吡啶与苄基溴衍生物Menschutkin反应的溶剂和取代基效应的理论研究

利用MP2/6-311++G(d,p)//B3LYP/6-31+G(d,p)方法和SMD溶剂化模型研究苄基溴及其衍生物和吡啶在气相和乙腈溶剂中的Menschutkin反应机理,对其主要的两条反应途径:吡啶由溴的异侧或同侧进攻,进行理论计算,解释乙腈溶剂及取代基对反应机理的影响.计算结果表明,在气相和乙腈中,吡啶从苄基溴...     

溶剂效应计算中两种积分方法的比较研究

采用多面体表面模拟溶质空腔, 讨论了溶剂效应计算中近似积分方法和解析积分方法的平行性和收敛性. 我们发现: 对所研究的40个中性分子, 近似方法和解析方法之间的平行性较好; 但是, 对于20个正离子和27个负离子, 当溶质空腔分别为0.002和0.001 a.u.的等电荷密度面时, 近似方法和解析方法之间的平行性较差, 因此, 近似方法的可靠性不一定有保证. 我们还发现当多面体的表面无限趋近空腔的表面时, 不管采用何种多面体序列, 近似方法和解析方法的基态总能量都基本趋向同一极限值.     

氢甲酰化反应溶剂效应的量子化学研究

在B3LYP/6-31G(d, p)(Rh和P采用LANL2DZ + Polar)水平下,利用自洽反应场（SCRF）的Onsager模型,系统研究了C6H12、C6H6、THF、CH2Cl2、CH3OH和H2O（相对介电常数ε分别为2.02、2.25、7.58、8.93、32.63和78.39）六种溶剂对乙烯氢甲酰化反应中各驻点的结构和反应机理的影响.分别在上述溶剂中优化了反应物、产物、中间体和过渡态的结构,并计算了自由能和活化自由能.计算结果表明,不同溶剂对反应势能面上各驻点的结构和能量均有一定的影响,而且随着相对介电常数ε的增加,反应的活化自由能下降.水是以上六种溶剂中最佳的溶剂,这与大量的实验研究结果一致.     

碳-碳键均裂反应的溶剂效应

测定了meso-2, 3-二氰基-2, 3-二苯基丁二酸二乙酯分别在乙苯、苯乙醚、氯苯、苯甲酸甲酯、苯甲腈及1, 2-二溴乙烷中, 于90, 100, 110, 120℃的异构化动力学、平衡常数、反应速率常数和活性参数。结果表明, 平衡常数对溶剂和反应温度都不敏感。     

分子筛催化下环氧氯丙烷开环反应的溶剂效应

环氧化合物与羧酸的开环加成酯化是有机化学中一类重要反应,开环形成的羧酸β-羟基酯有着十分广泛的用途。这类反应的进行通常需要高活性的催化剂,我们曾将Fe(Ⅲ)改性的ZSM-5分子筛应用于羧酸β-羟基酯的合成。本文用Fe-ZSM-5分子筛为催化剂,以环氧氯丙烷与丙酸反应作为模型,研究了取代苯为溶剂时对反应速率的影响,发现反应的速率     

溶剂效应

绝大多数化学反应在溶液中进行。很早以前人们就知道溶剂对化学反应有重要的影响。但从理论上认识这种影响是不容易的。要认识溶剂对溶质(反应物)的影响,需要知道它们的分布状态或聚集方式,而测量它们的聚集方式是困难的。各种波谱测试手段的出现,提供了认识它们聚集方式的可能性。最近一、二十年应用近代科学技术对溶剂效应展开了系统的和     

柴油脱硫的机理研究以及反应中的溶剂效应

柴油的脱硫技术分为加氢脱硫和非加氢脱硫。在非加氢脱硫的研究中,氧化脱硫技术具有反应条件温和、不使用昂贵的氢气、投资和操作费用低等优点日益受到重视。文章介绍了柴油的脱硫技术的机理方面的研究进展。其中包括加氢脱硫的反应网络;以及氧化脱硫研究中,光化学氧化体系和有机过氧化物氧化体系中DBT的氧化机理。在不同的反应体系中,溶剂对含硫化合物的脱除也有很大的影响.     

水杨酸激发态质子转移反应及其溶剂效应的理论研究

用AMI和INDO/CI方法对水杨酸的激发态质子转移反应进行了理论研究,求得反应的位能曲线、势垒和过渡态,对有关化合物的吸收和荧光光谱进行了理论指认,计算与实验结果符合较好。对光化学反应机理和应用前景进行了讨论,最后以乙醚作为氢键溶剂的例子研究了影响水杨酸激发态质子转移反应的溶剂效应。     

面包酵母催化不对称还原EOPB反应中的溶剂效应

研究了非水介质中面包酵母催化不对称还原2-氧代-4-苯基丁酸乙酯(EOPB)合成手性2-羟基-4-苯36基丁酸乙酯(EHPB)的反应.乙醚体系中湿酵母(WB)催化6mmol·L-1EOPB合成(R)-EHPB的e.e.值较之于干酵母(DB)提高了近19%,但WB稳定性较差.DB催化该反应的立体选择性随溶剂logP(0....     

