Meso Compounds
Start with the big picture
A meso compound has two or more stereogenic centers but is achiral because an internal symmetry element, such as a mirror plane or inversion center, relates its halves. In a symmetric molecule with two centers, opposite configurations such as R,S can allow the centers’ effects to cancel, giving zero optical rotation. Meso-tartaric acid is a representative example. Unlike a racemate, which is a mixture of enantiomers, a meso compound is a single achiral molecular form. It is a diastereomer of the corresponding R,R and S,S enantiomeric pair. Assessing meso character therefore requires checking both configurations and the whole molecule’s symmetry; stereocenters alone do not establish it.
What you'll learn
- Define meso compounds using stereogenic centers and molecular symmetry.
- Use opposite R/S configurations and internal symmetry to assess meso character.
- Distinguish internal compensation in a meso compound from a racemate.
- Describe how meso compounds relate to corresponding enantiomers and diastereomers.
- Recognize structural changes that can remove the symmetry required for meso character.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
