Question

The enantiomeric excess of a sample is a measure of its optical purity -True or False?

• A. True
• B. False

Answer 1

The correct option is A True

When we have a 50:50 mixture of a pair of enantiomers, it is called a racemic mixture or recemate. A racemic mixture does not show any optical activity although it is made up of two enantiomers which are each optically active. If we have a mixture in any other ratio, then the resultant sample is always shows optically active. The direction in which the sample rotates plane polarized light depends on the enantiomer which is in excess.
Suppose we have D-Lactic acid : L-Lactic acid = 70:30 , then the mixture will rotate plane polarized light to the right (net dextrorotatory). So there is an enantiomeric excess of 40%.
Enantiomeric excess (ee) reflects the degree to which a sample contains one enantiomer in greater amounts than the other. So, by definition, the enantiomeric excess of a sample is a measure of its optical purity.