前线分子轨道(FMO)在有机电环化反应中的应用

本文通过电环化反出实例,应用前线轨道理论清楚地解释了该反应中的高度立体选择性问题。阐述了前线分子轨道对探讨有机反应机理和预测产物构型的重要作用。     

电环化反应规律与教学实践

电环化反应是周环反应的一类,对于理解和掌握分子轨道理论非常有帮助,掌握了不同P电子的分子轨道形状和能量,但快速准确得到电环化反应立体结构产物也是不易的。分子轨道是原子轨道的线形组合,采用前线轨道理论解释电环化反应机理,并根据前线轨道对称性判别反应中分子轨道的旋转方式,从而得到立体专一性结构的产物。     

计算化学和虚拟仿真技术在制药工程专业有机化学教学中的应用实践

随着现代科技的迅速发展,计算化学和虚拟仿真技术在基础化学教学中的应用越来越广泛.借助于计算化学和虚拟仿真技术,可将有机化学中抽象的分子结构、分子轨道、反应机理等直观化,从而使相关知识点更容易理解和掌握.本文以绝对构型的判断、构型与构象的区分、反应机理的动态演示为例,对计算化学和虚拟仿真技术在制药工程专业有机化学课程教学...     

有机教材反应机理描述及其存在的问题与解决办法

反应机理是各个基元反应的集成。化学反应的本质是旧键的断裂与新键的形成。因此,无一个基元反应不涉及共价键改变的电子转移过程。电子转移方向必定是由电子源转向电子穴。如果将电子与轨道看作特殊的基团,那么,每一个基元反应可看作是一个简单的取代反应。本文对有机教材反应机理描述存在的问题进行剖析并提出解决办法,以便有机反应机理描述可以得到统一,有利于有机机理的学习与理解。     

Multiwfn在分子轨道理论教学中的应用

分子轨道理论是学生在学习无机化学过程较难理解和掌握的内容,文章使用gaussian和multiwfn软件对分子轨道成分和键级的计算,绘制了分子轨道能级图,并将这部分内容形象直观地呈现出来,有利于增加学生学习的主动性和积极性,提高教学质量.     

羧基羟肟酸浮选一水硬铝石高岭石的理论研究

通过密度泛函和分子动力学模拟方法,计算了药剂分子与一水硬铝石和高岭石的相互作用。得到了分子的稳定构型,最低空轨道,最高占据轨道,体系结合能,相互作用的相关联函数等数据.从理论角度解释药剂与矿物作用的机理。     

甲醇制烯烃、二甲醚反应机理研究新进展

正国家能源集团集团公司教授级高级工程师贺振富,利用杂化轨道理论研究"甲醇制烯烃反应机理研究"和"甲醇制二甲醚反应机理研究"等相关工作中发现了中间产物C↑↓~〇H_2,定义为He-form,C↑↓~〇H_2结构中碳原子外层有一对孤对电子和一个空轨道,↑↓代表孤对电子,〇代表空轨道。C↑↓~〇H_2是构成烯烃和醚类化     

膦铑催化剂对丁二烯系共聚物中C=C键加氢的模拟研究

采用分子模拟方法研究对C=C键的催化加氢过程,构建了各基元反应中的分子模型,并通过构建动力学模型计算了各分子所具有的能量,从而计算出各基元反应的能量变化,揭示了各基元反应的机理,最终解释三苯基膦氯化铑催化剂在丁二烯系共聚物中对C=C键催化加氢的反应机理。     

利用简化分子轨道对称性的表示方法——前线轨道奇偶性解释周环反应的立体化学

本文提出了新的分子轨道对称性的表示方法——-前线轨道的奇偶性来快速准确的确定周环反应的立体化学,任何开链共轭多烯烃:当分子轨道为奇数(ψ1、ψ3…)时,两端位相相同;当分子轨道为偶数(如ψ2,ψ4…)时,两端位相相反。它可用于解释Woodward一Hoffmann规则和周环反应的机埋,简单易懂,在周环反应的教学中发挥了较好的作用。     

密度函数方法研究第一副族过渡金属二聚物的电子结构和光谱特性

密度函数理论计算了 Cu2 ,Ag2 和 Au2 二聚物的电子结构和光谱性质。结果表明 ,随着电子数的增加 ,相对论效应也在增加。使用 ZORA相对论方法可以得到可靠的电子结构。应用 B3 LYP作为交换 -相关函数 ,Cu2 ,Ag2 和 Au2 三个二聚物分子得到了相同的轨道能级顺序。在该族双分子化合物中全充满的 d电子不是完全惰性的。d电子在这三个分子当中对前线分子轨道的贡献也是完全不同的。同时由于 d电子和 s电子强相互作用引起 d型分子轨道的向上移动和 S型分子轨道向下移动。结果还表明 ,对于 Cu2 和 Au2 来说 ,d-型分子轨道和 S-型分子轨道的能级是非常接近的 ,这导致上述轨道在激发状态下很多相似的特性。而对于 Ag2 来说 ,d-型分子轨道和 S-型分子轨道能级较大的差表明 d电子对前线分子轨道只有极其微小的贡献。通过 TDDFT和 DSCF方法 ,确定和归属了低激发态的光谱项 ,并通过 s-和 d电子对这些激发态的贡献解释了光谱项的性质。目前研究得出的计算结果与实验数据非常吻合     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.     

Highly moisture-proof polysilsesquioxane coating prepared via facile sol-gel process

A highly moisture-proof polysilsesquioxane coating was obtained from a new bis-silylated precursor, which was synthesized from 3-aminopropyltriethoxysilane (APTES) and m-xylylene diisocyanate (m-XDI) in tetrahydrofuran (THF) and verified by ¹H MAS NMR. For direct comparison purposes, an SiO₂ coating was also prepared by the Stöber method using tetraethoxysilane (TEOS) as the reactant. Interestingly, the coating obtained from the polysilsesquioxane sol exhibited a much higher moisture resistance capability than its counterpart, which was attributed to its more compact feature between nanoparticles as characterized by N₂ absorption experiment and transmission electron microscopy (TEM). Furthermore, its high transparency of about 92% showed potential for application in the protection of optical crystals.