改进的Hückel分子轨道方法(Ⅴ)——关于若干超共轭体系的MHMO计算

我们通过用三种HMO(诱导、杂原子、共轭)模型处理若干超共轭体系,发现所得结果不服从按键型预示的规律,与实验结果的符合很差。因此我们提出一种改进的HMO方法——甲基超共轭模型,处理了若干超共轭体系,结果比较满意。     

共轭与非共轭不饱和酯的振动光谱及其EHMO研究

用FT-IR、Laser Raman光谱和EHMO计算研究了β-羟基酯脱水反应, 发现反应产物α、β-烯酯和β、γ-烯酯两类共轭与非共轭构异体的分布, 主要取决于β-碳上的取代甲基超共轭效应, 该反应是受动力学控制的。     

共轭体系中极性交替现象在有机反应中的应用

电子效应和空间效应是影响有机反应的重要因素,共轭体系中极性交替的特点在共轭二烯与α,β-不饱和醛酮的1,2-加成和1,4-加成反应、苯环上的亲电取代反应等有机反应中表现明显,掌握共轭体系中极性交替的特点对于此类有机反应的学习可以起到事半功倍的效果。     

巯基/(甲基)丙烯酸(甲基)烯丙酯光固化特性

通过对羧酸盐法改进后合成同时含有高活性的丙烯酸酯型C=C和低自由基活性的烯丙基型C=C的烯类单体(甲基)丙烯酸(甲基)烯丙酯,以实现(甲基)丙烯酸酯类紫外光固化与巯/烯光聚合结合在二元体系中;并以1173为光引发剂,利用实时红外(RT-IR)跟踪此类烯烃与三羟甲基丙烷三(3-巯基丙酸酯)(TMMP)光固化过程,探究烯烃结构、光强和引发剂用量对含有两类碳碳双键的烯类单体与巯基化合物二元体系的光固化行为的影响.研究发现,这类二元巯-烯光聚合反应中均有(甲基)丙烯酸酯双键的反应活性最大,(甲基)烯丙基次之,巯基的反应活性最小;甲基取代在烯烃的不同C=C上,对巯-烯光固化特性影响不同,甲基取代在烯丙基C=C上比甲基取代在丙烯酸基C=C上对巯-烯光固化行为影响更大;巯基最终转化率随甲基取代基数目增多而减少;丙烯酸甲基烯丙酯体系中两类双键(丙烯酸型/甲基烯丙基型)反应活性几乎相同且均具有高的转化率.     

共轭体系的分类及结构特征

共轭体系是相邻原子或基团的电子轨道发生重叠,电子发生离域运动、体系能量降低、键长平均化的结构单元,具有独特的电子效应——共轭效应。共轭效应是有机化学课程的重点和难点内容,掌握共轭体系的分类及结构特征,对理解化合物的共轭效应以及物理化学性质具有重要作用。但一般的有机化学教材及文献对此没有系统的介绍。本文通过实例、价键(valence bond, VB)理论以及分子轨道(molecular orbital, MO)理论中的电子轨道示意图,阐明广义和狭义共轭体系的内涵,以及狭义共轭体系、超共轭体系、价键共轭与空间共轭的分类和结构特征。     

含羟基镱单酞菁配合物的定域化分子轨道研究

用定域化INDO法讨论了含羟基镱单酞菁配合物(YbPcOH)分子的几何构型和电子结构。YbPcOH分子为金字塔形结构,Yb突出在酞菁平面外的中心轴上(h=1.8),Yb-O键长约为2.5,O-H也沿中心轴取向。正则波函数的前线轨道呈现π键性质。定域分子轨道分析表明,酞菁骨架中16轮烯型的共轭体系在配位后共轭程度降低,形成多个较小的共轭结构。金属和配体之间的化学键主要为共价性质,Yb的5d轨道对共价键有主要贡献,4f轨道则不参与成键。     

