有机化学OrganicChemistry

1、有机化学有机化学 Organic Chemistry2008.105.1 芳烃的结构芳烃的结构5.2 芳烃的同分异构和命名芳烃的同分异构和命名25.3 单环芳烃的物理性质单环芳烃的物理性质35.4 单环芳烃的化学性质单环芳烃的化学性质45.5 苯环上亲电取代的定位规则苯环上亲电取代的定位规则515.6 稠环芳烃稠环芳烃 5.7芳香性芳香性6教教 学学 内内 容容本章教学基本要求本章教学基本要求：1 1、掌握苯、萘、蒽、菲的结构，并会用价键理论和分子轨道理论、掌握苯、萘、蒽、菲的结构，并会用价键理论和分子轨道理论、共振论对苯的结构进行解释；共振论对苯的结构进行解释；2 2、掌握芳烃的命名和异构；

2、、掌握芳烃的命名和异构；3 3、掌握单环芳烃的性质，理解亲电取代反应历程，掌握定位规则、掌握单环芳烃的性质，理解亲电取代反应历程，掌握定位规则的应用；的应用；4 4、了解单环芳烃的来源和制备；、了解单环芳烃的来源和制备；5 5、掌握多环芳烃的化学性质、萘的磺化反应、动力学控制和热力、掌握多环芳烃的化学性质、萘的磺化反应、动力学控制和热力学控制。学控制。6 6、理解芳香性概念、芳香性的判别、休克尔规则。、理解芳香性概念、芳香性的判别、休克尔规则。7 7、了解非苯芳烃的类型和代表物。、了解非苯芳烃的类型和代表物。本章重点和难点：本章重点和难点：苯的结构、命名、化学性质、亲电取代反应历程和定位规则；

3、苯的结构、命名、化学性质、亲电取代反应历程和定位规则；芳香芳香性的判别、休克尔规则。性的判别、休克尔规则。 Isomerism and Nomenclature of Aromatic Hydrocarbons. Structure and Stability of Benzene. Physical Properties of Monocyclic Aromatic Hydrocarbons. Chemical Properties of Monocyclic Aromatic Hydrocarbons. Chemical Properties of Polycyclic Aromatic

4、Hydrocarbons. Aromaticity and the Huckel Rule.Introduction(1) In 1834 the German chemist Eilhardt Mitscherlich (University of Berlin) firstly synthesized benzene by heating benzoic acid with calicum oxide. Using vapor density measurements, Mitscherlich further showed that benzene has the molecular f

5、ormula C6H6: The molecular formula itself was surprising. Benzene has only as many hydrogen atoms as it has carbon atoms, it should be a highly unsaturated compound. Eventually, chemists began to recognize that benzene does not show the behavior expected of a highly unsaturated compound.C6H5CO2HC6H6

6、CaCO3CaO+HeatBenzoic AcidBenzeneIntroduction(2) During the latter part of the nineteenth century the Kekule Couper-Butlerov theory of valence was systematically applied to all known organic compounds. Organic compounds were classified as being either aliphatic or aromatic. To be classified as alipha

7、tic meant that the chemical behavior of a compound was “fatlike”. To be classified as aromatic meant that the compound had a low hydrogen-carbon ratio and that it was “fragrant”.Isomerism and Nomenclature of Aromatic Hydrocarbons(2) Disubstituted benzenes are named using one of the prefixes ortho(o)

8、, meta(m), or para(p). An ortho-disubstituted benzene has its two substituents in a 1,2 relationship on the ring; a meta-disubstituted benzene has its two substituents in a 1,3 relationship; and a para-disubstituented benzene has its substituents in a 1,4 relationship. For example:CH3CH3CH3CH3CH3CH3

9、Xylenepara-Xylenemeta-Xyleneortho-BACKIsomerism and Nomenclature of Aromatic Hydrocarbons(1)Monosubstituted benzene are systematically named in the same manner as other hydrocarbons, with benzene as the parent name. For example:If the alkyl substituent has more than six carbons, or has carbon-carbon

10、 double bond and triple bond, the compound is named as a phenyl-substituted alkane, alkene or alkyne. For example:CH2CH2CH3CH(CH3)2PropylbenzeneIsopropylbenzeneCHCH2CH2CH2CH2CH3CH3CHCH2CH=CHCH3CH3Phenyl hexene5_2_Phenylheptane2_Structure and Stability of Benzene(1) In 1865, August Kekule, the origin

11、ator of the structual theory, proposed the first definite structure for benzene, a structure that is still used today. Kekule suggested that the carbon atoms of benzene are in a ring, that they are bonded to each other by alternating single and double bonds, and that one hydrogen atom is attached to

