南开大学有机化学有机化学反应的基本问题.pptVIP

本章的主要内容 热力学 Thermodynamics与反应方向 动力学 Kinetics与反应活性、选择性 反应机制 Reaction Mechanism 反应活泼中间体 Active Intermediates 有机反应机制的研究方法 Reaction Coordinate Diagrams反应坐标图或反应势能变化图 —— describs the energy changes in total reaction progress The field of chemistry that describes the properties of a system at equilibrium is called thermodynamics (热力学) 热力学第一定律：能量守衡与转化定律 ——能量可以从一种形式转化成另一种形式，在转化过程中，能量总值不变 热力学第二定律：自发过程的不可逆性 ——不可能从单一热源吸热，使之全部转化为功，而不引起其他变化 热力学第三定律：熵变的计算 热力学状态函数 ——内能 U，体系各种能量的总和，绝对值不可知 ——熵 S，体系无序程度，有规定熵 ——吉布斯自由能 G ——亥姆霍兹自由能 A ——焓 H 分析研究这些状态函数的变化值 Thermodynamics——几个基本概念和重要的关系式 For the generalized reaction: we have Keq —— equilibrium constant Thermodynamics Free Energy —— 自由能 △G0 —— Gibbs standard free energy change, thermodynamic parameters，是等温等压条件下判断反应变化方向的热力学状态函数 △G0 = (free energy of the products) – (free energy of the reactants) When △G0 is negative, the reaction is exergonic（放能的）, has a favorable equilibrium constant, and can occur spontaneously. When △G0 is positive, the reaction is endergonic（吸能的）, has an unfavorable equilibrium constant, and cannot occur spontaneously. Thermodynamics △H0 —— Enthalpy change （焓变） Enthalpy is the heat given off or the heat consumed during the course of a reaction. △H0 = (energy of the bonds being broken) – (energy of the bonds being formed) When △H0 is negative, the reaction releases heat and is exothermic（放热的）. When △H0 is positive, the reaction absorbs heat and is enderthermic（吸热的）. Thermodynamics △S0 —— Entropy change （熵变） Entropy is the degree of disorder △S0 = (freedom of motion of products) – (freedom of motion of reactants) When △S0 is negative, disorder decreases; when △S0 is positive, disorder increases. Thermodynamics Standard conditions (标准状态) ——1M, 25℃, 100 kPa下 （标准状况或条件： 1M, 25℃, 1 atm = 101.325 kPa） Thermodynamics △H0 can be calculated from bond dissociation energy Bond Dissociation Energy (DH0) （键的裂解能或离解能） —— defined as the amount of energy required t