有机化学教学课件：Chapter 6. Arenes.ppt

Chapter 6 Arenes and Aromaticity6.1 The Structure of Benzene 1. A resonance theory(共振论） 2. An orbital hybridization view6.2 Nomenclature of Benzene Derivatives6.3 Aromatic Ring as a Functional Group: Electrophilic Aromatic Substitution (芳环亲电取代）6.3.1 Halogenation of Benzene （卤化反应）6.3.2 Nitration of Benzene （硝化反应）6.3.3 Sulfonation of Benzene （磺化反应）6.3.4 Friedel-Crafts Alkylation of Benzene （傅-克烷基化反应）6.3.5 Friedel-Crafts Acylation of Benzene （傅-克酰基化反应）6.4 Effects of Substituents on Reactivity and Orientation （取代基定位规则） 6.4.1 Classification of Substituents （取代基分类） 6.4.2 Substituent Effects in Electrophilic Aromatic Substitution （取代基对芳环取代反应的影响）6.5 Multiple Substituent Effects （多取代基的影响）6.6 Oxidation of Arenes 6.7 Synthetic Applications6.1 Structure of BenzeneThree modern theories:1. A resonance theory(共振论)The structure of benzene is planar: regular hexagon(正六边型).The bond angles: 120 The CC bond lengths : 1.39sp2sp2 single bond: 1.46sp2sp2 double bond: 1.34A hybrid of the two Kekul structures:is equivalent toCyclic conjugation in benzene leads to a great stability. 2. An orbital hybridization view In a mole. of benzene, all C atoms aresp2hybridized.6 CC bonds: sp2sp2 overlap,6 C H bonds: sp21s overlap.The 6 2p orbitals thatare perpendicular to the frameworkoverlap to form orbital.The 6 electrons aredelocalized over all six C.Resonanceenergy:152 kJ/molA closed conjugate system.3. The molecular orbitals The 6 overlapping 2p orbitals combine to form a set of 6 molecular orbitals:Antibonding orbitalsBonding orbitals6.2 Nomenclature of Benzene Derivatives 1. Monosubstituted benzenes A. Benzene as the parent name.Toluene(甲苯)Chlorobenzene(氯苯)IsopropylbenzeneNitrobenzene( 硝基苯)B. Benzene as a substituentC6H5, Ph: phenyl.Phenylacetylene(苯乙炔)2-Phenyl-2-buteneDiphenylmethaneBenzylchloride(苄基氯)多官能团化合物的命名： 按照“官能团的优先次序”，以较优的 官能团为母体官能团的优先次序：醇 酚 除作为母体的官能团外，其它的官能团 均为取代基 命名： 取代基名称 + 母体名称官能团优先次序： 3甲氧基-4羟基苯甲醛 3硝基4羟基苯乙酮 4乙酰氨基1萘甲酸 2. Disubstituted benzenesThree isomers:1,2-Dibromobenzeneo-Dibromobenzeneortho-1,3-m-meta-1,4-p-para-o-Xylene(0-二甲 苯)3. Polysubstituted Benzenes2,5-dinitro-chlorobezene(2, 5- 二硝基-氯苯)1,3,5-Trimethylbezene( 均三甲苯)6.3Aromatic Ring as a Functional Group: Electrophilic Aromatic Substitution (芳环亲电取代反应) When the aromatic ring of benzene reacts with a electrophilic reagent, the substitutionreaction occurs:A benzene ring with 6 electrons in a cyclic conju-gated system is a site of electron-rich.Electron donor: benzene ringElectron acceptor（Electrophile): E+, a Lewis acid.Aromatic electrophilic substitution reactions: The electrophilic part of a reagent replaces a hydrogen atom from aromaticring.Figure 1 Types of electrophilic aromatic substitution of benzeneHalogenationNitrationSulfonationAlkylationAcylation(酰基化)(75%)The Lewis acids most commonly used are FeCl3, FeBr3 and AlCl3.The mechanism for bromination of benzene:Step 1 Polarization of Br2.The formation of the bromine-iron(III)bromide complex.6.3.1 Halogenation of BenzeneStep 2 The attack of polarized bromine to benzene ring .The formation of nonaromatic carbocation.Allylic cation: p- conjugationDelocalization of - electrons generatesthe resonance forms: Step 2 is rate-determining.Step 3 The loss of a proton to restore the aromatic system.Reactivity : F2 Cl2 Br2 I2 6.3.2 Nitration( 硝化反应) of Benzene Aromatic rings can be nitrated by reaction with a mixture of concentrated nitric acid and sulfuric acid:The generation of electrophile, E+:Nitronium ion(硝酰正离子)Nitrobenzene(85%)Trinitrotoluene(TNT)6.3.3 Sulfonation(磺化反应) of Benzene Benzene reacts with fuming sulfuric acid to produce benzene sulfonic acid: Sulfur trioxideBenzenesulfonic acid (苯磺酸)(56%)Fuming H2SO4: a mixture of H2SO4 and SO3.Mechanism of the reaction:Step 1 Generation of the electrophile:Step 2. Sulfur trioxide as a electrophile attacks benzene in the rate-determing step. Step 3. The loss of a proton to restore the aromatic system.Step 4. A rapid proton transfer to produce benzenesulfonic acid. 6.3.4 Friedel-Crafts Alkylation of Benzene Benzene reacts with alkyl halide in the presence of AlCl3 as catalyst:Cumene(枯烯)IsopropylbenzeneMechanism of the reaction:Step 1. The formation of carbocation:Step 2. The carbocation as a electrophile attacks benzene ring, a CC bond is formed: CH3X and RCH2X do not form the carbocation, they form the complex: The rearrangement can occur when especially a primary halides are used:(66%)Step 3. Loss of a proton to produce the alkylbenzene Friedel-Crafts alkylation can be availble to other systems that generate a carbocation:Ex.A alkene and a acid.A alcohol and a acid.(56%)Cyclohexyl benzene(65%) Polyalkylation 多烷基化MajorproductMinorproduct Another limitation to alkylation on ring Charles Friedel (1832-1899) Charles Friedel was born inStrabourg, Frans,and studiedat the Sorbonne in Paris. He was among the first to attempt manufacture synthetic diamonds. He was professor of chemistry at the Sorbonne(1884-1889). James Mason Crafts (1839-1917)James Mason Crafts was born in Boston, Ma。