Chapter 9aromatic compounds

1、Chapter 9 Aromatic compounds芳香化合物芳香化合物Text 1: chapter 16, 17Text 2: 第七章Contentsu 1. The structure of benzeneu 2. Aromaticityu 3. Nomenclature of benzene derivativesu 4. Physical propertiesu 5. Reactions of benzene and its derivatives Electrophilic aromatic substitution -Effects of substituents: Reac

2、tivity and orientation Nucleophilic aromatic substitution Addition reactions of benzene derivatives Side-chain reactions of benzene derivatives Reactions of phenolsDiscovery of Benzene Isolated in 1825 by Michael Faraday who determined C:H ratio to be 1:1. Synthesized in 1834 by Eilhard Mitscherlich

3、 who determined molecular formula to be C6H6. Other related compounds with low C:H ratios had a pleasant smell, so they were classified as aromatic(芳香性的). The Kekule Structure for benzene 苯的克庫(kù)勒結(jié)構(gòu)苯的克庫(kù)勒結(jié)構(gòu)1. The Structure of benzene (16-2, 3) Proposed in 1866 by Friedrich Kekul, shortly after multiple

4、bonds were suggested.Failed to explain existence of only one isomer of 1,2-dichlorobenzene.orCCCCCCHHHHHHClClClClSame compundModern theories of the structure of benzeneRTAntibonding MOBonding MO反鍵軌道成鍵軌道VBMOHydrogenation of just one double bond in benzene is endothermic（吸熱）!The unusual stability of b

5、enzeneDifferences in Reactions between alkene and benzeneBr2 / CCl4dark, 25oCKMnO4 / H2O25 oCH2O, HClheatH2 / NiNo additionNo hydrationNo oxidationSlow additionat hight temperatureand pressureBr2FeBr3BrAromatic Requirements Structure must be cyclic with conjugated pi bonds. Each atom in the ring mus

6、t have an unhybridized p orbital. The p orbitals must overlap continuously around the ring. (Usually planar structure) Compound is more stable than its open-chain counterpart2. Aromaticity芳香性Anti- and Nonaromatic反芳香性和非芳香性 Antiaromatic（反芳香性的） compounds are cyclic, conjugated, with overlapping p orbit

7、als around the ring, but the energy of the compound is greater than its open-chain counterpart. Nonaromatic（非芳香性的） compounds do not have a continuous ring of overlapping p orbitals and may be nonplanar. Hckels Rule （休克爾規(guī)則） If the compound has a continuous ring of overlapping p orbitals and has 4N +

8、2 pielectrons, it is aromatic. If the compound has a continuous ring of overlapping p orbitals and has 4N electrons, it is antiaromatic. The (4n+2) pi-Electron Rule(1) polynuclear aromatic hydrocarbons (PAH, 多核芳烴,16-10)789101234Phenanthrene菲65254106378Pyrene芘19Other aromatic compoundsNaphthalene萘123

9、45678Anthracene蒽12345678910Fused aromatic compounds稠環(huán)芳烴As the number of aromatic rings increases, the resonance energy per ring decreases, so larger PAHs will add Br2.(mixture of cis and trans isomers)HBrHBrHBrHBr 4Annulene is antiaromatic (4N e-s) 8Annulene would be antiaromatic, but its not planar

10、, so its nonaromatic. 10Annulene is aromatic except for the isomers that are not planar. Larger 4N annulenes are not antiaromatic because they are flexible enough to become nonplanar. (2) Nannulenes (輪烯)HH10annulenenonaromatic8annuleneNonaromatic非芳香性18annuleneAromatic if planar16annuleneAntiaromatic

11、 if planarHHHH14annulenenonaromaticOOABProblem: Which molecule is more stable? Azulene 奧(aromatic)The dipole moment is 1.0D( aromatic 具有芳香性)H3CCH3Answer: (A)MO Derivation of Hckels Rule Lowest energy MO has 2 electrons. Each filled shell has 4 electrons. =The Polygon Rule多邊形規(guī)則ringNumber of electrons

