Catalysis by transition metals: metal-carbon double and triple bonds

Several well-characterized transition metal catalysts contain a metal-carbon double bond or a metal-carbon triple bond. In other homogeneous (or heterogeneous) catalyst systems in which the metal is likely to be in a relatively high oxidation state, such as molybdenum(VI) or tungsten(VI), metal-carbon multiple bonds may play an important role. Some recent results suggest that even supposedly well understood reactions such as ethylene polymerization may actually involve catalysts that behave as if they contained a metal-carbon double bond instead of a metal-carbon single bond. The chemistry of metal-carbon double and triple bonds should eventually complement and perhaps. overlap the known chemistry of complexes containing metal-oxygen double bonds or metal-nitrogen triple bonds, respectively; unique catalytic reactions involving carbon, nitrogen, and oxygen ligands multiply bonded to transition metals are therefore possible.     

Esters from Bacterial Oxidation of Olefins

Identification of esters isolated from culture fluids of bacteria growing upon terminal olefins indicates that bacteria oxidize olefins at the saturated methyl group, leaving the double bond intact. The yeast Candida lipolytica produces alpha-glycols from olefins, presumably by attacking the double bond.     

Bond order and charge localization in nucleoside phosphorothioates

In the recent literature on nucleoside phosphorothioate anions the structural formulas show a double bond between phosphorus and sulfur and a single bond between phosphorus and oxygen with a negative charge localized on oxygen. However, a review of physical data on these compounds shows the reverse to be the case; that is, in phosphorothioate anions the P-S bond is a single bond with a negative charge localized on sulfur, while the P-O bond order for exocyclic and nonbridging oxygens is greater than 1, approaching 2 in O-alkyl phosphorothioate monoanions and O,O-dialkyl phosphorothioates. The P-O bond orders in phosphorothioate dianions and trianions approach 1 1/2 and 1 1/3, respectively, owing to delocalization of negative charge among two or three oxygens. These conclusions are based on bond lengths obtained from x-ray crystallographic data and electron diffraction, the magnitudes of the effects of 18O on the 31P-nuclear magnetic resonance chemical shifts of phosphorus in nucleoside [18O]phosphorothioates, the pH-dependence of 17O-NMR chemical shifts in [17O]phosphate and [17O]thiophosphate, the vibrational spectra of thiophosphate di- and trianions, and the pKa (dissociation constant) values for phosphoric and thiophosphoric acids.     

共轭双键对脂肪酸紫外吸收的影响

[目的]测定共轭亚油酸及部分非共轭脂肪酸的紫外吸收,研究共轭双键对脂肪酸紫外吸收的影响。[方法]测定多种脂肪酸及其混合物的吸光度,并利用气相色谱法测定脂肪酸组分含量。[结果]当加入少量的共轭亚油酸时,混合脂肪酸的紫外吸收曲线表现出明显变化。[结论]共轭双键对脂肪酸在230～240nm范围内的紫外吸收有显著影响,从而为共轭成分的存在提供了检测依据。     

风化煤腐植酸增效尿素红外光谱分析

采用碱性混合活化剂处理风化煤,研制腐植酸添加剂,按不同比例添加到尿素熔融液中,采用模拟喷浆造粒的方法,制备3类增效尿素。通过风化煤与添加剂、尿素与增效尿素红外光谱特征对比发现:风化煤经过活化后,碳单键数量降低,碳链缩短,活性腐植酸HA类提取物出现活性官能团,FR类除单键数量减少和碳链缩短外,生成部分胺、酰胺结构;增效剂与尿素在反应过程中,出现了三键和累积双键破坏、稳定性复合物形成、碳链缩短、双键结构增加等变化,但不同类型增效剂对产品红外光谱特征影响存在差异。     

