See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Analysis of Meso-tartaric Acid and D-Tartaric Acid **Step 1: Identify the structures** - **D-tartaric acid**: $(+)$-tartaric acid with two chiral centers, both having the same stereochemical configuration (RR or SS) - **Meso-tartaric acid**: Contains two identical chiral centers but with opposite configurations (RS), making it achiral due to internal symmetry **Step 2: Check if they are enantiomers** Enantiomers are non-superimposable mirror images. Meso-tartaric acid is achiral (has a plane of symmetry), while D-tartaric acid is chiral. They cannot be enantiomers. ✗ **Step 3: Check if they are diastereomers** Diastereomers are stereoisomers that are NOT enantiomers. They have different stereochemical configurations at some (but not all) chiral centers, and they are NOT mirror images. Meso-tartaric acid (RS) and D-tartaric acid (RR) differ in stereochemistry at one chiral center and are not mirror images. This makes them **diastereomers**. **Step 4: Verify with properties** Diastereomers have: - Different melting points ✓ (meso: 140°C, D: 170°C) - Different specific rotations ✓ (meso: 0°, D: +12°) - Different physical/chemical properties ✓ **Answer: (C) diastereomers** — they are stereoisomers that are not enantiomers.