You watched too much Breaking Bad and try to make methamphetamine. Before you tr

Question

You watched too much Breaking Bad and try to make methamphetamine. Before you try to sell it though, you want to see how good of a chemist you are by seeing how enantiomerically pure your sample is. You measure the specific rotation of your smaple to be -10°. What is the %ee of your sample?

a. 62.5% ee R

b. 62.5% ee S

c. 37.5% ee R

d. 37.5% ee S

Based on you % ee, what is the ratio of R to S in your illicit samplt of methamphetamine.

a. 81.25% R and 18.75% S

b. 81.25% S and 18.75% R

c. 62.5% R and 37.5% S

d. 62.5%S and 37.5% R

Explanation / Answer

Given that,

specific rotation of mixture = -10.0 oC

specific rotation of R isomer = -16.0 oC and S isomer = +16.0 oC

If we call the mole fraction of the R isomer x (with specific rotation of -16.0 oC) and the mole fraction of the S isomer 1-x (with a specific rotation of +16.0 oC), then will it not be true that

-16.0*x + [16.0*(1-x)] = -10
Solving,

we get x and hence , percentage = 81.25 (R isomer)

and 1-x = 0.1875 and hence, percentage = 18.75 (S isomer)

Answer A. = ee = excess enantiomer = 81.25-18.75 = 62.5 % ee R (a)

Answer B. 81.25 % of R and 18.75 % of S (a)

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