Before You Begin

Question #44907

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of $\ce{CoCl2}$ is oxidized by air in the presence of an excess of enantiomerically pure $(R)\text{-}1,2\text{-propanediamine}$ (denoted as $(R)\text{-}pn$ ) and activated charcoal to form the substitution-inert octahedral complex cation $\ce{[Co((R)-pn)3]^{3+}}$ . Assuming the chelate rings adopt only their thermodynamically most stable conformation, how many total stereoisomers of this complex cation are theoretically formed, and what is their stereochemical relationship?

Options

A.
2 isomers; a pair of enantiomers requiring a chiral resolving agent.
B.
4 isomers; two pairs of enantiomers.
C.
4 isomers; all are diastereomers separable by fractional crystallization.
D.
8 isomers; four pairs of enantiomers due to $\Delta/\Lambda$ and fac/mer combinations.

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Werner’s Theory Postulates|Optical Isomerism Logic

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of Werner's coordination theory with advanced stereochemistry.

The primary trap is the assumption that $\Delta$ and $\Lambda$ forms of a complex are always enantiomers (as in $\ce{[Co(en)3]^{3+}}$ ).

By introducing a chiral, unsymmetrical ligand ( $(R)\text{-}pn$ ), the problem forces students to recognize two hidden variables: 1) The unsymmetrical nature of $pn$ creates \textit{fac} and \textit{mer} geometrical isomers. 2) The fixed chirality of the ligand means the $\Delta$ and $\Lambda$ forms are diastereomers, not enantiomers.

Because they are diastereomers, they have different internal energies (e.g., 'lel' vs 'ob' interactions) and different solubilities, allowing separation by simple fractional crystallization without a chiral resolving agent.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Coordination Compounds - Class 12
Concept	Werner’s Theory Postulates
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free