△ hy 对旋 顺旋 △ CHsH 对旋 H Ch,H CH3CH H 顺旋 CH H/H 光照条件下,顺旋对称允许对旋对称禁阻。(4n+2体系对旋 顺旋 hv 3 4 对旋 CH3 H CH3 H CH3 H H CH3 CH3 H H CH3 + 顺旋 hv CH3 H CH3 H CH3 H CH3 H 光照条件下, 顺旋 对称允许, 对旋对称禁阻。(4n+2体系)