不同基团对烯烃亲电加成的影响

通过分析烯烃双键碳上连的不同基团对烯烃亲电加成反应的规律,从本质上掌握亲电加成反应的规律。     

茉莉酸相关化合物对水稻颖花开放的诱导效应

研究了茉莉酸结构类似物、功能类似物以及茉莉酸生物合成的前体物对水稻颖花开放的诱导效应.结果表明,以下结构对茉莉酸类诱导开颖具有重要作用:①一个完整的环戊烷酮结构,因为C-6上的羰基被换成羟基后颖花开放诱导活性大大降低;②C-7上的戊稀侧链,因为C-9与C-10之间双键的加氢饱和使活性降低,而C-12的羟化更使其完全失活;③C-3上的乙酸或其甲酯侧链,因为乙酸侧链的加长使其活性降低,而且乙酸侧链被已酸取代所形成的OPC-6:0的活性是来自其本身还是来自其转化形成的JA仍有待进一步的研究.     

Xenon Oxyfluoride

The incomplete hydrolysis of XeF(6) has been used to prepare a xenon oxyfluoride, XeOF(4). The latter is a clear, colorless liquid, freezing at -41 degrees C. The infrared and Raman spectra show that the XeOF(4) molecule has a fourfold symmetry axis. The large Xe-O stretching force constant indicates the Xe-O bond has appreciable double bond character.     

Complete photo-induced breakup of the H2 molecule as a probe of molecular electron correlation

Despite decades of progress in quantum mechanics, electron correlation effects are still only partially understood. Experiments in which both electrons are ejected from an oriented hydrogen molecule by absorption of a single photon have recently demonstrated a puzzling phenomenon: The ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state. Here, we report a complete numerical solution of the Schr?dinger equation for the double photoionization of H2. The results suggest that the distribution of photoelectrons emitted from aligned molecules reflects electron correlation effects that are purely molecular in origin.     

Tetramesityldisilene, a stable compound containing a silicon-silicon double bond

Irradiation of 2,2-bis(2,4,6-trimethylphenyl)hexamethyltrisilane in hydrocarbon solution produces tetramesityldisilene, which can be isolated as a yellow-orange solid stable to room temperature and above in the absence of air. Like the olefins of carbon chemistry, tetramesityldisilene undergoes addition reactions across the silicon-silicon double bond.     

Sweat in schizophrenic patients: identification of the odorous substance

The substance causing the peculiar odor in sweat of schizophrenic patients has been isolated and identified as trans-3-methyl-2-hexenoic acid by gas chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy. The natural and the synthetic compounds were cleaves across the double bond to give 2-pentanone and oxalic acid, thereby confirming the structure.     

离子注入水稻干种子光声谱分析

<正> 中国科学院等离子体物理所与安徽省农科院水稻研究所合作,利用高技术——离子注入——于水稻种子诱变育种生物效应的研究,在物理学与生命科学的交叉上做出了有益的尝试。两年多的研究表明:离子注入水稻种子诱变,较其他方法诱变有突变率高、突变谱广的特点。作者认为:荷能粒子注入到水稻干种子中去,不仅有能量交换过程,引起生物体内很强的生理生化反应,而且发生了质量沉积过程,沉积的粒子同生物体分子基团直接键合,改变了生物体原来的分子基团结构。这一切,都会引起水稻种子遗传基因的突变。     

核桃举肢蛾性信息素腺体提取物的成分分析

利用气相色谱技术对核桃举肢蛾性信息素腺体提取物进行分析发现:核桃举肢蛾性信息素是13碳和16碳的不饱和醇或酯的混合组分,但其双键位置有待进一步合成更多13碳和16碳的标准化合物进行GC分析及GC-MS分析鉴定。     

Brain edema: induction in cortical slices by polyunsaturated fatty acids

The presence of polyunsaturated and saturated fatty acids in leukocytic membranes prompted study of their possible role in the induction of brain edema. Polyunsaturated fatty acids including sodium arachidonate, sodium linoleate, sodium linolenate, and docasahexaenoic acids induced edma in slices of rat brain cortex. This cellular edema was specific, since neither saturated fatty acids nor a fatty acid containing a single double bond had such effect.     

