3.2 Electronic structure of alkenes 烯烃的电子结构 0.109nmH HH 0.13nm C116.7° H 1216°
3.2 Electronic structure of alkenes 烯烃的电子结构 H C C H H H C C H H H H 0.133nm 0.109nm 116.7° 121.6° p.11
Rotation of n bond is prohibitive C 90 rotation bond Broken m bond after rotation (p orbitals are parallel) (p orbitals are perpendicular
Rotation of p Bond Is Prohibitive
p91 3. 3 cis-trans isomers of alkenes 烯烃的顺一反异构体
3.3 cis-trans isomers of Alkenes 烯烃的顺―反异构体 p.91
CH3 CH3 The presence of a carbon carbon double can create two C-c possible structures cis isomer -two similar cis-2-Butene groups on same side of the ouble bond trans isomer similar groups on opposite sides H CH3 Each carbon must have two different groups for CH these(cis/trans ) isomers to trans-2-Butene occur
• The presence of a carboncarbon double can create two possible structures – cis isomer - two similar groups on same side of the double bond – trans isomer similar groups on opposite sides • Each carbon must have two different groups for these(cis/trans) isomers to occur
Cis-Trans Isomers Require That End 91 Groups must differ in pairs Bottom pair cannot D B C-C be superposed(重B D A 叠)by D B 180° rotation C=CX C=C B without breaking E A E C=C
Cis-Trans Isomers Require That End Groups Must Differ in Pairs Bottom pair cannot be superposed (重 叠) by 180° rotation without breaking C=C X p.91