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GATE 2023 CY – Question 27

Physical Chemistry · Group Theory: Symmetry elements and symmetry operations. Basic postulates of groups and group multiplication tables. Classes, reducible and irreducible representations of symmetry elements. Classification and labelling of molecular point groups. Symmetry based selection rules and their application to electronic and vibrational spectroscopy. Internal coordinates and symmetry labelling of vibrational modes; symmetry adapted linear combination of atomic orbitals (LCAO-MO); construction of hybrid orbitals using molecular point group symmetry. · 1 mark · Multiple choice

The point group of naphthalene ($C_{10}H_8$) is ______.

  1. $D_{2d}$
  2. $D_{2h}$
  3. $D_{3d}$
  4. $D_{3h}$

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Correct answer: (B) $D_{2h}$

Explanation

Planar naphthalene has three mutually perpendicularC2 axes, an inversion centre and three mirror planes. This combination is **D2h, B**. Its fused-ring geometry does not have a threefold principal axis oranimproper fourfold axis.