復(fù)旦大學(xué)有機(jī)化學(xué)課件

1、Chapter 6AlkenesThe carbon-carbon double bond (C=C) is the functional group of alkenes.General formula: CnH2nUnsaturated hydrocarbonsAlkenes contain less than theof hydrogen.um quantity6-1Structure of alkenes6-2Carbon skeletonsPosition of the double bond Geometric isomerismStability?acab and cd,geom

2、etric isomerismCCa=b or c=d, no geometric isomerismbdGeometric isomers have different physical properties.H3CCH3CCH3CHCCCH3HHHtrans-2-Butenecis-2-ButeneM.p.（oC） B.p.（oC）Relative density (at 20oC)-1060.90.6490-1393.50.66710-301.1Dipole moment(Cm)Their chemical properties are similar but not identical

3、; they react with the same reagents, but at different rates (especially in biological systems).HOHOHOHOHHOO6-3Nomenclature1. Selethe parent structure the longest continuouschain that contains the C=C bond.2. Indicate by a number the position of the double bond in the parent chain.3. Indicate by numb

4、ers the positions of the alkyl groups attached to the parent chain.4. Each name is derived by changing the ending ane of the corresponding alkane name to ene.5. When a geometric isomer is to be specified, a prefix is added: cis- or trans-, or (Z)- or (E)-.H2CCH2CH3CHCH2H2CCHCH2CH3CH3CHCHCH3Ethene Et

5、hyleneCH3Propene1-Butene2-Butene (cis- or trans-)CH3CH3H2CH2CC HCCH3CH3CHCHCHCH3CCH3CH32-Methylpropene3,3-Dimethyl-1-butene4-Methyl-2-pentene (cis- or trans-)CH3CH2CCH2CH3CHCH2CCH2CH2CH3CH3CH2CHCHCH3CH(CH2)2CH3CH2CH2CH32-乙基-1-戊烯CH3CH24-甲基-2-丙基-1-戊烯3-甲基-4-辛烯CH3CH2CH2CH3CH3C CH3CH2CH2CH(CH3)2 CCH2CH3B

6、rCl CH CCCHCH2CH3Cl(Z)-3-乙基-2-己烯(E)-2,4-二甲基-3-乙基-3-庚烯(Z)-1,2-二氯溴乙烯trans-1,2-二氯溴乙烯6-4Physical propertiesSimilar with the physical properties of alkanes.Insoluble in water, but quite soluble in non-polar solvents. Less dense than water.Boiling point (b.p.) Melting point (m.p.)Dipole moment: very small

7、, but larger than of alkanes.A methyl group is an electron-donating substituent on the double bond.CH3HCH3HC2H5HCH3HCH3HHH= 0HHCH3HoCoCb.p. +1b.p. +4= 0.35 D= 0.37 DoCoCm.p. -106m.p. -1396-5Chemical propertiesThe functional group determines the characteristic reactions of organic compound.Reactionso

8、f alkenes are of two kinds:(a) Reactions that take place at the double bond itself and destroy itaddition and oxidation.(b) Reactions that take place at certain positions having special relationships to the double bondsubstitution.Addition reaction: A reaction in which two molecules combineto yield

9、a single molecule of product.+CYCZYZCCReagentelectrophilic reagents free radicalsSubstratesource of electons (base)Productelectrophilic addition free-radical additionSubstitution reaction:HalogenationCCCHCCCX(X = Cl, Br)I. Catalytic hydrogenation:Pt, Pd, or Ni H = heat of hydrogenationCC+ H2CHCH1. H

10、eterogeneous hydrogenation and homogeneous hydrogenationor Rh(PPh3)3Cl2. Syn-addition100%3.Heat of hydrogenation and stability of alkenes(1) The trans isomer is the more stable than the cis isomer.(2) The greater the number of alkyl groups attached to thedoubly bonded carbon atoms the more stablethe

11、 alkene.D2, PtCH3Major productCH3DDD2, Pt+DDCH3CH3CH3DD( )II. Electrophilic addition1.Addition of HX:Mechanism:Electrophilic additionSlowFastIKI + H3PO488-90%80oC80%90%The regioselectivity of additionMarkovnikovs rule:In the addition of an acid to the carbon-carbon double bond of an alkene, the hydr

