See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1: Identify the molecule. The structure is 1-chloro-3-methylcyclohexane drawn in a chair-like perspective. The two stereocenters are C1 (bearing Cl and H) and C3 (bearing CH3 and H). Step 2: Analyze C1 (the carbon bearing Cl and H on the right side of the drawing). From the drawing, H is pointing up (axial-like, coming toward viewer) and Cl is pointing to the right (equatorial-like). The four substituents at C1 are: Cl, H, and two ring carbons (C2 and C6). Assign priorities: Cl (highest, #1), then the ring carbon leading toward C2 (which connects to C3 bearing Cl - higher substituents win), then the other ring carbon, then H (#4, lowest). With H pointing upward (toward viewer, i.e., on a wedge), we look at the remaining three in order 1→2→3. The rotation 1→2→3 traces a clockwise arc, but since H (#4) is coming toward us rather than going away, we must invert: clockwise becomes counterclockwise = S... Re-examining the drawing carefully: at C1 (Cl-bearing carbon on the right), H is shown explicitly pointing up and Cl to the right. In the chair perspective, the right carbon has H up (axial up = coming toward viewer on that side) and Cl equatorial. Priority order: Cl (#1) > ring-C toward C2 (#2) > ring-C toward C4 (#3) > H (#4). H is coming toward viewer, so after assigning 1→2→3 as counterclockwise (S), invert because H is toward viewer: gives R for C1. Step 3: Analyze C3 (the carbon bearing CH3 and H on the left side). CH3 is pointing up and H is pointing to the left (toward viewer). Priorities at C3: ring-C toward C2 (#1, as C2 connects to C1 which bears Cl), ring-C toward C4 (#2), CH3 (#3), H (#4). H is coming toward viewer. The sequence 1→2→3 is clockwise (R), but invert because H is toward viewer: gives S... Reassigning more carefully with standard priority rules: at C3, substituents are CH3, H, and two ring carbons. Priority: ring-C(C2, adjacent to C1-Cl) > ring-C(C4) > CH3 > H. With H toward viewer, 1→2→3 counterclockwise = S, invert = R. So C3 = R. Step 4: Both stereocenters are R, giving 1R, 3R configuration. Step 5: Why other options fail: (b) 1R,3S and (d) 1S,3R would require one center to be S; (c) 1S,3S would require both to be S. The spatial arrangement shown, with both H atoms on the same face and substituents (Cl and CH3) on the same face in the trans-diaxial or cis arrangement, leads to both centers having R configuration. Therefore, the correct answer is A.