Question

In the following reaction:
${\left[ {{\text{CoC}}{{\text{l}}_2}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]^ + } + {\text{C}}{{\text{l}}^ - } \to \left[ {{\text{CoC}}{{\text{l}}_3}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_3}} \right] + {\text{N}}{{\text{H}}_3}$. If two isomers of the product are obtained, which is true for the initial (reactant) complex:
A) Compound is in cis-form
B) Compound is in trans-form
C) Compound is in both (cis and trans) form
D) Can’t be predicted

Answer 1

Hint:We are given that the product of the reaction exists in two isomers i.e. cis-isomer and trans-isomer. To solve this we must know we must know which type of the reactant gives cis-isomer and trans-isomer as the product.

Complete answer:
We are given a reaction as follows:
${\left[ {{\text{CoC}}{{\text{l}}_2}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]^ + } + {\text{C}}{{\text{l}}^ - } \to \left[ {{\text{CoC}}{{\text{l}}_3}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_3}} \right] + {\text{N}}{{\text{H}}_3}$
We are given that in this reaction two isomers of the product are obtained. The two isomers are the cis-isomer and trans-isomer.

The product $\left[ {{\text{CoC}}{{\text{l}}_3}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_3}} \right]$ has six ligands. Thus, it is an octahedral complex. In this complex, when any two identical ligands are adjacent to each other then it is known as the cis-isomer. And when any three identical ligands and the metal ion are in one plane then it is known as trans-isomer.

The reactant is ${\left[ {{\text{CoC}}{{\text{l}}_2}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}} \right]^ + }$ and the product is $\left[ {{\text{CoC}}{{\text{l}}_3}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_3}} \right]$. When the reactant is in cis form then the product obtained has cis isomer and trans isomer. And when the reactant is in trans form then the product obtained has trans isomer only.
We are given that in this reaction two isomers of the product are obtained. Thus, the reactant is in cis form.Thus, the statement ‘compound is in cis-form’ is true.

Thus, the correct option is (A) compound is in cis form.

Note: We have the product $\left[ {{\text{CoC}}{{\text{l}}_3}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_3}} \right]$ which has six ligands. Thus, it is an octahedral complex. In this complex, when any two identical ligands are adjacent to each other then it is known as the cis-isomer. And when any three identical ligands and the metal ion are in one plane then it is known as trans-isomer. The cis isomer is known as facial or fac isomer and the trans isomer is known as meridional or mer isomer.