定义Definition
顺反异构是由于双键（或环）限制了自由旋转，取代基在双键或环平面同侧（顺，cis）或异侧（反，trans）而形成的立体异构，属于非对映异构。
Cis–trans isomerism arises when a double bond (or ring) prevents free rotation, so substituents lie on the same side (cis) or opposite sides (trans); the isomers are diastereomers.
条件Requirement
双键两端的每个碳上必须连有两个不同的基团（a≠b 且 c≠d）。环状化合物（如 1,2-二甲基环己烷）和平面正方形配合物（顺铂与反铂）也存在顺反异构。
Each double-bond carbon must carry two different groups. Rings (1,2-dimethylcyclohexane) and square-planar complexes (cisplatin vs transplatin) also show it.
性质差异Property differences
顺、反异构体物理性质不同：顺-2-丁烯沸点 3.7 °C，反式 0.9 °C；马来酸（顺）熔点 135 °C、易脱水成酸酐，富马酸（反）熔点 287 °C。顺铂有抗癌活性而反铂没有。
Cis and trans isomers differ physically: cis-2-butene boils at 3.7 °C, trans at 0.9 °C; maleic acid (cis) melts at 135 °C and forms an anhydride, fumaric acid (trans) at 287 °C. Cisplatin is anticancer; transplatin is not.
命名Naming
取代基复杂时“顺/反”含义模糊，应改用 E/Z 命名法。视觉过程中视黄醛的 11-顺 → 全反式光异构化是生物学上最重要的顺反异构化。
With complex substituents cis/trans is ambiguous, so E/Z is used. The 11-cis → all-trans photoisomerisation of retinal in vision is biology’s key cis–trans isomerisation.
年表Timeline
- 1887
维斯利策努斯用几何异构解释马来酸与富马酸
Wislicenus explains maleic and fumaric acids by geometric isomerism
- 1965
罗森伯格发现顺铂抗癌活性
Rosenberg discovers cisplatin’s anticancer activity