Question

What are the cis and trans isomers for cyclohexane?

Answer 1

When cyclohexane is substituted by 2 heteroatoms, `cis-trans` isomerism, and optical isomerism ARE possible.

Explanation:

Let's take a simple (achiral) example, 1,4-dihalocyclohexane, `1,4-X_2C_6H_10`. The halogen atoms can be trans with respect to the plane of the ring, or cis , each on the same side of the ring.

If the heteratoms are cis , then one heteroatom is in an axial position, whereas the other one is equatorially disposed. If the heteroatom are trans disposed, then both substituents are likely equatorial but on OPPOSITE sides of the ring with respect to each other.

If you haven't already done so, I urge you to get a set of models that depict cyclohexane and its derivatives, that shows how upon a ring-flip axial substituents become equatorial, and equatorial become axial.