(S)-Ibuprofen (C₁₃H₁₈O₂) - R or S Configuration

Chiral Center Analysis

(S)-Ibuprofen (C₁₃H₁₈O₂) contains 1 chiral center. The active enantiomer of this common NSAID. The phenyl ring (C bonded to C,C,C) outranks methyl (C bonded to H,H,H) but loses to the carboxyl group whose double-bonded oxygen creates phantom atoms.. 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: -COOH - Carboxyl: C bonded to O, O, O (=O phantom) - oxygen (8) at second level beats carbon
• Priority 2: -C₆H₄R - Phenyl ring: C bonded to C, C, C at second level - three carbons beat methyl's three hydrogens
• Priority 3: -CH₃ - Methyl: C bonded to H, H, H - lowest carbon substituent
• Priority 4: H - Hydrogen always lowest (atomic number 1)

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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