L-Glutamic Acid (HOOCCH₂CH₂CH(NH₂)COOH) - R or S Configuration

Chiral Center Analysis

L-Glutamic Acid (HOOCCH₂CH₂CH(NH₂)COOH) contains 1 chiral center. Like aspartic acid but with an extra CH₂ in the side chain. The side chain COOH is two carbons away, making it even clearer that the α-COOH wins at the second-level comparison.. 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 - directly bonded to α-carbon
• Priority 3: -CH₂CH₂COOH - Side chain COOH via CH₂CH₂: C bonded to C, H, H at second level - α-COOH's O, O, O wins
• 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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