生物化学ChapterArenesandAromaticity公开课一等奖优质课大赛微课获奖课件.pptx

Chapter 11Arenes and Aromaticity第1页第1页ExercisesExercises11.211.4-11.911.1511.1811.2011.28-11.3511.39-11.41第2页第2页Arenes are hydrocarbons based on the benzene ring as a structure unit.陈立陈立第3页第3页11.1 Benzane第4页第4页Some historySome history1825MichaelFaradayisolatesanewhydrocarbonfromilluminatinggas.1834EilhardtMitscherlichisolatessamesubstanceanddeterminesitsempiricalformulatobeCnHn.Compoundcomestobecalledbenzene.1845AugustW.vonHofmannisolatesbenzenefromcoaltar.1866AugustKekulproposesstructureofbenzene.第5页第5页lThearomaticcharacterofbenzeneinfersaninherentstabilitytothesystem.Asaresult,benzeneisnotparticularlyreactivecomparedtoalkenes.lThisstabilitycanbeexpressedbytheresonanceenergy,whichforbenzeneisabout36kcal/mol11.2 The Stability of Benzene苯结构能够是一个“环己三烯”类型结构，但苯性质却表现出与环状烯烃大相径庭性质。第8页第8页环己烯与苯对比环己烯与苯对比ReagentsCyclohexeneBenzeneKMnO4/H2OBr2/CCl4HI第9页第9页氢化热比较(KJ/mole)1202313120=360208“”苯氢化热低于假设中“环己三烯”推算数值,阐明苯比设想“环已三烯”稳定第10页第10页Heat of hydrogenation of cyclogenation of cyclohexene,1,3-cyclohexadiene,a hypothetical 1,3,5-cyclohextriene,and benzene.(KJ/mole)1201523120=360231208第11页第11页苯分子共振能苯分子共振能若以环己烯为原则测得其氢化热为若以环己烯为原则测得其氢化热为119.6kJmol1，假，假想苯分子存在三个孤立双键，其氢化热应为环己烯氢想苯分子存在三个孤立双键，其氢化热应为环己烯氢化热化热3倍，即倍，即(3119.6=358.8 kJmol1)。测得苯氢化热为测得苯氢化热为208.2 kJmol1。若而苯分子事实上是。若而苯分子事实上是主要包括两个共振结构共振分子，其进行氢化反应是主要包括两个共振结构共振分子，其进行氢化反应是要少放出要少放出358.8208.2=150.6(kJmol1)能量，此能能量，此能量即为破坏苯公正分子共振杂化体所消耗能量，也就量即为破坏苯公正分子共振杂化体所消耗能量，也就是苯分子共振能是苯分子共振能第13页第13页11.3 Kekul and the Structure of BenzeneKekul Formulation of BenzeneKekul Formulation of BenzeneKekulproposedacyclicstructureforC6H6withalternatingsingleKekulproposedacyclicstructureforC6H6withalternatingsingleanddoublebonds.anddoublebonds.第14页第14页Benzene has the shape of a regular hexagon.High electron density above and below plane of ringHigh electron density above and below plane of ring第15页第15页Inwhichall6Catomsin“aromatic”ringaresp2hybridised,withremaining6e-inunhybridisedporbitalsdelocalisedoverentirering,formingdoughnut/torusshapede-cloudsabove&belowringplane第16页第16页lAll 12 atoms in benzene,C6H6,lie in the same plane.lBenzene has a planar,cyclic,conjugated structure.lIf one draws benzene as alternating C=C and C-C then the two different Kekul structures are obtained.lThese are two equally valid resonance contributors.lAlternatively,these two forms can be combined in the resonance hybrid and the p system represented by a circle as in the Robinson structure.lNote that all of the C-C bonds are 1.4 (between typical C=C and C-C distances).140 pm 140 pm140 pm 140 pm140 pm140 pm第17页第17页140 pm140 pm140 pm140 pm140 pm140 pm 146 pm134 pm140 pm is the average between the CC single 140 pm is the average between the CC single bond distance and the double bond distance in 1,3-bond distance and the double bond distance in 1,3-butadiene.butadiene.