Cis and Trans, E and Z for Cyclic Compounds

Key Questions

  • Just as with acyclic compounds, cyclic compounds can have geometric and optical isomers.

    In general, if any two sp³ carbons in a ring have two different substituent groups (not counting other ring atoms), stereoisomerism is possible.

    Consider, for example, 1,2-dimethylcyclopentane.

    Geometric Isomers

    1,2-Dimethylcyclopentane exists as the cis isomer, with both CH₃ groups on the same side of the ring, or as the trans isomer, with the CH₃ groups on opposite sides of the ring.

    Optical Isomers

    trans-1,2-Dimethylcyclopentane exists as two optical isomers.

    They are nonsuperimposable mirror images of each other.