烯丙基硅烷的一步法合成研究

采用一步合成方式,将3-溴丙烯与金属镁在以甲苯和供电子溶剂(乙醚或THF)构成的混合溶剂中进行反应,继而与四氯化硅反应,成功合成了四烯丙基硅烷,其产率在乙醚与3-溴丙烯的摩尔比为4(V甲苯/V乙醚=1·1)时达到极值,超过了91%。研究同时发现,选择THF代替乙醚时,同样在THF与3-溴丙烯的摩尔比为4(V甲苯/VTHF=1·7)时产率达到极值(63·12%)。本过程可提高产率,降低成本,是一条好的生产四烯丙基硅烷的路线。     

钌催化末端炔丙醇经亚丙二烯基卡宾中间体氧化产生亚甲基烯酮:α,β-不饱和羧酸衍生物的合成（英文）

报道了钌催化末端炔丙醇经亚丙二烯基卡宾中间体氧化产生亚甲基烯酮合成α,β-不饱和羧酸衍生物的高效方法.机理研究实验表明,催化剂CpRuCl(PPh_3)_2/NaBPh)4和末端炔丙醇反应产生的钌亚丙二烯基卡宾与吡啶氧化物发生氧转移,生成高活性的亚甲基烯酮中间体,再发生亲核加成得到α,β-不饱和产物.该反应提供了一个机理上完全不同于传统方法的合成α,β-不饱和羧酸衍生物的新策略,是炔丙醇催化转化的一种新颖方法,也是金属亚丙二烯基催化的一种新途径.     

三岔共轭体系中的结构效应-氮杂查耳酮类与碘乙烷的反应动力学

本文用电导法研究了4＇-苯多烯酰基吡啶化合物4 pOnB中吡啶基的化学活性。反应动力学数据表明,4pOnB与碘乙烷在丙酮溶液中为二级反应,相关系数r均大于0.995。共轭主链的长度(n)对反应活化能的影响不大,这表明三岔共轭体系中基干结构的共轭作用不能通过三岔点影响吡啶环上氮原子的电子云密度。三岔共轭体系中较短的一支分岔与三岔体系中的共轭基干结构是互相隔离的,仅起代基作用。     

丙烯酰胺-丙烯酰氧乙基三甲基氯化铵共聚合的竞聚率测定

采用溶液聚合制备了新型阳离子共聚物--聚丙烯酰胺基-丙烯酰氧乙基三甲基氯化铵(P(AM-DAC)),采用滴定法测定了其阳离子共聚物的阳离子度.分别采用Fineman-Ross 法、Kelen-Tudos 法和Yezrielev-Brokhina-Roskin法计算出单体竞聚率.结果表明,KT法和YBR法计算较为准确,丙烯酰氧乙基三甲基氯化铵和丙烯酰胺的竞聚率分别为rDAC=0.383 5,rAM=2.286 4.     

Supramolecular origins of product selectivity for methanol-to-olefin catalysis on HSAPO-34.

Ethylene selectivity in methanol-to-olefin (MTO) catalysis is related to the number of methyl groups on benzene rings trapped in the nanocages of the preferred catalyst HSAPO-34. By correlating the time evolutions of the catalysts' 13C NMR spectra and the volatile product distribution following abrupt cessation of methanol flow, we discovered that (in the absence of other adsorbates) propene is favored by methylbenzenes with four to six methyl groups but ethylene is predominant from those with two or three methyl groups. We substantially increased ethylene selectivity by operating at lower methanol partial pressures or higher temperatures, either of which reduces the steady-state average methyl substitution. As a step toward a kinetic analysis of the MTO reaction on HSAPO-34, we treated each nanocage with a methylbenzene molecule as a supramolecule capable of unimolecular dissociation into ethylene or propene and a less highly substituted methylbenzene. Addition of a water molecule to a nanocage containing a methylbenzene produces a distinct supramolecule with unique properties. Indeed, co-feeding water with methanol significantly increased the average number of methyl groups per ring at steady state relative to identical conditions without additional water, and also increased ethylene selectivity, apparently through transition state shape selectivity.     

