(乙)4n+2个π电子体系 CH3 CH CH △ H LCH H H CH3 CH (Z, Z, E)-2, 4, 6-octatriene CH3 CH CH △ H CH3 H H CH CH (E, Z,E)-2, 4, 6-octatriene(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