12、 each carbon atom. The fact that the bond angles of the carbon atoms in the benzene ring are all 120o strongly suggests that the carbon atoms are sp2 hydridized.Structure and Stability of Benzene(2)Although benzene is clearly unsaturated, it is much more stable than other alkenes, and it fails to un

13、dergo typical alkene reactions. For example:We can get a quantitative idea of benzenes stability from the heats of hydrogenation.+Br2BrHBrFecatalyst+BromobenzeneHHBrBrAddition productNOT formed-CyclohexaneCyclohexeneBenzeneCyclohexadiene1,3-118kJ/mol-230kJ/mol-356kJ/mol-206kJ/mol(expected)(actual) 1

14、50kJ/mol(actual)(difference)Chemical Properties of Monocyclic AromaticHydrocarbons(1)Chemistry of Benzene: Electrophilic Aromatic Substitution. The most common reaction of aromatic compounds is electrophilic aromatic substitution. That is, an electrophile (E+) react with an aromatic ring and substit

15、utes for one of the hydrogens:Many different substituents can be introduced onto the aromatic ring by electrophilic substitution reactions. By choosing the proper reagents, its possible to halogenate the aromatic ring, nitrate it, sulfonate it, alkylate it, or acylate it. Halogenation Nitration Sulf

16、onation Alkylation AcylationHE+E+H+HXSO3HCORNO2RChemical Properties of Monocyclic Aromatic Hydrocarbons(2) Aromatic Halogenation: A. Bromination of Aromatic Rings A benzene ring , with its six electrons in a cyclic conjugated system, is a site of electron density. Thus, benzene acts as an electron d

17、onor (a Lewis base, or nucleophile) in most of its chemistry, and most of its reactions take place with electron acceptors (Lewis acids, or electrophiles). For example, benzene react with Br2 in the presence of FeBr3 as catalyst to yield the substitution product bromobenzene.+Br2BrHBrFeBr3+Chemical

18、Properties of Monocyclic Aromatic Hydrocarbons(3) The mechanism of the electrophilic bromination of benzene.FeBr3Polarized brominea weak electrophile a strong electrophile BrBrFeBr3 + -BrBr - +Br BromineSlowBrBrFeBr3 + -+FeBr4-+BrHBrH+BrH+FeBr3FeBr4-+BrH+ FastBrHBr+Step OneStep TwoStep Three.Chemica

19、l Properties of Monocyclic Aromatic Hydrocarbons(4) Aromatic Halogenation: B. Chlorination and Iodination of Aromatic Rings Chlorine and iodine can be introduced into aromatic rings by electrophilic substitution reactions, but fluorine is too reactive, and only poor yields of monofluoroaromatic prod

20、ucts are obtained by direct fluorination. For example:FeCl3 Cl2H+Cl+HClCuCl2 I2H+Chlorobenzene(86%) IIodobenzene(65%)Chemical Properties of Monocyclic Aromatic Hydrocarbons(5) Aromatic NitrationAromatic rings can be nitrated by reaction with a mixture of concentrated nitric and sulfuric acids. The e

21、lectrophile in this reaction is the nitronium ion, NO2+, which is generated from HNO3 by protonation and loss of water. The nitronium ion react with benzene to yield a carboncation intermediate in much the same way as Br+. Loss of H+ from this intermediate gives the product, nitrobenzene. +ONO+.O.+H

22、NOOH.O.NOO+HHONONHOO+N2OHSO4H2SO4H2OChemical Properties of Monocyclic Aromatic Hydrocarbons(6) Aromatic Sulfonation Aromatic rings can be sulfonated by reaction with fuming sulfuric acid, a mixture of H2SO4 and SO3. The reactive electrophile is either HSO3+ or SO3, depending on reaction conditions.

23、Substitution occurs by the same two-step mechanism seen previously for bromination and nitration. +OSOOHOSOOH+OSOOH2SO4HSO4OHSOOHHSO4SO3H+H2SO4Chemical Properties of Monocyclic Aromatic Hydrocarbons(7)Alkylation of Aromatic Rings: The Friedel-Crafts Reaction One of the most useful of all electrophil

24、ic aromatic substitution reactions is alkylation, the attachment of an alkyl group to the benzene ring. For example:The Friedel-Crafts alkylation reaction is an electrophilic aromatic substitution in which the electrophile is a carbocation, R+. Aluminum chloride catalyzes the reaction by helping the

25、 alkyl halide to ionize in much the same way that FeBr3 catalyzes aromatic brominations by polarizing Br2 . Loss of a proton then completes the reaction.BenzeneChloropropaneIsopropylbenzene2-CH3CHCH3Cl+AlCl3CHCH3CH3+HClChemical Properties of Monocyclic AromaticHydrocarbons(8)The mechanism of the Fri

