What characterizes a meso compound?

What characterizes a meso compound?

• A. A molecule with no stereocenters
• B. A molecule with chiral centers but internal symmetry, making it achiral
• C. A pair of enantiomers
• D. A molecule with at least two different chiral centers

Answer: (B)

Meso compounds are molecules that have stereocenters but are overall achiral because an internal plane of symmetry divides the molecule into two mirror-image halves. This symmetry allows the configurations at the stereocenters to cancel each other’s optical activity, so the molecule does not rotate plane-polarized light. A classic example is meso-tartaric acid, where the two stereocenters have opposite configurations and a plane of symmetry runs through the molecule, making it identical to its mirror image. If a molecule has no stereocenters, it’s simply achiral for a different reason and not a meso form. A pair of enantiomers refers to two nonsuperimposable mirror images that are each chiral, not a single meso compound. Having two or more chiral centers is often necessary for a meso form, but without an internal symmetry plane, those centers don’t yield a meso molecule.

Meso compounds are molecules that have stereocenters but are overall achiral because an internal plane of symmetry divides the molecule into two mirror-image halves. This symmetry allows the configurations at the stereocenters to cancel each other’s optical activity, so the molecule does not rotate plane-polarized light. A classic example is meso-tartaric acid, where the two stereocenters have opposite configurations and a plane of symmetry runs through the molecule, making it identical to its mirror image. If a molecule has no stereocenters, it’s simply achiral for a different reason and not a meso form. A pair of enantiomers refers to two nonsuperimposable mirror images that are each chiral, not a single meso compound. Having two or more chiral centers is often necessary for a meso form, but without an internal symmetry plane, those centers don’t yield a meso molecule.