Optical activity of an enantiomeric mixture is + 12 . 6 ° and the...

The "optical purity" is a comparison of the optical rotation of a pure sample of unknown stereochemistry versus the optical rotation of a sample of pure enantiomer. It is expressed as a percentage. If the sample only rotates plane-polarized light half as much as expected, the optical purity is 50%.

$$ optical purity $= \dfrac{observedrotationof mixture \times 100}{rotationofpure enantiomer}$

$= \dfrac{+ 12 . 6 °}{+ 30 °} \times 100 = 42$