12、*n nE ECyclopentadienyl Ions 環(huán)戊二烯離子4 electrons, antiaromatic.6 electrons, aromatic.HH+OC(CH3)3H+HOC(CH3)3pKa = 16pKa = 19AcidityAromatic ionsTropylium Ion 卓翁離子6 p electrons and an empty p orbital.Aromatic: more stable than open chain ion Cycloheptatrienyl cation環(huán)庚三烯陽(yáng)離子HOHH+, H2OHHAromatic ionsDianio

13、n of 8Annulene 8輪烯二價(jià)陰離子10 p electrons, aromatic. Cyclooctatetraenyl dianion環(huán)辛四烯二價(jià)陰離子+ 2K+ 2K+Aromatic ions(3) Heterocyclic aromatic compounds （16-9） 雜環(huán)芳香化合物（中文下冊(cè)）Npyridine吡啶NHpyrrole吡咯Ofuran呋喃Sthiophene噻噻吩吩Pyridine 吡啶Nonbonding pair of electrons in sp2 orbital, so weak base, pKb = 8.8.NPyrrole 吡咯Als

14、o aromatic, but lone pair of electrons is delocalized, so much weaker base.NHBasic or Nonbasic?NNPyrimidine（嘧啶） has two basicnitrogens.NNHImidazole（咪唑） has one basicnitrogen and one nonbasic.NNNNHPurine（嘌呤） ?=3. Nomenclature of benzene derivatives Monosubstituted benzenes “XXbenzene” ， XX苯Fluorobenz

15、ene(氟苯）Chlorobenzene（氯苯）Bromobenzene（溴苯）Nitrobenzene(硝基苯）FClBrNO2SO3HCOOHCOCH3OCH3Benzenesulfonic acid苯磺酸Benzoic acid苯甲酸Acetophenone苯乙酮Anisole苯甲醚CH3CH2CH3OHNH2MethylbenzeneToluene(甲苯）Ethylbenzene（乙苯）HydroxybenzenePhenol（苯酚）（苯酚）AminobenzeneAniline（氨基苯， 苯胺苯胺）BrBrBrBrBrBr1,3-Dibromobenzenem-Dibromobenz

16、ene間二溴苯1,2-Dibromobenzeneo-Dibromobenzene 鄰二溴苯1,4-Dibromobenzenep-Dibromobenzene對(duì)二溴苯(2) disubstituted benzenes 1,2-; 1,3-; 1,4- o- (鄰), m- (間), p- (對(duì)) CH3CH3CH3CH3CH3CH31,2-Dimethylbenzene 1,3-Dimethylbenzne 1,4-Dimethylbenzeneo-xylene m-xylene p-xyleneCOOHCOOHCOOHNO2NO2NO22-Nitrobenzoic acid 3-Nitr

17、obenzic acid 4-Nitrobenzic acido-Nitrobenzoic acid m-Nitrobenzoic acid p-Nitrobenzoic acidCH2BenzylCH2ClBenzyl chloride芐基氯芐基(3) benzene as substituent: phenyl group (苯基苯基)， Ph-CH2CH2CH2CH3CH3C=CHCH3PhCH3CHCH2CH2CH2CH2CH3PhButylbenzene2-Phenyl-2-butene2-PhenylheptaneBenzyl group (芐基芐基),Bn-Aryl group

18、(芳基芳基),Ar-Arene = Aromatic hydrocarbon 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 w

19、ater. Solubility: Generally insoluble in water.4. Physical properties and spectroscopy of aromatic compoundsUV: 254 nm (B 帶) IR: 3030 (C-H), 1600 (skeleton), 1500 cm-11H NMR: 79ppmMS:m/z, 91CH2+m/z, 65+spectroscopy of aromatic compoundsO1-phenylpropan-2-oneM+, 134m/z, 119m/z, 91CCH3OCOCH2m/z, 65lAss

