Question

Pure MSG, a common flavor enhancer, exhibits a specific rotation of +24. (a) Calculate the ee of a solution whose $\left[\text{α}\right]$is +10. (b) If the ee of a solution of MSG is 80%, what is $\mathbf{\left[}\mathbf{\text{α}}\mathbf{\right]}$for this solution?

MSG

monosodium glutamate

Short answer

(a) The ee of a solution whose $\left[\text{α}\right]$is +10 = 42%

(b) The $\left[\text{α}\right]$for this solution = +19.2

Step-by-step solution

Meaning of the term ee

The term ee refers to the enantiomeric excess. It is also known as optical purity. The amount of the isomers can be calculated from the racemic mixture by using ee.

$\text{Enantiomericexcess=percentageofoneenantiomer-percentageofotherenantiomer}$

Calculation of ee

(a)

The enantiomeric excess can also be calculated if the specific rotation of a mixture and the specific rotation of a pure enantiomer is known. It can be calculated as follows:

$\text{ee=}\frac{\left[\text{α}\right]\text{mixture}}{\left[\text{α}\right]\text{pure}}\text{×100\%}$

• $\left[\text{α}\right]\text{pure}$refers to the specific rotation of the pure enantiomer.
• $\left[\text{α}\right]\text{mixture}$refers to the specific rotation of a mixture.

The specific rotation of the pure MSG is given as +24, the specific rotation of the solution is given as +10.

Therefore,

role="math" localid="1648385408630" $$\begin{gathered} \text{ee=}\frac{\text{+10}}{\text{+24}}\text{×100\%} \\ =42\% \end{gathered}$$

(b)

The ee of the solution of MSG = 80%. The optical rotation of the solution can be calculated as follows:

$$\begin{gathered} \frac{\left[\text{α}\right]\text{solution}}{\text{+24}}\text{×100\%=80\%ee} \\ \left[\text{α}\right]\text{solution=+19.2} \end{gathered}$$