A sample of Limonene has a specific rotation of +76.9. What is the % ee and
molecular composition of this sample? R(+)- is +125.6 and S (-)- 122.1. I'm confused I don't know whether I should divided by 125.6 or 122.1. %ee=(76.9/125.6)*100=61%. Is this correct? I'm clueless as to how to find the molecular composition
I also have the same question for hw. Ibelieve you do divide by 125.6 since dividing by same sign. For molecular composition, I think it is saying 100-61.2= 38.8% and since this is a mixture of both R and S you give half on each side.
Thus R: 61.2 + 19.4= 80.6% composition
S: 19.4% composition
I hoping this is right. Goodluck
thank you so much
To determine the % ee (enantiomeric excess) and molecular composition of a sample of Limonene using its specific rotation, you need to compare the specific rotation of the sample to the specific rotations of the pure enantiomers (R(+) and S(-)).
First, let's clarify a couple of terms:
- Specific rotation: It is a measure of how a compound rotates plane-polarized light. It is represented by a numerical value and a sign indicating the direction of rotation (+ for clockwise or dextrorotatory, - for counterclockwise or levorotatory).
- Enantiomeric excess (% ee): It represents the excess of one enantiomer (R(+) or S(-)) over the other in a sample. It is expressed as a percentage and can be calculated using the following formula:
% ee = [(observed rotation) - (specific rotation of other enantiomer)] / [(specific rotation of pure enantiomer)] * 100.
To determine the % ee, you correctly calculated it using the formula:
% ee = (76.9 / 125.6) * 100 ≈ 61%.
This result indicates that the sample of Limonene has a 61% excess of one enantiomer over the other.
Now, regarding the molecular composition, the specific rotation alone cannot determine it. It only provides information about the chiral nature of the compound without specifying its molecular structure. To identify the molecular composition or configuration, additional techniques such as spectroscopy or chromatography are needed.
So, in summary, your calculation for % ee is correct, but the specific rotation alone does not provide information about the molecular composition.