第18页第18页11.3 A Resonance Description of Bonding in BenzeneKekul Formula for Benzene(1865)第20页第20页Kekul两种结构式符合共振条件：两种结构式仅在电子排列上结构不同依据共振理论,苯是，杂化体，因为二式完全等同，因此含有相同稳定性，对杂化体参加程度相等,共振作用大大提升了苯识所引发稳定性 第21页第21页Circle-in-a-ringnotationstandsforresonancedescriptionofCircle-in-a-ringnotationstandsforresonancedescriptionofbenzene(hybridoftwoKekulstructures).benzene(hybridoftwoKekulstructures).现在仍普遍地采用Kekul结构式表示苯环结构，但必须意识到其中碳碳单键和双键由于电子在闭合共轭体系中充足离域结果，两者是完全等同，是没有区别。RobinsonStructure第22页第22页11.4 An Orbital Hybridization Model of Bonding in Benzene苯分子中每个碳均采用sp2杂化，各个碳，氢均处于同一平面中。第23页第23页碳上未参与杂化轨道电子与相邻碳上电子产叠，形成平面上下两个连续面包圈形电子云第24页第24页第25页第25页Themoreredanareais,thehighertheelectrondensityandthemoreblueanareais,thelowertheelectrondensity.Notethenucleophiliccharacterofthearomaticpsystem.Theimageshowstheelectrostaticpotentialforbenzene.第26页第26页Benzene is much more stable than would be expected based on calculations for“cyclohexatriene”A reasonable prediction for the heat of hydrogenation of hypothetical cyclohexatriene is-360 kJ mol-1(3 times that of cyclohexene,-120 kJ mol-1)The experimentally determined heat of hydrogenation for benzene is-280 mol-1,152 kJ mol-1 more stable than hypothetical cyclohexatrieneThis difference is called the resonance energy第28页第28页11.5 Substituted Derivatives of Benzene and Their NomenclatureNomenclature:Functionalgroupsuffix=-benzene(review)Functionalgroupprefix=phenyl-Substitutedbenzenesareusuallynamedassuch.Therelativepositionscanbedenotedas1,2-=ortho-,1,3-=meta-and1,4-=para-substitution.Whenpolysubstituted,thenumbersaloneareused,e.g.1,2,3-trimethylbenzene第29页第29页第30页第30页 第31页第31页第32页第32页Name of Some Common Benzene DerivativeStructureNameStyrene 苯乙烯Acetophenone 苯乙酮Phenol 苯酚Anisole 苯甲醚Aniline 苯胺第33页第33页Common Names of Benzene Derivatives第34页第34页第35页第35页Easily confused namesphenylphenylphenolphenolbenzylbenzylOHOHCHCH2 2a groupa groupa groupa groupa compounda compound第36页第36页resonance energy=255 kJ/molresonance energy=255 kJ/molmost stable Lewis structure;most stable Lewis structure;both rings correspond to both rings correspond to Kekul benzeneKekul benzeneNaphthalene第38页第38页AnthraceneAnthracenePhenanthrenePhenanthreneresonance energy:resonance energy:347 kJ/mol347 kJ/mol381 kJ/mol381 kJ/molAnthracene and Phenanthrene第39页第39页11.7 Physical Properties of ArenesIntheabsenceofpolarsubstituents,arenesaretypicalofhydrocarbons:lowmeltingandboilingpoints,lowsolubilityinpolarsolvents.Melting points:More symmetrical than corresponding alkane,pack better into crystals,so higher melting points.Boiling points:Dependent on dipole moment,so ortho meta para,for disubstituted benzenes.Density:More dense than nonaromatics,less dense than water.Solubility:Generally insoluble in water.第41页第41页Arenes(aromatic hydrocarbons)resembleother hydrocarbons.They are:nonpolarinsoluble in waterless dense than water第42页第42页11.8 Reactions of ArenesThereactivityissuescanbeseparatedintotwotypesofreactions:1.Onemodeofchemicalreactivityinvolvestheringitselfasafunctionalgroupandincludes:1)Reduction:Catalytichydrogenation2)Electrophilicaromaticsubstitution:Themostimportantreactiontypeofbenzeneanditsderivatives3)2.Thereactionsencompassesthoseinwhichthearylgroupactsasasubstituentandaffectsthereactivityofunctionalunittowhichitisattached第43页第43页Eventhoughbenzeneishighlyunsaturateditdoesnotundergoanyoftheregularreactionsofalkenessuchasadditionoroxidation.