The specific rotation of pure enantiomer is known from the literature to be -20. The measured value of a solution containing A plus its enantiomer B (specific rotation must be +20) is -40. What is the ee (enantiomer excess) of this sample?
To calculate the enantiomer excess (ee), we need to compare the difference between the measured rotation and the expected rotation of the pure enantiomer. The enantiomer excess is the excess amount of one enantiomer over the other in a mixture, expressed as a percentage of the total amount of both enantiomers.
Given that the specific rotation of the pure enantiomer A is known to be -20, and the measured value of a solution containing A and its enantiomer B is -40, we can calculate the enantiomer excess using the following formula:
ee = (measured rotation - expected rotation) / (measured rotation + expected rotation) * 100
In this case:
Measured rotation = -40
Expected rotation = -20
Substituting these values into the formula, we get:
ee = (-40 - (-20)) / (-40 + (-20)) * 100
ee = (-40 + 20) / (-40 - 20) * 100
ee = -20 / -60 * 100
ee = 33.33%
Therefore, the enantiomer excess (ee) of this sample is 33.33%.