26、edel-Crafts alkylation reaction:Give the structures of the major products of the following reactions:How to prepare propylbenzene by Friedel-Crafts reaction?H CHCH3CH3AlCl4CH3CHCH3AlCl4+CHCH3CH3+HCl+AlCl3CH3CHCH3Cl+AlCl3CH3CHCH3AlCl4+CH3CH2CH2ClAlCl3+CH3CH=CH2HF0 COCH2CH2CH3?Chemical Properties of M

27、onocyclic Aromatic Hydrocarbons(9)An acyl group, -COR, is introduced onto the ring when an aromatic compound reacts with a carboxylic acid chloride, RCOCl, in the presence of AlCl3. For example, reaction of benzene with acetyl chloride yields the ketone, acetophenone.The mechanism of Friedel-Crafts

28、acylation:+CH3CH2CClOAlCl380 COCCH2CH3O+HClCH3CH2CClOAlCl3CH3CH2C OCH3CH2C O+AlCl4-An acyl cation+CCH2CH3O+CH3CH2C OAlCl3COCH2CH3H AlCl4-HCl+Chemical Properties of Monocyclic Aromatic Hydrocarbons(10)How to prepare propylbenzene by Friedel-Crafts reaction?By contrast, the Friedel-Crafts acylation of

29、 benzene with propanoyl chloride produces a ketone with an unrearranged carbon chain in excellent yield.This ketone can then be reduced to propylbenzene by several methods. One general method-called the Clemmensen reduction-consists of refluxing the ketone with hydrochloric acid containing amalgamat

30、ed zinc.CH2CH2CH3?+CH3CH2CClOAlCl380 COCCH2CH3O+HClCOCH2CH3Zn(Hg)HClrefluxCH2CH2CH3Ethyl phenyl ketonePropylbenzene( )80%Chemical Properties of Monocyclic Aromatic Hydrocarbons(11) Substituent Effects in Substituted Aromatic RingsOnly one product can form when an electrophilic substitution occurs on

31、 benzene, but when what would happen if we were to carry out a reaction on an aromatic ring that already has a substituent? A substituent already present on the ring has two effects:1. A substituent affects the reactivity of the aromatic ring. Some substituents activate the ring, making it more reac

32、tive than benzene, and some deactivate the ring, making it less reactive than benzene. For example:Reactive rate 1000 1 0.033 610-8of nitrationOHHClNO2Chemical Properties of Monocyclic Aromatic Hydrocarbons(12) Substituent Effects in Substituted Aromatic Rings2. Substituents affect the orientation o

33、f the reaction. The three possible disubstituted products-ortho, meta, and para- are usually not formed in equal amounts. Instead, the nature of the substituent already present on the benzene ring determines the position of the second substitution. For example: Orientation of Nitration in Substitued

34、 Benzenes Product (%) Product(%) Ortho Meta Para Ortho Meta Para Meta-directing deactivators Ortho- and para-directing deactivators-+N(CH3)3 2 87 11 -F 13 1 86 -NO2 7 91 2 -Cl 35 1 64-COOH 22 76 2 -Br 43 1 56 -CN 17 81 2 -I 45 1 54 -COOCH3 28 66 6 Ortho- and para-directing activators -COCH3 26 72 2

35、-CH3 63 3 34 -CHO 19 72 9 -OH 50 0 50 -NHCOCH3 19 2 79 Chemical Properties of Monocyclic Aromatic Hydrocarbons(13) Substituent Effects in Substituted Aromatic Rings Substituents can be classified into three groups: Ortho-and para-directing activators, ortho-and para-directing deactivators, and meta-

36、directing deactivators. Ortho-and para- ortho-and para- Meta-directing directing activators directing deactivators deactivatorsOH NHCOCH3 Ph H Cl I COCH3 CCH3 CN NR3OONH2 OCH3 CH3(alkyl) F Br C H C OH SO3H NO2OOReactivity+Chemical Properties of Monocyclic Aromatic Hydrocarbons(14) An Explanation of

37、Substituent Effects(1) Activation and Deactivation of Aromatic Rings The common feature of all activating groups is that they donate electrons to the ring, thereby stabilizing the carbocation intermediate from electrophilic addition and causing it to form faster. The common feature of all deactivati

38、ng groups is that they withdraw electrons from the ring, thereby destabilizing the carbocation intermediate from electrophilic addition and causing it to form more slowly.Chemical Properties of Monocyclic Aromatic Hydrocarbons(15)An Explanation of Substituent Effects(2)Ortho- and Para- Directing Act

39、ivators: Alkyl GroupsInductive and resonance effects account for the directing ability of substituents as well as for their activating or deactivating ability. Take alkyl groups, for example, which have an electron-donating inductive effect and behave as ortho and para directors. The results of tolu

