Meso Compounds

Another exception to the rule, these are compounds that remain achiral even though they have chiral centers!

  • Meso compounds have an internal line of symmetry (TEST 1), meaning they are actually achiral.
  • Follow the 2n – 1 rule. 

A compound will be meso if it meets the following 3 criteria:

  1. It has 2 or more chiral centers.
  2. It is atomically symmetrical, meaning that is symmetrical in connectivity, not shape.   
  3. An even number of chiral centers have opposite configuration to each other (i.e. if one is R, the other is S). 

Example: Which of the following molecules are meso, and therefore achiral?

3m

Example: Which of the following molecules are meso, and therefore achiral?

4m