Peroxide-mediated efficient addition of cycloalkanes to imines

A novel direct addition of cycloalkanes to imines mediated by peroxide was developed. The reaction tolerates a wide range of functionalities as well as aqueous conditions.     

Adsorption kinetics and dynamics of small organic molecules on a silica wafer: Butane, pentane, nonane, thiophene, and methanol adsorption on SiO2/Si(1 1 1)

The adsorption kinetics (by thermal desorption spectroscopy) and adsorption dynamics (by molecular beam scattering) have been determined for a number of alkanes, methanol, thiophene, and water on a silica wafer—SiO₂/Si(1 1 1). No indications for bond activation were present, i.e., all probe molecules adsorb molecularly obeying 1st order kinetics. The coverage-dependent heat of adsorption has been determined accordingly. The adsorption dynamics are precursor-mediated with Kisliuk-like shapes of the adsorption probabilities at low impact energies and adsorbate-assisted adsorption at large impact energies.     

催化剂活性位本质和构效关系的模型催化研究

明确催化剂的活性位本质和构建多相催化的结构和反应性能之间的准确关系是催化基础研究的重点,表面科学研究基于丰富的表征测试手段能够较好地在分子原子水平测定表面结构以明确催化剂活性位本质,并通过高压原位反应池测定相关催化反应性能,获得较可靠的催化剂构效关系。本文简要总结了近年来本人参与的几个模型催化研究例子,包括贵金属表面上CO和烷烃催化氧化的活性表面、纳米Au膜的制备和CO氧化的催化活性位、VO_x/Pt(111)上丙烷氧化的协同作用、Au Pd合金上醋酸乙烯酯合成Au的助催化作用、模型氧化物上纳米Pt的庚烷脱氢环化制甲苯的粒径关系等,以及相关模型催化研究技术的进展。     

原子距边矢量、三键数与烷烃的13C NMR化学位移

提出一个新的原子描述符-原子距边矢量(μ)来表达碳原子在烷烃中所处环境信息,用该矢量和三键数作为参数与烷烃碳原子(含2~9个碳原子共63个烷烃分子,计326个不等价碳原子)的¹³C NMR化学位移相关联,得到的多元线性回归分析结果为:标准偏差S仅0.9629ppm,相关系数R为0.9957.用所得线性方程预测得精度为:误差在1.0,1.5和2.0ppm以内的分别占83%,90%和95%.     

NaIO4-mediated C-H activation of alkylbenzenes and alkanes with LiBr

NaIO₄ oxidizes lithium bromide efficiently under acidic conditions to functionalize alkylbenzenes and alkanes and produce the corresponding bromo and acetoxy derivatives in excellent yields. The protocol also demonstrates the direct conversion of cyclohexane into trans-1,2-dibromocyclohexane in moderate yield.     

Assessment of competing mechanisms of the abstraction of hydrogen from CH4 on Li/MgO(0 0 1)

First-principles calculations based on the density functional theory (DFT)-pseudopotential method with plane wave basis sets are used to study the energetics of H abstraction from CH₄ on the Li-doped MgO(0 0 1) surface. Experimental work has led to the proposal of two competing mechanisms for the reaction: either direct interaction of CH₄ with an O⁻ hole state bound to the Li dopant, or interaction of CH₄ with a surface F-centre whose charge state is modified by the presence of the dopant. The calculations are performed in periodically repeated slab geometry, with attention given to system-size errors. For direct interaction with the hole state, the calculations indicate that the reaction is weakly endothermic, by about 0.2 eV, but for the F-centre mechanism it is endothermic by over 1 eV. Even allowing for likely DFT errors of a few tenths of an electron volt, this gives strong evidence against the F-centre mechanism.     

Effects of surface step on molecular propane adsorption

We have studied the effects of surface step on molecular propane adsorption using molecular-dynamics simulations and a model stepped surface, Pt(6 5 5). Incidences along the step edge (smooth azimuth) and perpendicular to the step edge with upstairs momentum (upstairs azimuth) and downstairs momentum (downstairs azimuth) are considered. In general, the surface step enhances the initial trapping probability of propane except for the downstairs incidences. The most efficient zone in facilitating adsorption is near the bottom of the surface step on the lower terrace where incident molecules experience stronger attraction and an “additional-layer” effect when crossing the step. The least efficient zone is the top of the surface step on the upper terrace due to an opposite “missing-layer” effect. Surface step also creates steric effects such that more incident molecules along the upstairs azimuth but significantly less molecules along the downstairs azimuth impact the step-bottom zone. The latter steric effect, a shadowing effect, undermines the high trapping efficiency of the step-bottom zone to cause the downstairs incidences to have the lowest trapping probabilities. While the shadowing effect can be enhanced by larger incident angles and lower incident energies, the other steric effect on the upstairs incidences is relatively insensitive to the incident energy. Overall, the influence of surface step on molecular adsorption diminishes at low incident energies and large incident angles because longer contact times and less normal momenta result in high trapping probability across the entire stepped surface.     

用亚图参数与回归技术估计和预测烷烃的核磁共振碳谱

系统研究了分子建模在波谱分析中的应用.采用多元线性回归算法(MLR)估计和预测了60余种烷烃的碳谱化学位移.烷烃中碳原子由十余种对应于所谓根亚树的相嵌频率描述子所决定.这些描述子等于由2~5个碳原子组成的更小结构骨架组成.说明了所用描述子作为很有用的工具可适当地描述烷烃中碳所处微观环境.同时还比较了与神经网络的计算结果.     

Mass Spectral Interaction between the Functional Groups of Multiply Substituted Alkanes

The mass spectral decomposition of di- and polyfunctional alkanes is characterized essentially by two, fundamentally different reactions: On the one hand the structures of the fragment ions are determined by separated degradation of each functional group; on the other hand, however, a relatively large number of fragment ions result from the combined action of two or even more functional groups. This special type of fragmentation has become an important topic in today's mass spectral research. In the present progress report an attempt has been made to summarize the results obtained so far.     

Chromatographic chemical characterization of solvent refined coal I and II liquids for toxicological testing

Summary High resolution gas chromatography and gas chromatography/mass spectrometry were employed to determine the components in samples of solvent refined coal (SRC) II naphtha, middle distillate, heavy distillate, and fuel oil blend and SRC-I light oil, wash solvent, and process solvent in concentrations higher than approximately 0.5%. Quantitation was based on the addition of n-alkane internal standards and peak area response of a flame ionization detector with the use of fused silica and glass capillary columns coated with SE-52 and SF-96. The major differences in the SRC-I and II materials were the molecular weight ranges and sizes of the chemical components found in the products, an effect of the differences in the nominal boiling ranges of the materials. Alkanes, alkenes, hydroxylated aromatics, hydrogenated and polycyclic aromatic hydrocarbon ring systems, and alkylated derivatives of the above were found in greatest concentration in the unfractionated materials. Sulfur and nitrogen heteroatomic species were in greates concentration in the higher nominal boiling range materials. A major purpose of these investigations was to develop a method to obtain data on the composition of these complex sample matrices for use in designing studies for toxicological evaluation of these materials.