Question

Which of the following does not have optical isomers?

• A. $[\mathrm{Co}{\left(\mathrm{en}\right)}_2{\mathrm{Cl}}_2]\mathrm{Cl}$
• B. $[\mathrm{Co}{\left(\mathrm{en}\right)}_3]{\mathrm{Cl}}_3$
• C. $\left[\mathrm{Co}\right(\mathrm{en}){\left({\mathrm{NH}}_3\right)}_2{\mathrm{Cl}}_2]\mathrm{Cl}$
• D. $[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$

Answer 1

The correct option is D

$[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$

The explanation for correct option:

(D) $[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$

Optical isomers:

• Optical Isomers are formed by the compounds whose mirror images are non-superimposable.
• It is sometimes very difficult to judge the optical isomerism by drawing the mirror images and checking the superimposable. Therefore, the use of elements of symmetry is very common.

Elements of symmetry:

1. Plane of symmetry
2. Axis of symmetry

$[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$ exists in two isomeric forms.

1. Facial
2. Meridional

The images of both isomers are attached below.

In both of the isomers there exists an element of symmetry. In the facial isomer, there is an axis of symmetry and in the meridional isomer, there is a plane of symmetry.

The explanation for incorrect options:

In the molecules (A), (B), and (C), there is no element of symmetry and therefore they all have optical isomers, whereas $[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$ does not have optical isomers.

Hence, the correct option D i.e. $[\mathrm{Co}{({\mathrm{NH}}_3)}_3{\mathrm{Cl}}_3]$.