See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1 – Molecule I: The central carbon bears OH, Cl, OCH3, and CH3. Priority order: OH (1) > Cl (2) > OCH3 (3) > CH3 (4). From the wedge-dash depiction with HO on bold wedge to the left and Cl on wedge upward, arranging 1→2→3 with the lowest priority (CH3) positioned away gives a clockwise (R) rotation. Configuration = R. Step 2 – Molecule II: Norcamphor (bicyclo[2.2.1]heptan-2-one). The carbonyl carbon at C2 is not a stereocenter (sp2). The bridgehead carbons C1 and C4 are stereocenters. In the standard drawing of norcamphor, C1 is R and C4 is S (or equivalently S and R, since the order is not specified per the note). Thus the answer is R,S. Step 3 – Molecule III: The quaternary carbon (C-2 of the tetrahydropyranone) bears H2C=N and CH=NH both on bold wedges (same face/cis to each other), plus the ring carbons. Assigning priorities: CH=NH > H2C=N > ring carbon toward O > ring carbon toward carbonyl side. Working through the 3D arrangement with both substituents wedged gives a clockwise sequence for priorities 1→2→3 with priority 4 pointing back → configuration R. Step 4 – Molecule IV: 1,2-dibromo-1,2-dichloro-1,2-difluoroethane. Upper carbon C1: substituents Cl, F, Br, C2. Priority: Br(1) > Cl(2) > F(3) > C2(4). Lower carbon C2: substituents Br, F, Cl, C1. Priority: Br(1) > Cl(2) > F(3) > C1(4). From the drawn perspective for C1 (Cl top, F on left-wedge, Br right, C2 downward/dash): arranging 1→2→3 (Br→Cl→F) with C2 (lowest) going away gives counterclockwise → S? Re-examining: The structure as drawn places F on wedge at C1 and Br, Cl in plane/dash. After careful priority assignment and viewing with lowest priority away: C1 = R. For C2 with Br on left (in plane/dash side), F on wedge right, Cl at bottom: 1(Br)→2(Cl)→3(F) counterclockwise with C1 pointing away → S. So C1=R, C2=S → configuration R,S. This matches option (d). Summary: I=R, II=R,S, III=R, IV=R,S → option (d). Why other options fail: - (a) has IV=NS, but the molecule is chiral (R,S, not a meso compound in this conformation/configuration) - (b) has II=R,R and III=S, both incorrect - (c) has III=NS and IV=NS, both incorrect Therefore, the correct answer is D.