Question

Why is the C=C bond length is benzene longer than that in ethylene?
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Answer 1

Benzene has bond in between the ethane and ethylene. Because of resonance, the bonds in benzene have some single bond and some double bond character. sp3−sp3 sigma longer than 1.5 bond order in benzene longer than sp2−sp2σ and p−p,π of ethylene and sp−spσ and 2 p−pπ of acetylene.