Practice: The [α] of pure S-epinephrine is +50°. Calculate the ee of a solution with an observed value of -40°. Calculate percent of each enantiomer. Then sketch the approximate mixture in our sample polarimeter tube.

Sometimes professors will ask us to solve for exact the percentage of each enantiomer in solution. For that we’ll need some new equations.

Concept #1: How to solve for the percentage of each enantiomer.

Example #1: The [α] of pure S-epinephrine is +50°. Calculate the ee of a solution with an observed value of +25°. Calculate percent of each enantiomer. Then sketch the approximate mixture in our sample polarimeter tube.

Practice: The [α] of pure S-epinephrine is +50°. Calculate the ee of a solution with an observed value of -40°. Calculate percent of each enantiomer. Then sketch the approximate mixture in our sample polarimeter tube.

When 0.075 g of penicillamine is dissolved in 10.0 mL of pyridine and placed in a sample cell 10.0 cm in length, the observed rotation at 20°C (using the D line of sodium) is –0.47°. Calculate the specific rotation of penicillamine.

When 0.300 g of glucose is dissolved in 10.0 mL of water and placed in a sample cell 10.0 cm in length, the observed rotation is +3.1°C. Calculate the specific rotation of glucose.

Compound C has an [a] D = +28°.a) Draw the structure of compund D, which is isomer of C and features an [a] D = -28°.b) Calculate the [a] D of a 25/75 mixture of derivatives C and D, respectively.c) Draw the structure of a compound E, which is an isomer of C and D, and features an [a] D = 0°

A mixture of a pair of enantiomers has 30% ee. The observed rotation of this mixture is +15º, and it is known by experiment that the (‐)‐enantiomer has the (R) configuration. (enantiomer excess (ee) = % one enantiomer – % the other enantiomer)(a) Calculate the percentage of (R) and (S) enantiomers of the natural product.(b) What is the optical rotation of a mixture of 20% (S) and 80% (R).

An attempt at synthesizing a certain optically active compound resulted in a mixture of its enantiomers. The mixture had an observed specific rotation of +12.6°. If it is known that the specific rotation of the R enantiomer is -36.7°, determine the percentage of each isomer in the mixture.