Question

If we have some 2-butanol with observed rotation of + 9.72, we compare this rotation with + 13.5 rotation of the pure (+) enantiomer.

Answer 1

That means 72% is pure (+) 2-Butanol and 28% is racemic (± mixture) 

Total (+) isomer = 72 + 14 = 86%, (–) isomer = 14%