(R)-Limonene (C₁₀H₁₆) - R or S Configuration

Chiral Center Analysis

(R)-Limonene (C₁₀H₁₆) contains 1 chiral center. D-Limonene - the terpene responsible for the smell of oranges. The chiral center is inside a cyclohexene ring. The isopropenyl substituent (C bonded to C,C,C from the double bond) outranks both ring paths, and the path toward the double bond in the ring outranks the other by reaching C=C phantom atoms deeper.. 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: -C(=CH₂)CH₃ - Isopropenyl: C bonded to C, C, C (=CH₂ gives two phantom C atoms + CH₃) - three carbons at second level
• Priority 2: ring→C=C - Ring path toward C2=C1 double bond: at C3 has C,H,H → at C2 reaches C=C (two phantom C atoms) - deeper chain wins
• Priority 3: ring→CH₂ - Ring path toward C6: at C5 has C,H,H → at C6 has C,H,H - only single bonds, loses to C=C path at third level
• 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 clockwise path from priority 1 to 2 to 3. This gives the R configuration.

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