Influence of Molybdenum on Ceria Activity and CO2 Selectivity in Propene Total Oxidation

A total oxidation of propene into CO₂ is obtained on pure ceria at 673 K. However, in the presence of molybdenum, propene can be partially oxidized at room temperature. The Electron Paramagnetic Resonance (EPR) indicates changes in the oxidation state of molybdenum occurring upon interaction with propene. It has been found that the concentration of Mo(V) influences the propene conversion. The interaction between propene and molybdenum leads to the formation of surface species that, depending on the strength of their bonding to the surface, can be decomposed to ethene or coke. These results have been confirmed by infrared (FTIR) study. The oxidation reaction of propene is in competition with that of coke or ethene deposit on the catalyst surface, which can explain the decrease of the catalyst activity and selectivity in the presence of high molybdenum loadings.     

苯与丙烯在β分子筛上吸附行为的蒙特卡罗研究

采用巨正则统计系综蒙特卡罗模拟方法研究了β分子筛上苯与丙烯分子的吸附行为. 由分子筛内吸附质粒子云分布可知, 在100 kPa时, 丙烯在分子筛上的吸附量要远远大于苯的吸附量. 由吸附相互作用能分布来看, 苯与分子筛之间相互作用能比丙烯与分子筛之间的相互作用能更负, 这就使苯分子的吸附相对于丙烯分子稳定. 相对而言, 温度变化对丙烯吸附影响远大于对苯吸附的影响, 如100 kPa时, 温度由298 K升高至443 K导致丙烯分子吸附量明显减少, 由每8个晶胞吸附98个丙烯分子减少到80个; 而对苯分子吸附却没有显著的影响. β分子筛上存在着苯和丙烯的竞争吸附, 并且吸附分子之间存在相互作用使两者与分子筛之间的相互作用能分布改变. 在压力范围1×10－3～5.0 kPa, 不同温度下苯与丙烯在分子筛内吸附等温线的模拟结果表明, 在较高温度、较低压力下丙烯的吸附量要小于苯的吸附量.     

Two New On-Purpose Processes Enhancing Propene Production: Catalytic Cracking of C4 Alkenes to Propene and Metathesis of Ethene and 2-Butene to Propene

A brief review of the work carried out at Dalian Institute of Chemical Physics, Chinese Academy of Sciences for development of two new on-purpose processes enhancing propene production is presented. This includes the processes of catalytic cracking of C₄ alkenes to propene and metathesis of ethene and 2-butene to propene, by which the large amounts of the C₄ recourses from the petrochemical can be upgraded and the severity of demand for propene can be lessened.     

Theoretical studies on the ene reaction mechanisms of propene and cyclopropene with ethylene and cyclopropene: concerted or stepwise

The potential energy surfaces of the ene reactions of propene and cyclopropene with ethylene and cyclopropene were studied by ab initio molecular orbital (MO) methods. The reaction mechanisms were analyzed by CiLC method on the basis of CASSCF MOs. The concerted and stepwise reaction pathways of the ene reaction of propene with ethylene as the parent reaction were located. The energy barrier of the stepwise process is about 4 kcal/mol lower than that of the concerted one. The other reactions can be found only the stepwise mechanism. Although the endo-type reaction of propene with cyclopropene, where cyclopropene is the enophile, probably occurs through a one-step process, the mechanism is divided into the CC bond formations and the hydrogen migration as a stepwise reaction. The CiLC-IRC analysis of the concerted process of propene with ethylene shows the different patterns of the electronic state variation for the CC bond formation/breaking and the hydrogen migration.     

改性对β沸石表面酸性及丙烯水合醚化反应性能的影响

采用浸渍法和离子交换法，制备出一系列改性β沸石催化剂，考察了改性剂对β沸石表面酸性及丙烯水合醚化反应性能的影响。结果表明：硼、锌、铝改性可以提高β沸石的L酸中心，磷、镧、铈改性后β沸石的B酸中心增加。催化剂的B酸和L酸中心与丙烯转化率和异丙醚选择性之间存在着一定的对应关系：B酸量增加有利于提高丙烯转化率，L酸量增加有利于提高异丙醚的选择性。合适的B／L酸比例是催化剂同时具有高活性和高异丙醚选择性的关键。     

Adsorption of benzene and propene in zeolite MCM-22: a grand canonical Monte Carlo study

