See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Phenanthrene Resonance Structures **Step 1: Identify bond types in each resonance structure** - **Structure 1 (left):** Shows alternating single/double bonds with the central B ring having one double bond - **Structure 2 (middle):** Central ring becomes aromatic (all single bonds); outer rings show shifted double bond positions - **Structure 3 (right):** Another distribution with double bonds in different positions - **Structures 4 & 5 (bottom):** Additional resonance forms with various double bond arrangements **Step 2: Count double bond contributions at each position** Equal contribution means each resonance form counts equally. Tracking bond A (top): - A has a **double bond in structures 1, 4, and 5** (3/5 structures) - A has a **single bond in structures 2 and 3** (2/5 structures) Bond B (central, between rings): - B has a **single bond in most structures** (contributes more single character) - B has occasional double bond character (contributes some double character) **Step 3: Apply resonance averaging** Since A participates in more double bonds across resonance forms → A has **shorter bond character** Since B has predominantly single bond character across resonance forms → B has **longer bond character** **Answer: (a) A shortest and B longest** The central bond between rings (B) is longest due to predominantly single-bond character, while the peripheral bond A is shortest due to significant double-bond resonance contribution.