12、ogen of the acid attaches itself to the carbon that already holds the greater number of hydrogens.Stability of carbocations: 3o 2o 1o CH3+100%ClHClH CHH CHCF3CH2ClCF3CH2Actual productCF3C HCH2HClClH CClCF3CHCH2 HCF3CH2 HMarkovnikovs rule:Electrophilic addition to a carbon-carbon double bond involves

13、 the intermediate formation of the more stable carbocation.The relative reactivities of alkenes:(CH3)2C=CH2 CH3CH2CH=CH2 CH2=CH2 CH2=CHClAddition is accompanied by rearrangements.(50%)(50%)2. Addition of sulfuric acid:The addition of sulfuric acid follows Markovnikovs rule.98% H2SO4H2OCH2CH2CH3CH2OS

14、O3HCH3CH2OH + H2SO43. Addition of waterHydration:4. Addition of halogens:100%Br2 / CCl4CH2CH2CH2CH2BrBrBr2 / CCl4CH3CHCH2CH3CHCH2Br BrRacemateRacemateBr2 / CCl4CH2CH2CH2CH2+CH2CH2NaClBrBrBrClMechanism:SlowAnti-additionFastThis reaction is useful for:Detection of the carbon-carbon double bond.Prepara

15、tion of vicinal dihalides.CH3BrBrHCH3BrBrCCH3C HHBrBrBrHBrCH3HH CH3CCCCCHHCH3 HCH33meso-2,3-DibromobutaneBrCHC BrBrHHCH3BrHC CH3 H BrBrBrHH CH3CH+CCCCH33HCH3BrCH3CH3rec-2,3-DibromobutaneStereoselective reaction：Reaction in which a single starting material has the capacity to form two or more stereoi

16、someric products but forms one of them in greater amounts than any of its stereoisomers. Terms such asaddition to the less hindered side describe stereoselectivity.Stereospecific reaction：Reaction in which stereoisomeric starting materials give stereoisomeric products. Terms such as syn addition, an

17、tielimination, and inversion of configuration describe stereospecific reactions.5. Halohydrin formation :Anti-additionBr-CH2BrCH2Br-ClCH2BrCH2ClBrCH2Br2I-CH2CH2H2CCH2BrCH2I- 3NOCH2BrCH2ONO2ROHCH2BrCH2ORH2OCH2BrCH2OH2-HCH2 CH2BrOHIII. Free-radical addition of HBrno peroxidesCH3CHCH3BrMarkovnikov addi

18、tionHBrCH3CHCH2peroxidesCH3CH2CH2BrAnti-Markovnikov additionCH3 CH3CCH3Brno peroxidesCH3HBrMarkovnikov additionCH2CH3Cperoxides(CH3)2CHCH2BrAnti-Markovnikov additionPeroxide effectStability:Stability of free radicals:3o 2o 1o CH3The presence or absence of peroxides has no effect on theorientation of

19、 addition of HCl, HI, H2SO4, H2O, etc.IV. Hydroboration-oxidationHydroborationOxidationH2O2, OH-CHC+HBCHCBCCOHAnti-Markovnikov orientationHBHR ,HBR2=HBH2,HBTHF3RCHCH2+ BH3(RCH2CH2)3B3RCH2CH2OHH2O2,OH-(RCH2CH2)3B+H3BO3(1)B2H6, THFCH3(CH2)7CHCH2CH3(CH2)7CH2CH2OH93%(2)H O , OH-22CH3CH2CH2CHCH26%94%No r

20、earrangementMechanism:+ CH2RCHCH2RCHHCH2BH2RCH - - HBHHHBHHSyn-additionTransition state for hydroborationAnti-Markovnikov99%(1) B2H6, THF(2) H2O2, OH-OHHHOH+CH3CH3CH3CH3CH3CH3V. Oxidation reactions:1. KMnO4cold alkaline KMnO4CCCCOHCCOOMn HOOOK1,2-diol (glycols)KMnO4RCRR CHRCRR+OOCHORC OHKMnO4, H2OCH

21、3CH2CHCH2CH3CH2COOH +CO2KMnO4, H+CH3CCHCH3CH3CO+CH3COOHCH3CH3KMnO4, H+CH3COCH2CH3+(CH3)2CHCOOHCH3CH2CCHCHCH3CH3CH3This reaction is useful for:Detection of the carbon-carbon double bond.Deduce the structure of alkenes.OOs OOOCCNa SO23OOOCCOHCCOsHOOAsymmetric dihydroxylationKolb, H.C.; Andersson, P.G.

