(S)-Mandelic Acid (C₈H₈O₃) - R or S Configuration

Chiral Center Analysis

(S)-Mandelic Acid (C₈H₈O₃) contains 1 chiral center. Tests OH vs COOH priority at the first atom level. Students wrongly assume "COOH is the biggest group" but -OH has O(8) directly bonded, while -COOH has C(6) at the first atom.. Each chiral center is analyzed below using CIP (Cahn-Ingold-Prelog) priority rules to determine R or S configuration.

CIP Priority Assignment

The four substituents on the chiral center are ranked by atomic number of the directly attached atom, with ties broken by exploring outward along each branch.

• Priority 1: -OH - O (Z=8) directly bonded to chiral center - beats COOH which has C (Z=6) first
• Priority 2: -COOH - C at 1st level → {O, O, O} at 2nd (double bond phantom) - beats phenyl's {C, C, C}
• Priority 3: -C₆H₅ - C at 1st level → {C, C, C} at 2nd - aromatic carbons lose to COOH's oxygens
• Priority 4: H - Hydrogen (Z=1) - always lowest

R/S Configuration

With the lowest priority group (priority 4) oriented away from the viewer, the remaining three substituents trace a counterclockwise path from priority 1 to 2 to 3. This gives the S configuration.

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