny梯度 法优化得到反应的过滤度,并进行了振动分析确诊。计算结果表明:臭氧在C_(70) 6-6单、双键上的环加成反应均为复杂反应,由三步组成:第一步是O_3分子与C_ (70)的6-6单、双键发生1,3-偶极环加成反应,生成分子臭氧化物(即中间体I), 6-6双键加成为放热反应,6-6单键加成为吸热反应,活化势垒分别为84.7和181. 2 kJ·mol~(-1);第二步是中间体I的加成,C-C键断裂,生成两性离子中间体II 的放热反应,其势垒分别为61.3和13.3 kJ·mol~(-1);第三步是中间体II脱去一 个Q_2分子生成具有环氧结构的C_(70)O,均为放热反应,活化势垒分别为169.3和 101.2 kJ·mol~(-1);第三步是中间体I脱去一个O_2分子生成具有环氧结构的C_ (70)O,均为放热反应,活化势垒分别为169.3和101.2 kJ·mol~(-1),从反应机理 和动力学角度解释了6-6双键加成优于6-6双键加成优于6-6双键加成优于6-6单键 加成的原因。O_3分子与C_(70)6-6双键的加成反应是协同且同步进行的,与6-6单 键的加成反应是协同但不同步的过程。 相似文献
232.
Selective amidation of simple hydrocarbons with pre-isolated and in-situ formed iminoiodanes catalyzed by ruthenium complexes [Ru(III)(Me(3)tacn)(CF(3)CO(2))(3).H(2)O] (2b, Me(3)tacn = N,N', N"-trimethyl-1,4,7-triazacyclononane) and cis-[Ru(II)(6, 6'-Cl(2)bpy)(2)Cl(2)] (3, 6,6'-Cl(2)bpy = 6,6'-dichloro-2, 2'-bipyridine) was investigated. With PhI=NTs as nitrogen source, both catalysts efficiently promote the amidation of adamantane, cyclohexene, ethylbenzene, cumene, indan, tetralin, and diphenylmethane to afford N-substituted sulfonamides in 80-93% yields with high selectivity. Competitive amidations of para-substituted ethylbenzenes and kinetic isotope effect for the amidation of cyclohexene/cyclohexene-d(10) suggest that the amidation processes probably proceed via the hydrogen abstraction by a reactive Ru=NTs species to form a carboradical intermediate. The amidation with PhI(OAc)(2)/TsNH(2) gave results comparable to those obtained with PhI=NTs. Extension of the "PhI(OAc)(2)/TsNH(2) + catalyst 2b or 3" protocol to MeSO(2)NH(2) and PhCONH(2) with ethylbenzene as substrate produced the corresponding N-substituted amides in up to 89% yield. 相似文献
233.
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235.
Lydia Außenhofer 《Mathematische Zeitschrift》2007,257(2):239-250
For a topological group G, we denote by G
a
the arc component of the neutral element and by the character group of G, i.e. the group of all continuous homomorphisms from G into T. We prove the following theorem: Let G be a connected locally compact abelian group and let be the embedding. Then is a topological isomorphism. In particular, the character group of the arc component of a compact abelian group is discrete.
Some conclusions will be drawn. 相似文献
236.
The drift, the risk-free interest rate, and the volatility change over time horizon in realistic financial world. These frustrations
break the necessary assumptions in the Black-Scholes model (BSM) in which all parameters are assumed to be constant. To better
model the real markets, a modified BSM is proposed for numerically evaluating options price-changeable parameters are allowed
through the backward Markov regime switching. The method of fundamental solutions (MFS) is applied to solve the modified model
and price a given option. A series of numerical simulations are provided to illustrate the effect of the changing market on
option pricing. 相似文献
237.
F. T. K. Au Y. S. Cheng Y. K. Cheung D. Y. Zheng 《Applied Mathematical Modelling》2001,25(12):1099-1115
An accurate analysis of the natural frequencies and mode shapes of a cable-stayed bridge is fundamental to the solution of its dynamic responses due to seismic, wind and traffic loads. In most previous studies, the stay cables have been modelled as single truss elements in conventional finite element analysis. This method is simple but it is inadequate for the accurate dynamic analysis of a cable-stayed bridge because it essentially precludes the transverse cable vibrations. This paper presents a comprehensive study of various modelling schemes for the dynamic analysis of cable-stayed bridges. The modelling schemes studied include the finite element method and the dynamic stiffness method. Both the mesh options of modelling each stay cable as a single truss element with an equivalent modulus and modelling each stay cable by a number of cable elements with the original modulus are studied. Their capability to account for transverse cable vibrations in the overall dynamic analysis as well as their accuracy and efficiency are investigated. 相似文献
238.
L. Krainer R. Paschotta J. Aus der Au C. Hönninger U. Keller M. Moser D. Kopf K.J. Weingarten 《Applied physics. B, Lasers and optics》1999,69(3):245-247
We demonstrate passive mode locking of a Nd:vanadate (Nd:YVO4) laser to repetition rates of up to 13 GHz. With Ti:sapphire pumping, we achieved mode locking at 13 GHz with 310 mW of average
output power and pulse widths of 9.5 ps. With diode pumping, we achieved mode locking at a repetition rate of 12.6 GHz with
198 mW of average output power and a pulse duration of 8.3 ps.
Received: 6 July 1999 / Published online: 30 July 1999 相似文献
239.
240.
CO2加氢合成甲醇催化反应中CO的作用 总被引:1,自引:0,他引:1
研究了铜基催化剂上CO2加氢合成甲醇反应中掺人CO的作用,结果表明,在原料中添加少量CO,甲醇的选择性提高38%,收率提高25%;TPD-MS和TPSR-MS结果表明,CO能抑制催化剂表面起逆水汽变换作用的活性位对CO2的吸附,从而提高了CO2加氢合成甲醇的选抒性. 相似文献