What is the primary thermodynamic driving force that makes aromatic compounds resistant to addition reactions, favoring substitution reactions instead?
Answer and explanation
Correct answer: A. Preservation of the exceptionally large aromatic resonance stabilization energy
- Step 1: Aromatic systems possess exceptional thermodynamic stability known as aromatic stabilization or resonance energy ( for benzene).
- Step 2: An addition reaction across the double bond would permanently destroy the cyclic -electron conjugation, sacrificing this large resonance stabilization.
- Step 3: In contrast, electrophilic substitution restores the intact aromatic sextet upon loss of a proton, preserving the full resonance stabilization energy.
Answer
Preservation of the exceptionally large aromatic resonance stabilization energy.
Why not the others: High steric hindrance of ring protons is negligible because the ring is flat and planar; Low polarity of carbon-carbon bonds does not prevent addition in alkenes; bond energy alone does not explain why alkenes add and arenes substitute.
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