基于离散元法玉米秸秆双层粘结模型力学特性研究

针对玉米秸秆外表皮与内穰力学特性存在显著差异问题,建立离散元玉米秸秆双层粘结双峰分布模型,通过力学试验与虚拟仿真试验对比,标定玉米秸秆外表皮和内穰力学参数,校正离散元模型,探究玉米秸秆力学特性.结果表明,采用离散元Hertz-Mindlin with bonding颗粒接触方法可建立玉米秸秆双层粘结双峰分布模型.完善DEM方法建立玉米秸秆颗粒粒度随机分布的双层粘结模型方法.通过力学试验得出青贮玉米秸秆外表皮弹性模量和剪切模量分别为982.52和387.58 MPa,青贮玉米秸秆内穰弹性模量和剪切模量分别为28.64和8.13 MPa,外表皮木质部与内穰纤维部力学特性差异显著.计算得出外表皮-外表皮、外表皮-内穰、内穰-内穰之间粘结参数.通过单轴压缩试验,剪切与虚拟仿真试验对比验证离散元模型可靠性.文章所建立玉米秸秆双层粘结双峰分布离散元模型表征两者力学特性差异,为青贮玉米饲料数值化研究提供理论依据.     

Chemical self-defense by termite workers: prevention of autotoxication in two rhinotermitids

Soldiers of the lower termites Prorhinotermes simplex and Schedorhinotermes lamanianus (Isoptera, Rhinotermitidae) have electrophilic contact poisons used in colony defense. Workers of these termites die when exposed to the defense secretion of the other species, but survive when exposed to chemicals from conspecific soldiers. Detoxication occurs by an initial substrate-specific reduction of the electron-deficient double bond of the nitroalkene (Prorhinotermes simplex) or vinyl ketone (Schedorhinotermes lamanianus) followed by complete catabolism to acetate.     

反式脂肪酸的危害及其检测方法的研究现状

反式脂肪酸是一种至少含有1个反式构型双键的不饱和脂肪酸。越来越多的研究表明,大量食用含有反式脂肪酸的食物会导致多种疾病的发生。反式脂肪酸日益成为人们研究的热点,科研工作者们正在不断开发用于反式脂肪酸检测的简便快捷的方法。就目前反式脂肪酸的来源、危害以及检测分析方法进行了综述。     

Asymmetric hydrogenation of unfunctionalized, purely alkyl-substituted olefins

Asymmetric hydrogenation of olefins is one of the most useful reactions for the synthesis of optically active compounds, especially in industry. However, the application range of the catalysts developed so far is limited to alkenes with a coordinating functional group or an aryl substituent next to the double bond. We have found a class of chiral iridium catalysts that give high enantioselectivity in the hydrogenation of unfunctionalized, trialkyl-substituted olefins. Because these catalysts do not require the presence of any particular functional group or aryl substituent in the substrate, they considerably broaden the scope of asymmetric hydrogenation.     

A stable silicon(0) compound with a Si=Si double bond

Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.     

基于键合图理论的间歇式精准喷施系统喷雾压力动态特性

为解决传统喷施系统农药利用率低的问题,设计基于双阀控制的精准间歇式喷施系统。针对喷施系统多能域相互耦合的特点,采用键合图方法建立系统状态方程,并基于20-sim键合图仿真平台进行仿真计算,得到不同压力工况下的喷雾压力动态特性。试验研究喷施系统在0.2、0.3和0.4MPa压力下喷头的喷雾压力动态特性,并采用轮廓分析统计学方法研究仿真结果的准确率。试验结果表明:车速为0.8m/s,作物间距20cm,作物茎叶覆盖直径10cm情况下,间歇式精准喷施系统的喷雾准确率89%,仿真计算与试验结果最大相合置信水平为0.088。基于键合图理论建立的数值模型能够很好的预测间歇式精准喷施系统的喷雾压力动态特性。