Question

What is present in a racemic mixture?

• A. Only dextrorotatory (D) form is present.
• B. Only laevorotatory (L) form is present.
• C. D and L forms are present in a 1:1 ratio, making the mixture optically inactive.
• D. It is a meso compound.

Hint:

Do not confuse these terms: \[ \boxed{ \begin{aligned} \text{Racemic mixture} &\rightarrow \text{External compensation}\\ \text{Meso compound} &\rightarrow \text{Internal compensation} \end{aligned} } \] A racemic mixture contains \[ \boxed{50\% \text{ D-form } + 50\% \text{ L-form}} \] and is therefore optically inactive.

Answer 1

The Correct Option is C

A racemic mixture contains equal molar amounts of the $R$ and $S$ enantiomers of a chiral compound. The two enantiomers rotate plane-polarized light by equal but opposite amounts, so their optical rotations cancel and the mixture is optically inactive with a net rotation of $0°$.