Some more facts about optical activity:
Concept #1: How to calculate enantiomeric excess.
Example #1: Calculate the ee and observed rotation for the following chiral mixture where S-enantiomer has [α] = +20.
Calculate the observed rotation when given the following ratio of enantiomers in solution.
Example #2: Calculate the ee and observed rotation for the following chiral mixture where S-enantiomer has [α] = +20.
We can also use these equations to calculate specific and observed rotation when other variables are given to us. Just plug the numbers in! Let's try a few.
Practice: When 0.200 g of lactose is dissolved in 10.0 ml of water and placed in a sample cell 10.0 cm in length, the observed rotation is +2°. Calculate the specific rotation of lactose.
Practice: Calculate the observed rotation of a chiral mixture that contains 65% (S)-stereoisomer where the [α] of pure (S)-stereoisomer = -118.
Practice: An optically pure (R)-stereoisomer of a molecule has a specific rotation of – 20°. What specific rotation would be observed for a mixture of the (R) and (S) stereoisomer where there is an enantiomeric excess equal to (S) 60%.