(乙)4n+2个π电子体系 CH CH CH3 H △ H H CH3对旋 顺旋 H CH3 CH (Z,Z,E)-2, 4, 6-octatriene CH CH CH3 H CH H对旋 H 顺旋 CH CH3 (E,Z,E)-2,4,6 H3C CH3 octatriene8 (乙)4n+2个π电子体系 (Z,Z,E)-2,4,6-octatriene (E,Z,E)-2,4,6 -octatriene △ CH3 H CH3 H CH3 H H CH3 CH3 H CH3 H CH3 CH3 H H △ CH3 H CH3 H hν hν CH3 H CH3 H H3C CH3 ( ) 对旋对旋 顺旋 顺旋