See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 – Concept: A molecule is chiral if it is non-superimposable on its mirror image. The key test is: does the molecule possess any symmetry element (plane, centre, or alternating axis of symmetry) that would make it identical to its mirror image (i.e., is it a meso compound)? A molecule with stereocenters is chiral unless internal symmetry renders it achiral (meso). Step 2 – Analyze molecule (I): Molecule I is a chain: CH3–C*(Br,H)–CH2–C*(Br,H)–CH2Cl. It has two stereocenters. Both Br groups are shown on wedge bonds (same relative configuration). Because the two ends of the chain are different (one end is CH3, the other is CH2Cl), the molecule cannot have an internal plane of symmetry regardless of configuration. It is not a meso compound. Therefore molecule I is chiral. Step 3 – Analyze molecule (II): Molecule II is a camphane-type bicyclic system (bicyclo[2.2.1]heptane with gem-dimethyl at the bridgehead). It has two OH groups shown, one exo and one endo (or both on the same face), at C2 and C3. In the drawn structure the two OH groups are on opposite faces of the bicyclic ring (one up, one down as drawn), giving a specific stereochemical arrangement. The molecule has multiple stereocenters and the rigid bicyclic framework with the gem-dimethyl group and the specific OH orientations means no internal mirror plane exists. Therefore molecule II is chiral. Step 4 – Analyze molecule (III): Molecule III is tartaric acid drawn in a cross/sawhorse style: top carbon (H left-back, OH up, COOH right) and bottom carbon (HO left, H right-back, COOH down). Reading the configuration: top carbon has OH on one face, bottom carbon has HO (OH) on the opposite face relative to the backbone. This corresponds to the meso form of tartaric acid, where the top and bottom halves are mirror images of each other, giving an internal plane of symmetry through the C–C bond. Meso tartaric acid is achiral despite having two stereocenters. Therefore molecule III is NOT chiral. Step 5 – Conclusion: Molecules I and II are chiral; molecule III is achiral (meso). The answer is I and II. Therefore, the correct answer is D.