Concept Explanation: Chirality in Chemical Reactions

This question involves determining the chirality of products P and Q formed from a reaction. Chirality refers to molecules that are non-superimposable on their mirror images (like left and right hands). A chiral molecule has at least one chiral center (usually a carbon with four different substituents) and lacks a plane of symmetry. An achiral molecule is superimposable on its mirror image or has a plane of symmetry.

Step 1: Analyze the Reactant

The reactant is a cyclic ketone. From the image, it appears symmetric. If the molecule has a plane of symmetry, it is achiral. Many symmetric cyclic ketones (like cyclopentanone or symmetric substituted ones) are achiral because they can be divided into mirror halves.

Step 2: Understand the Reaction

The reaction involves reduction of the ketone to an alcohol. Reduction can produce stereoisomers if the carbonyl carbon is prochiral (i.e., it becomes a chiral center upon reduction). The product mixture suggests two isomers: P and Q.

Step 3: Determine Chirality of Products

When a symmetric ketone is reduced, the carbonyl carbon becomes a new chiral center. For example, reduction of cyclopentanone gives cyclopentanol, which has a chiral center. However, if the molecule has a plane of symmetry (making it achiral), the reduction will produce a pair of enantiomers (mirror images). Enantiomers are chiral individually, but the mixture is racemic (achiral if not resolved).

In this case:

P and Q are enantiomers (mirror images).
Each enantiomer is chiral (non-superimposable).
The mixture is racemic and achiral due to equal amounts of enantiomers canceling optical activity.

Step 4: Match with Options

Thus, P is chiral, Q is chiral (both are enantiomers), but the mixture is achiral. However, the question asks for P and Q individually, not the mixture. So:

P = Chiral, Q = Chiral

Final Answer

The correct option is: P = Chiral, Q = Chiral

Related Topics & Formulae

Chirality: A molecule is chiral if it lacks an internal plane of symmetry and is non-superimposable on its mirror image. Chiral molecules often have chiral centers (e.g., carbon with four different groups).

Enantiomers: Stereoisomers that are mirror images of each other. They have identical physical properties except for optical rotation (which is equal in magnitude but opposite in direction).

Racemic Mixture: A 1:1 mixture of enantiomers. It is optically inactive (achiral) because the rotations cancel out.

Reduction of Ketones: Ketones reduced by agents like NaBH $4$ or LiAlH $4$ give secondary alcohols. If the ketone is symmetric and achiral, the product is chiral and forms a racemic mixture.

Symmetry Test: To check chirality, look for planes of symmetry. If no plane exists, the molecule is chiral.