(S)-Pent-1-yn-3-ol (C₅H₈O) - R or S Configuration

Chiral Center Analysis

(S)-Pent-1-yn-3-ol (C₅H₈O) contains 1 chiral center. Tests triple bond phantom atoms. The -C≡CH group gets two phantom C duplicates at the second level, giving {C, C, C} vs ethyl's {C, H, H}. Alkyne beats alkyl.. 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 - Oxygen (Z=8) directly bonded - highest atomic number
• Priority 2: -C≡CH - Triple bond: C at 1st → {C, C, C} at 2nd (two phantom C atoms from ≡) - beats ethyl
• Priority 3: -CH₂CH₃ - Ethyl: C at 1st → {C, H, H} at 2nd - only ONE C vs alkyne's THREE
• 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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