See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Determining L-form of Glucose **Step 1: Identify the chiral center for D/L designation** In sugars, the D/L configuration is determined by the stereochemistry at the **chiral center farthest from the carbonyl group** (the penultimate carbon). For a tetraldose (4-carbon sugar like those shown), this is the 3rd carbon from the top. **Step 2: Apply D/L naming rules** - **D-form**: $OH$ group on the penultimate carbon is on the **right** (in Fischer projection) - **L-form**: $OH$ group on the penultimate carbon is on the **left** (in Fischer projection) **Step 3: Examine each option at the penultimate carbon (3rd position from CHO)** | Option | 3rd C configuration | Classification | |--------|-------------------|---| | (A) | $OH$ on right | D-form | | (B) | $OH$ on left | **L-form** ✓ | | (C) | $OH$ on right | D-form | | (D) | $OH$ on left | **L-form** ✓ | **Step 4: Distinguish between B and D** Options B and D both have L-configuration. However, **option D** is the standard representation with: - $CHO$ at top - $CH_2OH$ at bottom - $OH$ groups on the **left** at both stereocenters **Answer: (D)** is the correct L-form because the penultimate carbon has its $OH$ group positioned on the left in the Fischer projection, which defines the L-configuration.