有机结构波谱中二级结构效应机理的新探索（Ⅱ）——π→p共轭效应和超共轭效应

当H原子和形成π键的原子相连时,π成键轨道和π反键轨道与H原子的2P空轨道相互作用,组成新的分子轨道,这样的结构称为π→P共轭体系,由π→P共轭作用引起的不饱键一系列性质的变化,称之为π→P共轭效应。     

超共轭效应解析与探讨

一、引言超共轭效应在有机化学中广泛存在,由于它在液相中对有机反应的影响有时表现的很微弱,往往被溶剂化效应所掩盖,因此长期以来引起人们的怀疑和争论。但是超共轭效应的提出确实解释了许多用诱导效应和共轭效应难以解     

共轭效应对有机反应的影响

共轭效应是共轭体系分子内的原子或原子团间的相互影响。与诱导效应一样也属于电子效应。所不同的是共轭效应的强弱只取决于共轭体系的化学结构,不会因共轭链的增长而削弱。它包括兀π-π、p-π共轭效应和σ-π、σ-p超共轭效应,其相对强弱为:π-π>p-π>>σ-π>σ-p。共轭效应通常通过影响反应物、中间体和产物的稳定性而对有机反应产生影响。     

丙烯和甲苯的超共轭效应的理论研究

用从头算对丙烯和甲苯2个超共轭体系进行计算,结果表明甲基上氢原子参与超共轭时,其碳氢键键长增大,氢上集居数减少,丙烯、甲苯的甲基旋转势垒为7.61及0.096 kJ/mol.超共轭基作用相当于一带有孤对电子参与共轭之杂原子,超共轭体系不同构型稳定性可用M=sum from i=1 to 3(sinθ_i[sin(θ_i-α)+sinα])来表征。     

超共轭作用的立体化学

介绍了超共轭作用对决定化合物和反应活性中间体的构型与构象所起的作用并举例说明了超共轭作用对有机反应立体化学的影响.     

氮酸和氮酸酯的结构和稳定性的相关性

在研究了迄今已知的一百多个氮酸和氮酸酯的结构特点和稳定性的基础上 ,运用共轭体系中电子效应的平衡理论 ,结合对分子结构类型的划分 ,提出了氮酸和氮酸酯的结构和稳定性关系的经验性规则 ,并且预言稳定的氮酸和氮酸酯应具有满足电子效应匹配原则的C类型的分子结构 .     

基团共轭效应的经验标度

本文以一取代苯为基本模型,假设取代基对苯环间位和对位上质子的诱导效应大致相等,且间位上的共轭效应受阻,则对位上质子的化学位移(δ_p)与间位上质子的化学位移(δ_m)之差与取代基的共轭效应成正比。因此,共轭效应强度R_H可由下式求得:R_H=1.6(δ_p-δ_m)利用此式,作者计算了一些常见的基团的共轭效应强度,其结果与文献报道值颇为一致,且表现出明显的变化规律。     

有机化学教学中使用共振式描述超共轭效应的探索

有机化学教学中通常使用分子轨道理论和价键理论中的共振论来描述π轨道的共轭效应,而对于类似的σ轨道的超共轭效应,通常只用轨道理论来描述,而基本不采用价键理论中的共振式描述。尝试用共振式来描述σ键的超共轭效应,发现不仅能够获得清晰易懂的图像,还能将有机化学中多个跨章节的知识点联系在一起,有利于知识的融会贯通,以及对电子结构和共振论的深入理解。     

有机结构波谱中二级结构效应机理的新探索(Ⅱ)

当H原子和形成π键的原子相连时，π成键轨道和π     

共轭效应和芳香性本质的争论和它们的历史发展

“共轭效应是稳定的”是有机化学的最最基本原理之一。但是,自30年代起,键长平均化,4N＋2芳香性理论,苯环D~6~h构架的起因,分子的构象和共轭效应的因果关系,π-电子离域的结构效应等已经受到了广泛的质疑。其中,最引人注目的是Vollhardt等合成了中心苯环具有环己三烯几何特征的亚苯类化合物,Stanger等合成了键长平均化,但长度在0.143～0.148nm的苯并类衍生物。最近(1999年),Stanger又获得了在苯环中具有单键键长的苯并类化合物。在理论计算领域,争论主要表现在计算方法上,集中在如何将作用能分解成π和σ两部分。随着论战的发展,作用能分解法在有机化学中的应用不断地发展和完善,Huckel理论在有机化学中的绝对权威也受到了挑战。为此,简要地介绍了能量分解法的发展史,对kollma法的合理性提出了质疑。此外特别介绍了我们新的能量分解法,及在共轭效应和芳香性的研究中的新观点和新的思维模式。     

