Computational studies of organic reactions

选择性反应是指在多种可能的反应途径中，只有一条途径占主导地位。每条途径都与一个过渡态相关联，但有些过渡态比其他过渡态更有利，能量更低。最低的能量过渡态对应于最有利的反应途径，从而导致选择性反应的主要产物。选择性反应，无论是区域选择性的，对映体的还是非对映选择性的，在化学上都具有重要的意义，因为它们在工业、研究和环境中都有广泛的意义。例如，不对称催化允许高度选择性地形成特定化合物的纯所需对映体。与相应的非选择性方法相比，这种方法通常更便宜，产量也更高。因此，可以减少废物的数量，同时可以提高选择性化学合成和过程的效率和简单性。了解反应背后的选择性取决于对反应机理和相关过渡态的了解，以及决定每个过渡态能量的潜在因素。这种对反应机制的洞察可以通过彻底探索它们的势能面来获得，势能面是一个数学函数，它给出了系统能量作为其中所有原子位置的函数。反应的基态物种，即反应物、中间体或产物，用势能面上的极小值表示，而过渡态用鞍点表示。有多种计算方法可以用来探索反应的势能面，例如密度泛函理论(DFT)，一种从头算的量子力学方法，它只根据体系的电子密度来推导体系的能量，以及分子力学，它使用经典力学来描述分子。因此，量子力学计算，如使用DFT进行的计算，可以用来定位和确定过渡态的能量，从而阐明反应机理。这些详细的见解使得合理设计改进的选择催化剂，将现有的催化剂应用于新的选择反应，以及调整现有的选择过程以提高产率和效率。这项研究的基础是使用计算方法，如密度泛函理论和分子力学，来研究各种选择反应的机理细节。过渡金属催化的芳烃选择性C-H硼化反应和有机催化的对映选择性羟醛缩合反应是两个有意义的反应。

A selective reaction is one where, of multiple possible reaction pathways, one pathway dominates. Each pathway is associated with a transition state, however some transition states are more favourable and lower in energy than others. The lowest energy transition state corresponds to the most favourable reaction pathway and hence leads to the major product of a selective reaction.Selective reactions, whether regio-, enantio- or diastereoselective, are of the significant interest in chemistry due to their widespread implications in both industry, research and on the environment. For example, asymmetric catalysis allows the highly selective formation of purely the desired enantiomer of a particular compound. This is often cheaper, and allows for much better yields, than corresponding unselective methods. Hence the amount of waste can be reduced while the efficiency and ease of selective chemical syntheses and processes can be improved.Understanding the selectivity behind a reaction relies on a knowledge of the reaction mechanism and relevant transition states, as well as the underlying factors that determine the energy of each transition state. Such insights into reaction mechanisms may be obtained by a thorough exploration of their potential energy surfaces, a mathematical function that gives the energy of the system as a function of the positions of all the atoms within it. The ground state species of a reaction, i.e. reactants, intermediates, or products, are represented by minima on the potential energy surface, whilst transition states are represented by saddle points. A variety of computational methods exist that can be used to explore the potential energy surface of a reaction, for example density functional theory (DFT), an ab initio, quantum mechanical method which derives the energy of a system based only on its electron density, and molecular mechanics, which uses classical mechanics to describe molecules.Hence quantum mechanical calculations, such as those carried out using DFT, can be used to locate and determine the energy of transitions states and hence elucidate reaction mechanisms. Such detailed insights enables the rational design of improved selective catalysts, the application of existing catalysts to new selective reactions, and the tuning of existing selective processes to improve yield and efficiency.The basis of this research involves the use of computational methods, such as DFT and molecular mechanics, to investigate the mechanistic details of a variety of selective reactions. Transition-metal catalysed selective C-H borylation of arenes and organocatalyzed enantioselective aldol condensations are two such examples of reactions of interest.