5.3 Historical origin of stereochemistry The following information was available to van t hoff and le bel 1. Only one compound for CH3 X is ever found 2. Only one compound for CH2X2 or CH3 XY ever found 3. Two enantiomeric compounds for CHXYZ are found
5.3 Historical origin of stereochemistry • The following information was available to van’t Hoff and le Bel. • 1. Only one compound for CH3X is ever found • 2. Only one compound for CH2X2 or CH3XY is ever found. • 3. Two enantiomeric compounds for CHXYZ are found
5.4 Tests for Chirality Planes of Symmetry(对称面) All molecules with a plane of symmetry are achiral All molecules with no plane of symmetry are chiral
5.4 Tests for Chirality: Planes of Symmetry( 对称面） All molecules with a plane of symmetry are achiral All molecules with no plane of symmetry are chiral
三、对称因素和手性分子判据 1对称因素 ◎对称面:可把分子分割成两部分的 平面,一部分正好是另一部分的镜象,这 个平面称为对称面。(图 CH 3 例1:1,1-二氯乙烷 例2:(E)-1,2-二氯乙烯 c Cl C=C Cl
三、对称因素和手性分子判据 • 1.对称因素 • ◎ 对称面σ：可把分子分割成两部分的 平面，一部分正好是另一部分的镜象，这 个平面称为对称面。 （图） • 例1：1，1-二氯乙烷 C CH3 Cl Cl H 例2：（E）-1，2-二氯乙烯 C C Cl Cl H H
Problem 5.7 write three dimensional formulas and designate a plane of symmetry for all of the achiral molecules in Problem 5. 4 a 1-Chloropropane b 2-Bromobutane CH CH HI I CH2Cl Br CH2CH3 a plane of symmetry (achiral) no plane of symmetry(chiral
Problem 5.7 Write threedimensional formulas and designate a plane of symmetry for all of the achiral molecules in Problem 5.4. a 1-Chloropropane CH3 CH2 Cl H H b 2-Bromobutane CH3 B CH2 CH3 r H a plane of symmetry (achiral) no plane of symmetry (chiral)
c 1-Chloro-2-methylpropane d 2-Chloro-2-methylpropane HIlliI H3 CllII CH2Cl H3C C CH a plane of symmetry(achiral) two planes of symmetry (achiral f 1-Chloropentane h 3-Chloropentane Cl CH2 CH3 HIIIIII HIlLII CH2CH2CHbCH Cl CH2 CH3 a plane of symmetry(achiral) a plane of symmetry(achiral)
c 1-Chloro-2-methylpropane CH3 CH2Cl H3C H d 2-Chloro-2-methylpropane CH3 C CH3 l H3C a plane of symmetry (achiral) two planes of symmetry (achiral) f 1-Chloropentane Cl CH2 CH2 CH2 CH3 H H h 3-Chloropentane CH2 CH3 Cl CH2 CH3 H a plane of symmetry (achiral) a plane of symmetry (achiral)