Theoretical analysis of the internal rotation in aminoborane and borylphosphine

Using a recently proposed orbital deletion procedure and the block-localized wavefunction method, the rotational barriers in H₂BNH₂ and H₂BPH₂ are analyzed in terms of conjugation, hyperconjugation, steric effect and pyramidalization. With the zero-point energy corrections, the π-binding strengths in the planar H₂BNH₂ and H₂BPH₂ are both around 20 kcal/mol at the HF level using the 6-311+G** basis set. With the deactivation of the π atomic orbitals on the boron atom and the evolution from a planar structure to a 90°-twisted structure, the steric repulsion between the B‐H and the N‐H or P‐H is relieved and moreover, the negative hyperconjugation from the lone electron pair or pairs on the nitrogen or phosphorus atoms to the antibonding orbital ^χ* _B H ₂ of the BH₂ group stabilizes the twisted structure by 7.4(8.8) or 4.0(5.0) kcal/mol at the HF/6-31G*(6-311+G**) level. However, the repulsive interaction between the lone pair(s) and the two BH σ bonds is so prominent that the overall steric effect contributes 20.3(22.9) and 19.3(19.8) kcal/mol to the rotational barriers in H₂BNH₂ and H₂BPH₂ with the 6-31G*(6-311+G**) basis set. The present techniques and analyses may also give some clues to justify the parameterization in the empirical molecular mechanics methods. Received: 17 April 1998 / Accepted: 17 September 1998 / Published online: 1 February 1999     

Theoretical Study of the Structural Stability,Chemical Reactivity,and Protein Interaction for NMP Compounds as Modulators of the Endocannabinoid System

The cannabinoid receptors (CB1/CB2) and the T-type calcium channels are involved in disorders associated with both physiological pain and depressive behaviors. Valuable pharmacological species carbazole derivatives such as the NMP-4, NMP-7, and NMP-181 (Neuro Molecular Production) regulate both biological entities. In this work, DFT calculations were performed to characterize theoretically their structural and chemical reactivity properties using the BP86/cc-pVTZ level of theory. The molecular orbital contributions and the chemical reactivity analysis reveal that a major participation of the carbazole group is in the donor-acceptor interactions of the NMP compounds. The DFT analysis on the NMP compounds provides insights into the relevant functional groups involved during the ligand-receptor interactions. Molecular docking analysis is used to reveal possible sites of interaction of the NMP compounds with the Ca_v3.2 calcium channel. The interaction energy values and reported experimental evidence indicate that the site denominated as “Pore-blocking”, which is formed mainly by hydrophobic residues and the T586 residue, is a probable binding site for the NMP compounds.     

电子效应对单取代苯定位效应和反应活性的影响

单取代苯的定位效应和反应活性主要受取代基的电子效应控制,列表总结了取代基的电子效应与定位效应和反应活性的关系,分析了烃基电子效应的特殊性,取代基具有-Ⅰ效应的普遍性。除卤素取代基外,探讨了共轭效应的方向对定位效应和反应活性的决定作用。     

纳米氢化钠的热稳定性和化学反应活性

Nanometric sodium hydride (NaH*) possesses a large specific surface area. Its chemical reactivity is in orders of magnitude higher than that of the conmercial one. After heat treatment at 2ll℃, the specific surface area of NaH* becomes smaller whereas its chemical reactivity is even higher. This fact indicates that the specific surface area of NaH* particles is an important but not the only factor for its high reactivity. NaH treated at (400℃, 6h) still retains a specific surface area of 30m2 g-1 and gives fairly high chemical reactivity.     

红外光谱法测定St—BMA的竞聚率

对于共聚合反应中同一对单体的竞聚率,由于采用的实验方法、计算方法不同,可能有几对、甚至上百对不同的数据。在实际生产中已逐渐趋向于在较高温度下进行共聚合,而文献的竞聚率一般均在较低温度下获得,因此缺乏实用意义。本文用FTIR方法测定苯乙烯(St)-甲基丙烯酸正丁酯(BMA)共聚竞聚率参数r_1和r_2,讨论了温度的影响。     

Molecular Simulation of the Effects of Cyclic Organic Compounds on the Stability of Lccbm Hydrates