第44页第44页BenzenecanbeinducedtoreactwithbromineifaLewisacidcatalystispresenthoweverthereactionisasubstitutionandnotanadditionBenzeneproducesonlyonemonobrominatedcompound,whichindicatesthatall6carbon-hydrogenbondsareequivalentinbenzene第45页第45页Reactions of the Benzylic position Thefunctionalgroupsinabenzylic苯甲基(即苄基)positionaregenerallymorereactivethantherelatedisolatedfunctionalgroup.1.BenzylicC-Hcaneasilyberadicallyhalogenatedsincethebenzylicradicalisresonancestabilized.2.BenzylicC-Hbondsofalkylbenzenescanbeoxidizedtogivebenzoic(苯甲酸)acids3.Benzylichalidesreadilyundergonucleophilicsubstitutionreactionsevenwithweaknucleophiles.4.Benzylichalidesoralcoholsreadilyeliminatetogiveconjugatedalkenes.第46页第46页11.9 The Birch ReductionThe overall reaction:Metal-ammonia-alcohol reductions of aromatic rings are known as Birch reductions.第47页第47页第48页第48页与苯环共轭双键首先发生Birch还原第49页第49页不与苯环共轭双键不发生不与苯环共轭双键不发生Birch还原还原第50页第50页H HH HH HH HH HH HStep 1:Electron transfer from sodiumStep 1:Electron transfer from sodium+NaNa Mechanism of the Birch Reduction+NaNa+H HH HH HH HH HH H 第51页第51页Step 2:Proton transfer from methanolStep 2:Proton transfer from methanolMechanism of the Birch Reduction(Figure 11.8)H HH HH HH HH HH H OCHOCH3 3H H H HH HH HH HH HH HH H OCHOCH3 3 第52页第52页Step 3:Electron transfer from sodiumStep 3:Electron transfer from sodiumMechanism of the Birch Reduction(Figure 11.8)H HH HH HH HH HH HH H+NaNa H HH HH HH HH HH HH H+NaNa+第53页第53页Step 4:Proton transfer from methanolStep 4:Proton transfer from methanolMechanism of the Birch Reduction(Figure 11.8)H HH HH HH HH HH HH H H HH HH HH HH HH HH HH H OCHOCH3 3 OCHOCH3 3H H 第54页第54页(86%)(86%)H HH HH HC(CHC(CH3 3)3 3H HH HH HH HH HH HC(CHC(CH3 3)3 3H HH HH HNa,NHNa,NH3 3CHCH3 3OOH HBirch Reduction of an AlkylbenzeneIf an alkyl group is present on the ring,it ends up asIf an alkyl group is present on the ring,it ends up asa substituent on the double bond.a substituent on the double bond.第55页第55页a)Reductiona)ReductionCatalytic hydrogenation(Section 11.4)Catalytic hydrogenation(Section 11.4)Birch reduction(Section 11.11)Birch reduction(Section 11.11)b)Electrophilic aromatic substitutionb)Electrophilic aromatic substitution(Chapter 12)(Chapter 12)c)Nucleophilic aromatic substitutionc)Nucleophilic aromatic substitution(Chapter 23)(Chapter 23)1.Reactions involving the ring2.The ring as a substituent(Sections 11.12-11.17)第56页第56页allylic radicalallylic radicalThe Benzene Ring as a Substituentbenzylic radicalbenzylic radicalbenzylic carbon is analogous to allylic carbonbenzylic carbon is analogous to allylic carbon C CC CC C C C11.10 Free-Radical Halogenation第57页第57页The mechanism:Step 1:第58页第58页Step 2:Benzyl radical苯甲基(苄基)自由基Afterhomolysis(均裂均裂)ofthebenzylicC-Hbond,theunpairedelectronissharedbybenzyliccarbonandbytheringcarbonsthatareorthoandparatoit.