初中化学立体化学课件

第四章立体化学OrganicStereochemistry第四章重点讲授内容一、烷烃和环烷烃的构象异构二、烯烃的顺反异构（几何异构）三、构型异构——对映异构与非对映异构四、环烷烃的构型异构IsomerismConstitutionalisomers----thosehavethesamemolecularformulabutvaryinthebondingattachmentsofatomsC2H6O:CH3OCH3CH3CH2OHC3H6O:CH2=CHOCH3CH2=CHCH2OHCH3C(OH)=CH2CH3CH=CHOHCH3COCH3CH3CH2CHOOHOOH3CIsomerismStereoisomers----withsamebondingattachmentsofatomsbutdifferentspatialorientationsCH3HHHOHHCH3HOCCHOHHCH3CCOHHHCH3OH3CCH3CH=CHOHIsomerismConfigurationalisomers----theycanbeinterconvertedonlybythebreakingandreformingofbonds----theycanbeseparatedCH3HHHOHHCH3HOCCHOHHCH3CCOHHHCH3OH3CCH3CH=CHOHIsomerismConformationalisomers----theycanbeinterconvertedbyrotationaboutoneormoresigma-bonds----theinterconversionaresorapidthatwecannotseparatethemHHHHHHHHHHHHStaggeredNewmanprojectionsawhorseprojection600HHHHHHHHHHHHEclipsed00Newmanprojectionsawhorseprojection一、烷烃和环烷烃的构象异构1.EthaneConformationalanalysis----describestheenergeticofsuchconformationalinterconversionHHHHHHHHHHHHStaggeredNewmanprojectionsawhorseprojection600HHHHHHHHHHHHEclipsed00Newmanprojectionsawhorseprojection一、烷烃和环烷烃的构象异构2.ButaneStericStrain----astericeffectvanderWaalsrepulsionofgroupsthatareclosetoeachotherHHCH3H3CHHCHH3CHH3CHHC'H3CHHH3CHHB'H3CHHHHCH3AsyneclipsedHHCH3H3CHHBgaucheconformerHCH3HH3CHHDanticonformerH3CHHHHCH3Asyneclipsed一、烷烃和环烷烃的构象异构思考题：已知乙烷中重叠式与交叉式的能量差为12.1KJ/mol，丁烷中邻位交叉、部分重叠、全重叠与对位交叉构象的能量差分别为3.8、14.6、22.6KJ/mol，请以乙烷的交叉式能量设为零来计算H-H、CH3-CH3、CH3-H重叠和CH3-CH3邻位交叉的能量H-H重叠4KJ/molCH3-CH3重叠14.6KJ/molCH3-H重叠5.3KJ/molCH3-CH3邻位交叉3.8KJ/mol一、烷烃和环烷烃的构象异构3.cyclohexaneHHHHHHHHChairconformationHHHCH2HCH2BoatconformationHHHH一、烷烃和环烷烃的构象异构CCCCCCCCCCaxialequatorial一、烷烃和环烷烃的构象异构4.InterconversionofChair,Half-chair,Boat,andTwist-boatConformations----pleaseseetextP73一、烷烃和环烷烃的构象异构5.Substitutedcyclohexane1)monosubstitutedthestableconformer----thesubstituentisinequatorialpositionequtorial(down)axial(down)CH3CH35.Substitutedcyclohexane2)disubstitutedcyclohexaneCH3equtorial(down)CH3axial(down)cis-CH3H3Caxial(down)equtorial(down)trans-CH3equtorial(down)CH3axial(down)CH3CH3equtorial(up)axial(up)5.Substitutedcyclohexane1,2-disubstitutedcyclohexane-----trans-isomerismorestable(foreeismorestablethanea)Howabout1,3-and1,4-disubstitutedcyclohexane?Pleasetrytodrawouttheirchairconformersandanswerthequestion二、烯烃的顺反异构（几何异构）1.请采用Z、E命名双键的顺反异构体2.双键的顺反异构是由于绕sigma-键的旋转受到Pi-键的阻碍3.