See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: Enantiomers are non-superimposable mirror images of each other. They must have opposite configurations at every stereocenter, and the molecule must be chiral (not a meso compound). A pair of enantiomers cannot be superimposed on each other by any rotation or translation. Step 2 - Analyze option (a): The two structures of 2-bromo-3-chlorobutane shown have Br on a wedge in both, but Cl changes from wedge to dash. This changes one stereocenter while keeping the other the same, producing diastereomers (not enantiomers). Option (a) is a pair of diastereomers. Step 3 - Analyze option (b): The cyclopentane structures show one methyl on a wedge and one on a dash (trans relationship) in the left, and what appears to be both methyls in a different arrangement in the right. Careful inspection shows these represent the same compound (superimposable) or diastereomers, not enantiomers. Option (b) does not represent a pair of enantiomers. Step 4 - Analyze option (c): The left cyclohexane has both methyl groups on dash bonds (both pointing behind the plane), and the right cyclohexane has both methyl groups on wedge bonds (both pointing in front of the plane). This is 1,2-dimethylcyclohexane. When both substituents are on the same face (cis relationship), if the molecule is not meso, the two structures with all-dash vs all-wedge are non-superimposable mirror images. The trans-1,2-dimethylcyclohexane with (1R,2R) vs (1S,2S) configuration: the left structure (both on dash = both going back, i.e., 1S,2S or 1R,2R depending on numbering) and right structure (both on wedge = both coming forward, opposite configuration at both centers) are non-superimposable mirror images. These are enantiomers. Option (c) is a pair of enantiomers. Step 5 - Analyze option (d): The multi-chloro compound structures with different wedge/dash arrangements at multiple stereocenters appear to represent diastereomers or the same compound, not enantiomers. Step 6 - Conclusion: Only option (c) represents a pair of true enantiomers — the (1R,2R) and (1S,2S) enantiomers of 1,2-dimethylcyclohexane, which are non-superimposable mirror images. Therefore, the correct answer is C.