第59页第59页Benzylradicalisstabilizedbyoverlapofitshalf-filledporbitalwiththe systemofthearomaticring.Step 3:第60页第60页Benzylic bromination is a more commonly used laboratory procedure than chlorination.N-Bromosuccinimide (NBS)Succinimiden.琥珀酰亚胺第61页第61页Free-radical chlorination of tolueneC CClCl3 3(Dichloromethyl)benzene(Dichloromethyl)benzeneCHCHClCl2 2(Trichloromethyl)benzene(Trichloromethyl)benzeneSimilarly,dichlorinationandtrichlorinationareselectiveforthebenzylicSimilarly,dichlorinationandtrichlorinationareselectiveforthebenzyliccarbon.Furtherchlorinationgives:carbon.Furtherchlorinationgives:第62页第62页is used in the laboratory to introduce a halogen at the benzylic positionBenzylic BrominationCHCH3 3NONO2 2+BrBr2 2CClCCl4 4,80C,80Clightlightp p-Nitrotoluene-Nitrotoluene+H+HBrBrNONO2 2CHCH2 2BrBrp p-Nitrobenzyl-Nitrobenzylbromide(71%)bromide(71%)第63页第63页is a convenient reagent for benzylic bromination is a convenient reagent for benzylic bromination N-Bromosuccinimide(NBS)N NBrBrOOOOCClCCl4 4benzoylbenzoylperoxide,peroxide,heatheatCHCH2 2CHCH3 3+CHCHCHCH3 3NHNHOOOO+BrBr(87%)(87%)第64页第64页Resonance in Benzyl RadicalResonance in Benzyl RadicalC CH HH HH HH HH HH HH H unpaired electron is delocalized between unpaired electron is delocalized between benzylic carbon and the ring carbons that are benzylic carbon and the ring carbons that are ortho and para to itortho and para to it第65页第65页Resonance in Benzyl RadicalResonance in Benzyl RadicalC CH HH HH HH HH HH HH H unpaired electron is delocalized between unpaired electron is delocalized between benzylic carbon and the ring carbons that are benzylic carbon and the ring carbons that are ortho and para to itortho and para to it第66页第66页Resonance in Benzyl RadicalResonance in Benzyl RadicalC CH HH HH HH HH HH HH H unpaired electron is delocalized between unpaired electron is delocalized between benzylic carbon and the ring carbons that are benzylic carbon and the ring carbons that are ortho and para to itortho and para to it第67页第67页Resonance in Benzyl RadicalResonance in Benzyl RadicalC CH HH HH HH HH HH HH H unpaired electron is delocalized between unpaired electron is delocalized between benzylic carbon and the ring carbons that are benzylic carbon and the ring carbons that are ortho and para to itortho and para to it第68页第68页Spin Density in Benzyl Radicalunpaired electron is delocalized between unpaired electron is delocalized between benzylic carbon and the ring carbons that are benzylic carbon and the ring carbons that are ortho and para to itortho and para to it第69页第69页industrial processindustrial processhighly regioselective for benzylic positionhighly regioselective for benzylic positionFree-radical chlorination of tolueneCHCH3 3ClCl2 2lightlightororheatheatCHCH2 2ClClTolueneTolueneBenzyl chlorideBenzyl chloride第70页第70页11.11 Oxidation of AlkylbenzenesOxidant:KMnO4,HNO3,Na2Cr2O7/H2SO4Noteregardlessofchainlengthofalkylgroups,alkylgroupsconvertedtocarboxylgroups(-COOH)attacheddirectlytothering.