顺反异构体的相互转化需要破坏Pi-键，能量较高，光照常可引发这种转化三、构型异构——对映异构和非对映异构1、对称性和对称因素1）对称轴Cn2）对称面3）对称中心请分析甲烷分子的对称因素CHHHHC3HFClClHFHHi，对称中心OOHHHHHHHH4个C3对称轴，2个C2对称轴6个对称面三、构型异构——对映异构和非对映异构4）更迭对称轴Sn=Cn+σ（垂直于Cn）1956年首次合成了一个有四重更迭轴的分子900CNCH3HHCH3H3CHH3CH(I)NHH3CH3CHHCH3HCH3(II)NCH3HHCH3H3CHH3CH(I)NHH3CH3CHHCH3HCH3(II)三、构型异构——对映异构和非对映异构如果分子中不存在对称面、对称中心和四重更迭对称轴，则这个分子具有手性三、构型异构——对映异构和非对映异构2、手性分子、手性碳原子和对映异构Handedness,Chirality,Chiralcenter,EnantiomerABCDACDB三、构型异构——对映异构和非对映异构3、绝对构型(AbsoluteConfiguration)和构型表示方法(RandS)ABCDABCDACDBACBABCDDclockwise----Rcounterclockwise----S三、构型异构——对映异构和非对映异构A.(R)-2-ButanolB.(S)-1-methoxy-2-propanamineC.(S)-5-chloro-6hepten-2-one使用左右手法则是十分方便的HH3CH2CCH3OHHH2NCH3CH2OCH3ClH2C=HCCH2CH2COCH3H三、构型异构——对映异构和非对映异构4、费歇尔投影式(Fischerprojections)建议使用“纸面分析法”判断R、S----注意最小基团在横线还是在竖线ABCDsawhorseprojectionCDBAACDBFischerprojection三、构型异构——对映异构和非对映异构A.(2S,3S)-3-chloro-2-pentanolB.(2R,3S)-3-amino-4-penten-2-olC.(2S,3R,4R)-2-bromo-4-floro-3-hydroxy-5-phenylpentanoicacidCH3HOHCH2CH3ClHCH3HOHCH=CH2H2NHCOOHBrHHOHCH2C6H5HF三、构型异构——对映异构和非对映异构5、手性分子的光学活性光学活性OpticalActivity1）偏振光(plane-polarizedlight)lightsourcepolarizersampletubeanalyzerobserver5、手性分子的光学活性2）左旋和右旋(-)and(+)(laevorotatoryanddextrorotatory)3）比旋光度(specificrotation)[α]=α/(c╳l)4）外消旋体----一对对映异构体的等量混合物Racemicmixture,racemate5、手性分子的光学活性5）光学纯度（OpticalPurity)----Amixtureofenantiomersina75:25ratiowillhaveanobservedrotationthatis50%ofthatforasingleenantiomer.Suchamixtureissaidtohaveanopticalpurityof50%αo.p.=╳100%[α]╳c╳l5、手性分子的光学活性6）对映体过量百分数e.e.（enantiomericexcess)e.e.=%ofmajorenantiomer-%ofminorenantiomer5、手性分子的光学活性----手性分子的光活性（左旋和右旋）是可以通过旋光仪测得----但是（+）和（-）并不对应于（R）和（S）----R、S的绝对构型如何测得呢？----X-射线单晶衍射(1950年）----相对构型6、含两个手性碳的分子1）含两个相同手性碳的分子COOHHOHCOOHHOHCOOHHOHCOOHHOHCOOHHOHCOOHHOHCOOHHOHCOOHHOHRRSSRSSRracematemeso-6、含两个手性碳的分子2）含两个不同手性碳的分子IisnotanenantiomerofIII,norofIVIIisnotanenantiomerofIII,notofIVTheyarediasteromersCOOHHOHCH2CH3HOHCOOHHOHCH2CH3HOHCOOHHOHCH2CH3HOHCOOHHOHCH2CH3HOHRSSRRRSSracemateracemateIIIIIIIV7、含多个手性碳的分子----最多可能有2n个光活异构体----差向异构体----假不对称碳（III和IV中的C-3）COOHHOHHOHCOOHHOHCOOHHOHHOHCOOHHOH(R)(R)(S)(S)COOHHOHHOHCOOHHOHCOOHHOHHOHCOOHHOH(R)(S)(R)(S)(r)(s)meso-racemateIIIIIIIV8、不含手性碳原子的手性分子----具有丙二烯结构的分子----具有联苯类结构的化合物CCCABA1B1CCCBAA1B1NO2COOHO2NHOOCHOOCO2NCOOHNO28、不含手性碳原子的手性分子----具有螺旋型结构的化合物9、含有其它不对称原子的手性分子----季铵阳离子和季鏻阳离子CH2CH3N(H3C)2HCCH3C6H5CH2CH3NC6H5H3CCH(CH3)2CH2CH=CH2P(H3C)2HCCH3C6H5CH2CH=CH2PC6H5H3CCH(CH3)29、含有其它不对称原子的手性分子----叔胺和30膦叔胺的异构体转化十分迅速，有的书中将它们归于构象异构体NH3CH2CCH3C6H5NC6H5CH3H3CH2CP(H3C)2HCCH3PC6H5H3CCH(CH3)2C6H5H3CH2CNCH3C6H510、手性化合物的物理性质Table.SomepropertiesofthestereoisomersoftartaricacidStereoisomersM.P.(0C)[α]20DensitySolubilityinH2O(+)168-170+121.7598139.0g/100ml(-)168-1