See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# R Configuration Determination **Apply CIP (Cahn-Ingold-Prelog) Rules** to assign priorities 1-4, then check stereochemistry. ## Structure (1): Lactic acid derivative - Priority 1: $COOH$ (C bonded to O,O,C) - Priority 2: Phenyl (C bonded to C,C,H) - Priority 3: $CH_3$ (C bonded to H,H,H) - Priority 4: $H$ Viewing with $H$ away: 1→2→3 goes **counterclockwise = S configuration** ## Structure (2): - Priority 1: $CN$ (C bonded to N,C,C) - Priority 2: $C≡CH$ (C bonded to C,C,C) - Priority 3: $CH_2OH$ (C bonded to O,H,H) - Priority 4: $CH_3$ Viewing with $CH_3$ away: 1→2→3 goes **clockwise = R configuration** ✓ ## Structure (3): Glyceraldehyde - Priority 1: $CHO$ (C bonded to O,O,H) - Priority 2: $CH_2OH$ (C bonded to O,H,H) - Priority 3: $OH$ - Priority 4: $H$ Viewing with $H$ away: 1→2→3 goes **counterclockwise = S configuration** ## Structure (4): Alanine - Priority 1: $COOH$ (C bonded to O,O,C) - Priority 2: $H_2N$ (N bonded to H,H,C) - Priority 3: $CH_3$ - Priority 4: $H$ Viewing with $H$ away: 1→2→3 goes **counterclockwise = S configuration** **Answer: Only structure (2) has R configuration.**