Racemic Mixture
An equimolar mixture of enantiomers (50%R, 50%S). One of the enantiomers in the mixture rotates the plane of polarization of light at the same angle but in the opposite direction as the other enantiomer, leading to the conclusion that an equal proportion mixture of both enantiomers shows no optical rotation and is therefore optically inactive.
Meso Form
An achiral molecule due to the presence of an element of symmetry (plane, center of inversion, or improper axis).
Although meso forms have asymmetric carbons, the plane of symmetry eliminates their chirality and therefore their ability to rotate polarized light.
