Enantiomeric Excess Definition:
A mixture that contains unequal amounts of a pair of enantiomers is said to have an enantiomeric excess which is the – difference between the percent concentration of the major enantiomer and the percent concentration of its mirror image.
Enantiomeric Excess Explained:
The enantiomeric excess of a solution is measured in percentage terms using the following formula.
ee is the enantiomeric excess and alpha is the specific rotation.
Another method to visualize the calculation is as by assuming a hypothetical mixture of a pair of enantiomers E. ( +E and -E). Consider % conc. of +E to be 60% and the % conc. of -E to be 40%. In this case, the %ee is 20% and the net optical rotation of the solution will be + or clockwise