Question

Figure \(21.17\) shows that the cis isomer of \(\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}^{+}\) is optically active while the trans isomer is not optically active. Is the same true for \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+} ?\) Explain.

Short answer

Neither the cis nor the trans isomer of \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+}\) is optically active, as both isomers lack chiral centers.

Step-by-step solution

Draw the cis and trans isomers

We are given the \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+}\) complex. The compound has a central Co atom surrounded by four NH3 and two Cl ligands. For the cis isomer, the two Cl ligands are adjacent to each other: Cl | NH3-Co-NH3 | \ NH3 NH3 For the trans isomer, the two Cl ligands are opposite to each other: NH3 Cl | \ NH3-Co-NH3 | Cl

Identify chiral centers

Now we need to analyze the structures to determine if there are any chiral centers present. In the cis isomer structure, there are no chiral centers because all ligands are not distinct around the cobalt atom, as we have two NH3 ligands. Looking at the trans isomer structure, once again, all the ligands are not distinct around the cobalt atom, as we have two NH3 ligands.

Determine if the isomers are optically active

Since neither the cis nor the trans isomers of \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+}\) possess any chiral centers, we can conclude that neither of them is optically active. To answer the question: Neither the cis nor the trans isomer of \(\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}^{+}\) is optically active, as both isomers lack chiral centers.