See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

# Analysis of 1,2-Diphenyl Ethane Conformation Stability **Step 1: Identify the structure** 1,2-Diphenyl ethane is $C_6H_5-CH_2-CH_2-C_6H_5$. We need to analyze the conformation around the central $C-C$ bond. **Step 2: Apply steric principles** The most stable conformation minimizes steric clashes between the two bulky phenyl groups ($C_6H_5$). This is achieved when phenyl groups are positioned as far apart as possible. **Step 3: Evaluate each option** - **(A)**: Both phenyl groups on the same side (eclipsed) → **high steric strain** - **(B)**: Phenyl groups appear eclipsed/gauche → **significant repulsion** - **(C)**: Phenyl groups in gauche position → **moderate strain** - **(D)**: Phenyl groups in **anti/staggered orientation** (180° apart) → **maximum separation, lowest strain** **Step 4: Confirm with Newman projection logic** In option (D), the two $C_6H_5$ groups are positioned on opposite sides of the $C-C$ bond axis, creating the **anti-periplanar conformation**. This arrangement maximizes the distance between bulky groups and minimizes van der Waals repulsion. **Answer: (D)** is correct because it represents the **anti-staggered conformation** where phenyl groups are maximally separated, resulting in minimum steric hindrance and maximum thermodynamic stability.