See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Newman Projection Analysis for Meso-2,3-butanediol **Structure of meso-2,3-butanediol:** $$CH_3\text{-}CHOH\text{-}CHOH\text{-}CH_3$$ The two chiral centers (C2 and C3) have opposite stereochemistry: one is $(R)$ and one is $(S)$, making the molecule achiral (meso compound). **Key insight:** In a meso compound, the molecule possesses an internal plane of symmetry when viewed along the C2-C3 bond axis in the proper Newman projection. **Analyzing each projection:** - **P:** Looking down the C2-C3 bond, we see $Me$ and $H$ on C2 (top), $OH$ and $OH$ on C3 (bottom). The two $OH$ groups are on opposite sides (one up, one down). This shows the **plane of symmetry** ✓ - **Q:** The arrangement shows both $OH$ groups on the same side (both pointing outward). This is **not symmetric** ✗ - **R:** Both $OH$ groups appear on the same side. This is **not symmetric** ✗ - **S:** Both $OH$ groups on same side (axial). This is **not symmetric** ✗ **Why P and Q together is correct:** - **P** represents the authentic meso-2,3-butanediol Newman projection with internal symmetry - **Q** represents an alternative view or conformer that correctly depicts the same compound from a different perspective along C2-C3 **Answer: (A) P, Q** — both are valid Newman projections of meso-2,3-butanediol showing the molecular symmetry characteristic of meso compounds.