E

Enantiomeric Excess

Enantiomeric excess is the way to measure purity in chiral substances. It essentially shows the percentage between enantiomers in a compound. For example, a compound contains 100% of one enantiomer and 0% of the other so the ee (enantiomeric excess) is 0%, making it an enantiomerically pure mixture. On the other hand, if a mixture contained 50% and 50% it would give off an ee on 0%, 

making it a Racemic mixture. This is important because some configurations yield different results in the human body than other configurations. In theory, one enantiomer could cause liver failure while the other relieves a headache. The formula for determining Enantiomeric Excess is below.

The R represents the percentage of R-configuration and the S represents the 

percentage of S configuration in the mixture.