CH₄ can be separated from low-concentration coal bed methane (LCCBM) by using the hydrate-based gas separation (HBGS) method. To study the contribution of different cyclic organic compounds to the separation of CH₄ in LCCBM, an LCCBM hydrate model was constructed. Based on the Monte Carlo and molecular dynamics theory, we simulated the effect of three cyclic organic compounds—cyclopentane (CP), cyclopentanone (CP-one), and cyclopentanol (CP-ol)—on the stability of the LCCBM hydrate at P = 2 MPa, various temperatures, and discussed the structural stability of the hydrate in depth in terms of final snapshots, radial distribution function, mean square displacement, diffusion coefficient, and potential energy change. The results showed that for the CH₄-N₂ LCCMM gas mixture, CP showed the best facilitation effect compared to the other two cyclic compounds by maintaining the stability of the LCCBM hydrate well at T = 293 K. The promotion effect of CP-one is between CP and CP-ol, and when the temperature increases to T = 293 K, the oxygen atoms in the water molecule can maintain the essential stability of the hydrate structure, although the orderliness decreases significantly. Moreover, the structure of the hydrate model containing CP-ol is destroyed at T = 293 K, and the eventual escape of CH₄ and N₂ molecules in solution occurs as bubbles. The research results are important for further exploration of the mechanism of action of cyclic promoter molecules with LCCBM hydrate molecules and promoter preferences.     

阴离子硫氧化还原与Li1-xNiO2-ySy的结构稳定性:第一性原理研究

Ni-rich layered oxides are the preferred cathode materials for high-energy-density lithium-ion batteries currently used in electric vehicles. In this paper, we present a systematic first-principles evaluation of the deintercalation process in the Li_1-xNiO_2-yS_y. The partial density of states (PDOS) characters of the electrons near the Fermi level, redox behaviors, and thermal stability have been investigated within the GGA+U scheme. The results show that the introduction of sulfur alleviates the lattice distortion during charging, suppresses nickel migration, and enhances the stability of oxygen according to the contribution of sulfur anion redox to the charge compensation for the overcharged Li_1-xNiO_2-yS_y. This study provides a new insight on improving the stability of Ni-rich cathode materials by tuning of the electrochemical behaviors based on sulfur anion redox.     

有机硫化物使Pd／树脂催化剂中毒的规律与机理

 在流体并流向上气液固三相固定床反应器中考察了同系有机硫化物对Pd／树脂催化剂上异戊二烯选择加氢活性的影响，并对中毒失活的催化剂进行了XPS和红外光谱研究．结果表明，在低温（60℃）和液相加氢条件下，硫醇和二硫醚同系物使Pd／树脂催化剂活性中毒的规律是，随着硫化物分子量的增大，其毒性减弱．在w（S）＝8×10－6的条件下，有机硫化物使催化剂上异戊二烯加氢活性失活的程度为：二甲基二硫醚≈乙硫醇二甲基硫醚＞噻吩．乙硫醇和二甲基二硫醚使Pd／树脂催化剂中毒的机理是，它们分别在催化剂上发生S－H和S－S键断裂，并与Pd形成带烷基基团的S－Pd吸附络合物，致使催化剂上异戊二烯选择加氢活性降低．     

Effect of Electrolytes on Redox Reactivity of Polypyrrole

Doping and dedoping characteristics of polypyrrole (PPy) formed electrochemically have been examined by means of energy-dispersive X-ray spectroscopy (EDS). Dodecylsulfate ions (DS⁻) and perchlorate ions (ClO⁻₄) were embedded simultaneously in PPy when both ions were present on the polymerization of pyrrole. Sequential formation of PPy in the single dopant system allowed PPy/ClO₄ to grow in the bulk of PPy/DS but not vice versa. DS⁻ was embedded not to leave the polymer on reduction but ClO⁻₄ moved in and out of the polymer on redox reaction. Cyclic voltammetry was employed to determine the redox reactivity of PPy in different electrolyte systems. NaClO₄ was a better electrolyte for cyclic redox reaction than LiClO₄ or KClO₄. NaCl was a good electrolyte for cyclic redox reaction but Cl⁻ failed to penetrate in the PPy/DS bulk on reoxidation. The cyclic redox reactivity lasted longest when PPy/DS was redox-cycled sequentially in the NaCl electrolyte system and then in the NaClO₄ system. © 1997 John Wiley & Sons, Ltd.     

有机液、消毒液中相关化合物的GC-MSD分析测定

禁止化武公约组织(OPCW)每年都要考核各参试国家的分析能力,我们实验室连续多年参加水平考试,并都取得了很好的成绩。本文报导了第14次OPCW水平考试其中的有机液(O／14)和消毒液(D／14)样品分析。有机液是模拟视查某生产、合成车间,采自1个未作标记包装容器内的样品(编号O／14)。在对有机液分析中发现有大量的干扰物,影响分析检测,经过进行液-液萃取,较好地排除了各种干扰;用DB5-MS石英毛细管色谱柱分析,发现有两种相关化合物分离不开,选用DB-1701柱进行试验,分离的效果较好。消毒液是采自1个明确标记为DS2消毒容器内的样品(编号为D／14)。样品经过调节pH值,用二氯甲烷萃取,萃取后的消毒液又进行旋转蒸干,硅烷化、甲基化等衍生反应,GC-MSD分析试验,检出了全部的相关化合物,取得了A等的考试成绩。