22、; Sharpless, K.B.J. Am. Chem. Soc. 1994, 116, 1278.Nobel Prize (2001)2. Ozonolysis:Ozonolysis has both synthetic and analytical applications in organic chemistry.3. Epoxidation52%86%Stereochemistry:syn-additionOCH3CH3 CH CCH CH3H3H+CH3CO3HCCCHCH H3H3HOOCH3H CHCH3HCH3 H3+CH3CO3H+ CHCCCCH3HHCHO3Ring-o

23、pening reaction:preparation of anti-1,2-diol()VI. Allylic substitution:heatHCCC+ X2lowXCCCX2 = Cl2, Br2concentrationStability of free radicals: CH2CHCH2 3o 2o 1o CH3 CH2CH low temp. Electrophilic additionCH3CHClCH2ClCH CHCH32Free-radical substitutionClCH2CHCH2gas phase80-85%BrOO(C6H5COO)2+NBrNHCCl4,

24、ON-bromosuccinimide（NBS）O82-87%Cl2CCl4500oCVII. Polymerization:PolymerizationMonomer (Alkenes)PolymerO2 (0.05%)CH2CH2n CH2CH2n1108 1.5108 Pa200300oCPolyethyleneZiegler-Natta CatalystTiCl4 / Al(C2H5)3n CH2CH2CH2CH2n1105 1106 Pa6075oCperoxides CH CHPoly(vinyl chloride) PVCCHCln CH22nClChemical propert

25、ies of alkenes1.2.3.4.5.6.7.Catalytic hydrogenationElectrophilic addition (HX, H2SO4, H2O, X2, HOX) Addition of free radicalsHydroboration-oxidation Oxidation reactions Allylic substitutionPolymerization2005年Nobel化學(xué)獎烯烴復(fù)分解反應(yīng)（Olefin Metathesis ）XXXn開環(huán)復(fù)分解R非環(huán)二烯復(fù)分解聚合+關(guān)環(huán)復(fù)分解RXX開環(huán)復(fù)分解聚合nn烯烴復(fù)分解催化劑的發(fā)展概況R R 195

26、0RMMM+發(fā)現(xiàn)烯烴 復(fù)分解反應(yīng)R1RRR21R2R12Chauvin催化機(jī)理, 19711960發(fā)現(xiàn)RuCl3水合物 催化開環(huán)復(fù)分解聚合 MePh MeChauvin提出金屬卡賓催化機(jī)理 1970NO Mo1FC3O MeChauvin機(jī)理的證明F3CSchrock, 1987MeF3C CF31980發(fā)展單組分催化劑PR3ClPCy3ClRu PhPRRu3Mo卡賓催化劑1的Cl2ClPhPCy331990PhRu卡賓催化劑2的Ru卡賓催化劑3的發(fā)現(xiàn)Ru卡賓催化劑4的發(fā)現(xiàn)Grubbs, 1992Grubbs, 19962000 4ClGrubbs, 1999RuClPhPCy36-6Pre

27、paration of alkenesI. Reduction of alkynes:H2RC HRC HR CHHCRSynLindlar catalystRCCRAntiliq. NH3Na or LiII. Dehydration of alcohols:Ease of dehydration of ROH:3o 2o 1oIII. Dehalogenation of vicinal dihalides:ZnCXCX+ZnX2CCBrZn / C2H5OH+ZnX2BrZnCH3CHCHCH3Br BrCH3CHCHCH3C2H5O- / C2H5OHCH2CHCHCH3IV. Dehy

28、drohalogenation of alkyl halides:KOHCHCX+KX+H2OCCalcohol3o 2o 1oReactivity of RX toward E2:Saytzeffs rule: in dehydrohalogenation, the more stable the alkene, the faster it is formed.1.XStereochemistry of the E2 reaction:-XOH-X-CCH+ HOHCCHCC-OHTransition state partly formed double bondanti-eliminationBHPhHHCH3CHHH HCH3Ph3CH3HPh BrBr PhPhPhPhPh(Z)-1,2-Diphenyl-1-propeneBrBHPhHPhCH3CHHBr PhCH3H3Ph CH3PhHBr PhHPhHPh(E)-1,2-Diphenyl-1-propeneBrE2 elim