20、ignments: l T-1: 16-27, 28, 30, 33, 365. Reactions of benzene and its derivatives(Chapter 17)1) Electrophilic aromatic substitution reactions17-217-317-417-1017-11X2, FeX3(X = Cl, Br)X+ HXHalogenation鹵化NO2HNO3H2SO4+ H2OSO3H2SO4SO3HRCl, AlCl3R+ HClRCOCl, AlCl3RONitration 硝化Sulfonation磺化Friedel-Crafts

21、 Alkylation傅-克烷基化Friedel-Crafts Acylation傅-克?；? HClElectrophilic addition-elimination mechanism親電加成-消除機(jī)理Arenium ion (芳基正離子) intermediate- complex (-絡(luò)合物）+ E+EH+EH+EH+additioneliminationEH+ H+EEact1Eact2TS 1TS 2Ereaction coordinationThe reaction-energy diagram (反應(yīng)能線(xiàn)圖反應(yīng)能線(xiàn)圖)rate-limiting stepreactants-

22、complexproductHalogenation of benzene: X2, FeX3Reactivity: F2 Cl2 Br2 I2BrBr FeBr3+BrH+BrH+BrH+ FeBr4BrBr+FeBr3BrBr FeBr3+BrH+Br+ H+ I2IHNO386%+ NO2 + H2ONitration of benzene: HNO3 + H2SO4H O NOOHO SOOO H+H O NOOH+ HSO4ON O+ H2ONitronium ionsrong electrophileSulfonation of benzene: fuming sulfuric a

23、cid (發(fā)煙硫酸) 7% SO3 in H2SO4Benzenesulfonic acidSO3H+ H2O+ H2SO4heatSOOOSOOOSOOOSOOOSOOO+SHOOOHSO3HThe Friedel-Crafts alkylation of benzene: RX, AlCl3( or ether Lewis acid)RXAlCl3+-E+:l R+ can rearrangement;l Polyalkylations often occur.C=C, H+C-C-OH, acidOther carbocation sourceLimitations:Problems:

24、Predict products for the reactions of benzene with the following reagents. ClCl+ HFOH+ BF3(a)(b)(c)(d)+ AlCl3+ AlCl3The Friedel-Crafts Acylation of benzene: RCOCl, AlCl3 (Lewis acid)E+:R-CXAlCl3+-OROROOCH3C+OCH3CO+Acylium ion 酰基正離子So-m-p- Reactivity: Electron donating group (給電子): Activiting (活化) El

25、ectron withdrawing (拉電子): deactivating (鈍化) (2) Orientation: o-, m-, p-, which is major?The effects of substituents on the electrophilic aromatic substitution: Reactivity and OrientationActivating groups: ortho-para directorsCH3HNO3H2SO4CH3NO2CH3NO2CH3NO2+89%37%4%ortho-para director group 鄰對(duì)位定位基鄰對(duì)位定

26、位基 CH3-, R-, CH3O-, CH3CONH-, HO-, -NH2和芳環(huán)碳相連的原子帶部分負(fù)電荷, 或有孤對(duì)電子, 因此有給電子作用.17-6Does not undergo a Friedel-Crafts reactionNH2+AlCl3(-NHR, -NR2)NH2+Cl3AlOH+AlCl3OH+Cl3Al(OR)Deactivating groups: Meta-DirectorsMeta-Directors 間位定位基-NO2, -COOH, -COOR, RCO-, SO3H, -CHO, CH3CO-, -CF3NO2HNO3H2SO4NO2NO2NO2NO2+6

