第4章：立体化学.ppt

第四章 立 体 化 学 Organic Stereochemistry 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 Isomerism Constitutional isomers ---- those have the same molecular formula but vary in the bonding attachments of atoms Isomerism Stereoisomers ---- with same bonding attachments of atoms but different spatial orientations Isomerism Configurational isomers ---- they can be interconverted only by the breaking and reforming of bonds ---- they can be separated Isomerism Conformational isomers ---- they can be interconverted by rotation about one or more sigma-bonds ---- the interconversion are so rapid that we cannot separate them 一、烷烃和环烷烃的构象异构 1.Ethane Conformational analysis ---- describes the energetic of such conformational interconversion 一、烷烃和环烷烃的构象异构 2. Butane Steric Strain ---- a steric effect van der Waals repulsion of groups that are close to each other 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12.1 KJ/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、22.6 KJ/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 4 KJ/mol CH3-CH3 重叠 14.6 KJ/mol CH3-H 重叠 5.3 KJ/mol CH3-CH3 邻位交叉 3.8 KJ/mol 一、烷烃和环烷烃的构象异构 3. cyclohexane 一、烷烃和环烷烃的构象异构 axial equatorial 一、烷烃和环烷烃的构象异构 4. Interconversion of Chair,Half-chair, Boat, and Twist-boat Conformations ---- please see text P73 一、烷烃和环烷烃的构象异构 5. Substituted cyclohexane 1) monosubstituted the stable conformer ---- the substituent is in equatorial position 5. Substituted cyclohexane 2) disubstituted cyclohexane 5. Substituted cyclohexane 1,2-disubstituted cyclohexane -----trans-isomer is more stable (for ee is more stable than ea) How about 1,3- and 1,4- disubstituted cyclohexane? Please try to draw out their chair confo