What is the % of the R enantiomer in a sample of carvone that has a specific rotation of -20,given that the specific rotation of R-carvone is -61?

Question

Quizplus · Accepted Answer

- The formula for specific rotation is: Observed rotation / (concentration in g/mL x path length in dm)
- We can calculate the % of R enantiomer using the following equation: % of R enantiomer = Observed rotation of the sample / Observed rotation of pure R-carvone x 100
- If the specific rotation of a pure R-carvone is -61, then the observed rotation of pure R-carvone is -61 x concentration x path length. Let's assume that the concentration is 1 g/mL and the path length is 1 dm (these are common values used in polarimetry experiments).
- Therefore, the observed rotation of pure R-carvone is -61 x 1 x 1 = -61
- Now, we can solve for the % of R enantiomer in the sample using the given specific rotation of -20: % of R enantiomer = (-20) / (-61) x 100 = 32.79%. Rounded to the nearest tenth, this is 33%.
- The closest answer choice to 33% is B, which is 66.5%, when we calculate the % of S enantiomer, it will give us 33.5%. Therefore, the correct answer is B.

What Is the % of the R Enantiomer in a Sample