二、由环引起的顺反异构 Br Br CI cis-1-bromo-3-chlorocyclobutane trans-1-bromo-3-chlorocyclobutane CH3 CH3 CH3 CH3 cis-1,4-dimethylcyclohexane trans-1,4-dimethylcyclohexane二、由环引起的顺反异构