Resonance
Chemical Bonding (Basics) · Chemistry
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Study notes
Benzene has two Kekulé structures with alternating double bonds. What is the real structure? Step 1: Each Kekulé form has 3 double + 3 single bonds. Step 2: Measured C–C lengths are ALL 139 pm — between single (154) and double (134). Step 3: Real benzene is the hybrid: 6 identical 1.5-order bonds. Step 4: The 6 pi electrons delocalise in rings above/below — extra stable (resonance energy 150 kJ/mol). Benzene doesn't behave like 3 alkenes — it resists addition reactions.