Question

Point group of naphthalene (C₁₀H₈) is

• A. \(D_{2d}\)
• B. \(D_{2h}\)
• C. \(D_{3d}\)
• D. \(D_{3h}\)

Hint:

Aromatic planar molecules like benzene belong to \(D_{6h}\).
Naphthalene, due to reduced symmetry compared to benzene, falls under \(D_{2h}\).
Always check for: principal axis, perpendicular axes, inversion center, and mirror planes.

Answer 1

The Correct Option is B

Step 1: Naphthalene is a polycyclic aromatic hydrocarbon consisting of two fused benzene rings. Its structure is planar and symmetric.
Step 2: To determine its point group, we analyze symmetry elements:
It has a principal \(C_2\) axis along the long axis of the molecule.
Two additional \(C_2\) axes are present perpendicular to the principal axis (orthogonal directions).
It possesses a horizontal mirror plane (\(\sigma_h\)) due to its planarity.
It also has inversion symmetry (\(i\)).
Step 3: The presence of three mutually perpendicular \(C_2\) axes and inversion center (\(i\)) characterizes the \(D_{2h}\) point group.
Therefore, the point group of naphthalene is \(D_{2h}\).