生物化学 Chapter 12 electrophilic Reactions of arenes课件.ppt

Chapter 12  Reactions of Arenes:Electrophilic Aromtic Sustitutions;Exercises; The reactivity issues of arenes can be separated into two types of reactions: ? Reactions of electrophiles directly on the aromatic ring Reactions of the substituents (since the neighbouring aromatic group influences its reactivity). ;Electrophilic aromatic substitution:;§12.1 Electrophilic Aromatic Substitution;Electrophilic Reactions:;H;Reaction;There are three fundamental components to an electrophilic substitution reaction:;Mechanistic Principles of Electrophilic Aromatic Substitution;12-10;Step 2: loss of a proton from the carbocationintermediate;Step 2: loss of a proton from the carbocationintermediate;H;Based on this general mechanism:;The mechanism is represented by the following series of events:;Why Substitution not Addition ? ;The first step is common to both, E+ adds a C=C to give a carbocation intermediate.?;§12.3 Nitration of Benzene;Mechanism: Attack of nitronium cation (NO2+);Step 2: Loss of a proton the cyclohexdienyl;Summary;§12.4 Sulfonation of Benzene;Mechanism: Attack of sulfur trioxide (SO3);Step 3: ;途与溯赊堕漳秀墟盐凋樱觉弧哥哑寸铭厦滓郝栏那先框戌较撅淬正尼荔戌生物化学 Chapter 12 electrophilic Reactions of arenes课件生物化学 Chapter 12 electrophilic Reactions of arenes课件;Summary;§ 12.5 Halogenations of Benzene;Step 1: The bromine-iron(Ⅲ) bromide complex is the active electrophile which attacks benzene.; Chlorination:;§12.6 Friedel - Craft Alkylation of Benzene;Mechanism:;Step 1:; Friedel-Crafts alkylation with primary alkyl halides can form secondary or teritary carbocation by rearrangement .; ; Alcohol:;§12.7 Friedel-Craft Acylation of Benzene;Mechanism:;Acyl cation for by coordination of an acyl chloride with aluminum chloride, followed by cleavage of the carbon-chlorine bond.; Step 1: The acyl cation attacks benzene; The reactivity of Friedel-Crafts acylation of acyl halide: RCOl RCOBr RCOCl RCOF Friedel-Crafts acylation cannot be carried out if deactivating