We’re being asked to calculate the enantiomeric excess for a mixture of (R) and (S)-carvone with an observed rotation of –55˚. The specific rotation of (S)-carvone is +61˚.
Recall that a pair of enantiomers would rotate plane-polarized light in opposite directions. This means if the specific rotation of (S)-carvone is +61˚, the specific rotation of (R)-carvone is –61˚.
The enantiomeric excess (ee) tells us the degree to which an enantiomer is in excess than the other.
• a racemic mixture (equal amounts of enantiomer) would have ee = 0%
• a pure enantiomer would have ee = 100%
The specific rotation of (S)-carvone (at 20°C) is +61. A chemist prepared a mixture of (R)-carvone and its enantiomer, and this mixture had an observed rotation of –55°.
(b) Calculate the % ee of this mixture.
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Our data indicates that this problem or a close variation was asked in Organic Chemistry - Klein 1st Edition. You can also practice Organic Chemistry - Klein 1st Edition practice problems.