两种氧氮杂环戊二烯类化合物的紫外和荧光光谱的溶剂效应

前文报道了1,4-二(5-苯基-1,3,4-嚼二唑基-2)苯(PDPDP)紫外、荧光光谱的溶剂效应.为了与PDPDP比较,又合成了1-(5-苯基-1,3,4-噁二唑基-2)-4-(5′-苯基-1′,3′-噁唑基-2′)苯(PDPOP)和1-(5-苯基-1,3,4-噁二唑基-2)-4-(2′-苯基-1′,3′噁唑基-5′)苯(PDPO′P).     

Solvent‐Free Passerini Reactions

The influence of the substrate structure and concentration on the yield of the Passerini reaction was studied. A new, solvent‐free methodology for a convenient preparation of α‐acyloxyamides 4 was established and compared to the classical methodology. A higher reaction yield was obtained in shorter time, especially in the case of aromatic aldehydes.     

Dynamic Solvent Effect in Reactions of Photoinduced Intramolecular Proton-Coupled Electron Transfer

Russian Journal of Physical Chemistry A - The dynamic solvent effect (DSE) in reactions of ultrafast proton-coupled electron transfer (PCET) under nonequilibrium conditions is studied. It is found...     

溶剂化效应在所谓“位阻效应”中的重要作用

SN2反应中 ,底物上的大基团会使反应速率明显降低。以前认为该现象完全源于位阻效应 ;但国外新近的研究结果显示 ,该现象的产生应当是溶剂化效应和位阻效应共同作用的结果 ,且溶剂化效应的贡献可能更大     

On the Apparent Compensation Effect Observed for Two Consecutive Reactions

A critical analysis is presented of the use of an overall single rate reaction equation instead of the true rate equation corresponding to a complex process consisting of two consecutive reactions. In accordance with this approximation, which is often used in the kinetic analysis of systems in which several reactions take place, the overall process is described by apparent activation parameters (the apparent activation energy E_ap and the apparent pre-exponential factor A_ap) and an apparent conversion function. The theoretical isotherms (α=α(t), where α is the conversion degree and t is time) were simulated for a system in which two consecutive reactions occur. In this case, the apparent activation parameters depend on (a) the considered range of temperature; and (b) the temperature for a given conversion degree. It is shown that the apparent activation parameters are correlated by the compensation effect relationship: ln A_ap = α^* + β^*E_ap where α^* and β^* are the linear regression parameters. The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those for which these parameters were evaluated is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the Apparent Compensation Effect Found for Two Consecutive Reactions

A critical analysis of the use of an overall single rate reaction equation instead of the true rate equation corresponding to a complex process consisting in two consecutive reactions is presented. In accordance with this approximation, often used in the kinetic analysis of the system in which several reactions take place, the overall process is described by the apparent activation parameters (the apparent activation energy, E _ap, and the apparent pre-exponential factor, A _ap) and the apparent conversion function. The theoretical isotherms (α=α(t), where a is the conversion degree and t is the time) have been simulated for a system in which two consecutive reactions occur. In this case, the apparent activation parameters depends on: (a) the considered range of the temperature; (b) the temperature, for a given conversion degree. It is shown that the apparent activation parameters are corrrelated by the compensation effect relationship: lnA _ap=α*+β*E _ap where α* and β* are the parameters of the linear regression. The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those for which these parameters were evaluated, is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Assessing Solvation Effects on Chemical Reactions with Globally Optimized Solvent Clusters

We have examined the influence of water solvent on the Menshutkin reaction of methyl chloride with ammonia by performing static, quantum chemical calculations. We have employed large, explicit, and globally structure‐optimized water clusters around the reaction center, in a mixed explicit/implicit solvent model. This approach deliberately deviates from attempts to capture the most likely solvent‐molecule distribution around a reaction center. Instead, it explores extremes on the scale of rearrangement speed in terms of the surrounding solvent cluster, relative to the reaction progress itself. A comparison to traditional theoretical and experimental results enables us to quantify the energy penalty that is induced by the inability of the water cluster to instantaneously and completely follow the reaction progress. In addition, the influence of water clusters on the reaction energy profile can be much larger than merely changing it somewhat. Certain clusters can completely annihilate the sizeable activation barrier of 23.5 kcal mol^?1.