The GCMC (grand canonical Monte Carlo) simulation technique was used to predict the competition adsorption characteristics of benzene and propene in different pore systems of MCM-22. The nine-site model of benzene was used, which proved to be effective and efficient. The zeolite was divided into three adsorption sites following a simulated annealing method. It is found that benzene and propene have the same preferential adsorption site and a similar adsorption order in different sites. Moreover, the pure and mixture isotherms of the three sites are drawn. From the isotherms, we obtained a selectivity reversal of the mixture isotherms of benzene and propene in different sites. It is also noted that the competition adsorption in the three adsorption sites for the two adsorbates can fall into three successive steps and the adsorption order of propene in mixture in these three sites is S3→S1→S2. A new model is presented to predict the benzene and propene adsorption equilibrium in MCM-22. This approach yields better multicomponent equilibrium predictions than ideal adsorbed solution theory (IAST). Isotherms at different mole fraction of benzene in gas phase indicate an advantage to increase the feed radio of benzene and propene. Thus, this work is helpful for a better understanding of the adsorption mechanism of benzene and propene in MCM-22 and hence the relation of the catalytic properties of the zeolite to its structure.     

A Duffing oscillator algorithm to detect the weak chromatographic signal

Based on the Duffing equation, a Duffing oscillator algorithm (DOA) to improve the signal-to-noise ratio (SNR) was presented. By simulated and experimental data sets, it was proven that the signal-to-noise ratio (SNR) of the weak signal could be greatly enhanced by this method. Using signal enhancement by DOA, this method extends the SNR of low concentrations of methylbenzene from 2.662 to 29.90 and the method can be used for quantitative analysis of methylbenzene, which are lower than detection limit of an analytical system. The Duffing oscillator algorithm (DOA) might be a promising tool to extend instrumental linear range and to improve the accuracy of trace analysis. The research enlarged the application scope of Duffing equation to chromatographic signal processing.     

Propene adsorption sites in zeolite ITQ-12: a combined synchrotron X-ray and neutron diffraction study

The adsorption site of propene in the small-pore, pure silica zeolite [Si24O48]-ITW-ITQ-12 has been characterized via Rietveld refinement of the crystal structure of propene-loaded ITQ-12 on the basis of synchrotron X-ray and neutron diffraction data taken at 298 K. The structure can be described with a monoclinic unit cell having Cm symmetry and unit cell parameters a = 10.436 angstroms, b = 15.018 angstroms, c = 8.855 angstroms, beta = 105.74 degrees, and volume = 1335.9 angstroms3. Four-fold disordered adsorption sites that are nearly equivalent relative to the cage's 2/m pseudosymmetry are located near the center of each ellipsoidally shaped [4(4)5(4)6(4)8(4)] cage. At this site, the adsorbed propene molecule lies on a plane close and approximately parallel to the equatorial plane of the cage and is aligned with its methylene group pointing toward the pore's eight-ring window. The refined propene concentration, 1.8 per unit cell content, is close to one propene molecule per [4(4)5(4)6(4)8(4)] cage and the amount observed in adsorption experiments at 298 K and 1 atm propene partial pressure.     

Periodic density functional theory study of propane oxidative dehydrogenation over V2O5(001) surface

The oxidative dehydrogenation (ODH) of propane on single-crystal V(2)O(5)(001) is studied by periodic density functional theory (DFT) calculations. The energetics and pathways for the propane to propene conversion are determined. We show that (i) the C-H bond of propane can be activated by both the terminal and the bridging lattice O atoms on the surface with similar activation energies. At the terminal O site both the radical and the oxo-insertion pathways are likely for the C-H bond activation, while only the oxo-insertion mechanism is feasible at the bridging O site. (ii) Compared to that at the terminal O site, the propene production from the propoxide at the bridging O site is much easier due to the weaker binding of propoxide at the bridging O. It is concluded that single-crystal V(2)O(5)(001) is not a good catalyst due to the terminal O being too active to release propene. It is expected that an efficient catalyst for the ODH reaction has to make a compromise between the ability to activate the C-H bond and the ability to release propene.