See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Conformational Stability Analysis for Ethane Derivatives **Step 1: Identify the molecule** All structures show ethane ($C_2H_6$) derivatives with two methyl groups ($CH_3$) attached, making this 2,2-dimethylethane or butane conformations. **Step 2: Recognize staggered vs. eclipsed conformations** - **Staggered**: Bonds on adjacent carbons are offset by 60° (lower energy, more stable) - **Eclipsed**: Bonds on adjacent carbons are aligned (higher energy, less stable due to electron repulsion) **Step 3: Analyze each option** - **(A)**: Eclipsed conformation — two $CH_3$ groups directly aligned - **(B)**: Eclipsed conformation — $H$ and $CH_3$ groups aligned - **(C)**: Eclipsed conformation — $H$ and $CH_3$ groups aligned - **(D)**: **Staggered conformation** — all groups maximally separated with 60° offsets; $CH_3$ and $H$ bonds are anti to each other **Step 4: Apply stability criteria** Option (D) has: - Maximum separation between all substituents - No electron pair repulsion between adjacent bonds - Anti relationship between bulky methyl groups (lowest steric strain) **Answer: (D)** is most stable because it represents the staggered conformation with optimal three-dimensional spacing, minimizing steric hindrance and torsional strain.