烷基极化效应与X=O键伸缩振动频率

烷基取代物R’X=0的X=0键伸缩振动频率ν与烷基R的极化效应指数PEI(R)的关系可表示为:ν=a bPEI(R)。研究结果表明,烷基的极化效应使X=0键的伸缩振动频率降低。     

不饱和硼烯HClN=B:重排反应的DFT研究

采用量子化学中的密度泛函方法, 在B3LYP/6-311G**水平上研究了不饱和硼烯HClN=B:的重排反应机理。结果表明, 无论是氢原子H迁移还是氯原子Cl迁移都经过1个三元环过渡态,生成直线型产物。但氢原子H迁移是在面内进行, 而氯原子Cl迁移是在面外进行。根据计算结果,详细研究了不饱和硼烯HClN=B:重排反应的热力学及动力学函数, 在此基础上讨论了不饱和硼烯HClN=B:的存在寿命问题。     

功能高分子活性材料硫酸根离子选择电极的研制

利用辐射方法制备硫酸根离子选择电极活性材料,至今未见报导,我们首次采用辐射接枝方法制备了以疏水性高分子为骨架的带有SO~-活性基团的功能高分子活性材料,研制了硫酸根离子选择电极。结果表明,该电极具有内阻低,响应快,稳定性较好的特点,且其功能曲线的线性范围为10~(-1)～10~(-4)MSO_4~-,适宜的pH范围为4～9。     

Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.     

Synthesis,crystal structure,magnetism, and absorption spectra of A2UX5 Type Halides (A = K,Rb; X = Cl,Br, I)

The ternary uranium(III) halides A₂UX₅ (A = K, Rb; X = Cl, Br, I) have been prepared from the binary components AX and UX₃ in sealed tantalum containers. According to their Guinier X-ray powder patterns, they all crystallize with the K₂PrCl₅/Y₂HfS₅ type of structure. Lattice constants for ambient temperature are reported. Single-crystal structure refinemens were undertaken for K₂UI₅ and Rb₂UCl₅. Magnetic susceptibility data were recorded with a SQUID magnetometer from liquid helium to room temperature. One-dimensional (intrachain) and three-dimensional antiferromagnetic ordering occur at low temperatures dependent upon the U³⁺? U³⁺ distance. Absorption spectra were recorded between 4 000 and 28 000 cm^?1. They show f—f transitions typical for U³⁺ and, depending on the halide, very strong f—d transitions above 14 000 to 15 000 cm^?1, respectively.     

Phosphinophosphiniden-Phosphorane tBu2P?P = P(R)tBu2 aus Li(THF)2[η2-(tBu2P)2P] und Alkylhalogeniden

The Phosphinophosphinidene-phosphoranes ^tBu₂P? P = P(R)^tBu₂ from Li(THF)₂[η²-(^tBu₂P)₂P] and Alkyl Halides We report the formation of ^tBu₂P? P = P(R)^tBu₂ a and (^tBu₂)₂PR b (with R = Me, Et, ⁿPr, ⁱPr, ⁿBu, PhCH₂, H₂C = CH? CH₂ and CF₃) reactions of Li(THF)₂[η²-(^tBu₂P)₂P] 2 with MeCl, MeI, EtCl, EtBr, ⁿPrCl, ⁿPrBr, ⁱPrCl, ⁿBuBr, PhCH₂Cl, H₂C = CH? CH₂Cl or CF₃Br. In THF solutions the ylidic compounds a predominate, whereas in pentane the corresponding triphosphanes b are preferrably formed. With ClCH₂? CH = CH₂ only b is produced; CF₃Br however yields both ^tBu₂P? P = P(Br)^tBu₂ and ^tBu₂P? P = P(CF₃)^tBu₂, but no b . The ratio of a:b is influenced by the reaction temperature, too. The compounds ^tBu₂P? P = P(Et)^tBu₂ 4a and (^tBu₂P)₂PEt 4 b , e. g., are produced in a ratio of 4:3 at ?70°C in THF, and 1:1 at 20°C; whereas 1:1 is obtained at ?70°C in pentane, and 1:2 at 20°C. Neither ^tBuCl nor H₂C = CHCl react with 2 . The compounds a decompose thermally or under UV irradiation forming ^tBu₂PR and the cyclophosphanes (^tBu₂P)_nP_n.     

