See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

**Step-by-step solution:** **Analyzing C–O bond character in each structure:** **(A) Cyclohexenone (α,β-unsaturated ketone):** - Double bond conjugated with C=O - Resonance delocalizes π-electrons onto oxygen - C=O has partial single bond character → shorter bond **(B) Benzene ring with ketone:** - Aromatic ring conjugated with C=O - Strong resonance stabilization through aromatic system - Oxygen lone pairs delocalize into aromatic π-system - C=O has significant single bond character → **longest bond** **(C) Saturated cyclohexanone:** - No conjugation with C=O - Pure ketone with typical C=O double bond length - Standard carbonyl bond (~1.22 Å) **(D) Cyclohexanone with $CH_2$ substituent:** - Saturated ketone similar to (C) - $CH_2$ is non-conjugating group - Standard C=O double bond length **Why (B) is longest:** Benzene's aromatic electrons are highly delocalized and can extensively stabilize the negative charge on oxygen through resonance. This greater delocalization weakens the C=O double bond more than in (A), converting more of it to single bond character. Although (A) is also conjugated, benzene's aromaticity provides superior resonance stabilization compared to a simple alkene. **Answer: (B)** ✓