(S)-α-Methyldopa (C₁₀H₁₃NO₄) - R or S Configuration

Chiral Center Analysis

(S)-α-Methyldopa (C₁₀H₁₃NO₄) contains 1 chiral center. A real antihypertensive drug (Aldomet) with a quaternary stereocenter. The chiral carbon has NO hydrogen - it bears NH₂, COOH, a catechol-bearing side chain, and CH₃. A challenging molecule with a dihydroxyphenyl ring system.. 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: -NH₂ - Nitrogen directly bonded (atomic number 7) - highest first-atom priority
• Priority 2: -COOH - Carboxyl: C bonded to O, O, O at second level - oxygen beats carbon
• Priority 3: -CH₂-C₆H₃(OH)₂ - Catechol-methyl: C bonded to C, H, H at second level - COOH's oxygens win at second level despite ring complexity
• Priority 4: -CH₃ - Methyl: C bonded to H, H, H - lowest priority (no hydrogen on this chiral center!)

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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