Question

Which one of the following statements is false ?

• A. R and S configurations correspond to the enantiomers of an optically active compound
• B. The process of converting an optically active compound into a racemate is called racemization
• C. A molecule containing a plane of symmetry can be optically active
• D. Optical isomers that are not enantiomers are called diastereoisomers
• E. All chiral objects are asymmetric

Hint:

Always look for a plane of symmetry first when checking for optical activity. If you find one, the molecule is "Meso" or achiral, regardless of how many chiral centers it has.

Answer 1

The Correct Option is C

Concept: Optical activity is the ability of a chiral molecule to rotate plane-polarized light. Symmetry elements determine whether a molecule is chiral or achiral.

Step 1: Evaluate Statement (C).
A plane of symmetry (or a center of inversion) makes a molecule superimposable on its mirror image. Such molecules are achiral and therefore optically inactive. This statement is false.

Step 2: Verify other statements.

• (A) True: R/S denotes the absolute configuration of enantiomeric pairs.
• (B) True: Racemization leads to an equal mixture of enantiomers (zero net rotation).
• (D) True: This is the definition of diastereomers (e.g., cis-trans or molecules with multiple centers where only some are inverted).
• (E) True: Chirality implies a lack of symmetry (dissymmetry).