Chapter12ReactionsofArenes:ElectrophilicAromticSustitutionsExercisesThereactivityissuesofarenescanbeseparatedintotwotypesofreactions:ReactionsofelectrophilesdirectlyonthearomaticringReactionsofthesubstituents(sincetheneighbouringaromaticgroupinfluencesitsreactivity).Electrophilicaromaticsubstitution:§12.1ElectrophilicAromaticSubstitutionElectrophilicReactions:HReactionTherearethreefundamentalcomponentstoanelectrophilicsubstitutionreaction:MechanisticPrinciplesofElectrophilicAromaticSubstitution12-10Step2:lossofaprotonfromthecarbocationintermediateStep2:lossofaprotonfromthecarbocationintermediateHBasedonthisgeneralmechanism:Themechanismisrepresentedbythefollowingseriesofevents:WhySubstitutionnotAddition?Thefirststepiscommontoboth,E+addsaC=Ctogiveacarbocationintermediate.§12.3NitrationofBenzeneMechanism:Attackofnitroniumcation(NO2+)Step2:LossofaprotonthecyclohexdienylSummary§12.4SulfonationofBenzeneMechanism:Attackofsulfurtrioxide(SO3)Step3:Summary§12.5HalogenationsofBenzeneStep1:Thebromine-iron(Ⅲ)bromidecomplexistheactiveelectrophilewhichattacksbenzene.Chlorination:§12.6Friedel-CraftAlkylationofBenzeneMechanism:Step1:Friedel-Craftsalkylationwithprimaryalkylhalidescanformsecondaryorteritarycarbocationbyrearrangement.Alcohol:§12.7Friedel-CraftAcylationofBenzeneMechanism:Acylcationforbycoordinationofanacylchloridewithaluminumchloride,followedbycleavageofthecarbon-chlorinebond.Step1:TheacylcationattacksbenzeneThereactivityofFriedel-Craftsacylationofacylhalide:RCOl>RCOBr>RCOCl>RCOFFriedel-Craftsacylationcannotbecarriedoutifdeactivatingsubstituents(electron-withdrawinggroup)attachedonthebenzenering.Friedel-Craftsacylationonlyintroducemonoacylonbenzeneringbecauseacylisadeactivatingsubstituentandintroducedacyldepressreactivityofbenzene.Friedel-CraftsacylationisnonreversibleFriedel-Craftsacylationdoesnottakeplacerearrangement.AnilineisdifficulttotakeplaceFriedel-Craftsalkylationbecauseaminoofanilineacylatefirstly.Acylchloridesarepreparedbythereactionofacarboxylicac