Question

How can I draw two achiral isomers of 3,4,5-trimethylheptane?

Answer 1

You must draw structures that have an internal mirror plane.

Explanation:

The only two possibilities are:

(`3S,4r,5R`)-3, 4, 5-trimethylheptane

and

(`3S,4s,5R`)-3, 4, 5-trimethylheptane

They each have an internal plane of symmetry that is perpendicular to the plane of the paper and bisects the atoms of the `"CH"_2` group at `"C"-4`.