See image — Biomolecules Chemistry Question

💡 Solution & Explanation

Step 1 - Understand the framework: Fischer projections show horizontal bonds coming toward the viewer and vertical bonds going away. The D/L system is based on comparison to D-glyceraldehyde (OH on right = D, OH on left = L). The R/S system uses CIP priority rules with the lowest priority group going away from viewer in Fischer projections (it is on a vertical bond, so it points away — but we must verify which substituent is lowest priority). Step 2 - Molecule (a): CHO(top), H(left), OH(right), CH2OH(bottom) This is glyceraldehyde. OH is on the RIGHT → D-configuration (matches r). For R/S: The four groups on the chiral center are CHO, OH, CH2OH, H. CIP priorities: OH(1) > CHO(2) > CH2OH(3) > H(4). H (lowest priority) is on the left horizontal bond → it points TOWARD the viewer in a Fischer projection. We assign rotation 1→2→3 (OH→CHO→CH2OH): OH is right, CHO is top (going away), CH2OH is bottom (going away). With H toward viewer, the apparent rotation is counterclockwise (S), but since H is toward us we invert: actual configuration = R. So (a) matches R (p) and D (r) → a-p,r. Step 3 - Molecule (b): CHO(top), HO(left), H(right), CH2OH(bottom) OH is on the LEFT → L-configuration (matches s). For R/S: Same groups as (a) but mirror image. By the same logic, configuration is S. So (b) matches S (q) and L (s) → b-q,s. Step 4 - Molecule (c): NH2(top), H(left), CO2H(right), CH3(bottom) This is alanine. In the D/L system for amino acids, comparison is made to glyceraldehyde using the amino group analogous to OH. NH2 on the LEFT in a Fischer projection with CO2H at top corresponds to L-alanine — but here CO2H is NOT at top; NH2 is at top and CO2H is on the right horizontal bond. Re-orient mentally: to use D/L for amino acids, place CO2H at top. Rotating the Fischer projection 180° (allowed, keeping it in plane): CO2H goes to top, CH3 goes to bottom, H goes to right, NH2 goes to left → NH2 on LEFT = L-configuration (matches s). For R/S: Groups on chiral center: NH2, H, CO2H, CH3. CIP priorities: NH2(1) > CO2H(2) > CH3(3) > H(4). H (lowest) is on the LEFT horizontal bond → toward viewer. Rotation 1(NH2,top)→2(CO2H,right)→3(CH3,bottom) appears clockwise (R), but since H is toward us, invert → actual = S. So (c) matches S (q) and L (s) → c-q,s. Step 5 - Molecule (d): NH2(top), H(left), CH3(right), CO2H(bottom) To apply D/L, place CO2H at top by rotating 180°: CO2H(top), NH2(bottom), CH3(left), H(right) → NH2 is on the bottom after rotation, which is not the reference position directly. Alternatively, note this is the mirror of (c) in terms of NH2/H arrangement relative to a vertical CO2H axis. Since (c) was L, (d) is D (matches r). For R/S: Same groups, mirror arrangement of (c). Since (c) = S, (d) = R (matches p). So (d) matches R (p) and D (r) → d-p,r. Therefore, the correct answer is a-p,r; b-q,s; c-q,s; d-p,r.