Question

What are the symmetry operations possible for the following structures, and what is the expected point group?

a). The tetrahedral CoCl₄^2-

b). Cl-I-Cl^-

c). C₆H₁₂ (chair form)  

Answer 1

Part A

$CoCl_4^{2-}$ is a symmetric tetrahedral molecule. It belongs to a special point group $T_d$ . The symetry operations of the point group are,

Identity (E)

Three fold rotation axis ( $C_3$ )

Two fold rotation axis ( $C_2$ )

Four fold improper rotation axis ( $S_4$ )

Dihedral mirror planes ( $\sigma _d$ )

Part B

$ICl_2^-$ is a linear molecule. This belongs to a special point group, $D_{\infty h}$ . The operations possible are,

Infintite rotational axes of any fold ( $C_\infty$ )

Centre of inversion ()

Infintite improper rotational axes of any fold ( $S_\infty$ )

An infininite number of two fold rotational axes through the centre of inversion ( $C_2$ )

An infinite number of verticle mirror planes ( $\sigma _v$ )

Part C

The chair conformation of cyclohexane belongs to the $D_{3d}$ point group and has the following operations.

Identity (E)

Three fold rotation axis ( $C_3$ )

Two fold rotation axis (perpendicular to the 3-fold axis) ( $C_2$ )

Centre of inversion ()

Six fold improper rotation axis ( $S_6$ )

Dihedral mirror planes ( $\sigma _d$ )