Plane of symmetry and chirality: which statement is correct?

• A. A molecule can be chiral even if it has a plane of symmetry.
• B. Chirality is determined solely by the number of stereocenters.
• C. Molecules with identical stereochemistry are always chiral.
• D. A molecule with a plane of symmetry is achiral.

Answer: (D)

The test is about how symmetry relates to chirality. If a molecule has a plane of symmetry, reflecting the molecule across that plane yields the same arrangement, so the mirror image is superimposable on the original. That means the molecule is not chiral.

This is why the statement about having a plane of symmetry leading to achirality is the correct one. A plane of symmetry guarantees the molecule cannot be handed, so it cannot exist as a non-superimposable mirror image.

The other ideas fail because chirality isn’t decided just by how many stereocenters exist, and having stereocenters doesn’t automatically make a molecule chiral if symmetry can render it identical to its mirror image. There are cases where symmetry, such as a plane of symmetry, makes an otherwise seemingly stereogenic molecule achiral. Likewise, identical stereochemical configurations at multiple centers do not guarantee chirality if an internal symmetry element cancels handedness.