An achiral molecule has a plane of symmetry in the molecule. The structure of the achiral stereoisomer of 1,2-dimethylcyclohexane is shown in the image attached to this answer.
In organic chemistry, a chiral compound refers to a compound that is not superimposible on its mirror image. This compound must contain a carbon atom that is bonded to four different atoms or groups.
The opposite of a chiral molecule is an achiral molecule which is superimposible on its mirror image. A chiral molecules have a plane of symmetry in the molecule. The structure of the achiral stereoisomer of 1,2-dimethylcyclohexane is shown in the image attached to this answer.
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