* Meso compounds are achiral: They possess chiral centers but have an internal plane of symmetry. This symmetry cancels out the optical activity that would normally be associated with chiral centers.
* Optical activity is a result of chirality: The ability of a molecule to rotate plane polarized light (optical activity) is a direct consequence of its chirality.
* Meso compounds lack net optical activity: Because meso compounds are achiral, they do not rotate plane polarized light. They are optically inactive.
Example:
Consider tartaric acid. It exists in three forms:
* D-Tartaric acid: Chiral, rotates plane polarized light to the right.
* L-Tartaric acid: Chiral, rotates plane polarized light to the left.
* Meso-tartaric acid: Achiral, does not rotate plane polarized light.
In summary: Meso compounds are achiral and therefore do not exhibit optical activity. They will not rotate plane polarized light.