27、%1%93%NO2NO2和芳環(huán)碳相連的原子帶部分正電荷, 因此有拉電子作用.17-7Halo substituents: Deactivating but ortho-para directors ClHNO3H2SO4ClNO2ClNO2+30%70%ClClClCl+39%55%Cl2FeCl3+ClCl6%Cl17-8ortho-para directors (鄰-對(duì)位定位基）meta directors (間位定位基)Strongly Activating -NH2, -NHR, -NR2, -OH, -O-Strongly Deactivating-NO2, -NR3+, -CF3,

28、 -CCl3Moderately Activating-NHCOCH3, -NHCOR, -OCH3, -ORModerately Deactivating-CN, -SO3H, -COOH, -COOR, -CHO, -CORWeakly Activating-CH3, -CH2CH3, -R, -C6H5Weakly Deactivating-F, -Cl, -Br, -IClassification of substituentsInductive effect explanation 誘導(dǎo)效應(yīng)解釋SE+-+SE+-+Explanation of the orientaionResona

29、nce effect explanation共振效應(yīng)解釋CF3+E+CF3ENH2OHOCH3ClAnilinePhenolChlorobenzeneanisoleCH3toluenem- directoro-, p- directorConclusion:-CF3 is a m-director。+ charges adjacent,unstableo-p-m-HECF3HECF3HECF3HECF3HECF3HECF3CF3EHCF3EHCF3EH+Conclusion:-CH3 is a o- and p-director.3favorable3favorableo-p-m-HECH3H

30、ECH3HECH3HECH3HECH3HECH3CH3EHCH3EHCH3EH4 resonance structure, more stableo-p-m-HEOHHEOHHEOHHEOHHEOHHEOHHEOHHEOHOHEHOHEHOHEHConclusion:-OH is a o- and p-director.4 resonance structures, more stable3 resonance structures, less stableo-p-m-HEClHEClHEClHEClHEClHEClHEClHEClClEHClEHClEHConclusion:-Cl is a

31、 o- and p-director.4 resonance structure, more stable4 resonance structure, more stable3 resonance structures, less stableOrientation in disubstituted benzenesu兩個(gè)取代基定位效應(yīng)一致兩個(gè)取代基定位效應(yīng)一致-共同指向位置共同指向位置u兩個(gè)取代基定位效應(yīng)不一致兩個(gè)取代基定位效應(yīng)不一致-由鄰對(duì)位基確定指向位置由鄰對(duì)位基確定指向位置; 如兩個(gè)都是間位定位基或鄰對(duì)位定位基，由強(qiáng)者確定指向位如兩個(gè)都是間位定位基或鄰對(duì)位定位基，由強(qiáng)者確定指向位置。置

32、。NHCOCH3SO3HCF3NO2OHNO2NHCOCH3HO3SCF3NO2OHNO2biphenyl聯(lián)苯2) Nucleophilic aromatic substitutionSubstrate: aryl halide (芳基鹵)ClNO2OHNO2+ OH-aq. NaHCO3130CH+ClNO2NO2OHNO2NO2+ OH-aq. NaHCO3100CH+ClNO2NO2O2NOHNO2NO2O2N+ OH-aq. NaHCO335CH+鄰、對(duì)位有吸電子基有利。Addition-elimination mechanismClNO2+ OH-additionslowOHClNO

33、2eliminationfastOH-+ Cl-O-NO2OHNO2+ Cl-Cl350(high pressure)ONaNaOHHClOHBrK+NH2-NH2-NH3NH2NH2(50%)(50%)14141414Elimination-addition mechanism: benzyne 苯炔機(jī)理苯炔機(jī)理base = NaNH2or high pressure3) Addition reactions of benzene derivatives(1) Chlorination ClClClClClClCl2hvor high T, pFree radical mechanism(2

34、) Addition of hydrogen (reduction)Catalytic hydrogenation of aromatic ringH2catalystcatalyst: Pt, Pd, Ru, Rh, NiNo The Birch reduction 伯奇還原伯奇還原Developed by the Australian chemist A.J. BirchBenzeneNH3, EtOH1,4-CyclohexadieneNa or KMechanism: similar as trans- reduction of alkyne with Na/NH3(liq.) (p-

