How would you determine the percentage of each isomer in the mixture?
An attempt at synthesizing a certain optically active compound resulted in a mixture of its enantiomers. The mixture has an observed specific rotation of +11.2'. If it is known that the specific rotation of the R enantiomer is -39.839, determine the percentage of each isomer in the mixture.
R enantiomer = %
S enantiomer= %?
An attempt at synthesizing a certain optically active compound resulted in a mixture of its enantiomers. The mixture has an observed specific rotation of +11.2'. If it is known that the specific rotation of the R enantiomer is -39.839, determine the percentage of each isomer in the mixture.
R enantiomer = %
S enantiomer= %?
1 Answer
The mixture contains
Explanation:
I assume that the specific rotation of the mixture is +11.2 ° and that of the
The rotations of the two enantiomers cancel each other, so the rotation of the mixture will be that of the excess enantiomer.
The mixture has a positive sign of rotation, so the
The formula for enantiomeric excess is
#color(blue)(|bar(ul(color(white)(a/a) ee = "observed specific rotation"/"maximum specific rotation" × 100 %color(white)(a/a)|)))" "#
We can calculate the percent of each enantiomer as described in this Socratic question.
If we have a mixture of (+) and (-) isomers and (+) is in excess,
We have a 28 % enantiomeric excess of (+).
∴
So, the mixture contains 64 % (