第71页第71页Site of Oxidation is Benzylic CarbonSite of Oxidation is Benzylic CarbonCHCH3 3CHCH2 2R RCHRCHR2 2ororororCOHCOHOONaNa2 2CrCr2 2OO7 7H H2 2SOSO4 4H H2 2OOheatheat第72页第72页ExampleExampleNaNa2 2CrCr2 2OO7 7H H2 2SOSO4 4H H2 2OOheatheatCOHCOHOOCHCH3 3NONO2 2p p-Nitrotoluene-NitrotolueneNONO2 2p p-Nitrobenzoic-Nitrobenzoicacid(82-86%)acid(82-86%)第73页第73页ExampleExampleNaNa2 2CrCr2 2OO7 7H H2 2SOSO4 4H H2 2OOheatheatCH(CHCH(CH3 3)2 2CHCH3 3(45%)(45%)COHCOHOOCOHCOHOO第74页第74页Atert-alkylgroupisnotsusceptible(易受影响)tooxidationundertheseconditionsbecauseitlacksbenzylichydrogens.第75页第75页11.12 Nucleophilic Substitution in Benzylic HalidesPrimary Benzylic HalidesPrimary Benzylic Halidesacetic acidacetic acidCHCH2 2ClClOO2 2N NNaNaOOCCHCCH3 3OOCHCH2 2OOCCHCCH3 3OO2 2N NOOMechanism is SN2Mechanism is SN2(78-82%)(78-82%)第76页第76页tertiary benzylic carbocation is formedtertiary benzylic carbocation is formedmore rapidly than tertiary carbocation;more rapidly than tertiary carbocation;therefore,more stabletherefore,more stableWhat about SWhat about SN N1?1?C CCHCH3 3CHCH3 3ClCl6006001 1C CCHCH3 3CHCH3 3ClClCHCH3 3Relative solvolysis rates in aqueous acetoneRelative solvolysis rates in aqueous acetone第77页第77页What about SN1?What about SN1?C Cmore stablemore stableless stableless stableC CCHCH3 3Relative rates of formation:Relative rates of formation:CHCH3 3CHCH3 3+CHCH3 3CHCH3 3+第78页第78页allylic carbocationallylic carbocationCompare.Compare.+C CC CC C+C Cbenzylic carbocationbenzylic carbocationbenzylic carbon is analogous to allylic carbonbenzylic carbon is analogous to allylic carbon第79页第79页Resonance in Benzyl CationResonance in Benzyl CationC CH HH HH HH HH HH HH H+positive charge is delocalized between benzylic positive charge is delocalized between benzylic carbon and the ring carbons that are ortho and carbon and the ring carbons that are ortho and para to itpara to it第80页第80页Resonance in Benzyl Cation Resonance in Benzyl Cation C CH HH HH HH HH HH HH H+positive charge is delocalized between benzylic positive charge is delocalized between benzylic carbon and the ring carbons that are ortho and carbon and the ring carbons that are ortho and para to itpara to it第81页第81页Resonance in Benzyl CationResonance in Benzyl CationC CH HH HH HH HH HH HH H+positive charge is delocalized between benzylic positive charge is delocalized between benzylic carbon and the ring carbons that are ortho and carbon and the ring carbons that are ortho and para to itpara to it第82页第82页Resonance in Benzyl CationResonance in Benzyl CationC CH HH HH HH HH HH HH H+positive charge is delocalized between benzylic positive charge is delocalized between benzylic carbon and the ring carbons that are ortho and carbon and the ring carbons that are ortho and para to itpara to it第83页第83页第84页第84页SolvolysisSolvolysisC CCHCH3 3CHCH3 3ClClCHCH3 3CHCH2 2OHOHC CCHCH3 3CHCH3 3OCHOCH2 2CHCH3 3(87%)(87%)第85页第85页11.13 Preparation of Alkenylbenzenesdehydrogenationdehydrationdehydrohalogenation第86页第86页industrial preparation of styreneAlmost 1