35、756)1,2-DimethylbenzeneNH3, EtOHNaCH3CH31,2-Dimethyl-1,4-cyclohexadiene 77-92 %CH3CH3(o-xylene)Methoxybenzene苯甲醚NH3, EtOHLiOCH3OCH31-Methoxy-1,4-cyclohexadiene 80 %Sodium benzoateNH3, EtOHNa(苯甲酸鈉)COONaCOONaH3O+COOH89-52 %electron donating給電子基，氫加在給電子基，氫加在2,5-位位electron withdrawing拉電子基拉電子基, 氫加在氫加在1,4-

36、 位位4) Reactions of the side chain of alkylbenzenes(1) Halogenation of the side chain benzylic radicalslightCCl4CH2BrBenzyl bromide 64%CH3+NBrOONBS+NHOOToluenelightCCl4CHBrCH2CH3NBSCH3useful in synthesis氯代產(chǎn)物復(fù)雜，除芐基位外還有位取代產(chǎn)物。(2) Oxidation of the side chainCH2CH2CH31) KMnO4, OH-2) H3O+COOHBenzoic acid 1

37、00%An alkylbenzeneCH2CH2CH31) KMnO4, OH-2) H3O+C(CH3)3COOHC(CH3)3除叔丁基外，烷基都被氧化COOH The alkyl side chain with - H on a benzene ring is oxidized to benzoic acid by chromic acid(鉻酸) or KMnO4:O2+OOOV2O54505005) Reaction of phenols (17-15)CH3OHCH3OHH3COH2-Methylphenol(鄰-甲酚）3-Methylphenol(間-甲酚）4-Methylphen

38、ol(對(duì)-甲酚）OHOHOHOHHOOH1,2-Benzenediol(兒茶酚,鄰苯二酚)1,3-Benzenediol(雷瑣酚,間苯二酚）1,4-Benzenediol (對(duì)苯二酚)Synthesis of phenolin laboratory Ar-NH2HONOAr-N2+H3O+heatAr-OHCl350(high pressure)ONaNaOHHClOHindustrial synthesisOxidization:+ O295-135O O HCumene hydroperoxide(過(guò)氧化異丙基苯)Hydrolytic rearrangement:O O HH+, H2O5

39、0-90OHO+Acetone (丙酮）OH+ NaOHO-Na+ H2OStronger acidpKa = 10(slightly soluble)Stronger baseWeaker base (soluble)Weaker acid pKa = 16H2OArOHNaOHArO-Na+R-XX = Cl, Br, I, OSO2R or ,OSO2OR.ArOR + NaXOOHCOOHOCCH3COOHCH3C_2O+H+O+ CH3COHOSalicylic acid (水楊酸）Acetic anhydride (乙酸酐）Axetylsalicylic acid (乙酰水楊酸）a

40、spirin阿斯匹林Reactions of phenolsOH+ 3Br2H2OOHBrBrBr+ 3 HBr2,4,6-Tribromophenol (2,4,6-三溴苯酚）White precipitate.OHOHOHNO2NO220% HNO325+(30 - 40 %)(15 %)The ortho and para can be separated by steam distillationOHOHOHSO3HSO3HconcdH2SO425100concd H2SO4, 100Major product, rate controlMajor product, equilibrium controlElectrophilic aromatic substitutionOxidation of phenolsOHOOK2Cr2O7-H2SO4在合成中酚羥基要保護(hù)，以防止氧化p-Benzoquinone (對(duì)-苯醌)Reaction with FeCl3phenol , 藍(lán)紫色，烯醇的特殊性質(zhì)。用來(lái)檢驗(yàn)酚或烯醇結(jié)構(gòu)。6) Naphthalene 萘萘分子中碳碳鍵長(zhǎng)不等同分子中碳碳鍵長(zhǎng)不等