Synthese und Struktur eines Molybdän–Gadolinium-Heterometall-Komplexes Die Struktur von [Li(thf)4]2[Cp2MoSGdBr4(thf)]2

Synthesis and structure of a Molybdenum–Gadolinium Heterometallic Complex. The Structure of [Li(thf)₄]₂[Cp₂MoSGdBr₄(thf)]₂ [Cp₂MoHLi] reacts in THF with S and GdBr₃ to yield the tetranuclear heterobimetallic complex [Li(thf)₄]₂[Cp₂MoSGdBr₄(thf)]₂. The bonding situation and the structure of this compound were characterized by X-ray structure analysis (space group P1 (No. 2), Z = 1, a = 10.845(2) Å, b = 12.166(2) Å, c = 15.881(2) Å, α = 101.74(2)°, β = 97.62(2)°, γ = 103.97(2)°). Each S atom of the central Mo₂S₂-ring is coordinated by a GdBr₄(thf) fragment. Additionally each Mo atom is connected to two Cp ligands. This leads to a tetrahedral coordination of the Mo atoms and a octahedral coordination of the Gd ions.     

Performance of Pt/SnO2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO₂ catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn₂ formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.     

分子CH_3NH=B:的结构及重排反应的理论研究

采用量子化学中的从头计算方法, 在MP2/6-31G(d,p)水平上研究了不饱和硼烯CH3NH=B:的结构及重排反应机理。结果表明, CH3NH=B:的单线态结构比三线态结构稳定, 该分子的基态是单线态。分子CH3NH=B:可以发生3种不同的重排反应。本文找到了这3种重排反应的过渡态, 并详细计算了不饱和硼烯CH3NH=B:重排反应的动力学函数, 据此讨论了不饱和硼烯CH3NH=B:的稳定性问题。     

Crystal structures of the organic metals (ET)2[Hg(SCN)Cl2] and (ET)2[Hg(SCN)2Br]

The compositions and structures of two new organic metals based on ET [where ET = bis(ethylenedithio)tetrathiafulvalene], viz., (ET)₂[Hg(SCN)Cl₂], with a metal-dielectric transition temperature (T_m-d) of 35°K, and (ET)₂[Hg(SCN)₂Br], with T_m-d = 140°K, were established by x-ray diffraction analysis. The crystal structures of the investigated compounds are similar to the structure of the previously studied organic metal (ET)₂[Hg(SCN)₂Cl] with T_m-d = 50°K. The principal crystallographic data for (ET)₂[Hg(SCN)Cl₂] are as follows: a = 36.64(1), b = 8.300(4), c = 11.798(1) Å, = 89.91(3)°, V = 3588.1(9) ų, space group Cc, Z = 4, d_calc = 2.05 g/cm³. The principal crystallographic data for (ET)₂[Hg(SCN)₂Br] are as follows: a = 37.088(14), b = 8.338(3), c = 11.738(5) Å, = 89.71(3)°, V = 3629.6(8) ų, space group C2/c, Z = 8, d_calc = 2.15 g/cm³. A characteristic feature of the crystal structure of the investigated compounds is alternation of the anion and cation layers along the a axis of the crystal. In the cation layer of the k type the ET are interconnected by shortened S...S intermolecular contacts (3.39–3.58 Å). The [Hg(SCN)_3–nX_n]^– anions (X = Cl, Br; n = 1, 2) form polymeric chains with one or two bridged SCN groups. A tendency for a decrease in the metal-dielectric transition temperature with a decrease in the volume of the anion is detected in the (ET)₂[Hg(SCN)_3–nX_n] salts, where X = Cl and Br, and n = 1 and 2.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2323–2331, October, 1992.