苯取代机理.ppt

本章主要内容 一、苯的亲电取代反应及机制 二、取代基对苯环亲电取代反应的影响 三、稠环芳烃的亲电取代反应 四、芳香杂环的亲电取代反应 五、芳环和芳香杂环的亲核取代反应 六、芳环取代基的反应 ——芳香重氮盐的形成及其在合成中的应用 一、芳环的亲电取代反应及机制 1. Mechanism: Step 1: 类似烯烃，亲电试剂进攻苯环的pi-键，形成碳正离子 一、芳环的亲电取代反应及机制 Activated Electrophiles (活化的亲电试剂) —Cation formation by reaction of an elcerophile with an aromatic ring is accompanied by the loss of aromatic stabilization. 正离子的形成伴随着芳香性的丧失 — Therefore, the electrophile that can effect aromatic subsitution of benzene must be more reactive than those addition to alkenes. 因此，与苯环反应的亲电试剂需要更高的反应活性 一、芳环的亲电取代反应及机制 2. Reaction coordinate diagrams: 一、芳环的亲电取代反应及机制 3.The five most common electrophilic aromatic substitution reactions are the following: 一、芳环的亲电取代反应及机制 以上几种亲电取代反应仅亲电试剂不同： —— Cl-Cl+ - -AlCl3 —— Br-Br+ - -FeBr3 —— I+ (obtained by I2 + HNO3) —— +NO2 (obtained by HNO3 + H2SO4) —— +SO3H (from H2SO4) or SO3 —— R+ (obtained by R-Cl + AlCl3) —— RC+=O (obtained by RCOCl + AlCl3) 一、芳环的亲电取代反应及机制 (2) Nitration 一、芳环的亲电取代反应及机制 (3) Sulfonation —— reversible reaction 一、芳环的亲电取代反应及机制 一、芳环的亲电取代反应及机制 二、取代基对芳环亲电取代反应的影响 A study of the chemistry of aromatic compounds leads to deeper understanding of the effects of electronic and steric factors on reactivity, which will be of benefit in the further study of chemistry and biochemistry. 二、取代基对芳环亲电取代反应的影响 1. Experimental Facts: 2. The effect of substituents on reactivity ① Activating substituents (致活基) —— Electron-donating substituents (给电子基) increase the reactivity of the benzene ring toward electrophilic aromatic substitution. ② Deactivating substituents (致钝基) —— Electron-withdrawing substituents (吸电子基) decrease the reactivity of the benzene ring toward electrophilic aromatic substitution. Relative reactivity: 二、取代基对芳环亲电取代反应的影响 3. The effect of substituents on orientation ① ortho/para directors (邻对位定位基) —— all activating substituents are ortho/para dire