40、ene nitration are shown as below:CH3CH3HNO2CH3HNO2CH3HNO2CH3HNO2CH3HNO2CH3HNO2CH3HNO2CH3HNO2CH3HNO2OthroMetaParaMost stableMost stableChemical Properties of Monocyclic Aromatic Hydrocarbons(15)An Explanation of Substituent Effects(3)Ortho- and Para- Directing Activators: OH and NH2 Hydroxyl, alkoxyl

41、, and amino groups are also ortho-para activators, but for a different reason than for alkyl groups. Hydroxyl, alkoxyl, and amino groups have a strong, electron-donating resonance effect that is most pronounced at the ortho and para positions and outweighs a weaker electron-withdrawing inductive eff

42、ect. When phenol is nitrated, only ortho and para attack is observed:OHHNO2OHOrthoMetaParaMost stableMost stableOHNO2HOHNO2HHNO2OHHNO2OHHNO2OHHNO2OHHNO2OHHNO2OHOHNO2HOHNO2HChemical Properties of Monocyclic Aromatic Hydrocarbons(16)An Explanation of Substituent Effects(4)Ortho- and Para- Directing De

43、activators: HalogensHalogens are deactivating because their stronger electron-withdrawing inductive effect outweighs their weaker electron-donating resonance effect. Though weak, that electron-donating resonance effect is felt only at the ortho and para positions.ClHNO2ClOrthoMetaParaMost stableMost

44、 stableHNO2 ClHNO2ClHNO2ClHNO2ClHNO2 ClHNO2 ClNO2HClNO2HClNO2HClNO2HClChemical Properties of Monocyclic Aromatic Hydrocarbons(17)An Explanation of Substituent Effects(5)Meta- Directing DeactivatorsMeta-directing deactivators act through a combination of inductive and resonance effects that reinforce

45、 each other. Inductively, both ortho and para intermediates are destabilized because a resonance form places the positive charge of the carbocation intermediate directly on the ring carbon atom that bears the deactivating group. At the same time, resonance electron withdrawal is also felt at the ort

46、ho and para positions. Reaction with an electrophilic therefore occurs at the meta position.CHOOrthoMetaParaHClCHOHClCHOClHCHOClHCHOClHCHOHClCHOHClCHOHClCHOHClCHOLeast stableLeast stableChemical Properties of Monocyclic Aromatic Hydrocarbons(18)Trisubstituted Benzenes: Additivity of EffectsFurther e

47、lectrophilic substitution of a disubstituted benzene is governed by the same resonance and inductive effects just discussed. The only difference is that its necessary to consider the additive effects of two different groups. In practice, three rules are usually sufficient:Rule 1. If the directing ef

48、fects of the two groups reinforce each other, there is no problem.Rule 2. If the directing effects of the two groups oppose each other, the more powerful activating group has the dominant influence, but mixtures of products often result.Rule 3. Further substitution rarely occurs between the two grou

49、ps in a meta- disubstituted compound because this site is too hindered. Some examples:CH3NO2OHCH3CH3ClCOOHSOH3NHCOCH3Chemical Properties of Monocyclic Aromatic Hydrocarbons(19) Synthesis of Substituted BenzenesOne of the surest ways to learn organic chemistry is to work synthesis problems. The abili

50、ty to plan a successful multistep synthesis of a complex molecule requires a working knowledge of the uses and limitations of many hundreds of organic reactions. Not only must you know which reactions to use, you must also know when to use them. The order in which reactions are carried out often cri

51、tical to the success of the overall scheme.The ability to plan a sequence of reactions in the right order is particularly valuable in the synthesis of substituted aromatic rings, where the introduction of a new substituent is strongly affected by the directing effects of other substituents. Planning

52、 synthesis of substituted aromatic compounds is therefore an excellent way to gain facility with the many reactions learned in the past few chapters. Some examples:BrCOOHClNO2CH2CH2CH3NO2C(CH3)3ABCChemical Properties of Monocyclic Aromatic Hydrocarbons(20) Reduction of Aromatic Compounds To hydrogen

53、ate an aromatic ring, its necessary to use a platinum catalyst with hydrogen gas at several hundred atmospheres pressure. For example: Oxidation of Benzene:CH3CH3H2/Pt/ethanol200atm, 25CoCH3CH3CH3CH3V2O5+O2Co400500OOOChemical Properties of Monocyclic Aromatic Hydrocarbons(21) Oxidation of Alkylbenzene Side Chains Alkyl side chains are readily attacked by oxidizing agents and are converted into carboxyl groups, -COOH. For example: Bromination of Alkylbenzene Side Chains BACKCH2CH3KMnO4/H2OCOOHC(CH3)3CH3KMnO4/H2OC(CH3)3HOOCCH2CH3NBS/CCl4CHCH3BrhvChemical Properties