Explain why the product of a nucleophilic addition to butanone does not effect plane polarized light.

The nucleophile will attack the d⁺ carbon atom of the carbonyl group. Since the carbonyl group is planar, attack can occur from either side with equal probability. The product of this reaction will contain a chiral centre and two chiral forms are possible as attack can occur on either side of the carbonyl group. Because attack is equally likely from either side of the carbonyl these enantiomers will be present in equal quantities.

Each enantiomer from a pair will rotate plane polarized light equally but in opposite directions. This means when plane polarized light passes through the product, the light is uneffected as the rotational effects of each enantiomer will cancel out.