Question

Of all the possible cyclooctanes that have one chloro substituent and one methyl substituent, which ones do not have any asymmetric centers?

Answer 1

The only isomers without chiral centres are 1-chloro-1-methylcyclohexane, cis-1-chloro-5-methylcyclohexane, and trans-1-chloro-5-methylcyclohexane.

Explanation:

In order for the centres to be achiral, they must have a plane of symmetry passing through them.

The only possibilities are

The first structure, 1-chloro-1-methylcyclohexane, has a vertical plane of symmetry that includes, `C-5`, `C-1`, `CH3`, and `Cl`.

The other two structures, cis- and trans-1-chloro-5-methylcyclohexane, have a vertical plane of symmetry that includes `C-1`, `C-5`, and the wedged and dashed bonds that are directly attached to them.